Temperature dependence of interfacial fluctuations of polymerized fatty acid salt multilayers.

X-ray scattering was used to study the temperature dependence of the profile structure of polymerized 10,12-tricosadiynoic acid salt multilayers. The stacking periodicity of the multilayers was found to decrease with increasing temperature due to the conformational changes of the alkyl chains. When the samples were fully hydrated in water, the reflectivity measurement showed that the thermal fluctuations of the interfaces are enhanced with temperature, resulting in reduced ordering. Meanwhile, the diffuse scattering indicated that the thermal fluctuations renormalize the elasticity of the multilayers; both the bending and the compression moduli are reduced. Similar measurements performed in air, however, do not show this thermal enhancement although the stacking periodicity decreases in the same manner. It is implied that water might weaken the interaction between the carboxyl groups and the metal ions so that the polymerized bilayers are softened in water.