Modification of ion permeability utilizing pH-dependent selective swelling of polyelectrolyte multilayer films

The selective swelling behavior of polyelectrolyte multilayer (PEM) films prepared by layer-by-layer (L-b-L) assembly influences the ion-permeability in contrast to surface charge density of the films. The cation terminated polyethylene amine (PEI) and anion terminated polyacrylic acid (PAA) were dissolved in Dl water, and the pH was adjusted to 10 and 4, respectively, exemplifies thick denser film with good layering structure. The layered polyelectrolyte films has selective swelling behavior at pH 4 (PEI) or pH 10 (PAA), influences the permeability of both Ru(NH ₃) ²⁺ ₆ and Fe(CN) ^3- ₆ rather than surface charge character or film charge density. The swollen top most layer shows "on" character, whereas, shrunken top most layer shows "off" character for the ion-permeability. Such "on-off" character can be used for the pH-dependent switches based on surface morphology.