(148f) Layer-by-Layer Surface Modification of Functional Nanoparticles for Non-Aqueous Dispersions

Considerable research has been focused on nanostructured materials composed of nanoparticles, such as polymer composites, ceramic composites, composite particulates, and assembled structures because of their wide range of important applications. In order to fabricate perfect nanostructured materials with improved properties, it is absolutely essential to develop a method for complete dispersion of nanoparticles in a required solvent. Until today, many researches have reported the synthesis of nanoparticles that are completely redispersible in organic solvents using various methods such as reverse micelle method, nonhydrolytic sol-gel reactions of metal halides with capping agents, and thermal decomposition of metal complexes. Though various oxides, sulfides, and metal nanoparticles that are redispersible in low-polarity solvents can be obtained by this process, there still lays the problem that these nanoparticles became unstable when transferred into polar matrix such as alcohols, ketones and polymers. To overcome this problem, we have previously reported the design of novel functional anionic surfactant which branches into hydrophobic and hydrophilic chain. By applying this surfactant to TiO2 nanoparticles, they became dispersible in many organic solvents such as toluene, methanol and ketones. However, it was also found that this surfactant was not applicable to other oxides such as SiO2 nanoparticles because of their low adsorption ratios. Herein we report the layer by layer surface modification route of functional nanoparticles toward their complete dispersion in various organic solvents. The functional nanoparticles such as SiO2 and ZnO were first modified by cationic polymeric surfactant (polyethyleneimine (PEI)) and then modified by an anionic surfactant comprises from an organic chain branches into hydrophobic and hydrophilic group. Functional nanoparticles only modified by PEI were redispersible in polar solvents such as water and ethanol but they slowly became aggregated within several hours. Contrary, it was found that functional nanoparticles modified by layer by layer modification route were dispersible into wide range of organic solvent such as toluene, ethanol and acetone and they became stable over several months.