Hydrophobic Modification And Application Of Nano-silica In Preparation Of Styrene-acrylic Emulsion And Pervaporation Membrane

Nano-silica is widely used in many fields such as rubber, plastics, electronics, paint, ceramic (enamel) porcelain, paint, plexiglass, environmental protection.There is a large number of unsaturated bonds and different states of residual hydroxyl on the surface of nano-silica three-dimensional network structure, which makes high nano-silica surface energy. This thermodynamic non-steady state has difficult in dispersing in the base body uniformly and results in nano-silica "secondary structure", thus affects the practical application of nano-silica. Surface modification is an important application of nano-silica and relates to application performance and industry prospects.of nano-silica.In this thesis, reflux method was used for nano-silica surface modification research, pretreatment temperature, effect of pretreatment time, the amount of modifier on the nano-silica surface modification were discussed in the solvent heptane when polydimethylsiloxane was used as modifier. Best conditions were that the amount of polydimethylsiloxane, pretreatment temperature roasting temperature and pretreatment time was 50%,600℃,6h respectively. Unmodification and modification nano-silica were characterized by infrared IR spectroscopy, TEM, XRD and studies showed that the condensation reaction occured between nano-silica surface hydroxyl groups and hydroxyl-terminated PDMS. Modified samples are more uniform particle size distribution, and dispersion is improved due to the change from hydrophilic to hydrophobic.We synthesized modification nano-silica-styrene-acrylic hybrid emulsion applied nano-silica modified with silicone rubber to hybridizate styrene-acrylic emulsion under the action of the silane coupling agent, the test performance of the emulsion, and its application properties were characterized. The results show that:modified styrene-acrylic emulsion properties are improved and the modified hybrid emulsion paint scrub obtained high-performance, in which contrast ratio, brightness, storage stability, stain resistance, and freeze-thaw stability have a more substantial increase. The mechanism of modification was studied in which chemical adsorption occurred not physical adsorption. Applied to the polymer, certain chemical reaction occurs between surface modification of nano-silica and the polymer matrix with the silane coupling agent, thus improves the compatibility and thereby increases the comprehensive performance of composite materials. So high performance exterior wall paint was prepared. The polydimethylsiloxane membranes filled with nano-silica modified with hexamethyldisiazane were prepared for the separation of ethanol from water. The pervaporation properties of nano-silica filled silicone rubber membranes was studied by contrast with no filled. It shows that the separation factor is higher than the PDMS membrane. During the 5%to 6%of the concentration of the alcohol the separation and the permeation rate were 18.06 and 117.27 g/(m2·h) respectively, While in the same separation condition the separation factor and flux of silica pervaporation without silicone is only 6.54 and 9.5 g/m2, h.