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Slippery Solutions for Sticky ProblemsTM
www.slipstechnologies.com
‘Sticky’ Problems!
Wetting of Liquid on Solid Surface
Young (1805)
Wenzel (1936)
Cassie-Baxter (1944)
Cassie (1948)
γLVcos𝜃 = γSV − γLS
cos𝜃* = rcos𝜃
cos𝜃* = -1 + ɸs(cos𝜃 +1)
cos𝜃* = A1cos𝜃1 + A2cos𝜃2
solid
vapor
liquid𝜃
contact angle (CA): 𝜃
ideal flat
texturedwetted
texturednon-wetted
chemicallyheterogeneous
Removal of Liquid on Solid Surface
𝜃R𝜃A
α
gravity
contact angle hysteresis (CAH): 𝜃A - 𝜃R
γLV (cosθR – cosθA) = mg sinα/w Furmidge (1962)
minimizing liquid pinning is the KEYto extreme liquid repellency
solid
𝜃R𝜃A
α
Gibbs (1873)Dyson (1988)
Oliver, Huh, Mason (1977)
θ ≤ θA ≤ θ + (180° - β) Gibbs Inequalities:
𝜃𝜃
β
𝜃A
solidrough solid
Water-Repellent, Self-Cleaning Surfaces in Nature
20µm
200 nm
Planta 202 1-8 1997!
Nature 432 36 2004!
Soft Matter 3 178-182 2007!
Water-Repellent, Self-Cleaning Surfaces in Nature
20µm
200 nm
Planta 202 1-8 1997!
Nature 432 36 2004!
Soft Matter 3 178-182 2007!
Lessons learned from Nature:• Often hierarchical structures• Covered with hydrophobic materials• High contact angles
Bio-inspired Superhydrophobic Surfaces
Wenzel
State
low surface tension liquidhigh temperature
high pressuremechanical damage
high humidity
‘sticky’droplet
Cassie-BaxterState
‘non-sticky’ droplet
A Radically Different Strategy
• Can we make the surface ‘slippery’?- ultrasmooth interface�- essentially eliminates ‘pinning points’ �- can we (practically) do this with a solid material?
• What about using a ‘liquid’?�- but how can we hold such liquid?�- what about using non-interacting, immiscible liquid (e.g. PFPE, silicone)?
• Of course, durability, scale-up, manufacturing, and cost are the pressing issues
Tree2(12)364–369(1987),PNAS10114138–14143(2004),Proc.R.Soc.B(2008),PlantSignaling&Behavior(2009),Prog.Nat.Sci.(2009)
Another Source of Inspiration:Carnivorous Nepenthes Pitcher Plant
Tree2(12)364–369(1987),PNAS10114138–14143(2004),Proc.R.Soc.B(2008),PlantSignaling&Behavior(2009),Prog.Nat.Sci.(2009)
Lessons learned from Nature:• Immiscible liquid layer
• Chemical Affinity• Capillarity
Another Source of Inspiration:Carnivorous Nepenthes Pitcher Plant
Pitcher Plant-Inspired Surface and Coating
Slippery Liquid-Infused Porous Surfaces
infuse witha lubricant
liquid/solidbeing repelled
surface functionalization/conditioningsurface
roughening
self-healing and repellent !lubricating film in and on a porous solid!
• Sub-nanometer smoothness• Excellent repellency to almost everything • High pressure/temperature tolerance• Self-healing characteristics• Highly customizable system
Key Features Nature 477 443-447 2011!ACS Nano 6(8) 6569-6577 2012!PNAS 109(33) 13182-13187 2012!PCCP 15 581-585 2013!Nano Lett. 13(4) 1793-1799 2013!Nature Materials 12 529-534 2013!Appl. Phys. Lett. 102 231603 2013!Nature Commun. 4 2013!Nanotechnology 25 2013!Angew. Chem. Int. Ed. 53 2014!
Design Principle: Modeling the Film Stability
Wong et al., Nature 477 443-447 2011!
Teflon vs. Superhydrophobic vs. SLIPS
Crude Oil Blood
Stable up to 250°C and ~700 atm (10,000 psi)
Wong et al., Nature 477 443-447 2011!
Temperature Resistance Self-healing
SLIPS Prevent Bacterial Biofilm Formation�(static culture)
Epstein et al., PNAS 109(33) 13182-13187 2012!
Epstein et al., PNAS 109(33) 13182-13187 2012!
CtrlPTFE SLIPS
P. aeruginosa in media is pumped through PTFE and SLIPS PTFE tubing
48 hour growth10 mL/min flow
SLIPS Prevent Bacterial Biofilm Formation�(under flow)
Yet another approach to create ‘liquid interface’
SLIPS vs. Biofouling (Lab Test)
Chlamydomonas reinhardtii algal biofilm, 2 weeks culture
R-SLIPS against Marine Biofouling (Field Test)
silicone coating
Slippery Solutions for Sticky ProblemsTM
www.slipstechnologies.com
Thank You!!
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