Nondestructive light-initiated tuning of layer-by-layer microcapsule permeability

A nondestructive way to achieve remote, reversible, light-controlled tunable permeability of ultrathin shell microcapsules is demonstrated in this study. Microcapsules based on poly{[2-(methacryloyloxy)ethyl] trimethylammonium iodide} (PMETAI) star polyelectrolyte and poly(sodium 4-styrenesulfonate) (PSS) were prepared by a layer-by-layer (LbL) technique. We demonstrated stable microcapsules with controlled permeability with the arm number of a star polymer having significant effect on the assembly structure: the PMETAI star with 18 arms shows a more uniform and compact assembly structure. We observed that in contrast to regular microcapsules from linear polymers, the permeability of the star polymer microcapsules could be dramatically altered by photoinduced transformation of the trivalent hexacyanocobaltate ions into a mixture of mono- and divalent ions by using UV irradiation. The reversible contraction of PMETAI star polyelectrolyte arms and the compaction of star polyelectrolytes in the presence of multivalent counterions are considered to cause the dramatic photoinduced changes in microcapsule properties observed here. Remarkably, unlike the current mostly destructive approaches, the light-induced changes in microcapsule permeability are completely reversible and can be used for light-mediated loading/unloading control of microcapsules.