Qualitative evaluation of pyroelectric mechanisms in Langmuir–Blodgett films containing a cyclic polysiloxane substituted with aliphatic side chains using Fourier transform infrared (FTIR) spectroscopy

Alternate layer Langmuir–Blodgett (LB) films containing cyclic polysiloxane substituted with aliphatic side chains alternated with monomeric eicosylamine have been shown to exhibit pyroelectric activity. The pyroelectric activity for 5, 11, 15, 21, 25 and 31 monolayer LB films, is recorded at 21°C and shows highest activity for 5 monolayers with a pyroelectric coefficient of 0.5 μC m −2 K −1. The coefficient decreases as the thickness of the film increases from 5 to 15 monolayers, increases in the thickness range of 15–25 monolayers and decreases again for 31 monolayers film. Fourier transform infrared (FTIR) spectroscopy shows that proton transfer between the acid headgroups at the terminal end of the cyclic polysiloxane and the headgroups of the eicosylamine increases as the number of monolayer increases. However, the angle at which the molecular axis of the LB film tilts from the surface normal, α (as indicated by the overall ratio of symmetric stretching of CH 2 to CH 3, or asymmetric stretching of CH 2 to CH 3) increases as the number of monolayer increases from 5 to 15 layers and remains stable for 21–31 layers.