| Textiles with liquid repellency that exhibit excellent waterproof,reduction of liquid viscosity and self-cleaning properties have been widely used in protective,medical,and outdoor clothing,and have been one of the research hotspots in the field of functional textiles.At present,textiles finished with organic fluorine agents show good liquid-repellency,due to the lower surface energy.However,most of the organic fluorine finishing agents contain perfluorooctanesulfonyl compounds(PFOS)and perfluorooctanoic acid(PFOA),or will eventually degrade to produce PFOS/PFOA compounds.Both PFOS and PFOA are hard to degrade,leading to bioaccumulation and toxicity,which have become new pollutants in the world.Therefore,the development of environmentally friendly fluorine-free liquid repellent materials has aroused great interest among researchers.In general,it is easier to obtain fluorine-free water repellent,while the realization of fluorine-free oil repellent is challenging.The surface tension of oil(e.g.,hexadecane,27.3 mN/m)is much lower than that of water(27.3 mN/m).It is necessary to adopt low surface energy chemical agents with fluorinecontaining for oil repellant modification.In recent years,it has been found that fluorine-free oil repellency can be realized to a certain extent via the rational design of polysiloxane structure.However,there is still no systematic research on the application of polysiloxane membrane with different molecular structures for preparting liquid repellent fabrics.Three-dimensional(3D)network polysiloxane containing methyl groups films and 3D network polysiloxane containing propyl groups films,crosslinked polysiloxane films and linear polysiloxane molecular brush were fabricated in this thesis.The effects of fabrication parameters on the morphology,chemical composition and wettability of the proposed four films were studied;the wettability of fabrics coated with these four polysiloxane layer was investigated.According to the fabrication parameters and the characteristics of superhydrophobic layer,functional applications of polysiloxane,such as superhydrophobic silk,superhydrophobic elastic conductive fabric for underwater strain sensor and fluorinefree oil-repellent nylon fabric were designed and developed by selecting suitable fabric and combining it with other surface treatment methods.It was found that all the four polysiloxane coatings can endow the fabric superhydrophobicity,while only the fabric coated with linear polysiloxane could realize both superhydrophobic and oil-repellent properties.The specific research results are as follows:(1)Chemical vapor deposition of 3D network polysiloxane film with methyl and superhydrophobic silk fabrics:3D network polysiloxane layer was constructed via chemical vapor deposition of trichorosilane at low temperature(66℃),and then superhydrophobic silk was obtained by combining with the enzyme etching to increase the roughness of the surface(WCA:153.5°,SA:8.5°;oil spreads within 0.48 s).No nanoparticles(NPs)or organic solvent was used during the whole process of sample preparation,and the temperature for chemical vapor deposition was low.The obtained fabric could still remain the good mechanical resistance,wearability(air permeability,whiteness)and high-efficient self-cleaning and oil-water separation.Apart from this,the proposed method could be applied to a variety of substrates according to the characteristics of enzymes(cellulase etches cotton fabric,and alkaline protease etches wool fabric),showing good versatility.(2)Chemical vapor deposition of 3D network polysiloxane film with propyl groups and superhydrophobic fabric-based strain sensor:Taking advantage of the controllable thickness of the layer via vapor deposition,3D network polysiloxane film with propyl groups was fabricated on the elastic conductive fabric via vapor deposition,which didn’t affect the conductivity of the fabric.Compared with the coating containing methyl,higher CA and lower SA can be obtained,and the complete wetting time of oil droplet increased to 9.45 s.The superhydrophobic property of the processed fabric allowed the sample to monitor finger and elbow movements not only in air,but also under water.The repulsion of the superhydrophobic conductive coating to acid and alkali droplets made the sample suitable to be applied in wet and acid/alkali environment.(3)Polysiloxane film with linear molecules randomly stacked and cross-linked and multifunctional durable super-hydrophobic surface:Linear polydimethylsiloxane(PDMS)was randomly stacked on the surface of the substrate by high temperature vapor deposition to form a dense nanoparticle coating.Then the multifunctional superhydrophobic fabric was obtained by spray coating with cross-linked PDMS and functional NPs on the polysiloxane layer with linear molecules randomly stacked.The WCA was 165.5°,and the adhesion force between substrate and water droplet was only 4 μN.The time of oil spreading was 0.35 s.The superhydrophobic surface exhibited excellent resistance to acid and alkali,high speed water impact and tape peeling.Additionally,the introduced different functional NPs during the process of spraying endowed the surface reversible wettability,anti-icing,photodegradation of dyes and self-cleaning.(4)Chemical vapor deposition of linear polysiloxane melocular brush and superhydrophobic/oil-repellent fabric:Oil-repellent surfaces grafted with brush of liquidlike linear PDMS long chains were prepared by chemical vapor deposition.The CAs of the prepared superhydrophobic and oil-repellent nylon fabric to water droplets,soybean oil,mineral oil,cetane,sunflower seed oil and diesel oil were 147.7°,133.6°,92.5°,75.7°,65.1°,53.3°,82.5°and 54.7°,respectively.According to ISO 14419 in 2010,the oil repellent grade of the coated fabric was 5,which could statically keep dodecane for a long time.It was found that the smooth substrates(titanium,aluminum and glass)modified with linear PDMS brush exhibited low adhesion to oil(hexadecane:Δθ=1.7°,SA～8°).As comparison,the 3D network fluoropolymer silane film obtained by trichlorofluorosilane showed higher oil adhesion(Δθ=46.1°,SA～81°).According to the mechanism analysis,it is believed that the brush of liquid-like linear polysiloxane molecules swells and forms an air layer,which introduce air and reduce the solid-liquid contact line,preventing oil droplets directly contact the surface of the fabric.Combined with low surface energy,the polysiloxane brush can endow the surface of the fabric with oil repellency.In addition,the brush of linear PDMS molecules has highly movable flexible segments,and the droplets combine with the segments from the smooth substrate surface and slide down with the movement of the segments,therefore the surface shows a very low contact angle hysteresis for oil droplets.A comprehensive comparison of the fluorine-free liquid repellent fabrics prepared by the above four polysiloxane layers is made,and the conclusion is as follows:The preparation method of chemical vapor deposition methyltrichlorosilane combined with enzymatic etching is suitable for liquid-repellent modification of natural fiber fabrics in low temperature environments,and then superhydrophobic and superlipophilic silk,cotton and wool fabrics are obtained.The method of combining chemical vapor deposition propytrichlorosilane and in-situ polymerization can be used for synthetic fiber fabrics including polyester,spandex,etc.,to obtain a superhydrophobic and superlipophilic and stretchable polyester-spandex fabric(the liquid repellency was higher than polysiloxane film containing methyl).The preparation method of spraying crosslinked polysiloxane combined with high temperature thermal treatment of linear polysiloxane segment is suitable for high temperature resistant fabrics,such as carbon cloth and aramid.Compared with the above two methods,fabrics coated with crosslinked polysiloxane exhibit superior superhydrophobic performance,but no oil repellency.Finally,the preparation method for the combination of chemical vapor deposition of linear polysiloxane brush and sol-gel is suitable for fabric with low porosity,like nylon fabric.Fluorine-free and oil repellent nylon fabric with oleophobic level of 5 can be obtained... |
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