The crystallization of the thin and ultra-thin polymer films has been studied by different research groups due to their importance in the development of advanced coating materials. Studies have revealed that thin and ultra-thin polymer films behave differently from their bulk counterparts; in semi-crystalline polymers, the differences include the morphology, degree of crystallinity, chain and lamellar orientation, crystallization rate and surface modulus, etc. Reiter et al. studied the crystallization of polyethylene oxide (PEO) in quasi-two dimensions and observed the dependence of morphology on the crystallization temperature and molecular weight; Taguchi et al. studied the morphology and crystallization rate of isotactic polystyrene (PS) ultra-thin films as a function of film thickness; Schönherr et al. used an in situ scanning force microscope (SFM) method which could image the growth of surface directed spherulites growth of PEO; Despotopoulou et al. systematically investigated the effect of confinement on the crystallinity and chain orientation of ultrathin poly(di-n-hexylsilane) films. The influence of confinement and surface interaction on the melting temperature and the crystallite orientation has only recently been studied. With the advancement of modern technology, more and more properties of the films thinner than 20 nm have been revealed and precisely measured, and the distinct influence of these two factors can be clearly identified. With the aid of SFM and near edge X-ray absorption fine structure spectroscopy (NEXAFS), Wang et al. have shown that the crystal lamellae took a highly preferential orientation on strongly attractive substrate, and the orientation changes from edge-on to flat-on below the threshold thickness of 20-30 nm, while lamellar twisting occurred on weakly attractive substrate; by using the shear modulus force microscopy (SMFM), Wang et al. have found that the melting temperature (Tm) of the ultra-thin films on the highly attractive substrate was lower for up to 38oC than the bulk polymer, while on the weakly attractive substrate, the Tm depression of the film with the same thickness was only 12oC. Fitting with Thomson-Gibbs equation, the interfacial reaction was demonstrated to be the key factor that led to the large Tm depression.
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