Wettability Of SiO₂/PVA Coatings

Surface wettability means the capability of stretching on the surface of solid matters,which is a very important interface phenomenon, as well as an important trait of solidmaterials. Special invasive materials of surface has wide prospects in the areas ofcoatingsing, defending of fog because of its unique surface properties.The hydrophilia of hydrophilic layer of SiO2/PVA has been represented throughchanging factors like size of silica particles, polarity of the coating surfaces and ratio ofdispersion, and analyzing roughness and surface wettabilitythe of the coatings bymeasuring contact angles on the surfaces. First of all，St ber sol-gel method has beenperfected to prepare silica particles in the thesis, making cover glass as substrate, a layer ofPVA solution has been painted to fix silica particles. By changing conditions and methodsof experiment, the law has been examined that SiO2with different particle sizes and ratioof dispersion, affects wettability of hydrophilic coatings. Secondly， the effects thatsurface modification has had on surface wettability, roughness, features and so forth andthe law that surface modification has produced have been analyzed through implementinghydrophobic modification of the prepared SiO2/PVA hydrophilic coatings via stearic aidand G502hydrophobic liquid. Finally，making composite silica particles which imitate thestructure of micron and nano through mixing different sizes of particles (modified by silanecoupling agent KH-550and KH-560)， and by using the prepared composite particles toprepare hydrophobic layer of SiO2/PVA， comparison of the differences of roughness andwettability between the hydrophobic coatings prepared by directly mixing particals andcomposite particles. The objective of the experiment is to reveal the influence that thechange of size and quantity of nano-silica particles has on biomimetic surface of SiO2/PVAand that various factors have on surface wettability and roughness when constructing， andto find out change law of surface roughness of hydrophilic/hydrophobic coatings.By using dynamic light scattering to examine the size of nano-silica particles and scanning electron microscope to observe the size and distribution of nano-silica particles.The results show that size distribution of mono-dispersed SiO2particles prepared byoptimized St ber sol-gel was centralized which could mainly guarantee that the size ofparticles could be in the controllable range. Particles could basically form singlepermutation on the substrate, and the distribution and intensive degree had beenstrengthened as the increase of dispersion ration, changing the structure of surfaceroughness.Via the representation of static contact angle on the surface of coatings, thehydrophilia of SiO2/PVA hydrophilic coatings decreased as the silica particles becamebigger, but it was strengthened as the increase of dispersion ratio. Making stearic acidethanol solution and G502hydrophobic liquid (C14F12H20SiO3) as modifier to modifyhydrophilic SiO2/PVA coatings could reduce surface polarity effectively， making coatingsshift from hydrophilic to hydrophobic. When the ratio between silica particles anddispersion concentration of water was1:250, the effect of hydrophobic modification ofcoatings was the best, and in such a condition, the modification result of G502hydrophobic liquid was better than that of stearic acid. When silane coupling agent，KH-550and KH-560， modified silica particles， composite silica particles that imitatemicron and nano could be made. The surface hydrophobicity of the hydrophobic coatingsprepared by such particles was much better than that prepared by the direct-mixed particlesand single level particles with the same size.