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[[File:Drops I.jpg|thumb|Water drops on the hydrophobic surface of grass]]
[[File:Drops I.jpg|thumb|Water drops on the hydrophobic surface of grass]]


In [[chemistry]], '''hydrophobicity''' is the [[chemical property]] of a [[molecule]] (called a '''hydrophobe''') that is seemingly [[intermolecular force|repelled]] from a mass of [[water]].<ref>{{cite book |first=Aryeh|last=Ben-Na'im |title=Hydrophobic Interaction |date=31 January 1980 |publisher=[[Springer Science+Business Media|Plenum Press]] |location=New York |isbn=0-306-40222-X}}</ref> In contrast, [[hydrophile]]s are attracted to water.
In [[chemistry]], '''hydrophobicity''' is the [[chemical property]] of a [[molecule]] (called a '''hydrophobe''') that is seemingly [[intermolecular force|repelled]] from a mass of [[water]].<ref>{{cite book |first=Aryeh|last=Ben-Na'im |title=Hydrophobic Interaction |date=31 January 1980 |publisher=[[Springer Science+Business Media|Plenum Press]] |location=New York |isbn=0-306-40222-X}}</ref> In contrast, ''[[hydrophile]]s'' are attracted to water.


Hydrophobic molecules tend to be [[chemical polarity#Nonpolar molecules|nonpolar]] and, thus, prefer other neutral molecules and nonpolar [[solvent]]s. Because water molecules are polar, hydrophobes do not [[dissolution (chemistry)|dissolve]] well among them. Hydrophobic molecules in water often cluster together, forming [[micelle]]s. Water on hydrophobic surfaces will exhibit a high [[contact angle]].
Hydrophobic molecules tend to be [[chemical polarity#Nonpolar molecules|nonpolar]] and, thus, prefer other neutral molecules and nonpolar [[solvent]]s. Because water molecules are polar, hydrophobes do not [[dissolution (chemistry)|dissolve]] well among them. Hydrophobic molecules in water often cluster together, forming [[micelle]]s. Water on hydrophobic surfaces will exhibit a high [[contact angle]].


Examples of hydrophobic [[molecule]]s include the [[alkane]]s, [[oil]]s, [[fat]]s, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of [[oil spill]]s, and chemical separation processes to remove non-polar substances from polar compounds.<ref>{{cite journal |vauthors=Akhavan B, Jarvis K, Majewski P |title=Hydrophobic Plasma Polymer Coated Silica Particles for Petroleum Hydrocarbon Removal |journal=[[ACS Applied Materials & Interfaces|ACS Appl. Mater. Interfaces]] |volume=5 |issue=17 |pages=8563–8571 |date=November 2013 |pmid=23942510 |doi=10.1021/am4020154}}</ref>  
Examples of hydrophobic [[molecule]]s include the [[alkane]]s, [[oil]]s, [[fat]]s, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of [[oil spill]]s, and chemical separation processes to remove non-polar substances from polar compounds.<ref>{{cite journal |vauthors=Akhavan B, Jarvis K, Majewski P |title=Hydrophobic Plasma Polymer Coated Silica Particles for Petroleum Hydrocarbon Removal |journal=[[ACS Applied Materials & Interfaces|ACS Appl. Mater. Interfaces]] |volume=5 |issue=17 |pages=8563–8571 |date=November 2013 |pmid=23942510 |doi=10.1021/am4020154 |bibcode=2013AAMI....5.8563A }}</ref>  


The term ''hydrophobic''—which comes from the [[Ancient Greek]] {{Lang|grc|ὑδρόφοβος}} ({{Transliteration|grc|hydróphobos}}), "having a fear of water", constructed {{ety|grc|ὕδωρ (húdōr)|water|grc|φόβος (phóbos)|fear}}<ref name="Liddell & Scott">Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie.'' Oxford: Clarendon Press.</ref>—is often used interchangeably with ''[[lipophilic]]'', "fat-loving". However, the two terms are not synonymous. While hydrophobic substances are usually lipophilic, there are exceptions, such as the [[silicones]] and [[fluorocarbon]]s.<ref>{{Cite journal |last=Xi |first=J. |date=1987 |title=The effect of hydrophobic-lipophilic interactions on chemical reactivity——3.Contributions of lipophilic interactions to the binding of hydrocarbon substrates by amylose-type hosts and of hydrophobic interactions to the binding of fluorocarbon su |s2cid=101053755 }}</ref><ref>{{Cite web |title=Transport of Lipophilic Substances - LabCE.com, Laboratory Continuing Education |url=https://www.labce.com/spg254711_transport_of_lipophilic_substances.aspx |access-date=2025-02-22 |website=www.labce.com}}</ref>
The term ''hydrophobic''—which comes from the [[Ancient Greek]] {{Lang|grc|ὑδρόφοβος}} ({{Transliteration|grc|hydróphobos}}), "having a fear of water", constructed {{ety|grc|ὕδωρ (húdōr)|water|grc|φόβος (phóbos)|fear}}<ref name="Liddell & Scott">Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie.'' Oxford: Clarendon Press.</ref>—is often used interchangeably with ''[[lipophilic]]'', "fat-loving". However, the two terms are not synonymous. While hydrophobic substances are usually lipophilic, there are exceptions, such as the [[silicones]] and [[fluorocarbon]]s.<ref>{{Cite journal |last=Xi |first=J. |date=1987 |title=The effect of hydrophobic-lipophilic interactions on chemical reactivity——3.Contributions of lipophilic interactions to the binding of hydrocarbon substrates by amylose-type hosts and of hydrophobic interactions to the binding of fluorocarbon su |s2cid=101053755 }}</ref><ref>{{Cite web |title=Transport of Lipophilic Substances - LabCE.com, Laboratory Continuing Education |url=https://www.labce.com/spg254711_transport_of_lipophilic_substances.aspx |access-date=2025-02-22 |website=www.labce.com}}</ref>


==Physicochemical basis==
==Chemistry==
{{Main|Hydrophobic effect}}
{{Main|Hydrophobic effect}}


For small solutes, the hydrophobic interaction is mostly an [[entropy|entropic]] effect originating from the disruption of the highly dynamic [[hydrogen bond]]s between molecules of liquid water by the nonpolar solute, causing the water to compensate by forming a [[clathrate]]-like cage structure around the non-polar molecules. This structure is more highly ordered than free water molecules due to the water molecules arranging themselves to interact as much as possible with themselves, and thus results in a lower entropic state at the interface. This causes non-polar molecules to clump together to reduce the [[accessible surface area|surface area exposed to water]] and thereby increase the entropy of the system.<ref>{{cite book |last1=Garrett |first1=Reginald |last2=Grisham |first2=Charles|title=Biochemistry |date=January 5, 2012|publisher=Cengage Learning |pages=31–35 |isbn=978-1133106296}}</ref><ref>{{cite journal |vauthors= Silverstein TP |title= The Real Reason Why Oil and Water Don't Mix |journal= Journal of Chemical Education |volume= 75 |issue= 1 |pages= 116–346 |year= 1998 |doi= 10.1021/ed075p116 |url= https://www.docdroid.net/file/download/EnMrRWi/the-real-reason-why-oil-and-water-dont-mix.pdf |via=DocDroid |access-date= 9 December 2011 |bibcode= 1998JChEd..75..116S}}</ref> Thus, the two immiscible phases (hydrophilic vs. hydrophobic) will change so that their corresponding interfacial area will be minimal. This effect can be visualized in the phenomenon called [[phase (matter)|phase]] separation.{{Citation needed|date=January 2021}}
For small solutes, the hydrophobic interaction is mostly an [[entropy|entropic]] effect originating from the disruption of the highly dynamic [[hydrogen bond]]s between molecules of liquid water by the nonpolar solute, causing the water to compensate by forming a [[clathrate]]-like cage structure around the non-polar molecules. This structure is more highly ordered than free water molecules due to the water molecules arranging themselves to interact as much as possible with themselves, and thus results in a lower entropic state at the interface. This causes non-polar molecules to clump together to reduce the [[accessible surface area|surface area exposed to water]] and thereby increase the entropy of the system.<ref>{{cite book |last1=Garrett |first1=Reginald |last2=Grisham |first2=Charles|title=Biochemistry |date=January 5, 2012|publisher=Cengage Learning |pages=31–35 |isbn=978-1-133-10629-6}}</ref><ref>{{cite journal |vauthors= Silverstein TP |title= The Real Reason Why Oil and Water Don't Mix |journal= Journal of Chemical Education |volume= 75 |issue= 1 |pages= 116–346 |year= 1998 |doi= 10.1021/ed075p116 |url= https://www.docdroid.net/file/download/EnMrRWi/the-real-reason-why-oil-and-water-dont-mix.pdf |via=DocDroid |access-date= 9 December 2011 |bibcode= 1998JChEd..75..116S}}</ref> Thus, the two immiscible phases (hydrophilic vs. hydrophobic) will change so that their corresponding interfacial area will be minimal. This effect can be visualized in the phenomenon called [[phase (matter)|phase]] separation.{{Citation needed|date=January 2021}}


For larger nonpolar solutes that cannot be adequately "clathrated" by the hydrogen-bond network of water, the disruption of these bonds becomes inevitable, leading to a high enthalpic cost. Under ambient conditions, this transition from an entropy-dominated regime to one governed by enthalpy occurs at around ~1 nm in size, reflecting a shift in hydration free energy behavior from scaling with the solute volume to depending on the exposed surface area.<ref> Patel AJ et al., ''Proc. Natl. Acad. Sci. U.S.A.'' 108(43), 17678–17683 (2011), https://doi.org/10.1073/pnas.1110703108</ref><ref> Rajamani S et al., ''Proc. Natl. Acad. Sci. U.S.A.'' 102, 9475–9480 (2005), https://doi.org/10.1073/pnas.0504089102</ref>
For larger nonpolar solutes that cannot be adequately "clathrated" by the hydrogen-bond network of water, the disruption of these bonds becomes inevitable, leading to a high enthalpic cost. Under ambient conditions, this transition from an entropy-dominated regime to one governed by enthalpy occurs at around ~1 nm in size, reflecting a shift in hydration free energy behavior from scaling with the solute volume to depending on the exposed surface area.<ref> Patel AJ et al., ''Proc. Natl. Acad. Sci. U.S.A.'' 108(43), 17678–17683 (2011), https://doi.org/10.1073/pnas.1110703108</ref><ref> Rajamani S et al., ''Proc. Natl. Acad. Sci. U.S.A.'' 102, 9475–9480 (2005), https://doi.org/10.1073/pnas.0504089102</ref>
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Additionally, the DIT helps determine the regimes of filling, partial filling, and drying in nanoconfined water, depending on how many of the water molecule's interaction sites (among its four tetrahedral sites) exceed this threshold. This analysis for quantifying hydrophobicity or wetting can be performed using a structural indicator, the '''V<sub>4S</sub>''' index, which reveals the existence of two inherently preferential interaction states for water.<ref> Loubet NA, Verde AR & Appignanesi GA, ''J. Chem. Phys.'' (2024), https://doi.org/10.1063/5.0203989</ref>
Additionally, the DIT helps determine the regimes of filling, partial filling, and drying in nanoconfined water, depending on how many of the water molecule's interaction sites (among its four tetrahedral sites) exceed this threshold. This analysis for quantifying hydrophobicity or wetting can be performed using a structural indicator, the '''V<sub>4S</sub>''' index, which reveals the existence of two inherently preferential interaction states for water.<ref> Loubet NA, Verde AR & Appignanesi GA, ''J. Chem. Phys.'' (2024), https://doi.org/10.1063/5.0203989</ref>
== See also ==
* [[Wetting]] – discusses how hydrophobicity affects spreading and contact angles
* [[Contact angle]] – classical macroscopic measure linked to hydrophobicity via the DIT molecular criterion


=== Superhydrophobicity ===
{{Main|Superhydrophobe}}


==Superhydrophobicity==
{{Main|Superhydrophobe}}
[[File:DropConnectionAngel.jpg|thumb|A water drop on a lotus plant leaf]]
[[File:DropConnectionAngel.jpg|thumb|A water drop on a lotus plant leaf]]
'''Superhydrophobic''' surfaces, such as the leaves of the lotus plant, are those that are extremely difficult to wet. The [[contact angle]]s of a water droplet exceeds 150°.<ref>{{cite journal |vauthors= Wang S, Jiang L |title= Definition of superhydrophobic states |journal=[[Advanced Materials]] |volume=19 |pages=3423–3424 |year=2007 |doi=10.1002/adma.200700934 |issue=21|bibcode= 2007AdM....19.3423W |s2cid= 138017937 }}</ref> This is referred to as the [[lotus effect]], and is primarily a physical property related to [[interfacial tension]], rather than a chemical property.<ref>{{Cite journal |last=Tg |date=2008 |title=BIOMIMICRY: The Lotus Effect |url=https://www.jstor.org/stable/24162971 |journal=ASEE Prism |volume=18 |issue=2 |pages=23 |jstor=24162971 |issn=1056-8077}}</ref>
'''Superhydrophobic''' surfaces, such as the leaves of the lotus plant, are those that are extremely difficult to wet. The [[contact angle]]s of a water droplet exceeds 150°.<ref>{{cite journal |vauthors= Wang S, Jiang L |title= Definition of superhydrophobic states |journal=[[Advanced Materials]] |volume=19 |pages=3423–3424 |year=2007 |doi=10.1002/adma.200700934 |issue=21|bibcode= 2007AdM....19.3423W |s2cid= 138017937 }}</ref> This is referred to as the [[lotus effect]], and is primarily a physical property related to [[interfacial tension]], rather than a chemical property.<ref>{{Cite journal |last=Tg |date=2008 |title=BIOMIMICRY: The Lotus Effect |url=https://www.jstor.org/stable/24162971 |journal=ASEE Prism |volume=18 |issue=2 |page=23 |jstor=24162971 |issn=1056-8077}}</ref>


===Theory===
==== Theory ====
In 1805, Thomas Young defined the contact angle ''θ'' by analyzing the forces acting on a fluid droplet resting on a solid surface surrounded by a gas.<ref>{{cite journal |first=T. |last=Young |title=An Essay on the Cohesion of Fluids |journal=[[Philosophical Transactions of the Royal Society|Phil. Trans. R. Soc. Lond.]] |volume=95 |pages=65–87 |year=1805 |doi=10.1098/rstl.1805.0005|s2cid=116124581 |doi-access=free }}</ref>
In 1805, Thomas Young defined the contact angle ''θ'' by analyzing the forces acting on a fluid droplet resting on a solid surface surrounded by a gas.<ref>{{cite journal |first=T. |last=Young |title=An Essay on the Cohesion of Fluids |journal=[[Philosophical Transactions of the Royal Society|Phil. Trans. R. Soc. Lond.]] |volume=95 |pages=65–87 |year=1805 |doi=10.1098/rstl.1805.0005|s2cid=116124581 |doi-access=free }}</ref>


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:<math>\cos\theta_\text{CB}* = \varphi(\cos\theta + 1) - 1 \,</math>
:<math>\cos\theta_\text{CB}* = \varphi(\cos\theta + 1) - 1 \,</math>


where ''φ'' is the area fraction of the solid that touches the liquid.<ref>{{cite journal |vauthors= Baxter AB, Cassie S |title= Wettability of Porous Surfaces |journal=[[Trans. Faraday Soc.]] |volume=40 |pages=546–551 |year=1944 |doi=10.1039/tf9444000546}}</ref> Liquid in the Cassie–Baxter state is more mobile than in the Wenzel state.{{Citation needed|date=January 2021}}
where ''φ'' is the area fraction of the solid that touches the liquid.<ref>{{cite journal |vauthors= Baxter AB, Cassie S |title= Wettability of Porous Surfaces |journal=[[Trans. Faraday Soc.]] |volume=40 |pages=546–551 |year=1944 |doi=10.1039/tf9444000546}}</ref> Liquid in the Cassie–Baxter state is more mobile than in the Wenzel state.<ref>{{Cite journal |last1=McHale |first1=G. |last2=Shirtcliffe |first2=N. J. |last3=Newton |first3=M. I. |title=Contact-angle hysteresis on superhydrophobic surfaces: Hydrophobicity, hydrophilicity and Young's law |journal=Langmuir |volume=20 |issue=23 |pages=10146–10149 |year=2004 |doi=10.1021/la048629t |pmid=15350093 }}</ref>


We can predict whether the Wenzel or Cassie–Baxter state should exist by calculating the new contact angle with both equations. By a minimization of free energy argument, the relation that predicted the smaller new contact angle is the state most likely to exist. Stated in mathematical terms, for the Cassie–Baxter state to exist, the following inequality must be true.<ref>{{cite journal |first=D |last=Quere |title=Non-sticking Drops |journal=[[Reports on Progress in Physics]] |volume=68 |pages=2495–2532 |year=2005 |doi=10.1088/0034-4885/68/11/R01 |issue=11 |bibcode=2005RPPh...68.2495Q|s2cid=121128710 }}</ref>
We can predict whether the Wenzel or Cassie–Baxter state should exist by calculating the new contact angle with both equations. By a minimization of free energy argument, the relation that predicted the smaller new contact angle is the state most likely to exist. Stated in mathematical terms, for the Cassie–Baxter state to exist, the following inequality must be true.<ref>{{cite journal |first=D |last=Quere |title=Non-sticking Drops |journal=[[Reports on Progress in Physics]] |volume=68 |pages=2495–2532 |year=2005 |doi=10.1088/0034-4885/68/11/R01 |issue=11 |bibcode=2005RPPh...68.2495Q|s2cid=121128710 }}</ref>
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A recent alternative criterion for the Cassie–Baxter state asserts that the Cassie–Baxter state exists when the following 2 criteria are met:1) Contact line forces overcome body forces of unsupported droplet weight and 2) The microstructures are tall enough to prevent the liquid that bridges microstructures from touching the base of the microstructures.<ref>{{cite journal |vauthors= Extrand CW |title= Modeling of ultralyophobicity: Suspension of liquid drops by a single asperity |journal= Langmuir |volume= 21 |issue= 23 |pages= 10370–10374 |year= 2005 |pmid= 16262294 |doi= 10.1021/la0513050}}</ref>
A recent alternative criterion for the Cassie–Baxter state asserts that the Cassie–Baxter state exists when the following 2 criteria are met:1) Contact line forces overcome body forces of unsupported droplet weight and 2) The microstructures are tall enough to prevent the liquid that bridges microstructures from touching the base of the microstructures.<ref>{{cite journal |vauthors= Extrand CW |title= Modeling of ultralyophobicity: Suspension of liquid drops by a single asperity |journal= Langmuir |volume= 21 |issue= 23 |pages= 10370–10374 |year= 2005 |pmid= 16262294 |doi= 10.1021/la0513050}}</ref>


A new criterion for the switch between Wenzel and Cassie-Baxter states has been developed recently based on surface roughness and [[surface energy]].<ref>{{cite journal |vauthors= Zhang YL, Sundararajan S |title= Superhydrophobic engineering surfaces with tunable air-trapping ability |journal= Journal of Micromechanics and Microengineering |volume=18 |pages=035024 |year=2008 |doi=10.1088/0960-1317/18/3/035024|issue=3|bibcode= 2008JMiMi..18c5024Z|s2cid= 137395618 }}</ref> The criterion focuses on the air-trapping capability under liquid droplets on rough surfaces, which could tell whether Wenzel's model or Cassie-Baxter's model should be used for certain combination of surface roughness and energy.{{Citation needed|date=January 2021}}
A new criterion for the switch between Wenzel and Cassie-Baxter states has been developed recently based on surface roughness and [[surface energy]].<ref>{{cite journal |vauthors= Zhang YL, Sundararajan S |title= Superhydrophobic engineering surfaces with tunable air-trapping ability |journal= Journal of Micromechanics and Microengineering |volume=18 |article-number=035024 |year=2008 |doi=10.1088/0960-1317/18/3/035024|issue=3|bibcode= 2008JMiMi..18c5024Z|s2cid= 137395618 }}</ref> The criterion focuses on the air-trapping capability under liquid droplets on rough surfaces, which could tell whether Wenzel's model or Cassie-Baxter's model should be used for certain combination of surface roughness and energy.<ref>{{Cite journal |last1=Jäger |first1=Tobias |last2=Mokos |first2=Athanasios |last3=Prasianakis |first3=Nikolaos I. |last4=Leyer |first4=Stephan |date=2024-03-05 |title=Validating the Transition Criteria from the Cassie-Baxter to the Wenzel State for Periodically Pillared Surfaces with Lattice Boltzmann Simulations |journal=ACS Omega |volume=9 |issue=9 |pages=10592–10601 |doi=10.1021/acsomega.3c08862 |doi-access=free |issn=2470-1343 |pmc=10918652 |pmid=38463292}}</ref>


Contact angle is a measure of static hydrophobicity, and [[Contact angle#Contact Angle Hysteresis|contact angle hysteresis]] and slide angle are dynamic measures. Contact angle hysteresis  is a phenomenon that characterizes surface heterogeneity.<ref>{{cite journal |vauthors= Johnson RE, Dettre RH |title=Contact Angle Hysteresis |volume=68 |pages=1744–1750 |year=1964 |journal=[[J. Phys. Chem.]] |doi=10.1021/j100789a012 |issue=7}}</ref> When a pipette injects a liquid onto a solid, the liquid will form some contact angle. As the pipette injects more liquid, the droplet will increase in volume, the contact angle will increase, but its three-phase boundary will remain stationary until it suddenly advances outward. The contact angle the droplet had immediately before advancing outward is termed the advancing contact angle. The receding contact angle is now measured by pumping the liquid back out of the droplet. The droplet will decrease in volume, the contact angle will decrease, but its three-phase boundary will remain stationary until it suddenly recedes inward. The contact angle the droplet had immediately before receding inward is termed the receding contact angle. The difference between advancing and receding contact angles is termed contact angle hysteresis and can be used to characterize surface heterogeneity, roughness, and mobility.<ref>{{Cite web|url=https://blog.biolinscientific.com/how-to-measure-contact-angle-hysteresis|title=How to measure contact angle hysteresis?|last=Laurén|first=Susanna|website=blog.biolinscientific.com|language=en-us|access-date=2019-12-31}}</ref> Surfaces that are not homogeneous will have domains that impede motion of the contact line. The slide angle is another dynamic measure of hydrophobicity and is measured by depositing a droplet on a surface and tilting the surface until the droplet begins to slide. In general, liquids in the Cassie–Baxter state exhibit lower slide angles and [[Contact angle#Contact Angle Hysteresis|contact angle hysteresis]]  than those in the Wenzel state.{{Citation needed|date=January 2021}}
Contact angle is a measure of static hydrophobicity, and [[Contact angle#Contact Angle Hysteresis|contact angle hysteresis]] and slide angle are dynamic measures. Contact angle hysteresis  is a phenomenon that characterizes surface heterogeneity.<ref>{{cite journal |vauthors= Johnson RE, Dettre RH |title=Contact Angle Hysteresis |volume=68 |pages=1744–1750 |year=1964 |journal=[[J. Phys. Chem.]] |doi=10.1021/j100789a012 |issue=7}}</ref> When a pipette injects a liquid onto a solid, the liquid will form some contact angle. As the pipette injects more liquid, the droplet will increase in volume, the contact angle will increase, but its three-phase boundary will remain stationary until it suddenly advances outward. The contact angle the droplet had immediately before advancing outward is termed the advancing contact angle. The receding contact angle is now measured by pumping the liquid back out of the droplet. The droplet will decrease in volume, the contact angle will decrease, but its three-phase boundary will remain stationary until it suddenly recedes inward. The contact angle the droplet had immediately before receding inward is termed the receding contact angle. The difference between advancing and receding contact angles is termed contact angle hysteresis and can be used to characterize surface heterogeneity, roughness, and mobility.<ref>{{Cite web|url=https://blog.biolinscientific.com/how-to-measure-contact-angle-hysteresis|title=How to measure contact angle hysteresis?|last=Laurén|first=Susanna|website=blog.biolinscientific.com|language=en-us|access-date=2019-12-31}}</ref> Surfaces that are not homogeneous will have domains that impede motion of the contact line. The slide angle is another dynamic measure of hydrophobicity and is measured by depositing a droplet on a surface and tilting the surface until the droplet begins to slide. In general, liquids in the Cassie–Baxter state exhibit lower slide angles and [[Contact angle#Contact Angle Hysteresis|contact angle hysteresis]]  than those in the Wenzel state.{{Citation needed|date=January 2021}}
== Soil science ==
[[File:Rim Fire 20130817-FS-UNK-0094 (9898761875).jpg|thumb|The [[Rim Fire]] caused soil hydrophobicity, as demonstrated by this water that won't infiltrate into the dry soil]]
Soil tends to become hydrophobic in response to [[Wildfire|wildfires]]. Depending on the severity of the fire, this can lead to more precipitation being rendered as [[surface runoff]], traveling over the surface without infiltrating into the soil.<ref>{{Cite journal |last1=Vore |first1=Margot E. |last2=Déry |first2=Stephen J. |last3=Hou |first3=Yiping |last4=Wei |first4=Xiaohua |date=2020-11-30 |title=Climatic influences on forest fire and mountain pine beetle outbreaks and resulting runoff effects in large watersheds in British Columbia, Canada |url=https://onlinelibrary.wiley.com/doi/10.1002/hyp.13908 |journal=Hydrological Processes |language=en |volume=34 |issue=24 |pages=4561 |doi=10.1002/hyp.13908 |bibcode=2020HyPr...34.4560V |issn=0885-6087|url-access=subscription }}</ref>


==Research and development==
==Research and development==
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[[File:Hydrophoby2.webm|thumb|Water droplets on an artificial hydrophobic surface (left)]]
[[File:Hydrophoby2.webm|thumb|Water droplets on an artificial hydrophobic surface (left)]]


Dettre and Johnson discovered in 1964 that the superhydrophobic [[lotus effect]] phenomenon was related to rough hydrophobic surfaces, and they developed a theoretical model based on experiments with glass beads coated with paraffin or TFE telomer. The self-cleaning property of superhydrophobic micro-[[nanotechnology|nanostructured]] surfaces was reported in 1977.<ref name=Barthlott1977>{{cite book |first1=Wilhelm |last1=Barthlott |first2=Nesta |last2=Ehler |year=1977 |title=Raster-Elektronenmikroskopie der Epidermis-Oberflächen von Spermatophyten |series=Tropische und subtropische Pflanzenwelt |page=110 |language=de |isbn=978-3-515-02620-8}}</ref> Perfluoroalkyl, perfluoropolyether, and RF plasma -formed superhydrophobic materials were developed, used for [[electrowetting]] and commercialized for bio-medical applications between 1986 and 1995.<ref>{{cite web|title= US Patent 4,911,782|author= J. Brown|url= http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4,911,782.PN.&OS=PN/4,911,782&RS=PN/4,911,782|access-date= 2015-01-13|archive-date= 2018-07-14|archive-url= https://web.archive.org/web/20180714221932/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4,911,782.PN.&OS=PN/4,911,782&RS=PN/4,911,782|url-status= dead}}</ref><ref>{{cite web|title= US Patent 5,200,152|author= J. Brown|url= http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=5,200,152.PN.&OS=PN/5,200,152&RS=PN/5,200,152|access-date= 2015-01-13|archive-date= 2017-07-27|archive-url= https://web.archive.org/web/20170727230714/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=5,200,152.PN.&OS=PN/5,200,152&RS=PN/5,200,152|url-status= dead}}</ref><ref>{{cite web|title= Stopped-Flow Cytometer|author= National Science Foundation|url= https://www.nsf.gov/awardsearch/advancedSearchResult?PIFirstName=james&PILastName=brown&PIOrganization=cytonix&PIState=MD&PICountry=US&ExpiredAwards=true&#results}}</ref><ref>{{cite web|title= US Patent 5,853,894|author= J. Brown|url= http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=5,853,894.PN.&OS=PN/5,853,894&RS=PN/5,853,894|access-date= 2015-01-13|archive-date= 2017-01-22|archive-url= https://web.archive.org/web/20170122184631/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=5,853,894.PN.&OS=PN/5,853,894&RS=PN/5,853,894|url-status= dead}}</ref> Other technology and applications have emerged since the mid-1990s.<ref name=Barthlott1997>{{cite journal |last= Barthlott|first= Wilhelm|author2=C. Neinhuis |year= 1997|title= The purity of sacred lotus or escape from contamination in biological surfaces|journal= [[Planta (journal)|Planta]] |volume= 202|issue= 1|pages= 1–8 |doi= 10.1007/s004250050096|bibcode= 1997Plant.202....1B|s2cid= 37872229}}</ref> A durable superhydrophobic hierarchical composition, applied in one or two steps, was disclosed in 2002 comprising nano-sized particles ≤ 100 nanometers overlaying a surface having micrometer-sized features or particles ≤&nbsp;100 micrometers. The larger particles were observed to protect the smaller particles from mechanical abrasion.<ref>{{cite web|title= US Patent 6,767,587|author= J. Brown|url= http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6,767,587.PN.&OS=PN/6,767,587&RS=PN/6,767,587|access-date= 2015-01-13|archive-date= 2018-07-14|archive-url= https://web.archive.org/web/20180714221921/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6,767,587.PN.&OS=PN/6,767,587&RS=PN/6,767,587|url-status= dead}}</ref>
Dettre and Johnson discovered in 1964 that the superhydrophobic [[lotus effect]] phenomenon was related to rough hydrophobic surfaces, and they developed a theoretical model based on experiments with glass beads coated with paraffin or TFE telomer. The self-cleaning property of superhydrophobic micro-[[nanotechnology|nanostructured]] surfaces was reported in 1977.<ref name=Barthlott1977>{{cite book |first1=Wilhelm |last1=Barthlott |first2=Nesta |last2=Ehler |year=1977 |title=Raster-Elektronenmikroskopie der Epidermis-Oberflächen von Spermatophyten |series=Tropische und subtropische Pflanzenwelt |page=110 |language=de |isbn=978-3-515-02620-8}}</ref> Perfluoroalkyl, perfluoropolyether, and RF plasma -formed superhydrophobic materials were developed, used for [[electrowetting]] and commercialized for bio-medical applications between 1986 and 1995.<ref>{{cite web|title= US Patent 4,911,782|author= J. Brown|url= http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4,911,782.PN.&OS=PN/4,911,782&RS=PN/4,911,782|access-date= 2015-01-13|archive-date= 2018-07-14|archive-url= https://web.archive.org/web/20180714221932/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4,911,782.PN.&OS=PN/4,911,782&RS=PN/4,911,782}}</ref><ref>{{cite web|title= US Patent 5,200,152|author= J. Brown|url= http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=5,200,152.PN.&OS=PN/5,200,152&RS=PN/5,200,152|access-date= 2015-01-13|archive-date= 2017-07-27|archive-url= https://web.archive.org/web/20170727230714/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=5,200,152.PN.&OS=PN/5,200,152&RS=PN/5,200,152}}</ref><ref>{{cite web|title= Stopped-Flow Cytometer|author= National Science Foundation|url= https://www.nsf.gov/awardsearch/advancedSearchResult?PIFirstName=james&PILastName=brown&PIOrganization=cytonix&PIState=MD&PICountry=US&ExpiredAwards=true&#results}}</ref><ref>{{cite web|title= US Patent 5,853,894|author= J. Brown|url= http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=5,853,894.PN.&OS=PN/5,853,894&RS=PN/5,853,894|access-date= 2015-01-13|archive-date= 2017-01-22|archive-url= https://web.archive.org/web/20170122184631/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=5,853,894.PN.&OS=PN/5,853,894&RS=PN/5,853,894}}</ref> Other technology and applications have emerged since the mid-1990s.<ref name=Barthlott1997>{{cite journal |last= Barthlott|first= Wilhelm|author2=C. Neinhuis |year= 1997|title= The purity of sacred lotus or escape from contamination in biological surfaces|journal= [[Planta (journal)|Planta]] |volume= 202|issue= 1|pages= 1–8 |doi= 10.1007/s004250050096|bibcode= 1997Plant.202....1B|s2cid= 37872229}}</ref> A durable superhydrophobic hierarchical composition, applied in one or two steps, was disclosed in 2002 comprising nano-sized particles ≤ 100 nanometers overlaying a surface having micrometer-sized features or particles ≤&nbsp;100 micrometers. The larger particles were observed to protect the smaller particles from mechanical abrasion.<ref>{{cite web|title= US Patent 6,767,587|author= J. Brown|url= http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6,767,587.PN.&OS=PN/6,767,587&RS=PN/6,767,587|access-date= 2015-01-13|archive-date= 2018-07-14|archive-url= https://web.archive.org/web/20180714221921/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=6,767,587.PN.&OS=PN/6,767,587&RS=PN/6,767,587}}</ref>


In recent research, superhydrophobicity has been reported by allowing alkylketene [[dimer (chemistry)|dimer]] (AKD) to solidify into a nanostructured fractal surface.<ref>{{cite journal |vauthors= Onda T, Shibuichi S, Satoh N, Tsujii K |title= Super-Water-Repellent Fractal Surfaces |journal=Langmuir |volume=12 |pages=2125–2127 |year=1996 |doi=10.1021/la950418o |issue=9}}</ref> Many papers have since presented fabrication methods for producing superhydrophobic surfaces including particle deposition,<ref name= "Miwa_2000">{{cite journal |vauthors= Miwa M, Nakajima A, Fujishima A, Hashimoto K, Watanabe T |title= Effects of the Surface Roughness on Sliding Angles of Water Droplets on Superhydrophobic Surfaces |journal=Langmuir |volume=16 |pages=5754–60 |year=2000 |doi=10.1021/la991660o |issue=13|s2cid= 97974935 }}</ref> sol-gel techniques,<ref>{{cite journal |vauthors= Shirtcliffe NJ, McHale G, Newton MI, Perry CC |title= Intrinsically superhydrophobic organosilica sol-gel foams |journal=Langmuir |volume=19 |pages=5626–5631 |year=2003 |doi=10.1021/la034204f |issue=14}}</ref> plasma treatments,<ref name="TeareSpanos2002">{{cite journal|last1=Teare|first1=D. O. H.|last2=Spanos|first2=C. G.|last3=Ridley|first3=P.|last4=Kinmond|first4=E. J.|last5=Roucoules|first5=V.|last6=Badyal|first6=J. P. S.|author-link6=Jas Pal Badyal|last7=Brewer|first7=S. A.|last8=Coulson|first8=S.|last9=Willis|first9=C.|title=Pulsed Plasma Deposition of Super-Hydrophobic Nanospheres|journal=Chemistry of Materials|volume=14|issue=11|year=2002|pages=4566–4571|issn=0897-4756|doi=10.1021/cm011600f}}</ref> vapor deposition,<ref name= "Miwa_2000"/> and casting techniques.<ref>{{cite journal |vauthors= Bico J, Marzolin C, Quéré D |title= Pearl drops |journal=[[Europhysics Letters]] |volume=47 |pages=743–744 |year=1999 |doi=10.1209/epl/i1999-00453-y |issue=6 |bibcode=1999EL.....47..743B|doi-access=free }}</ref> Current opportunity for research impact lies mainly in fundamental research and practical manufacturing.<ref>{{cite journal |vauthors= Extrand C |title= Self-Cleaning Surfaces:An Industrial Perspective |journal= MRS Bulletin |pages=733 |year=2008}}</ref> Debates have recently emerged concerning the applicability of the Wenzel and Cassie–Baxter models. In an experiment designed to challenge the surface energy perspective of the Wenzel and Cassie–Baxter model and promote a contact line perspective, water drops were placed on a smooth hydrophobic spot in a rough hydrophobic field, a rough hydrophobic spot in a smooth hydrophobic field, and a hydrophilic spot in a hydrophobic field.<ref>{{cite journal |vauthors= Gao L, McCarthy TJ |title= How Wenzel and Cassie Were Wrong |journal= Langmuir |volume= 23 |issue= 7 |pages= 3762–3765 |year= 2007 |pmid= 17315893 |doi= 10.1021/la062634a|s2cid= 23260001 }}</ref> Experiments showed that the surface chemistry and geometry at the contact line affected the contact angle and [[Contact angle#Contact Angle Hysteresis|contact angle hysteresis]], but the surface area inside the contact line had no effect. An argument that increased jaggedness in the contact line enhances droplet mobility has also been proposed.<ref>{{cite journal |vauthors= Chen W, Fadeev AY, Hsieh ME, Öner D, Youngblood J, McCarthy TJ |title= Ultrahydrophobic and ultralyophobic surfaces: Some comments and examples |journal=Langmuir |volume=15 |pages=3395–3399 |year=1999 |doi=10.1021/la990074s |issue=10}}</ref>
In recent research, superhydrophobicity has been reported by allowing alkylketene [[dimer (chemistry)|dimer]] (AKD) to solidify into a nanostructured fractal surface.<ref>{{cite journal |vauthors= Onda T, Shibuichi S, Satoh N, Tsujii K |title= Super-Water-Repellent Fractal Surfaces |journal=Langmuir |volume=12 |pages=2125–2127 |year=1996 |doi=10.1021/la950418o |issue=9}}</ref> Many papers have since presented fabrication methods for producing superhydrophobic surfaces including particle deposition,<ref name= "Miwa_2000">{{cite journal |vauthors= Miwa M, Nakajima A, Fujishima A, Hashimoto K, Watanabe T |title= Effects of the Surface Roughness on Sliding Angles of Water Droplets on Superhydrophobic Surfaces |journal=Langmuir |volume=16 |pages=5754–60 |year=2000 |doi=10.1021/la991660o |issue=13|s2cid= 97974935 }}</ref> sol-gel techniques,<ref>{{cite journal |vauthors= Shirtcliffe NJ, McHale G, Newton MI, Perry CC |title= Intrinsically superhydrophobic organosilica sol-gel foams |journal=Langmuir |volume=19 |pages=5626–5631 |year=2003 |doi=10.1021/la034204f |issue=14}}</ref> plasma treatments,<ref name="TeareSpanos2002">{{cite journal|last1=Teare|first1=D. O. H.|last2=Spanos|first2=C. G.|last3=Ridley|first3=P.|last4=Kinmond|first4=E. J.|last5=Roucoules|first5=V.|last6=Badyal|first6=J. P. S.|author-link6=Jas Pal Badyal|last7=Brewer|first7=S. A.|last8=Coulson|first8=S.|last9=Willis|first9=C.|title=Pulsed Plasma Deposition of Super-Hydrophobic Nanospheres|journal=Chemistry of Materials|volume=14|issue=11|year=2002|pages=4566–4571|issn=0897-4756|doi=10.1021/cm011600f}}</ref> vapor deposition,<ref name= "Miwa_2000"/> and casting techniques.<ref>{{cite journal |vauthors= Bico J, Marzolin C, Quéré D |title= Pearl drops |journal=[[Europhysics Letters]] |volume=47 |pages=743–744 |year=1999 |doi=10.1209/epl/i1999-00453-y |issue=6 |bibcode=1999EL.....47..743B|doi-access=free }}</ref> Current opportunity for research impact lies mainly in fundamental research and practical manufacturing.<ref>{{cite journal |vauthors= Extrand C |title= Self-Cleaning Surfaces:An Industrial Perspective |journal= MRS Bulletin |page=733 |year=2008}}</ref> Debates have recently emerged concerning the applicability of the Wenzel and Cassie–Baxter models. In an experiment designed to challenge the surface energy perspective of the Wenzel and Cassie–Baxter model and promote a contact line perspective, water drops were placed on a smooth hydrophobic spot in a rough hydrophobic field, a rough hydrophobic spot in a smooth hydrophobic field, and a hydrophilic spot in a hydrophobic field.<ref>{{cite journal |vauthors= Gao L, McCarthy TJ |title= How Wenzel and Cassie Were Wrong |journal= Langmuir |volume= 23 |issue= 7 |pages= 3762–3765 |year= 2007 |pmid= 17315893 |doi= 10.1021/la062634a|bibcode= 2007Langm..23.3762G |s2cid= 23260001 }}</ref> Experiments showed that the surface chemistry and geometry at the contact line affected the contact angle and [[Contact angle#Contact Angle Hysteresis|contact angle hysteresis]], but the surface area inside the contact line had no effect. An argument that increased jaggedness in the contact line enhances droplet mobility has also been proposed.<ref>{{cite journal |vauthors= Chen W, Fadeev AY, Hsieh ME, Öner D, Youngblood J, McCarthy TJ |title= Ultrahydrophobic and ultralyophobic surfaces: Some comments and examples |journal=Langmuir |volume=15 |pages=3395–3399 |year=1999 |doi=10.1021/la990074s |issue=10 |bibcode= 1999Langm..15.3395C }}</ref>


Many hydrophobic materials found in nature rely on [[Cassie's law]] and are [[phase (matter)|biphasic]] on the submicrometer level with one component air. The lotus effect is based on this principle. [[Biomimetics|Inspired by it]], many functional superhydrophobic surfaces have been prepared.<ref>{{cite book |doi= 10.1142/9789812772374_0013 |isbn= 978-981-270-564-8|chapter= Recent Progress on Bio-Inspired Surface with Special Wettability|title= Annual Review of Nano Research|date= 2006|last1= Wang|first1= Shutao|last2= Liu|first2= Huan|last3= Jiang|first3= Lei|volume= 1|pages= 573–628}}</ref>
Many hydrophobic materials found in nature rely on [[Cassie's law]] and are [[phase (matter)|biphasic]] on the submicrometer level with one component air. The lotus effect is based on this principle. [[Biomimetics|Inspired by it]], many functional superhydrophobic surfaces have been prepared.<ref>{{cite book |doi= 10.1142/9789812772374_0013 |isbn= 978-981-270-564-8|chapter= Recent Progress on Bio-Inspired Surface with Special Wettability|title= Annual Review of Nano Research|date= 2006|last1= Wang|first1= Shutao|last2= Liu|first2= Huan|last3= Jiang|first3= Lei|volume= 1|pages= 573–628}}</ref>
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Active recent research on superhydrophobic materials might eventually lead to more industrial applications.<ref>{{Cite journal |last1=Bo |first1=Wang |last2=Xueqin |first2=Zhang |last3=Bingkun |first3=Li |last4=Yijie |first4=Liu |last5=Chenguang |first5=Yang |last6=Yujun |first6=Guo |last7=Song |first7=Xiao |last8=Wenfu |first8=Wei |last9=Guoqiang |first9=Gao |last10=Guangning |first10=Wu |date=2024 |title=Advances in superhydrophobic material research: from preparation to electrified railway protection |journal=RSC Advances |language=en |volume=14 |issue=17 |pages=12204–12217 |doi=10.1039/D3RA08180J|pmid=38628488 |pmc=11019352 |bibcode=2024RSCAd..1412204B }}</ref>
Active recent research on superhydrophobic materials might eventually lead to more industrial applications.<ref>{{Cite journal |last1=Bo |first1=Wang |last2=Xueqin |first2=Zhang |last3=Bingkun |first3=Li |last4=Yijie |first4=Liu |last5=Chenguang |first5=Yang |last6=Yujun |first6=Guo |last7=Song |first7=Xiao |last8=Wenfu |first8=Wei |last9=Guoqiang |first9=Gao |last10=Guangning |first10=Wu |date=2024 |title=Advances in superhydrophobic material research: from preparation to electrified railway protection |journal=RSC Advances |language=en |volume=14 |issue=17 |pages=12204–12217 |doi=10.1039/D3RA08180J|pmid=38628488 |pmc=11019352 |bibcode=2024RSCAd..1412204B }}</ref>


A simple routine of coating cotton fabric with [[silica]]<ref>{{cite journal |vauthors= Xue CH, Jia ST, Zhang LQ, Chen HZ, Wang M|title=Preparation of superhydrophobic surfaces on cotton textiles|journal=Science and Technology of Advanced Materials|date=1 July 2008|volume=9|issue=3|pages=035008|doi=10.1088/1468-6996/9/3/035008|pmid=27878005|bibcode=2008STAdM...9c5008X|pmc=5099662}}</ref> or [[titanium dioxide|titania]]<ref>{{cite journal |vauthors= Xue CH, Jai ST, Chen HZ, Wang H|title=Superhydrophobic cotton fabrics prepared by sol–gel coating of TiO and surface hydrophobization|journal=Science and Technology of Advanced Materials|date=1 July 2008|volume=9|issue=3|pages=035001|doi=10.1088/1468-6996/9/3/035001|pmid=27877998|bibcode=2008STAdM...9c5001X|pmc=5099655}}</ref> particles by [[sol–gel process|sol-gel technique]] has been reported, which protects the fabric from UV light and makes it superhydrophobic.
A simple routine of coating cotton fabric with [[silica]]<ref>{{cite journal |vauthors= Xue CH, Jia ST, Zhang LQ, Chen HZ, Wang M|title=Preparation of superhydrophobic surfaces on cotton textiles|journal=Science and Technology of Advanced Materials|date=1 July 2008|volume=9|issue=3|article-number=035008|doi=10.1088/1468-6996/9/3/035008|pmid=27878005|bibcode=2008STAdM...9c5008X|pmc=5099662}}</ref> or [[titanium dioxide|titania]]<ref>{{cite journal |vauthors= Xue CH, Jai ST, Chen HZ, Wang H|title=Superhydrophobic cotton fabrics prepared by sol–gel coating of TiO and surface hydrophobization|journal=Science and Technology of Advanced Materials|date=1 July 2008|volume=9|issue=3|article-number=035001|doi=10.1088/1468-6996/9/3/035001|pmid=27877998|bibcode=2008STAdM...9c5001X|pmc=5099655}}</ref> particles by [[sol–gel process|sol-gel technique]] has been reported, which protects the fabric from UV light and makes it superhydrophobic.


An efficient routine has been reported for making [[polyethylene]] superhydrophobic and thus self-cleaning.<ref>{{cite journal |vauthors= Yuan Z, Chen H, Zhang J, Zhao D, Liu Y, Zhou X, Li S, Shi P, Tang J, Chen X|title=Preparation and characterization of self-cleaning stable superhydrophobic linear low-density polyethylene|journal=Science and Technology of Advanced Materials|date=1 December 2008|volume=9|issue=4|pages=045007|doi=10.1088/1468-6996/9/4/045007|pmid=27878035|bibcode=2008STAdM...9d5007Y|pmc=5099649}}</ref> 99% of dirt on such a surface is easily washed away.
An efficient routine has been reported for making [[polyethylene]] superhydrophobic and thus self-cleaning.<ref>{{cite journal |vauthors= Yuan Z, Chen H, Zhang J, Zhao D, Liu Y, Zhou X, Li S, Shi P, Tang J, Chen X|title=Preparation and characterization of self-cleaning stable superhydrophobic linear low-density polyethylene|journal=Science and Technology of Advanced Materials|date=1 December 2008|volume=9|issue=4|article-number=045007|doi=10.1088/1468-6996/9/4/045007|pmid=27878035|bibcode=2008STAdM...9d5007Y|pmc=5099649}}</ref> 99% of dirt on such a surface is easily washed away.


Patterned superhydrophobic surfaces also have promise for lab-on-a-chip microfluidic devices and can drastically improve surface-based bioanalysis.<ref name=Ressine2007>{{cite book |vauthors= Ressine A, Marko-Varga G, Laurell T |title= Porous silicon protein microarray technology and ultra-/superhydrophobic states for improved bioanalytical readout |volume= 13 |pages= 149–200 |year= 2007 |pmid= 17875477 |doi= 10.1016/S1387-2656(07)13007-6 |isbn= 9780444530325 |series= Biotechnology Annual Review}}</ref>
Patterned superhydrophobic surfaces also have promise for lab-on-a-chip microfluidic devices and can drastically improve surface-based bioanalysis.<ref name=Ressine2007>{{cite book |vauthors= Ressine A, Marko-Varga G, Laurell T |title= Porous silicon protein microarray technology and ultra-/superhydrophobic states for improved bioanalytical readout |volume= 13 |pages= 149–200 |year= 2007 |pmid= 17875477 |doi= 10.1016/S1387-2656(07)13007-6 |isbn= 978-0-444-53032-5 |series= Biotechnology Annual Review}}</ref>


In pharmaceuticals, hydrophobicity of pharmaceutical blends affects important quality attributes of final products, such as [[Dissolution testing|drug dissolution]] and [[Tablet hardness testing|hardness]].<ref>{{Cite journal|last1=Wang|first1=Yifan|last2=Liu|first2=Zhanjie|last3=Muzzio|first3=Fernando|last4=Drazer|first4=German|last5=Callegari|first5=Gerardo|date=2018-03-01|title=A drop penetration method to measure powder blend wettability|journal=International Journal of Pharmaceutics|volume=538|issue=1|pages=112–118|doi=10.1016/j.ijpharm.2017.12.034|pmid=29253584|issn=0378-5173|doi-access=free}}</ref> Methods have been developed to measure the hydrophobicity of pharmaceutical materials.<ref>{{Cite journal|last1=Emady|first1=Heather N.|last2=Kayrak-Talay|first2=Defne|last3=Litster|first3=James D.|date=2013|title=A regime map for granule formation by drop impact on powder beds|journal=AIChE Journal|language=en|volume=59|issue=1|pages=96–107|doi=10.1002/aic.13952|bibcode=2013AIChE..59...96E |issn=1547-5905}}</ref><ref>{{Cite journal|last1=Llusa|first1=Marcos|last2=Levin|first2=Michael|last3=Snee|first3=Ronald D.|last4=Muzzio|first4=Fernando J.|date=2010-02-20|title=Measuring the hydrophobicity of lubricated blends of pharmaceutical excipients|journal=Powder Technology|volume=198|issue=1|pages=101–107|doi=10.1016/j.powtec.2009.10.021|issn=0032-5910}}</ref>
In pharmaceuticals, hydrophobicity of pharmaceutical blends affects important quality attributes of final products, such as [[Dissolution testing|drug dissolution]] and [[Tablet hardness testing|hardness]].<ref>{{Cite journal|last1=Wang|first1=Yifan|last2=Liu|first2=Zhanjie|last3=Muzzio|first3=Fernando|last4=Drazer|first4=German|last5=Callegari|first5=Gerardo|date=2018-03-01|title=A drop penetration method to measure powder blend wettability|journal=International Journal of Pharmaceutics|volume=538|issue=1|pages=112–118|doi=10.1016/j.ijpharm.2017.12.034|pmid=29253584|issn=0378-5173|doi-access=free}}</ref> Methods have been developed to measure the hydrophobicity of pharmaceutical materials.<ref>{{Cite journal|last1=Emady|first1=Heather N.|last2=Kayrak-Talay|first2=Defne|last3=Litster|first3=James D.|date=2013|title=A regime map for granule formation by drop impact on powder beds|journal=AIChE Journal|language=en|volume=59|issue=1|pages=96–107|doi=10.1002/aic.13952|bibcode=2013AIChE..59...96E |issn=1547-5905}}</ref><ref>{{Cite journal|last1=Llusa|first1=Marcos|last2=Levin|first2=Michael|last3=Snee|first3=Ronald D.|last4=Muzzio|first4=Fernando J.|date=2010-02-20|title=Measuring the hydrophobicity of lubricated blends of pharmaceutical excipients|journal=Powder Technology|volume=198|issue=1|pages=101–107|doi=10.1016/j.powtec.2009.10.021|issn=0032-5910}}</ref>
Line 107: Line 108:
* {{annotated link|Superhydrophobic coating}}
* {{annotated link|Superhydrophobic coating}}
* {{annotated link|Ultrahydrophobicity|aka=superhydrophobicity}}
* {{annotated link|Ultrahydrophobicity|aka=superhydrophobicity}}
* [[Wetting]] – discusses how hydrophobicity affects spreading and contact angles
* [[Contact angle]] – classical macroscopic measure linked to hydrophobicity via the DIT molecular criterion


==References==
==References==

Latest revision as of 12:01, 30 March 2026

For other uses, see Hydrophobia (disambiguation).
File:150 deg water contact angle.png
165° water contact angle on a surface modified using plasma technology system surface chemistry. The contact angle is the red angle plus 90°.
File:Dew 2.jpg
Dew drop on a hydrophobic leaf surface
File:Cutting a water droplet using a superhydrophobic knife on superhydrophobic surfaces.ogv
Cutting a water droplet using a superhydrophobic knife on superhydrophobic surfaces
File:Drops I.jpg
Water drops on the hydrophobic surface of grass

In chemistry, hydrophobicity is the chemical property of a molecule (called a hydrophobe) that is seemingly repelled from a mass of water.[1] In contrast, hydrophiles are attracted to water.

Hydrophobic molecules tend to be nonpolar and, thus, prefer other neutral molecules and nonpolar solvents. Because water molecules are polar, hydrophobes do not dissolve well among them. Hydrophobic molecules in water often cluster together, forming micelles. Water on hydrophobic surfaces will exhibit a high contact angle.

Examples of hydrophobic molecules include the alkanes, oils, fats, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of oil spills, and chemical separation processes to remove non-polar substances from polar compounds.[2]

The term hydrophobic—which comes from the Ancient Greek ὑδρόφοβος (Template:Transliteration), "having a fear of water", constructed Template:Ety[3]—is often used interchangeably with lipophilic, "fat-loving". However, the two terms are not synonymous. While hydrophobic substances are usually lipophilic, there are exceptions, such as the silicones and fluorocarbons.[4][5]

Chemistry

Main article: Hydrophobic effect

For small solutes, the hydrophobic interaction is mostly an entropic effect originating from the disruption of the highly dynamic hydrogen bonds between molecules of liquid water by the nonpolar solute, causing the water to compensate by forming a clathrate-like cage structure around the non-polar molecules. This structure is more highly ordered than free water molecules due to the water molecules arranging themselves to interact as much as possible with themselves, and thus results in a lower entropic state at the interface. This causes non-polar molecules to clump together to reduce the surface area exposed to water and thereby increase the entropy of the system.[6][7] Thus, the two immiscible phases (hydrophilic vs. hydrophobic) will change so that their corresponding interfacial area will be minimal. This effect can be visualized in the phenomenon called phase separation.[citation needed]

For larger nonpolar solutes that cannot be adequately "clathrated" by the hydrogen-bond network of water, the disruption of these bonds becomes inevitable, leading to a high enthalpic cost. Under ambient conditions, this transition from an entropy-dominated regime to one governed by enthalpy occurs at around ~1 nm in size, reflecting a shift in hydration free energy behavior from scaling with the solute volume to depending on the exposed surface area.[8][9]

In this context, a quantitative molecular definition of hydrophobicity has been proposed, based on the energetic cost for a system to induce hydrogen-bond defects in its hydration shell. According to this approach, a system is considered hydrophobic if it cannot compensate for the missing hydrogen bonds with an energy at least as favorable as the cost of generating such a defect in pure water, a value known as the Defect Interaction Threshold (DIT), estimated at approximately −6 kJ/mol (around 30% of the typical energy of a hydrogen bond). This criterion coincides with the classical 90° contact angle threshold, thus providing a molecular justification for the transition to hydrophobic behavior.[10][11]

Additionally, the DIT helps determine the regimes of filling, partial filling, and drying in nanoconfined water, depending on how many of the water molecule's interaction sites (among its four tetrahedral sites) exceed this threshold. This analysis for quantifying hydrophobicity or wetting can be performed using a structural indicator, the V4S index, which reveals the existence of two inherently preferential interaction states for water.[12]

Superhydrophobicity

Main article: Superhydrophobe
File:DropConnectionAngel.jpg
A water drop on a lotus plant leaf

Superhydrophobic surfaces, such as the leaves of the lotus plant, are those that are extremely difficult to wet. The contact angles of a water droplet exceeds 150°.[13] This is referred to as the lotus effect, and is primarily a physical property related to interfacial tension, rather than a chemical property.[14]

Theory

In 1805, Thomas Young defined the contact angle θ by analyzing the forces acting on a fluid droplet resting on a solid surface surrounded by a gas.[15]

File:Contact angle.svg
A liquid droplet rests on a solid surface and is surrounded by gas. The contact angle, θC, is the angle formed by a liquid at the three-phase boundary where the liquid, gas, and solid intersect.
File:Contact angle microstates.svg
A droplet resting on a solid surface and surrounded by a gas forms a characteristic contact angle θ. If the solid surface is rough, and the liquid is in intimate contact with the solid asperities, the droplet is in the Wenzel state. If the liquid rests on the tops of the asperities, it is in the Cassie–Baxter state.
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \gamma_\text{SG}\ =\gamma_\text{SL}+\gamma_\text{LG}\cos\theta \,}

where

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \gamma_\text{SG}\ } = Interfacial tension between the solid and gas
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \gamma_\text{SL}\ } = Interfacial tension between the solid and liquid
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \gamma_\text{LG}\ } = Interfacial tension between the liquid and gas

θ can be measured using a contact angle goniometer.

Wenzel determined that when the liquid is in intimate contact with a microstructured surface, θ will change to θW*

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \cos\theta_W* = r \cos\theta \, }

where r is the ratio of the actual area to the projected area.[16] Wenzel's equation shows that microstructuring a surface amplifies the natural tendency of the surface. A hydrophobic surface (one that has an original contact angle greater than 90°) becomes more hydrophobic when microstructured – its new contact angle becomes greater than the original. However, a hydrophilic surface (one that has an original contact angle less than 90°) becomes more hydrophilic when microstructured – its new contact angle becomes less than the original.[17] Cassie and Baxter found that if the liquid is suspended on the tops of microstructures, θ will change to θCB*:

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \cos\theta_\text{CB}* = \varphi(\cos\theta + 1) - 1 \,}

where φ is the area fraction of the solid that touches the liquid.[18] Liquid in the Cassie–Baxter state is more mobile than in the Wenzel state.[19]

We can predict whether the Wenzel or Cassie–Baxter state should exist by calculating the new contact angle with both equations. By a minimization of free energy argument, the relation that predicted the smaller new contact angle is the state most likely to exist. Stated in mathematical terms, for the Cassie–Baxter state to exist, the following inequality must be true.[20]

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \cos\theta<\frac{\varphi-1}{r-\varphi}}

A recent alternative criterion for the Cassie–Baxter state asserts that the Cassie–Baxter state exists when the following 2 criteria are met:1) Contact line forces overcome body forces of unsupported droplet weight and 2) The microstructures are tall enough to prevent the liquid that bridges microstructures from touching the base of the microstructures.[21]

A new criterion for the switch between Wenzel and Cassie-Baxter states has been developed recently based on surface roughness and surface energy.[22] The criterion focuses on the air-trapping capability under liquid droplets on rough surfaces, which could tell whether Wenzel's model or Cassie-Baxter's model should be used for certain combination of surface roughness and energy.[23]

Contact angle is a measure of static hydrophobicity, and contact angle hysteresis and slide angle are dynamic measures. Contact angle hysteresis is a phenomenon that characterizes surface heterogeneity.[24] When a pipette injects a liquid onto a solid, the liquid will form some contact angle. As the pipette injects more liquid, the droplet will increase in volume, the contact angle will increase, but its three-phase boundary will remain stationary until it suddenly advances outward. The contact angle the droplet had immediately before advancing outward is termed the advancing contact angle. The receding contact angle is now measured by pumping the liquid back out of the droplet. The droplet will decrease in volume, the contact angle will decrease, but its three-phase boundary will remain stationary until it suddenly recedes inward. The contact angle the droplet had immediately before receding inward is termed the receding contact angle. The difference between advancing and receding contact angles is termed contact angle hysteresis and can be used to characterize surface heterogeneity, roughness, and mobility.[25] Surfaces that are not homogeneous will have domains that impede motion of the contact line. The slide angle is another dynamic measure of hydrophobicity and is measured by depositing a droplet on a surface and tilting the surface until the droplet begins to slide. In general, liquids in the Cassie–Baxter state exhibit lower slide angles and contact angle hysteresis than those in the Wenzel state.[citation needed]

Soil science

File:Rim Fire 20130817-FS-UNK-0094 (9898761875).jpg
The Rim Fire caused soil hydrophobicity, as demonstrated by this water that won't infiltrate into the dry soil

Soil tends to become hydrophobic in response to wildfires. Depending on the severity of the fire, this can lead to more precipitation being rendered as surface runoff, traveling over the surface without infiltrating into the soil.[26]

Research and development

File:A-simple-and-fast-fabrication-of-a-both-self-cleanable-and-deep-UV-antireflective-quartz-1556-276X-7-430-S1.ogv
Water droplets roll down an inclined hydrophobic surface.
File:Hydrophoby2.webm
Water droplets on an artificial hydrophobic surface (left)

Dettre and Johnson discovered in 1964 that the superhydrophobic lotus effect phenomenon was related to rough hydrophobic surfaces, and they developed a theoretical model based on experiments with glass beads coated with paraffin or TFE telomer. The self-cleaning property of superhydrophobic micro-nanostructured surfaces was reported in 1977.[27] Perfluoroalkyl, perfluoropolyether, and RF plasma -formed superhydrophobic materials were developed, used for electrowetting and commercialized for bio-medical applications between 1986 and 1995.[28][29][30][31] Other technology and applications have emerged since the mid-1990s.[32] A durable superhydrophobic hierarchical composition, applied in one or two steps, was disclosed in 2002 comprising nano-sized particles ≤ 100 nanometers overlaying a surface having micrometer-sized features or particles ≤ 100 micrometers. The larger particles were observed to protect the smaller particles from mechanical abrasion.[33]

In recent research, superhydrophobicity has been reported by allowing alkylketene dimer (AKD) to solidify into a nanostructured fractal surface.[34] Many papers have since presented fabrication methods for producing superhydrophobic surfaces including particle deposition,[35] sol-gel techniques,[36] plasma treatments,[37] vapor deposition,[35] and casting techniques.[38] Current opportunity for research impact lies mainly in fundamental research and practical manufacturing.[39] Debates have recently emerged concerning the applicability of the Wenzel and Cassie–Baxter models. In an experiment designed to challenge the surface energy perspective of the Wenzel and Cassie–Baxter model and promote a contact line perspective, water drops were placed on a smooth hydrophobic spot in a rough hydrophobic field, a rough hydrophobic spot in a smooth hydrophobic field, and a hydrophilic spot in a hydrophobic field.[40] Experiments showed that the surface chemistry and geometry at the contact line affected the contact angle and contact angle hysteresis, but the surface area inside the contact line had no effect. An argument that increased jaggedness in the contact line enhances droplet mobility has also been proposed.[41]

Many hydrophobic materials found in nature rely on Cassie's law and are biphasic on the submicrometer level with one component air. The lotus effect is based on this principle. Inspired by it, many functional superhydrophobic surfaces have been prepared.[42]

An example of a bionic or biomimetic superhydrophobic material in nanotechnology is nanopin film.[citation needed]

One study presents a vanadium pentoxide surface that switches reversibly between superhydrophobicity and superhydrophilicity under the influence of UV radiation.[43] According to the study, any surface can be modified to this effect by application of a suspension of rose-like V2O5 particles, for instance with an inkjet printer. Once again hydrophobicity is induced by interlaminar air pockets (separated by 2.1 nm distances). The UV effect is also explained. UV light creates electron-hole pairs, with the holes reacting with lattice oxygen, creating surface oxygen vacancies, while the electrons reduce V5+ to V3+. The oxygen vacancies are met by water, and it is this water absorbency by the vanadium surface that makes it hydrophilic. By extended storage in the dark, water is replaced by oxygen and hydrophilicity is once again lost.[citation needed]

A significant majority of hydrophobic surfaces have their hydrophobic properties imparted by structural or chemical modification of a surface of a bulk material, through either coatings or surface treatments. That is to say, the presence of molecular species (usually organic) or structural features results in high contact angles of water. In recent years, rare earth oxides have been shown to possess intrinsic hydrophobicity.[44] The intrinsic hydrophobicity of rare earth oxides depends on surface orientation and oxygen vacancy levels, and is naturally more robust than coatings or surface treatments, having potential applications in condensers and catalysts that can operate at high temperatures or corrosive environments.[45]

Applications and potential applications

Hydrophobic concrete has been produced since the mid-20th century.[citation needed]

Active recent research on superhydrophobic materials might eventually lead to more industrial applications.[46]

A simple routine of coating cotton fabric with silica[47] or titania[48] particles by sol-gel technique has been reported, which protects the fabric from UV light and makes it superhydrophobic.

An efficient routine has been reported for making polyethylene superhydrophobic and thus self-cleaning.[49] 99% of dirt on such a surface is easily washed away.

Patterned superhydrophobic surfaces also have promise for lab-on-a-chip microfluidic devices and can drastically improve surface-based bioanalysis.[50]

In pharmaceuticals, hydrophobicity of pharmaceutical blends affects important quality attributes of final products, such as drug dissolution and hardness.[51] Methods have been developed to measure the hydrophobicity of pharmaceutical materials.[52][53]

The development of hydrophobic passive daytime radiative cooling (PDRC) surfaces, whose effectiveness at solar reflectance and thermal emittance is predicated on their cleanliness, has improved the "self-cleaning" of these surfaces. Scalable and sustainable hydrophobic PDRCs that avoid VOCs have further been developed.[54]

See also

References

  1. ↑ Ben-Na'im, Aryeh (31 January 1980). Hydrophobic Interaction. New York: Plenum Press. ISBN 0-306-40222-X.
  2. ↑ Akhavan B, Jarvis K, Majewski P (November 2013). "Hydrophobic Plasma Polymer Coated Silica Particles for Petroleum Hydrocarbon Removal". ACS Appl. Mater. Interfaces. 5 (17): 8563–8571. Bibcode:2013AAMI....5.8563A. doi:10.1021/am4020154. PMID 23942510.
  3. ↑ Liddell, H.G. & Scott, R. (1940). A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie. Oxford: Clarendon Press.
  4. ↑ Xi, J. (1987). "The effect of hydrophobic-lipophilic interactions on chemical reactivity——3.Contributions of lipophilic interactions to the binding of hydrocarbon substrates by amylose-type hosts and of hydrophobic interactions to the binding of fluorocarbon su". S2CID 101053755. Cite journal requires |journal= (help)
  5. ↑ "Transport of Lipophilic Substances - LabCE.com, Laboratory Continuing Education". www.labce.com. Retrieved 2025-02-22.
  6. ↑ Garrett, Reginald; Grisham, Charles (January 5, 2012). Biochemistry. Cengage Learning. pp. 31–35. ISBN 978-1-133-10629-6.
  7. ↑ Silverstein TP (1998). "The Real Reason Why Oil and Water Don't Mix" (PDF). Journal of Chemical Education. 75 (1): 116–346. Bibcode:1998JChEd..75..116S. doi:10.1021/ed075p116. Retrieved 9 December 2011 – via DocDroid.
  8. ↑ Patel AJ et al., Proc. Natl. Acad. Sci. U.S.A. 108(43), 17678–17683 (2011), https://doi.org/10.1073/pnas.1110703108
  9. ↑ Rajamani S et al., Proc. Natl. Acad. Sci. U.S.A. 102, 9475–9480 (2005), https://doi.org/10.1073/pnas.0504089102
  10. ↑ Loubet NA, Verde AR & Appignanesi GA, J. Chem. Phys. 160, 064502 (2025), https://doi.org/10.1063/5.0276390
  11. ↑ Accordino SR, Menendez CA, Loubet NA, Alarcon LM & Appignanesi GA, J. Phys.: Condens. Matter 37, 305101 (2025), https://doi.org/10.1088/1361-648X/adebd4
  12. ↑ Loubet NA, Verde AR & Appignanesi GA, J. Chem. Phys. (2024), https://doi.org/10.1063/5.0203989
  13. ↑ Wang S, Jiang L (2007). "Definition of superhydrophobic states". Advanced Materials. 19 (21): 3423–3424. Bibcode:2007AdM....19.3423W. doi:10.1002/adma.200700934. S2CID 138017937.
  14. ↑ Tg (2008). "BIOMIMICRY: The Lotus Effect". ASEE Prism. 18 (2): 23. ISSN 1056-8077. JSTOR 24162971.
  15. ↑ Young, T. (1805). "An Essay on the Cohesion of Fluids". Phil. Trans. R. Soc. Lond. 95: 65–87. doi:10.1098/rstl.1805.0005. S2CID 116124581.
  16. ↑ Wenzel, RN (1936). "Resistance of Solid Surfaces to Wetting by Water". Ind. Eng. Chem. 28 (8): 988–994. doi:10.1021/ie50320a024.
  17. ↑ de Gennes, Pierre-Gilles (2004). Capillarity and Wetting Phenomena. Springer. ISBN 0-387-00592-7.
  18. ↑ Baxter AB, Cassie S (1944). "Wettability of Porous Surfaces". Trans. Faraday Soc. 40: 546–551. doi:10.1039/tf9444000546.
  19. ↑ McHale, G.; Shirtcliffe, N. J.; Newton, M. I. (2004). "Contact-angle hysteresis on superhydrophobic surfaces: Hydrophobicity, hydrophilicity and Young's law". Langmuir. 20 (23): 10146–10149. doi:10.1021/la048629t. PMID 15350093.
  20. ↑ Quere, D (2005). "Non-sticking Drops". Reports on Progress in Physics. 68 (11): 2495–2532. Bibcode:2005RPPh...68.2495Q. doi:10.1088/0034-4885/68/11/R01. S2CID 121128710.
  21. ↑ Extrand CW (2005). "Modeling of ultralyophobicity: Suspension of liquid drops by a single asperity". Langmuir. 21 (23): 10370–10374. doi:10.1021/la0513050. PMID 16262294.
  22. ↑ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  23. ↑ Jäger, Tobias; Mokos, Athanasios; Prasianakis, Nikolaos I.; Leyer, Stephan (2024-03-05). "Validating the Transition Criteria from the Cassie-Baxter to the Wenzel State for Periodically Pillared Surfaces with Lattice Boltzmann Simulations". ACS Omega. 9 (9): 10592–10601. doi:10.1021/acsomega.3c08862. ISSN 2470-1343. PMC 10918652 Check |pmc= value (help). PMID 38463292 Check |pmid= value (help).
  24. ↑ Johnson RE, Dettre RH (1964). "Contact Angle Hysteresis". J. Phys. Chem. 68 (7): 1744–1750. doi:10.1021/j100789a012.
  25. ↑ Laurén, Susanna. "How to measure contact angle hysteresis?". blog.biolinscientific.com. Retrieved 2019-12-31.
  26. ↑ Vore, Margot E.; Déry, Stephen J.; Hou, Yiping; Wei, Xiaohua (2020-11-30). "Climatic influences on forest fire and mountain pine beetle outbreaks and resulting runoff effects in large watersheds in British Columbia, Canada". Hydrological Processes. 34 (24): 4561. Bibcode:2020HyPr...34.4560V. doi:10.1002/hyp.13908. ISSN 0885-6087.
  27. ↑ Barthlott, Wilhelm; Ehler, Nesta (1977). Raster-Elektronenmikroskopie der Epidermis-Oberflächen von Spermatophyten. Tropische und subtropische Pflanzenwelt (in German). p. 110. ISBN 978-3-515-02620-8.
  28. ↑ J. Brown. "US Patent 4,911,782". Archived from the original on 2018-07-14. Retrieved 2015-01-13.
  29. ↑ J. Brown. "US Patent 5,200,152". Archived from the original on 2017-07-27. Retrieved 2015-01-13.
  30. ↑ National Science Foundation. "Stopped-Flow Cytometer".
  31. ↑ J. Brown. "US Patent 5,853,894". Archived from the original on 2017-01-22. Retrieved 2015-01-13.
  32. ↑ Barthlott, Wilhelm; C. Neinhuis (1997). "The purity of sacred lotus or escape from contamination in biological surfaces". Planta. 202 (1): 1–8. Bibcode:1997Plant.202....1B. doi:10.1007/s004250050096. S2CID 37872229.
  33. ↑ J. Brown. "US Patent 6,767,587". Archived from the original on 2018-07-14. Retrieved 2015-01-13.
  34. ↑ Onda T, Shibuichi S, Satoh N, Tsujii K (1996). "Super-Water-Repellent Fractal Surfaces". Langmuir. 12 (9): 2125–2127. doi:10.1021/la950418o.
  35. ↑ 35.0 35.1 Miwa M, Nakajima A, Fujishima A, Hashimoto K, Watanabe T (2000). "Effects of the Surface Roughness on Sliding Angles of Water Droplets on Superhydrophobic Surfaces". Langmuir. 16 (13): 5754–60. doi:10.1021/la991660o. S2CID 97974935.
  36. ↑ Shirtcliffe NJ, McHale G, Newton MI, Perry CC (2003). "Intrinsically superhydrophobic organosilica sol-gel foams". Langmuir. 19 (14): 5626–5631. doi:10.1021/la034204f.
  37. ↑ Teare, D. O. H.; Spanos, C. G.; Ridley, P.; Kinmond, E. J.; Roucoules, V.; Badyal, J. P. S.; Brewer, S. A.; Coulson, S.; Willis, C. (2002). "Pulsed Plasma Deposition of Super-Hydrophobic Nanospheres". Chemistry of Materials. 14 (11): 4566–4571. doi:10.1021/cm011600f. ISSN 0897-4756.
  38. ↑ Bico J, Marzolin C, Quéré D (1999). "Pearl drops". Europhysics Letters. 47 (6): 743–744. Bibcode:1999EL.....47..743B. doi:10.1209/epl/i1999-00453-y.
  39. ↑ Extrand C (2008). "Self-Cleaning Surfaces:An Industrial Perspective". MRS Bulletin: 733.
  40. ↑ Gao L, McCarthy TJ (2007). "How Wenzel and Cassie Were Wrong". Langmuir. 23 (7): 3762–3765. Bibcode:2007Langm..23.3762G. doi:10.1021/la062634a. PMID 17315893. S2CID 23260001.
  41. ↑ Chen W, Fadeev AY, Hsieh ME, Öner D, Youngblood J, McCarthy TJ (1999). "Ultrahydrophobic and ultralyophobic surfaces: Some comments and examples". Langmuir. 15 (10): 3395–3399. Bibcode:1999Langm..15.3395C. doi:10.1021/la990074s.
  42. ↑ Wang, Shutao; Liu, Huan; Jiang, Lei (2006). "Recent Progress on Bio-Inspired Surface with Special Wettability". Annual Review of Nano Research. 1. pp. 573–628. doi:10.1142/9789812772374_0013. ISBN 978-981-270-564-8.
  43. ↑ Sun Lim, Ho; Kwak, Donghoon; Yun Lee, Dong; Goo Lee, Seung; Cho, Kilwon (2007). "UV-Driven Reversible Switching of a Roselike Vanadium Oxide Film between Superhydrophobicity and Superhydrophilicity". J. Am. Chem. Soc. 129 (14): 4128–4129. Bibcode:2007JAChS.129.4128L. doi:10.1021/ja0692579. PMID 17358065.
  44. ↑ Tribonet: Rare earth oxides make water repellent surfaces that last
  45. ↑ Fronzi, M (2019). "Theoretical insights into the hydrophobicity of low index CeO2 surfaces". Applied Surface Science. 478: 68–74. arXiv:1902.02662. Bibcode:2019ApSS..478...68F. doi:10.1016/j.apsusc.2019.01.208. S2CID 118895100.
  46. ↑ Bo, Wang; Xueqin, Zhang; Bingkun, Li; Yijie, Liu; Chenguang, Yang; Yujun, Guo; Song, Xiao; Wenfu, Wei; Guoqiang, Gao; Guangning, Wu (2024). "Advances in superhydrophobic material research: from preparation to electrified railway protection". RSC Advances. 14 (17): 12204–12217. Bibcode:2024RSCAd..1412204B. doi:10.1039/D3RA08180J. PMC 11019352 Check |pmc= value (help). PMID 38628488 Check |pmid= value (help).
  47. ↑ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
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  50. ↑ Ressine A, Marko-Varga G, Laurell T (2007). Porous silicon protein microarray technology and ultra-/superhydrophobic states for improved bioanalytical readout. Biotechnology Annual Review. 13. pp. 149–200. doi:10.1016/S1387-2656(07)13007-6. ISBN 978-0-444-53032-5. PMID 17875477.
  51. ↑ Wang, Yifan; Liu, Zhanjie; Muzzio, Fernando; Drazer, German; Callegari, Gerardo (2018-03-01). "A drop penetration method to measure powder blend wettability". International Journal of Pharmaceutics. 538 (1): 112–118. doi:10.1016/j.ijpharm.2017.12.034. ISSN 0378-5173. PMID 29253584.
  52. ↑ Emady, Heather N.; Kayrak-Talay, Defne; Litster, James D. (2013). "A regime map for granule formation by drop impact on powder beds". AIChE Journal. 59 (1): 96–107. Bibcode:2013AIChE..59...96E. doi:10.1002/aic.13952. ISSN 1547-5905.
  53. ↑ Llusa, Marcos; Levin, Michael; Snee, Ronald D.; Muzzio, Fernando J. (2010-02-20). "Measuring the hydrophobicity of lubricated blends of pharmaceutical excipients". Powder Technology. 198 (1): 101–107. doi:10.1016/j.powtec.2009.10.021. ISSN 0032-5910.
  54. ↑ Chen, Meijie; Pang, Dan; Yan, Hongjie (April 2022). "Sustainable and self-cleaning bilayer coatings for high-efficiency daytime radiative cooling". Journal of Materials Chemistry. 10 (2).

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