Hydrophilic Nano-Silica

In this paper, a method for modifying hydrophilic nano-silica using water soluble SDS and silane coupling agents was studied. Since SDS dissolves in water, the mixing of nano-silica in SDS gives a better dispersion and it modifies the surface of nano-silica well. By subsequent analysis, the SDS concentration as well as the dispersion time and temperature have been optimized. The optimum concentration of SDS was identified as 1 wt%. The temperature was controlled at 50±2°C and a dispersion time of 15 min was used and kept for 3 hours for obtaining a stable dispersion of nano-silica. Owing to the high surface energy and presence of large number of hydroxyl groups on the surface, nano-silica exhibits strong hydrophilicity and agglomeration and

Surface treatments are usually carried out by the chemical reaction between the surface silanol groups with silane coupling agents. One end of the silane coupling agent can react with the silanol groups of nano-silica and the other end with the polymer. In the present study, two types of silane coupling agents, i.e., APS and GPS, were used. When silane coupling agents are added to ethanol:water mixture, hydrolysis of alkoxy groups to silanol takes place (Fig. 5a). The silanol thus formed on the silane undergo condensation reaction with hydroxyl groups on the fiber surface and silanol on nano-silica forming a crosslinked network structure (Fig. 5b). In the case of APS, the NH2 group of APS interacts with the -OH groups on silica forming a polyaminosiloxane network containing more than two APS units. The peak observed in FTIR at 1560 cm-1, which is attributed to the deformation mode of amino group in APS forming hydrogen bond with silanol, confirm this observation. The grafting of surface modified nano-silica particles on the ramie fiber introduced a nano-scale fiber surface roughness . A schematic representations of ramie fiber treated with silane/nano-silica are shown in Fig. 6a and

The SEM images of the ramie fiber with nano-hybrid coating are shown in Fig. 7. The images of ramie fiber treated with SDS/nano-silica (1wt%), APS/nano-silica (1wt%), and GPS/nano-silica (1wt%) indicated the appearance of nano-silica on the fiber surface as compared to the untreated fiber. The nano-silica grafted fiber surface showed an uneven surface in the SEM image with high magnification. It is clearly observed that the nano-silica particles increased the fiber surface roughness and uniformly deposited on the fiber surface. GPS/nano-silica fiber morphology showed more closely packed nanoparticles on the surface than the other two nano-silica grafted ramie fiber surfaces. The surface morphology of SDS/nano-silica and APS/nano-silica were found to be similar in grafting nano-silica on the fiber