AFM STUDY OF THERMOTROPIC STRUCTURAL TRANSITIONS IN POLY(DIETHYLSILOXANE)

Structure and phase transitions of polydiethylsiloxane (PDES) were stu died with AFM at temperatures in the 300-268 K range. The measurements were performed on a polymer layer deposited on a Si substrate by rubb ing. It is shown that at room temperature the layer is a polymer mixtu re in amorphous and mesomorphic states. With the decrease of temperatu re to 273 K, all material converts into the mesomorphic state. The pol ymer structure in the mesomorphic state is formed of elongated pattern s oriented perpendicular to the rubbing direction. They are assigned t o edge-on standing and hat-lying lamellae. Disk-Like substructures wer e found in some amorphous patches lying on the substrate. Solid-solid crystallization of PDES from the mesomorphic state was observed at 268 K. The transition is accompanied by changes of sample morphology and nanostructure. Lamellar arrays are transformed into ribbons whose shap e reveals their monoclinic crystalline structure. The ribbons have a l inear substructure with 50 nm wide stripes oriented along the rubbing direction. The molecular rearrangements during crystallization are dis cussed. Copyright (C) 1996 Elsevier Science Ltd.