Nanoparticles have already became an indispensable material for industries because of their unique size dependent properties such as electrical, magnetic, mechanical, optical and chemical properties, which largely differ from those of their bulk materials. Nanoparticles have an extremely high tendency of adhesion and aggregation due to different surface structures and surface interactions. Hence it is necessary to control their dispersion/aggregation phenomena of nanoparticles in order to apply them into functional materials and products.
It is still a challenging issue to control the stability of suspension with highly loaded nanoparticles or sus-pensions in organic media. Surface modification of nanoparticles is one of the mostly accepted methods to improve the dispersion stability. Surface structure can be designed based on the type of nanoparticles and the liquid media in order to modify the surface by polymeric surfactants or other modifiers to generate an effective repulsive force between nanoparticles.
The adsorption of polymeric dispersant is one of the simplest surface modification techniques to improve the dispersion stability of nanoparticles in liquid media.
Surface modification of the particle surface chemically is an also an useful technique to improve the stability of nanoparticles in various liquid media. The surface modification of nanoparticles by silane coupling agents is also useful to improve the dispersion stability in organic media.
Mechanical milling method and other physical techniques such as ultrasonic dispersion can be applied to redisperse various nanoparticle into liquid media by the simultaneous processing of the surface modification cited above and the bead milling.
On preparing nanoparticles dispersible in aqueous or high-polar solvents, a polyol method is also widely accepted by many researchers.
Based on abovementioned methods, various nanoparticles including metals, oxides, sulfides, and fluorides that are redispersible into many solvents can be synthesized by in-situ surface modification techniques.