Controlled permeability in polyelectrolyte films via solvent treatment

The influence of solvents (alcohols and binary mixtures of alcohol and water) on the structure and permeability of self-assembled layer-by-layer polyelectrolyte multilayers (PEMs) has been investigated by in situ atomic force microscopy (AFM), cyclic voltammetry (CV), and confocal laser scanning microscopy (CLSM). A decrease in the dielectric constant of the solvent medium increases the strength of electrostatic interactions between the polyelectrolyte chains because the Coulombic force is inversely proportional to the dielectric constant. The stronger attractions as a result of increased alcohol volume percentage in water drive the polyelectrolyte chains to contract, collapse, and coagulate. Consequently, subtle changes in the PEM film structure are observed. AFM images show that the originally smooth surface of the PEM film becomes rougher with aggregates and holes developing with increasing alcohol amount. The diffusion of Fe(CN)(6)(3-/4-) through PEM films is promoted upon solvent treatment. The entrapment of Fe(CN)(6)(3-/4-) in the film occurs at a high amount of ethanol content (> 60%). The permeability of large macromolecules, i.e., dextran with molecular weight of 66 kDa, to polymeric capsules is also enhanced by solvent treatment. By the methods of "additional PEM coating" and solvent treatment, the mesh size of capsules becomes tunable as does the capsule permeability. The conversion between microporous capsules to mesoporous capsules has a potential application in smart encapsulation and controlled delivery.