Salt-induced fusion of microcapsules of polyelectrolytes

Abstract

Fusion of microcapsules of the polyelectrolytes poly-diallyldimethylammonium chloride (PDADMAC) and sodium poly-styrenesulfonic acid (PSS) is achieved during the evaporation of NaCl solution in open chambers. The increasingly concentrated salt solution induces a series of faster and accumulating effects in the structure of the membranes and the cores of microcapsules. It creates defects in the membranes, decreases the electrostatic repulsion of polyelectrolytes in the membranes, causes a conformational change of the polyelectrolytes, increases the osmotic pressure gradient across the microcapsule membranes, and decreases the supporting force of the core by sucking water outwards. Due to the surface tension of the microcapsules and the hydrophobic interaction of the polyelectrolytes, microcapsules decrease the surface area and finally fuse. During fusion, their shapes change from peanut to oblate and then finally to round spheres. The neutral polymer molecules in the core diffuse and mix but do not leak out. The polyelectrolytes in the membranes do not mix due to the molecular entanglement. The work on fusion with salt as a critical parameter is important to approach promising artificial micro-containers, whose novel functions arise from the mixing of the inner content.