Bilayer-coated capsule membranes. IV. : Control of NaCl permeability by phase transition of synthetic bilayer coatings, depending on their hydrophilic head groups

Abstract

Ultrathin nylon capsule membranes coated with synthetic bilayers, the hydrophilic head groups of which had cationic, anionic, zwitterionic and nonionic charges, were prepared. Permeation of NaCl trapped in the inner aqueous phase was reduced by a factor of 10-1000 relative to that of the uncoated, semipermeable capsules, and drastically changed at the phase transition temperature, T c, of the coating bilayers, depending on the charge of their hydrophilic head group. In the case of capsules coated with positively or negatively charged bilayers, NaCl permeation was enhanced at temperatures above the T c of the coating bilayers, as expected. On the other hand, NaCl release of capsules coated with neutral charged (nonionic and zwitterionic) bilayers was largely reduced at temperatures above the T c. From activation energy data of Arrhenius plots, the permeation mechanism of NaCl, depending on the membrane surface charge, below and above the T c was discussed.