Reproducibility of temperature response and long-term stability of thermo-responsive membrane prepared by adsorption of binary liquid crystals

A binary mixture containing 36% cholesteric oleyl carbonate (COC) and 64% cholesteryl nonanoate (CN) was adsorbed onto the cellulose nitrate membrane to prepare a thermo-responsive membrane. The thermophysical properties and long-term stability of this binary COC/CN mixture were examined by using the differential scanning calorimeter (DSC) and microscopic Fourier transform infrared (FT-IR) spectrometer combined with DSC system. Its long-term thermo-responsive efficacy was also evaluated by in vitro drug penetration study via a step-wise change in temperature cycle. The results indicate that the IR spectral peak intensity near 1265–1252 and 1172 cm−1 at 37 °C were markedly stronger than those peaks at 30 °C, as the C–O stretching mode of ester for binary COC/CN mixture exhibited more intense IR spectral absorption at higher temperature. The phase transition temperature obtained from the microscopic FT-IR/DSC system was 35.7 °C, almost near the endothermic peak at 34.8 °C in the DSC curve. The result of isothermal FT-IR/DSC microscopic system also confirmed the good temperature response in precision, sensitivity, obedience and reproducibility of the binary COC/CN mixture after eight repeated temperature cycles. Long-term stability revealed that this solid-cholesteric transitional temperature at 34.8 °C was, respectively, transited to 30.2, 44.1 or 50.9 °C after storage at 4, 25 or 37 °C for 3 days and then maintained almost constant, suggesting the constant thermal-stability of the binary COC/CN mixture. However, the incomplete thermo-responsive function of binary COC/CN mixture-adsorbed membrane was obtained due to the changes in the solid-cholesteric transitional temperature of COC/CN mixture after long-term storage at different temperatures if the temperature cycle was still set within 30 and 37 °C.