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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> | ||
== | ==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- | 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> | ||
=== 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 | | '''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.{{ | 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 | | 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 | 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 ≤ 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 | | 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| | 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| | 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= | 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> | ||
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* {{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== | ||