Solvent-filled matrix polyelectrolyte capsules: preparation, structure and dynamics

Abstract

Stable surfactant-free, water-dispersed, micron-sized organic solvent colloids have been a challenging subject of major interest both experimentally and theoretically in recent years. In this article, novel matrix capsules are introduced to carry an organic solvent (e.g. toluene) into water and form a stable solvent dispersion in the aqueous phase without the addition of a surfactant. The structure and dynamics of the dispersion are investigated by confocal Raman microscopy, surface force microscopy, and pulsed field gradient nuclear magnetic resonance (PFG-NMR). The matrix capsules are fabricated according to a literature method using alternating layer-by-layer adsorption of oppositely charged polyelectrolytes onto porous calcium carbonate (CaCO₃) particles, followed by core removal. The highly rough surface and the inner cavities of CaCO₃ particles result in a heavy matrix capsule, which can achieve a high solvent encapsulation efficiency and form a micron-sized carrier for the solvent in water that is stable for long times (i.e. at least one week.) Two distinct diffusion coefficients are evidenced by PFG-NMR, which may indicate two distinct diffusion environments in the sample. This suggests that the toluene undergoes a partial exchange between environments within the 100 ms time frame of the NMR experiment.