The Influence Of Different Interface On The Melting Behavior Of Polymer Single Crystals

As the rapid development of many areas of science and technology, including surface modification, coating and electronics, polymer films desired get thinner and thinner, and even reach nanometer scale. Interfacial interaction has a great influence on the structure and performance of polymer thin films. In this thesis, we used the poly(ethylene oxide) single crystals with definite thickness instead of the ultrathin films to study the influence of interfacial interaction between polymer film and different substrates on the melting behavior of PEO film by means of atomic force microcopy(AFM). The main conclusions are as follows:PEO and PBS mono-layer and multi-layer single crystals with definite thickness were obtained by self-seeding method. The thickness of each single crystal layer is well controlled by crystallization temperature after self-seeding.The melting of PEO single crystals on edge-on and flat-on iPB-1 surfaces with different lamellar orientation was monitored by in situ AFM observation. It was found that the PEO single crystals on edge-on and flat-on iPB-1 crystalline film surface melt approximately at same temperature, which is confirmed by theoretical calculation. However, The acquired contact angle of PEO melt on the iPB-1 surface with edge-on and flat-on lamellae was 45±2°and 55±2°. The dewetting behavior of the molten PEO single crystals depends on the lamellar orientation of the iPB-1 evidently. The PEO melt on edge-on iPB-1 film surface shows somewhat a better wetting ability than on flat-on iPB-1 crystalline film surface. We have investigated the characteristic wavelength of spinodal dewetting of PEO film at smooth and rough surface by theoretical prediction and experimental AFM observation. The characteristic wavelength at smooth surface can be estimated by the film thickness and contact angle without any fitting parameters, and the results are in good agreement with the experimental results of polystyrene film at smooth surface reported in the literature.The melting behavior of PEO single crystal placed on PVPh ultrathin films with different thickness was studied in a comparison with that on the Si wafer. The results show that PEO/substrate interactions have a pronounced influence on the melting behavior of the PEO single crystals and the spreading of the PEO melt.The melting point of the PEO single crystals also depends on the thickness of PVPh layer, which may due to the different chain mobility and surface energy of PVPh films with different thicknesses. A melting point depression of PEO single crystal was observed with increasing PVPh layer thickness. This has been correlated to the enhanced interaction between PEO and PVPh based on hydrogen bonding. It is speculated that the thickening of PVPh layer is in favor of the formation of hydrogen bonds between PVPh and PEO due to the increased amount of exposed hydroxyl groups of PVPh and their ability to build hydrogen bond with the oxygen groups of PEO.The melting behaviour of PBS single crystals on PVPh thin films with different thicknesses was studied in situ by AFM. Similarly to PEO/PVPh system, the strong hydrogen bonding interaction between PBS and PVPh results in a PVPh layer thickness dependent melting temperature depression of PBS, which further validated our previous experiments and conclusions.