CHARACTERIZATION OF LONG-PERIODIC LAYERED STRUCTURES BY X-RAY-DIFFRACTION .3. STRUCTURE OF A LANGMUIR-BLODGETT-FILM OF CADMIUM ARACHIDATE AT ELEVATED-TEMPERATURES

The thermal behavior of a Langmuir-Blodgett (LB) multilayer of cadmium arachidate (CdA) was investigated by small-angle X-ray diffraction. Before melting, the LB multilayer underwent a three-step structural change: (1) from room temperature to 60-degrees-C, rearrangement of the CdA layers; (2) between 60 and 80-degrees-C, onset of the pretransitional disordering; (3) above 80-degrees-C, conformational change from trans to gauche state in the hydrocarbon chain. The 001 reflection intensity, a measure of the short-range disorder of the multilayer structure, is sensitive to these changes. In contrast, the lattice distortion parameter tends to increase monotonously up to 100-degrees-C. This indicates that the long-range order of the multilayer structure is well preserved at temperatures close to the melting point. On cooling down to room temperature after melting, the crystallites of a periodic lamellar structure grow. Their lattice distortion and dimension in the [001] direction are much larger than those of the multilayer before melting.