Characterization of nanostructure of stimuli-responsive polymeric composite membranes.

To elucidate the mechanism of stimuli-responsive permeability and to optimize the design, the nanostructure of polymeric composite membranes, developed in our laboratory, was characterized. The membranes were prepared to contain various amounts of stimuli-responsive nanoparticles of poly(N-isopropylacrylamide-co-methacrylic acid), with or without polyelectrolyte coating. Scanning electron microscopy and X-ray photoelectron spectroscopy were used respectively to examine the morphology and surface chemical composition, whereas atomic force microscopy and laser scanning confocal microscopy were employed to characterize the in situ surface and internal structure of the membranes in aqueous media of various pHs. The porous structure was evidenced in the presence of the nanoparticles. The surface content of the nanoparticles increased with increasing particle concentration while the polyelectrolyte coating was nearly undetectable. AFM images revealed that the particles in the membranes shrank with a concomitant increase in pore size as the buffer pH decreased. LSCM results indicated that particles were distributed through the membrane as interconnected clusters.