Preparing Hydrophobic Silica Nanoparticles By Phase Transfer

This paper is mainly on the research of preparing hydrophobic silica nanoparticles by phase transfer.Firstly, to obtain stable and concentrated aqueous silica nanoparticles, the water glass was acidified with dilute hydrochloride acid, and then some chemical and physical modification methods were used to modify the surface of the silica in the water phase, and made it hydrophobic, so it can be transferred to some immiscible organic solution..The chemical modification method was that isopropanol were used to modify the surface of the silica in water phase by esterification, and it became hydrophobic, and then it can be transferred.The physical modification method was that some organic micromoleculer were used to combine with the surface of the nanosilica by hydrogen bonds to cover the silica nanoparticles and made it hydrophobic, and then it can be transferred.In this paper, we firstly discussed the effect of four kinds of alcohol and the reaction temperature in the chemical modification methods. And then the effect of the aqueous silica, transfer agents, organic phase, the reaction time and the reaction temperature and so on in the physic modification which used micromolecular as phase transfer agent were discussed. TEM was used to character the morphology of the nanoparticles and Zetasizer-Nano-series was used to analysis the particle diameter distributing. At last the mechanism of the phase transfer by a serious of experiments was discussed.It was proved that the chemical modification method was not effective to transfer the silica, but the silica can be transfered from water to organic phase effectively by the physical modification method; and when non-polar solvents as organic phase were used, the transformation is rarely happened. But the solvents which have strong polarity such as butanol can be transferred effectively. And we find the higher polarity the transfer agents were, the more effective the transfer were. But the two phases will be separated hardly when the polarity of the transfer agent is too high. And the length and the shape of the transfer agents also affect the phase transfer. We discussed the system which contained n-butanol as organic phase and THF as transfer agent and find that the transfer ratio :1) increased steeply with the volume of the transfer agent, 2) firstly increase with the organic phase and then gradually decrease, 3) increased slowly with the mixing time between the transfer agents and the aqueous silica sol, 4) firstly increase with the temperature of the reaction and then decrease, and in 20°C,the transfer ratio was a highest which was 80.71%. And the particle size in the sols obtained was about 100nm. It was also found the particle size in the sols which obtained in some case was about 50nm which observed by TEM.