Synergistic stabilization of emulsions by poly(oxypropylene)diamine and Laponite particles

Abstract

Liquid paraffin–water emulsions were prepared which were stabilized by Laponite particles in situ modified with poly(oxypropylene)diamines in the absence of electrolytes. First, the characteristics of the Laponite dispersions in the presence of increasing concentrations of diamines were studied in detail. Infrared absorption spectra and zeta potential measurements confirm the adsorption of diamines on the Laponite particles. Adsorption isotherms further indicate highly affinitive L-type behaviors and the diamine molecules are deduced to lie with both end groups anchored on the particle surface and the poly(oxypropylene) chain exposed to the aqueous solution. Then, emulsions were prepared using the diamine-modified particles. Diamines and Laponite particles alone are ineffective emulsifiers, but a strong synergism is exhibited between them. Laser-induced fluorescent confocal micrographs and TEM observations demonstrate the arrangement of the particles on the emulsion surfaces and also reveal the stability mechanisms. The emulsion stability was also explored with optical microscopy and droplet size measurements. As the diamine concentration increases, the extent of emulsion creaming decreases and the droplet size correspondingly decreases. At a certain low diamine concentration, the extent of emulsion creaming decreases down to a minimum and the corresponding droplet size is the smallest. This optimal emulsion state is unchanged when the diamine concentration is further increased.