Layer-by-Layer Surface Modification of Functional Nanoparticles for Dispersion in Organic Solvents

In order to prepare SiO2 nanoparticles that are dispersible in various organic solvents, an anionic surfactant I, which branches into a hydrophobic chain and a hydrophilic chain, was adsorbed on to SiO2 nanopartieles through a layer-by-layer sit-face modification route using polyethyleneimine (PEI). First, the relationship among the additive content of PEI, adsorbed content of PEI, and the redispersion stability of the SiO2 nanoparticles in water was investigated. While almost the entire PEI was adsorbed when the additive PEI content was lower than 67 mg/g of SiO2, the adsorbed content of PEI became saturated when the additive content was increased above 90 mg/g of SiO2 SiO2 nanoparticles that were saturated with PEI could be redispersed into water at sizes close to their primary particle size without the large-scale formation of aggregates. Next, the anionic surfactant 1 was adsorbed on the SiO2 nanoparticles by using a SiO2 aqueous suspension saturated with adsorbed PEI. It was found that the adsorbed content of I increased almost linearly as the additive content was increased when the additive condition was below 1400 mg/g of SiO2. Furthermore, SiO2 nanoparticles adsorbed with 80 mg/g of SiO2 of PEI and 810 mg/g of SiO2 of 1 could be dispersed into various organic solvents with different polarities. This layer-by-layer modification technique can also be applied to Ag nanoparticles in order to prepare Ag nanoparticles that can be dispersed in various organic solvents.