The Synthesis Of Low-surface-energy Fluorinated Emulsions And Fabrication Of Superhvdrophobic Surfaces

The superhydrophobic surface is an extremely hydrophobic surface with a water contact angle greater than 150°.Because of its unique wetting property,super hydrophobic surface has outstanding application potentials on anti-fogging,anti-icing,self-cleaning,anti-corrosion,anti-fouling and other fields.Reducing surface energy and increasing roughness are the most important ways to fabricate superhydrophobic surfaces.Fluorinated emulsions with low surface energy are prepared by simple emulsion polymerization,which is an effective way to reduce surface energy and increase the.hydrophobicity of materials.However,fluorine-containing emulsions contain a large number of amphiphilic emulsifiers.The hydrophilic groups in emulsifiers may remain in the emulsion coatings,which greatly reduces the hydrophobicity of coatings.To solve the problems of low fluorine content,large amounts of hydrophilic groups and lack of hydrophobicity,the influence of emulsifiers on the stability of emulsion polymerization and hydrophobicity of emulsion coatings was systematically studied in this paper,which contains the molecular design of emulsifiers' composition and charges,added with the subsequent reaction of transforming hydrophilic groups into hydrophobic groups.The purpose is to fabricate superhydrophobic surfaces by simple emulsion coatings.This paper first used 2-(perfluorohexyl)ethyl acrylate(PFHEA)as hydrophobic monomers,methyl methacrylate(MMA)as polymerization-controlling monomers,2-acrylanmido-2-methylpropanesulfonic acid(AMPS)as hydrophilic monomers,to synthetize amphiphilic macromolecular fluorine-containing emulsifier P(PFHEA-co-MMA-co-AMPS)by free radical polymerization of solution.Emulsion polymerization of PFHEA,MMA and methyl butyl acrylate(BMA)was emulsified by macromolecular emulsifiers.Then the stability,composition and hydrophobic properties of emulsions with different emulsifier concentration were investigated.With suitable ratio of hydrophilic monomers,the emulsion based on macromolecule emulsifiers had high stability,high fluorine content and very little content of hydrophilic component,which was far less than the emulsion using traditional emulsifier.As a consequence,surface energy of the drying latex film could be very low,which was only 9.8 mN/m.The crosslinking agent consisted of hexamethoxymethylmelamine with higher reactivity could react with hydroxyl and sulfonic groups easily,and hydrophobic cross linking networks were formed.Based on this cross-linking reaction,fluorinated emulsions emulsified by the sulfonic emulsifier and the crosslinker were used together for the first time.After dip-coat-cure process on high porosity glass fiber nonwoven fabric and wool nonwoven,superhydrophobic surfaces were obtained simply and effectively.By comparing the fluorine-containing emulsions with different emulsifier concentration,it is found that when the concentration of macromolecule emulsifier was 1.2 wt%,the size of the emulsion was only 87.5 nm,and it had the highest stability and the lowest surface energy(10.7 mN/m),which is the most suitable emulsifier concentration.The subsequent crosslinking agent could react with the sulfonic groups in the emulsifier and the hydroxyl groups on the substrate fibers,which formed a crosslinking network between the coatings and fibers.It could not only increase the combination of polymers and substrates and improve the long-term stability,but also limit the migration of the hydrophilic group in the emulsifiers.As a result,the largest water contact angle of the coated glass fiber obtained is 151.40 and the smallest slide angle measured is only 3.9°,exhibiting superior water repellency to other fluorinated emulsion coatings.Moreover,the great anti-fouling properties and water/oil separation performance suggest that the facile method is promising for varied applications.Cationic emulsifiers are mostly quaternary ammonium salt emulsifiers,which are highly hydrophilic and unable to react and transform.In this paper,highly reactive amphiphilic protonated octadecylamine was used as emulsifiers to emulsify PFHEA,MMA and BMA,and cationic fluorinated acrylate emulsions with high stability and high fluorine content were obtained.The emulsions contained only one kind of hydrophilic amine group,and the hydrophilic groups were converted into hydrophobic perfluoro side chains using the Michael addition reaction.The reaction efficiency was above 70%.After added with PFHEA,the content of hydrophobic groups on the surfaces were obviously increased,meanwhile the content of the hydrophilic groups were correspondently decrased.As a result,the surface energy of emulsion coatings was extremely low as 10.78mN/m after the fluorination and the contact angle of coated rough glass fiber reached to 150°and the slide angle was only 4.7°.Moreover,the Michael acceptors were alternative and acrylates with different hydrophobic side groups were added to amine groups.All the contact angles of the coated glass fibers were greatly improved and the rolling angles were all below 10°.Notably,other functional groups can be introduced into the coatings to broaden the application area of fluorinated coatings through molecular design.Silane coupling agents can hydrolyze and conduct condensation polymerization to form crosslinking networks under mild conditions,which are commonly used crosslinking binders.Based on the synthesized cationic fluoroacrylate emulsion containing primary amine group,3-(trimethoxysilyl)propyl methacrylate(MPTMS)was added to the emulsion coatings by the Michael addition reaction,and then the superhydrophobic Fluorinated siliane crosslinking coatings were constructed by hydrolysis and condensation of siloxane.When the concentration of silane coupling agent was 10wt%,the hydrophilic amine groups in the emulsifier and the hydroxyl groups on the substrate fibers were reacted and crosslinked respectively to the hydrophobic siloxane crosslinking network,which results in the superhydrophobic states with water contact angles all above 150°.Due to the introduction and crosslinking reaction of MPTMS,a more rough and uniform crosslinking network was formed between the emulsion and fibers,resulting in excellent stability,abrasion resistance and anti-fouling properties.Robust chemical bond between coatings and substrates gives the modified cotton fabric outstanding washing fastness,which enlarges the application area of fluorinated siliane crosslinking coatings.