Infrared studies of pyroelectric Langmuir–Blodgett films of arachidic acid and 1,2-bis(dodecyloxy)-4,5-diaminobenzene

Fourier Transform Infrared (FTIR), p-polarized grazing angle (GAIR) and Horizontal Attenuated Total Reflectance (HATR) spectra have been recorded of arachidic acid (AA)/1,2-bis(dodecyloxy)-4,5-diaminobenzene (DADB) Y-type alternate LB films deposited on an aluminium plate with 31 layers. It is well known that the frequencies of CH₂ stretching bands of a hydrocarbon chain are sensitive to the conformational ordering of the chain. Changes in frequency and intensity can be used to characterize film ordering and preferential molecular packing. The observed peak frequencies and intensities of these bands indicate that the alkyl chains are present in a mostly trans conformation and tilted from the normal direction with respect to the substrate in LB films. The FTIR–GAIR and HATR spectra of 31 layers alternate film show significant changes in the region 1700–1400 cm⁻¹ due to the partial proton transfer between acid and amine head groups. According to the HATR spectrum, the peak at 1731 cm⁻¹ is observed due to a proportion of the carboxylic acid groups forming sideways dimers indicating that if the carboxylic acid groups form sideways dimers, they are less likely to undergo proton transfer with the amino groups.