Thermal softening of superswollen polyelectrolyte microcapsules

We study the effect of temperature on the mechanical properties of polyelectrolyte microcapsules assembled by layer-by-layer (LbL) deposition of polystyrene sulfonate (PSS)/polyallylamine hydrochloride (PAH). Capsules are initially significantly swollen (superswollen) as a result of the osmotic effect caused by in situ polymerization of inner PSS. It is well known that hollow PSS/PAH microcapsules are insensitive to temperature changes. However, we show that the heat treatment of superswollen capsules introduces additional plastic deformation and leads to an additional softening of a highly stretched polyelectrolyte shell. A simple model is provided to characterize the elasto-plastic behavior of the microcapsules under consideration. This finding suggests an alternative method to control mechanical properties of the multilayer shell.