“Complete” Thermocontrol of Ion Permeation Through Ternary Composite Membranes Composed of Polymer/liquid Crystal/amphiphilic Crown Ethers

Composite membranes composed of polymer (polycarbonate (PC))/liquid crystal (N-(4-eth-oxybenzylidene)-4'-butylaniline (EBBA))/amphiphilic crown ethers (la, 2a, and 2b) have been prepared. The DSC study established that la (single-chain amphiphile) is dispersed homogeneously in the PC/EBBA composite membrane, whereas 2a and 2b (double-chain amphiphiles) exist as phase-separated aggregates in the membrane. Also prepared were ternary composite membranes containing natural ionophores such as X-537A (lasalocid) or monensin, which were dispersed homogeneously in the PC/EBBA composite membrane. Above T_kn(crystal-nematic liquid crystal phase transition temperature of EBBA), ion permeation through these composite membranes was very fast (19-34-fold compared with the conventional membranes). This is due to the high fluidity of EBBA forming a continuous phase in the composite membrane. Permeation of K⁺ion through PC/EBBA/la and PC/EBBA/natural ionophore was observed below and above T_KN, and the Arrhenius plots consisted of two straight lines intersecting at T_KN.This indicates that carrier-mediated K⁺permeation is directly affected by the molecular motion of the liquid crystal phase. Surprisingly, K⁺permeation through PC/EBBA/2a and PC/EBBA/2b was “completely” suppressed below T_KNand increased with increasing transport temperature above T_kn.Furthermore, Cs⁺, which forms sandwich-type complexes with 18-crown-6 and its analogues, could permeate through PC/EBBA/2a but not at all through PC/EBBA/la above T_KN.The difference in the permeation mechanism between PC/EBBA/la and PC/EBBA/2a is discussed in relation to the dispersion state of the crown ethers. The Arrhenius thermodynamic parameters show a good en-thalpy-entropy compensation relationship expressed by E_a= 5.42 log A + 50.4, but the permeability coefficient for K⁺(P_K+) was affected more significantly by the log A term. Finally, the PC/EBBA/2a membrane, which exhibits an all-or-nothing change in the ion permeability, was applied to the reversible thermocontrol of K⁺permeation and to the temperature-dependent “catch-and-release” of K⁺ion. This is the first example for “complete” thermocontrol of ion permeation through the polymer composite membrane.