Liquid-impregnated surface
A slippery liquid-infused porous surface (SLIPS), liquid-impregnated surface (LIS), or multi-phase surface consists of two distinct layers. The first is a highly textured or porous substrate with features spaced sufficiently close to stably contain the second layer which is an impregnating liquid that fills in the spaces between the features.{{cite web | url=https://patents.google.com/patent/US9121306B2/ | title=Slippery surfaces with high pressure stability, optical transparency, and self-healing characteristics }}{{cite web|title=US Patent # US 20130032316 A1|url=https://patents.google.com/patent/US20130032316|work=US Patent|publisher=USPTO|access-date=18 October 2013}}{{cite web|title=US Patent # US 20090191374 A1|url=https://patents.google.com/patent/US20090191374|work=US Patent|publisher=USPTO|access-date=10 August 2022}} The liquid must have a surface energy well-matched to the substrate in order to form a stable film.{{cite journal | last1=Wong | first1=Tak-Sing | last2=Kang | first2=Sung Hoon | last3=Tang | first3=Sindy K. Y. | last4=Smythe | first4=Elizabeth J. | last5=Hatton | first5=Benjamin D. | last6=Grinthal | first6=Alison | last7=Aizenberg | first7=Joanna | title=Bioinspired self-repairing slippery surfaces with pressure-stable omniphobicity | journal=Nature | volume=477 | issue=7365 | date=2011 | issn=0028-0836 | doi=10.1038/nature10447 | doi-access=free | pages=443–447 | pmid=21938066 | bibcode=2011Natur.477..443W | url=https://dash.harvard.edu/bitstream/1/27417441/1/Jasman%20%20Ware%20-%20Bioinspired%20self-repairing%20slippery%20surfaces%20with%20pressure-stable%20omniphobicity.pdf | access-date=2025-05-06}} Slippery surfaces are finding applications in commercial products, anti-fouling surfaces, anti-icing{{cite journal | last1=Wilson | first1=Peter W. | last2=Lu | first2=Weizhe | last3=Xu | first3=Haojun | last4=Kim | first4=Philseok | last5=Kreder | first5=Michael J. | last6=Alvarenga | first6=Jack | last7=Aizenberg | first7=Joanna | title=Inhibition of ice nucleation by slippery liquid-infused porous surfaces (SLIPS) | journal=Phys. Chem. Chem. Phys. | volume=15 | issue=2 | date=2013 | issn=1463-9076 | doi=10.1039/C2CP43586A | pages=581–585 | pmid=23183624 | bibcode=2013PCCP...15..581W | url=https://xlink.rsc.org/?DOI=C2CP43586A | access-date=2025-05-06}} and biofilm-resistant medical devices.{{cite journal | last1=Epstein | first1=Alexander K. | last2=Wong | first2=Tak-Sing | last3=Belisle | first3=Rebecca A. | last4=Boggs | first4=Emily Marie | last5=Aizenberg | first5=Joanna | title=Liquid-infused structured surfaces with exceptional anti-biofouling performance | journal=Proceedings of the National Academy of Sciences | volume=109 | issue=33 | date=2012-08-14 | issn=0027-8424 | pmid=22847405 | pmc=3421179 | doi=10.1073/pnas.1201973109 | doi-access=free | pages=13182–13187 | url=https://www.pnas.org/content/pnas/109/33/13182.full.pdf | access-date=2025-05-06}}
Adaptive Surface Technologies {{Cite web |title=Adaptive Surface Technologies |url=https://www.adaptivesurface.tech/ |access-date=2022-08-17 |website=Adaptive Surface Technologies |language=en-US}} and LiquiGlide are commercial examples of liquid-impregnated surfaces, invented at Harvard University{{cite web | url=https://patents.google.com/patent/US9121306B2/ | title=Slippery surfaces with high pressure stability, optical transparency, and self-healing characteristics }} and the Massachusetts Institute of Technology.{{cite web|title=LiquiGlide website|url=http://www.liquiglide.com|publisher=LiquiGlide Inc.|access-date=5 November 2013}}{{cite book | last1=Solomon | first1=Brian R. | last2=Subramanyam | first2=Srinivas Bengaluru | last3=Farnham | first3=Taylor A. | last4=Khalil | first4=Karim S. | last5=Anand | first5=Sushant | last6=Varanasi | first6=Kripa K. | title=Soft Matter Series | chapter=CHAPTER 10. Lubricant-Impregnated Surfaces | publisher=Royal Society of Chemistry | publication-place=Cambridge | date=2016 | isbn=978-1-78262-154-6 | doi=10.1039/9781782623953-00285 | url=https://books.rsc.org/books/monograph/618/chapter-abstract/298796/ | access-date=2025-05-06 | pages=285–318}}{{cite journal | last=Chang | first=Kenneth | title=Solving a Sticky Problem | journal=The New York Times | date=2015-03-24 | issn=0362-4331 | pages=D4(L)–D4(L) | url=https://go.gale.com/ps/i.do?id=GALE%7CA406690474&sid=googleScholar&v=2.1&it=r&linkaccess=abs&issn=03624331&p=AONE&sw=w&userGroupName=anon~ba5e43e4&aty=open-web-entry | access-date=2025-05-06}}
SLIPS type surfaces have a number of advantages over traditional lotus based superhydrophobic surfaces. The free flowing liquid allows for the creation of a smooth surface with the ability to self-repair. This smooth surface often results in a low sliding angle for both high and low surface tension liquids, enhancing droplet shedding and heat transfer.{{cite journal | last1=Yogi | first1=Yashwant S. | last2=Parmar | first2=Harsharaj B. | last3=Fattahi Juybari | first3=Hamid | last4=Nejati | first4=Sina | last5=Rao | first5=Akshay K. | last6=Roy | first6=Rishav | last7=Zarei | first7=Mojtaba | last8=Li | first8=Longnan | last9=Sett | first9=Soumyadip | last10=Das | first10=Abhimanyu | last11=Miljkovic | first11=Nenad | last12=Weibel | first12=Justin A. | last13=Warsinger | first13=David M. | title=Slippery liquid infused porous surface (SLIPS) condensers for high efficiency air gap membrane distillation | journal=Communications Engineering | volume=4 | issue=1 | date=2025-03-15 | issn=2731-3395 | pmid=40089632 | pmc=11910583 | doi=10.1038/s44172-025-00348-y | doi-access=free | page=48}} Finally, SLIPS surfaces can be made optically transparent unlike many traditional superhydrophobic surfaces that scatter light due to having structure on the same order as visible light.
However, the longevity of SLIPS for prolonged anti-icing applications have been of concern.{{Cite journal|last1=Rykaczewski|first1=Konrad|last2=Anand|first2=Sushant|last3=Subramanyam|first3=Srinivas Bengaluru|last4=Varanasi|first4=Kripa K.|date=2013-04-30|title=Mechanism of Frost Formation on Lubricant-Impregnated Surfaces|journal=Langmuir|volume=29|issue=17|pages=5230–5238|doi=10.1021/la400801s|pmid=23565857|issn=0743-7463}} In this regard, replacing the lubricant in SLIPS with a phase switching liquid (PSL) {{Cite journal|last1=Chatterjee|first1=Rukmava|last2=Beysens|first2=Daniel|last3=Anand|first3=Sushant|title=Delaying Ice and Frost Formation Using Phase-Switching Liquids|journal=Advanced Materials|language=en|issue=17|pages=1807812|doi=10.1002/adma.201807812|pmid=30873685|issn=1521-4095|year=2019|volume=31|bibcode=2019AdM....3107812C |doi-access=free}} can yield promising results. PSLs are a class of phase change materials, which are in liquid state under ambient conditions and have a melting point higher than the freezing point of water. Thus the PSL changes into solid phase in a cold environment before water freezing can happen. While PSL impregnated textured surface behave as a traditional SLIPS in ambient conditions, when operated below the melting point of PSL, they resist PSL displacement out of surface texture by water, engendering enhanced icephobicity even on hydrophilic substrates.