The Construction And Properties Of Slippery Liquid-Infused Porous Surface Prepared By Infusing Lubricant Into Polystyrene With Porous Structure

Inspired by special surface structures from plants and animals in nature,omniphobic material with self-cleaning,anti-icing and anti-adhesion properties has been investigated widely,which has a broad application in fields of energy,transportation,medical treatment,membrane separation and heat transfer.Nowadays,most of superhydrophobic surfaces were inspired by the macro-/nano-textured surface from lotus,but they have poor oleophobic property and the disability of self-repairing after physical damage which limits their applications.However,slippery liquid-infused porous surface(SLIPS)inspired by Nepenthes pitcher plants,has much better properties than traditional hydrophobic surfaces,such as excellent high-pressure stability,hydrophobic and oleophobic,self-cleaning and self-repairing properties.SLIPS is prepared by infusing lubricant oil with low surface tension into macro-/nano-textured surfaces or substrate with inter-connective porous structure,to form a stable lubricant film on the substrate surface resulting in omniphobic property.The substrate offers a storage for storing lubricant and its internal porous structure provides transportation for infusing lubricant.In this thesis,two kinds of polystyrene based porous material(PS-HIPE and PSBM-HIPE),prepared by high internal phase emulsion(HIPE),were used as substrates to construct SLIPS by infusing silicon or perfluorinated lubricant oil.The main works are shown as follows:1.Preparation of PS-HIPE and construction of PDMS infused PS-HIPE based SLIPS(1)Preparation and characterization of PS-HIPE.PS-HIPE was prepared by adding aqueous phase(K2S2O8 as initiator,CaCl2 as stabilizer and water as porogen)dropwise into oil phase(Styrene as monomer,DVB as crosslinking agent,Span 80 as surfactant)under high speed stirring(homogenizer),which was polymerized at 60? after sealing and then removed unreacted monomers and surfactants by Soxhlet Extraction.Effect of crosslinked agent DVB content(5wt%,10wt%,20wt%)on the internal structure of PS-HIPE was investigated by SEM.The results show that PS-HIPE10 with 10 wt%DVB has the biggest openness(19.8%),and the size of pore decreases with the increase of DVB which can result in apparent shrinkage and collapse of internal structure.(2)The construction of PS-HIPE based SLIPS.To construct SLIPS,PDMS was infused into PS-HIPE automatically by capillary force.Effects of the pore size of PS-HIPE and PDMS viscosity(100 mpa·s,500 mpa·s,1000 mpa·s)on PDMS loading are characterized by weight differentiation.The results show that PS-HIPE10 has the biggest PDMS loading content and the speed of PDMS loading decreased with the PDMS viscosity increased.(3)The wettability of PS-HIPE10 and SLIPS was characterized by water contact angle(WCA)and water sliding angle(WSA).The results show that The construction of PS-HIPE based SLIPS improved the slippery performance of PS-HIPE10 greatly since water droplet could slide down from SLIPS at 3°instead of pinning on PS-HIPE10 surface even inclined at 90°.The WSA of SLIPS declined with PDMS viscosity increased.(4)Self-cleaning property of SLIPS was tested by whether there are residual stains of liquid and solid smudges on its surface.The result shows that it has excellent self-cleaning property that liquid smudges(water,milk,coffee and ink),immiscible with PDMS,can slide off from SLIPS easily without stain leaving,while other liquids(oil and solvents),miscible with PDMS,spread on the material or infiltrate into it.The solid contaminants can be washed by water without any leaving.Therefore,it has good hydrophobic property,but has poor oleophobic and anti-solvent properties.(5)Self-repairing property of SLIPS was characterized by imitating the physical damage with a scalpel slashing the surface of the SLIPS.The water droplet could smoothly slide across the dent without any stains leaving,showing that the dent can be refilled by PDMS to form a continuous lubricant film thereby recovering the self-cleaning property.(6)The durability of PDMS on SLIPS was characterized by testing the WSA repeatedly in the same position of SLIPS.The mechanical property of SLIPS was measured by stress-strain curve of PS-HIPE10 before and after PDMS loading.The results show that the WSA can maintain 50 even after 80 times without extra PDMS supplied at the bottom of SLIPS,so PDMS consumption is in acceptable level when SLIPS is in use.The PS-HIPE and SLIPS show similar stress-strain curve which can be concluded that PDMS loading don't have negative effect on mechanical property of PS-HIPE.2.Preparation of PSBM-HIPE and construction of fluorinated fluid infused PSBM-HIPE based SLIPS(1)Preparation of PSBM-HIPE.In order to alleviate the brittleness of PS-HIPE and improve the ability of substrate to lock lubricant oil,butyl acrylate(BA)and methacryloxy propyl trimethoxyl silane(MPS)were introduced into oil phase of HIPE polymerization,with poly(St70-BA20-MPS10)prepared(marked as PSBM-HIPE).When the content of BA is lower than 30wt%,the toughness of substrate can be improved and the porous structure is suitable for constructing SLIPS.However,when it is over 30wt%,the substrate has apparent volume shrinkage.The WCA of PSBM-HIPE is about 137°,but water droplet cannot slide down the surface of PSBM-HIPE which is similar as PS-HIPE.(2)Sol-gel and fluorinated modification of PSBM-HIPE.At first,PSBM-HIPE was only modified by sol-gel for loading SiO2 nanoparticles to prepare SiO2@PSBM-HIPE.Lots of SiO2 nanoparticles appeared on the outer surface of PSBM-HIPE,but there is very few in the inner surface,resulted in the disability of providing macro-/nano-textured structure from substrate after wearing outer surface.Therefore,during sol-gel process,1H,1H,2H,2H-perfluorodecyltri ethoxy silane(PFDTOS)was introduced to prepare F-SiO2@PSBM-HIPE with the sol-gel and fluorinated modification finished simultaneously.SEM shows that there is a layer of F-SiO2 nanoparticles attaching on the outer and inner surface of PSBM-HIPE uniformly.The WCA of F-SiO2@PSBM-HIPE reached to 149.30 and aqueous smudges can slide down at 100 within 1 s,but it also has poor oleophobic and anti-solvent properties similar as PDMS infused PS-HIPE based SLIPS.(3)Construction and characterization of F-SiO2@PSBM-HIPE based SLIPS.The fluorinated fluid(Krytox GPL 105)was infused into F-SiO2@PSBM-HIPE to construct F-SLIPS.The omniphobic property of F-SLIPS was tested by WCA and the wettability of ethanol and hexadecane on its surface.The results show that its WCA reach to 113°,and ethanol(represented solvent)and hexadecane(represented oil)can slide off from its surface with hemispherical states,instead of spreading on its surface or infiltrating into it.Thus,F-SLIPS has excellent omniphobic property that can repel water,solvent and oil.