Journal of Membrane Science, Vol.139, No.2, 243-257, 1998
Electric field induced permeability modulation in pure and mixed Langmuir-Blodgett multilayers of hemicyanine dyes and octadecanoic acid on nanoporous solid supports
Composite structures have been prepared, in which nanoporous (nuclear track-etched) membranes are coated with supported Langmuir-Blodgett (LB) barrier layers. Permeability in these structures is a strong function of membrane composition and applied rte and ac electric fields. Absolute permeabilities fall in the range 3x10(-11) cm(2) s(-1) less than or equal to P less than or equal to 3x10(-9) cm(2) s(-1), depending on composition of the barrier layer, identity (charge state) of the probe, and presence of a supporting electrolyte. Zero-field permeabilities showed a definite dependence on composition, with membranes possessing barrier layers on both sides performing better than single-sided membranes, barrier layers with LB multilayers performing better than those with just the support layer, and LB layers composed of mixed stilbazolium amphiphiles and octadecanoic acid performing better than those composed purely of stilbazolium amphiphile. All types of barrier layers studied exhibit permeability changes in the presence of applied electric fields. The magnitude of the effect is a strong function of composition of the barrier layer and the presence of supporting electrolyte. The results support electroporation over iontophoresis as the dominant mechanism for field-mediated increases in permeability. Details of the field-induced permeability changes in phosphate buffer and deionized water suggest that at least two effects are important in determining the transport behavior in these structures : a field-induced structural change in the barrier layer which mediates the electroporation and a field-mediated alteration in transport through nanopores of the nuclear track-etched membrane.
Keywords:FUNCTIONAL CAPSULE MEMBRANES;POROUS-GLASS PLATE;AMBIENT PH CHANGES;REDOX-SENSITIVE PERMEATION;SURFACTANT TRANS-STILBENES;AIR-WATER-INTERFACE;CONTROLLABLE MEMBRANES;BILAYER-MEMBRANES;PHOTOCHEMICAL-REACTIONS;ORGANIZED ASSEMBLIES