ELECTRIC-FIELD-INDUCED PERMEABILITY MODULATION IN PURE AND MIXED LANGMUIR-BLODGETT MULTILAYERS OF HEMICYANINE DYES AND OCTADECANOIC ACID ONNANOPOROUS SOLID SUPPORTS

Composite structures have been prepared, in which nanoporous (nuclear track-etched) membranes are coated with supported Langmuir-Blodgett (L B) barrier layers. Permeability in these structures is a strong functi on of membrane composition and applied rte and ac electric fields. Abs olute 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 o n composition of the barrier layer, identity (charge state) of the pro be, and presence of a supporting electrolyte. Zero-field permeabilitie s showed a definite dependence on composition, with membranes possessi ng barrier layers on both sides performing better than single-sided me mbranes, barrier layers with LB multilayers performing better than tho se with just the support layer, and LB layers composed of mixed stilba zolium amphiphiles and octadecanoic acid performing better than those composed purely of stilbazolium amphiphile. All types of barrier layer s studied exhibit permeability changes in the presence of applied elec tric fields. The magnitude of the effect is a strong function of compo sition of the barrier layer and the presence of supporting electrolyte . The results support electroporation over iontophoresis as the domina nt mechanism for field-mediated increases in permeability. Details of the field-induced permeability changes in phosphate buffer and deioniz ed water suggest that at least two effects are important in determinin g the transport behavior in these structures: a field-induced structur al change in the barrier layer which mediates the electroporation and a field-mediated alteration in transport through nanopores of the nucl ear track-etched membrane. (C) 1998 Elsevier Science B.V.