Preparation and Property of (Fluoro) Polysiloxane Superhydrophobic Surfaces on Cotton Fabrics
|School||Shaanxi University of Science and Technology|
|Keywords||superhydrophobic polysiloxane organofluorine cotton fiber nano silica|
Wettability, which is determined by chemical compositions andmicrostructure of one solid surface, is an important property for solid surface,and thus can be well controlled via the exact regulation of surface free energyand roughness. Due to their unique structure, inorganic-polymer hybridmaterials can endow the matrix with novel properties and thus have become oneof the hot topics in fabrication of the biomimetic super-hydrophobic surfaces. Itis generally recognized that microscopic roughness on solid surface couldmainly be realized by the inorganic nano-materials. However, it should not beignored what design and synthesis of hydrophobic polymeric films withmicroscopic roughness plays in construction of surface with multi-scaleroughness. Furthermore, how to achieve the chemical bonds between inorganicnano-particle and polymer, to improve their compatibility and thenano-particle’s dispersity, and to finally construct superhydrophobic hybridcoatings on cotton fabrics/fibers surface with multi-function and high durabilityis a worthy scientific theme to explore.Therefore, on basis of the “Lotus effect” principle in fabrication ofsuperhydrophobic surface and the low surface free energy characteristic oforganic fluorosilicone polymer, we exploited the principle of molecular designand series of chemical reactions to first prepare several organic fluorosiliconepolymers, and then to synthesize series of fluorosilicone nanocomposites viachemical grafting or structural modification in which silica nanoparticles ofvarious structures were bonded onto pendant groups of the fluorosilicone polymers. Finally, we fabricated the biomimetic super-hydrophobic surfaces oncotton with softness and high durability via simple dip-coating of thosenanocomposites. The main research works are listed as followings:1. Preparation of stearyl methacrylate modified polysiloxane/silicananocomposite and fabrication of superhydrophobic cotton fabric from it.Comb-like stearyl/epoxy groups modified polysiloxane （PSAMS） wasfirstly prepared by hydrosilylation of stearyl methacrylate （SMA）, allylglyeidylether （AGE） and polyhydromethylsiloxane （PHMS）. Then a series of themonodispersed and amorphous aminopropyl modified silicas （H2N-SiO2） withthe average particle sizes from55.54to231.4nm were fabricated through thehydrolysis-condensation reaction of tetraethyl orthosilicate under alkalinecondition followed by the modification of aminopropyl triethoxysilane（KH-550）. At last, a stearyl methacrylate modified polysiloxane/silicananocomposite （PSAMS-SiO2） was synthesized from graft copolymerization ofamino-modified silica and PSAMS. Structures of the intermediates and the finalproducts, their film morphology and properties were characterized by IR,1H/13C-NMR, SEM, AFM, XPS, and contact angle meter, repectively. Thereaction conditions were discussed and the preparation technology of thePSAMS-SiO2was ultimately established. Then, a superhydrophobic cottonfabric with softness and high durability was constructed via one-stepimmersing-padding-baking processes. Results indicated that film morphology ofthe PSAMS presented a coarse film of the molecular sieve pattern, and more theamount of the imported stearyl ester groups were, rougher the PSAMS film was.Particle size and graft ratio of the H2N-SiO2as well as the PSAMS structureplayed an important role in the morphology and performance properties of theresultant PSAMS-SiO2. In the hybrid hierarchy, fine film morphology of thePSAMS-SiO2could be further roughened by introduction of H2N-SiO2anddisplayed a multi-phase pattern, which could enhance the hydrophobicity andthe thermal stability of the hybrid film. While the average diameter of H2N-SiO2was176.2nm and the grafting ratio of SiO2attained6.3wt%based on the massof PSAMS, the root-square-mean roughness （Rq） of the PSAMS-SiO2filmcould be increased from0.370nm prior to hybridization to4.066nm, and thestatic water contact angle （WCA） and the roll-off angle on the treated fabric could reach to158.5°and reduce to10°, respectively. During the baking process,the crosslinking and immobilizing effects between the Si-OH, C-OH groups ofthe polysiloxane molecules and hydroxyl groups of cotton cellulose can avoidthe detachment of nano silica and afford the PSAMS-SiO2film with goodwashing durability. Thus, WCA could still retain140°after20cycles ofsoaping.Finally, the superhydrophobic mechanism of the PSAMS-SiO2hybrid filmon the cotton fibers surface had been interpreted by the Cassie’s theoreticalmodel. The area portions of the liquid/vapor contact area was89%on thecomposite interface of the PSAMS-SiO2treated fabric surface and there were alot of gases embedded in air pockets from the multi-scaled rough cottonsurfaces, which impelled the water droplets as the suspended state on cottonsurface and those should be the inherent reason of acquiring thesuperhydrophobic effect. Hereby, the directional arrangement and film-formingmanners of the PSAMS-SiO2on cotton fiber surface are proposed.2. Synthesis of comb-like organo-fluorosilicone copolymer/silicananocomposite and construction of superhydrophobic cotton fabric from it.A novel comb-like fluorosilicone copolymer （PFAMS） was firstly preparedby hydrosilylation of perfluorooctyl ethylene （PFOE）, allylglyeidyl ether （AGE）and polymethyltrifluoropropylhydrosiloxane （PFHMS）. Then series offluorosilicone copolymer/silica nanocomposites （PFAMS-SiO2） with combstructure were synthesized from graft copolymerization of H2N-SiO2andPFAMS and used in fabrication of superhydrophobic cotton fabrics. Structuresof the intermediates and the final products, their film morphology and propertieswere characterized using above the same methods. Results indicated that thesuperhydrophobicity of the treated cotton fabric by PFAMS-SiO2was superiorto that of the PSAMS-SiO2treated fabric. When the average diameter of thesilica sol was204.7nm and the graft ratio of silica was9.7%, the bestsuperhydrophobicity was obtained with WCA of161.5°and roll-off angle of9°.It was probably originated from the facts that the fluoroalkyl groups was proneto migrate into the surface compared to long-chain alkyl, and thus, the surfacefree energy of the treated fabric was reduced to a lower extent. Furthermore, bycomparison with PSAMS, RMS of the PFAMS was larger and its Rq could attain0.567nm on silicon wafer. Nanoscale roughness of the PFAMS-SiO2could be further enlarged by introduction of SiO2particles and its Rq couldachieve4.104nm. Thus the combination of the long chain fluoroalkyl with lowsurface free energy and the multi-scaled rough surface would preferablyengender the bigger WCA and the smaller roll-off angle. At last, thesuperhydrophobic mechanism of the PFAMS-SiO2hybrid film on the cottonfibers surface had been interpreted by the Cassie’s theoretical model and thearea portions of the liquid/vapor contact area was91%on the compositeinterface of the PFAMS-SiO2treated fabric surface, which implies thatmicro-nano embossments resembling lotus leaf surface have been produced onthe PFAMS-SiO2treated cotton surface and the air pockets in thosecharacteristic dual-scaled rough films make the water droplets contact the top ofthe films, therefore, superhydrophobicity of the PFAMS-SiO2treated cotton ismore favorable.3. Fabrication of superhydrophobic cotton fabric using polysiloxane/SiO2hybrid material with crosslinked network structure.Firstly, epoxy group-terminated polyvinylmethylsiloxane precursors（Ep-PDMS-Vi） were prepared via the alkaline equilibration reaction ofoctamethylcyclotetrasiloxane （D4）,2,4,6,8-Tetramethyl-2,4,6,8-tetravinyl-cyclotetrasiloxane （DVi4）, and3-glycidyl ether propyl-1,1,3,3-tetramethyldi-methylsiloxane （DEP2）. Then, a sort of epoxy group-terminated polysiloxaneintermediates with network structure （Ep-JNPDMS） was acquired byhydrosilylation of Ep-PDMS-Vi and PHMS. Next, those Ep-JNPDMS wouldreact with KH-550to produce series of alkoxy silane-containing hydrophobicpolysiloxane with network strucuture （JNPDMS）. On this basis, a series of lowcost and environmental benign polysiloxane/SiO2hybrid materials withcrosslinked network structure （JNPDMS-SiO2） were made by in-situcondensation reaction among silicon hydroxyls. IR and XPS were utilized tocharacterize the JNPDMS-SiO2. The emphasis was put in this context onthermal stability, micro-morphology, film-forming mechanism andhydrophobicity of the JNPDMS-SiO2film on fiber surface. Results indicatedthat the grafting ratio of SiO2onto the JNPDMS-SiO2skeletons was effectivelyenhanced by the in-situ condensation method and it could maximumly attain 23%. Furthermore, that crosslinked network structure of the JNPDMS would bebeneficial to the enhancement of thermal stability and hydrophobicity of theJNPDMS-SiO2. AFM result demonstrated that the characteristic crosslinkednetwork of JNPDMS could form a homogeneous, smooth and dense film on theimitated cotton fiber surface with RMS of0.256nm in2×2μm2scanning range.However, in hybrid system, fine film morphology of the JNPDMS-SiO2couldbe greatly roughened by introduction of SiO2and displayed an irregular andmulti-phase pattern. There were many peaks and hills with different levels andthus Rq of the JNPDMS-SiO2could reach to4.528nm. Those showed thatdurable superhydrophobic and soft properties of the treated fabric are ascribedto the synergistic effect of the hydrophobic JNPDMS and micro-nanoembossments resembling lotus leaf surface resulting from the JNPDMS-SiO2treated cotton fiber surface. While the average particle size of SiO2was134.3nm and the dose of the JNPDMS-SiO2was0.5%, the superhydrophobicity ofthe JNPDMS-SiO2treated cotton was the best and WCA as well as roll-off angleon its surface could attain158.3°and9°, respectively. WCA could still reach144°after20cycles of soaping. Finally, the film-forming mechanism of theJNPDMS-SiO2hybrid material on the cotton fibers surface has been furtherproposed.4Fabrication of superhydrophobic cotton fabric from perfluoroalkylacrylate and trifluoropropyl modified polysiloxane/SiO2hybrid material.The same preparation method with the PFAMS was implemented toprepare the polysiloxanes with pendant perfluoroalkyl ester, trifluoropropyl, andepoxy groups which then were reacted with KH-550to produce a series ofcomb-like perfluoroalkyl ester/trifluoropropyl/ethoxy silane containingpolysiloxanes （FPFAS）. Subsequently, a kind of perfluoroalkyl ester/ethoxysilane modified polytrifluoropropylsiloxane silica hybrid materials（FPFAS-SiO2） were successfully synthesized via in-situ condensation reaction.Finally, the FPFAS-SiO2was used in fabrication of the superhydrophobic cottonfabric and the optimal preparation process was ultimately established. Therelationship between the molecular structure and micro-morphology of thePFAMS and PFAMS-SiO2and their hydrophobicity was chiefly investigated.Results demonstrated that the FPFAS film also presented a phase-separated and micro-rough pattern with Rq of0.650nm by comparison with PFAMS film.There were vast and large peaks with different levels on silicon waferoriginating from the perfluoroalkyl ester groups and that manner was muchdifferent from thin and high peaks of the perfluoroalkyl on the PFAMS film inevidence. It is speculated that capability of the perfluoroalkyl ester to beenriched at the surface is preferably strong. In addition, due to the greatimmiscibility between fluorine and silicon, the perfluoroalkyl ester groups areprone to close up each other and then to form big aggregates directing at theoutmost. Nanoscale roughness of the FPFAS-SiO2can be further improved byintroduction of SiO2particles and its Rq can achieve5.293nm, immdiately, anddirectional arrangement of the FPFAS-SiO2on fiber surface will be profitablygenerated. Thus, its hydrophobicity is thereby enhanced. While the optimaldiameter of nano silica was134.3nm, and the graft ratio of nano silica inFPFAS-SiO2could attain24.3%as well as the dose of the FPFAS-SiO2was0.5%, the superhydrophobic cotton fabric with WCA of163.3°and roll-offangle of7°was fabricated.Ultimately, the superhydrophobic mechanism of the FPFAS-SiO2hybridfilm on the cotton fibers surface had been analyzed by the Cassie’s theoreticalmodel and the area portions of the liquid/vapor contact area was91%on thecomposite interface of the FPFAS-SiO2treated fabric surface, which furtherimplies that the synergistic effect of the micro-rough FPFAS and FPFAS-SiO2,and the cotton fiber itself make the FPFAS-SiO2treated cotton fiber surfaceengender a multi-scaled roughness, which is the key point in fabrication ofbionic superhydrophobic surface.