Tuneable thickness barriers for composite o/w and w/o capsules, films, and their decoration with particles

Abstract

Oil-in-water and water-in-oil capsules, and flat membranes of tuneable thickness and composition were prepared in one single facile step, based on the interfacial complexation between chitosan and anionic phosphatidic fatty acids. The phosphatidic acid molecules were introduced via the oil phase. The thickness of the capsule shell or the membrane grows by a diffusion-controlled mechanism, hence can be tuned using e.g. concentration and formation time parameters. A mechanism is proposed to explain the observed behavior. The capsule size is set by the emulsification conditions applied. Microfluidic methods proved useful for the generation of hollow capsules of uniform size and thickness in one step. The capsules and membranes display remarkable integrity over several years in a pH window 2–14. The thickness can easily reach several micrometres within an hour for the wet capsule shell or membrane, which explains the high interfacial rheological properties measured. Hence various processes can be envisaged after their formation. The simple preparation opens the way to tailored, environment-responsive composite systems for fabricating biopolymer-based materials for various applications. The capsules could be washed from the surrounding continuous phase and placed into one of arbitrary choice. Furthermore, the surface of the w/o capsules and of the membranes could be decorated by particles that attach to the water/oil interface with a high energy. The choice of the particle functionality is left open.