pH-responsive behavior of hydrogel microspheres altered by layer-by-layer assembly of polyelectrolytes

We used the layer-by-layer method and an anionic microgel as a substrate to study the influence of consecutive polyelectrolyte adsorption treatment on the pH-responsive changes in the size of the microgel. Treatments with poly(allylamine hydrochloride) and branched poly(ethyleneimine), which penetrated the microgel, led to the formation of a “complex shell” and the behavior analogous to that of an amphoteric microgel, respectively. In contrast, high molecular weight chitosan adsorbed almost at the edge of the microgel surface; and the resultant microgel maintained nearly the same pH-response as the original microgel. This study shows that the pH-response of the microgel can be controlled by the type of polyelectrolytes adsorbed.