Free-Standing Phytantriol Q224 Cubic-Phase Films: Resistivity Monitoring and Switching

Phytantriol Q(224) cubic phase, as a bicontinuous meso-structured material stable in contact with aqueous electrolyte, has found applications in drug delivery and cosmetics and is employed here as a free-standing film separating two aqueous compartments in order to study i) ion conductivity (at low potential bias within +/- 0.8 V), ii) conductivity switching effects (at high potential bias beyond +/- 0.8 V), and iii) phase switching effects (as a function of temperature). A microhole of approximately 20 mu m diameter in a mu m thick poly-ethylene-terephthalate film is employed as the support coated with phytantriol (on a single side or on both sides) in contact with aqueous electrolyte phase on both sides in a classic four-electrode measurement cell. The conductivity of the phytantriol phase within the microhole is shown to be ionic strength, applied potential, time/history, and temperature dependent. The experimental data for asymmetric phytantriol deposits are indicative of a microhole resistance that can be switched between two states (high and low resistance associated with a filled or empty microhole, respectively). When heating symmetrically applied films of phytantriol, Q(224)-to-H-II phase transition linked to a jump to a higher specific resistivity is observed, which is consistent with differential scanning calorimetry data for this phase transition.