Langmuir, Vol.19, No.1, 63-71, 2003
Pyroelectric activity in calix[8]arene/amine Langmuir Blodgett films: New insights into the mechanism of polarization variation with temperature
We have carefully examined the attenuated total reflection Fourier transform infrared spectra of Langmuir-Blodgett (LB) alternate multilayers of two different calixarene carboxylic acid/amine systems as a function of temperature. Neither the molecular arrangements nor the degree of proton transfer appears to change (within the detection limits) over the 20-80 degreesC temperature range. The use of a simple model to calculate the degree of proton transfer needed to produce the measured pyroelectric coefficient leads to the conclusion that dipole formation is not the underlying origin of the large measured deltaP/deltaT. Instead, it is the change of length scale of the hydrogen-bonding molecular interactions of the non-proton-transferred molecules, which controls the Gamma value. This conclusion is confirmed by a detailed analysis of the IR spectra for different acid/amine LB films (including ones published previously). A good correlation between Gamma and the degree of proton transfer is found, which leads to a better understanding of the nanoscale molecular arrangements needed to achieve a high Gamma value and/or its sensitivity to temperature.