"Turnover" of amphiphile molecules in Langmuir Blodgett films of salts of fatty acids: an X-ray diffraction study

We have studied the reorganization of lead salts of mixed fatty acid films of stearic and behenic acids deposited either by mixing the acids in the Langmuir monolayers or by depositing them from various troughs. The observed 00l intensities in the X-ray diffraction patterns of the c-axis oriented films are quite different from that calculated. The calculated X-ray diffraction pattern matches the observed pattern when "turnover" mechanisms are taken into account. The nature of such "turnover" mechanisms is discussed in terms of swelling of the interlamellar spaces between the solvated headgroups of the salts of fatty acids and fluctuations in the interlamellar separation.