| 초록 |
Although most works on the liquid crystalline polymers were concerned with bulk properties, less work was done on the thin films of such materials. In this work, order and surface properties are investigated with side chain liquid crystalline polymers, poly(oxyethylene) containing various length of n-alkylsulfonylmethyl side chains (CH2SO2(CH2)m-1CH3, m=5, 7, 10 and 16). X-ray reflectivity results reveal that the spin-coated films on silicon wafer form a bilayer structure upon annealing in the mesophase. In study of NEXAFS spectroscopy and AFM, side chains are loosely oriented when alky chain length in side group is longer than the critical length. The loose orientation of side chains results in roughening of the air-polymer surface and interface between layers. From x-ray reflectivity data of the thin films with different thickness, it can be concluded that the layer thickness near the substrate increases because hydrophobic side chains can not relax laterally on the hydrophilic substrate. Also, the glass transition and smectic-to-isotropic transition in thin films are observed. The film thickness and layer spacing begin to decrease above the glass transition temperature. At the isotropic transition temperature, the film thickness starts to increase because the poly(oxyethylene) backbone and side chains favor coiling with increasing temperature. The coiling of the chains results in the abrupt change of surface properties. |
