THERMALLY-INDUCED PHASE-TRANSITIONS IN LB MULTILAYERS OF LEAD STEARATE

Pb-stearate multilayers prepared by the Langmuir-Blodgett (LB) techniq ue on silicon show a change of layer structure just below the melting point. At temperatures between 98 degrees C and 112 degrees C the samp les have been investigated by energy dispersive X-ray scattering in sp ecular and diffuse scattering geometry. The time constants of the tran sition at fixed temperature was determined. After the disappearance of the old structure, new Bragg peaks grow out of an amorphous intermedi ate phase corresponding to a 20% smaller layer distance compared with the initial LB structure. At fixed temperature the intensity of the re spective Bragg peaks increases and, after reaching a maximum, it decre ases again until the new peaks disappear. Maximum Bragg intensity was observed at a transition temperature of 106 degrees C. The new phase i s instable in time. Our results are compared with related effects of C d stearate, which have been interpreted as a transformation into a two -dimensional ordered hexagonal structure of long columns.