Stepwise crystallization and the layered distribution in crystallization kinetics of ultra-thin poly(ethylene terephthalate) film

Abstract

Crystallization is an important property of polymeric materials. In conventional viewpoint, the transformation of disordered chains into crystals is usually a spatially homogeneous process (i.e., it occurs simultaneously throughout the sample), that is, the crystallization rate at each local position within the sample is almost the same. Here, we show that crystallization of ultra-thin poly(ethylene terephthalate) (PET) films can occur in the heterogeneous way, exhibiting a stepwise crystallization process. We found that the layered distribution of glass transition dynamics of thin film modifies the corresponding crystallization behavior, giving rise to the layered distribution of the crystallization kinetics of PET films, with an 11-nm-thick surface layer having faster crystallization rate and the underlying layer showing bulk-like behavior. The layered distribution in crystallization kinetics results in a particular stepwise crystallization behavior during heating the sample, with the two cold-crystallization temperatures separated by up to 20 K. Meanwhile, interfacial interaction is crucial for the occurrence of the heterogeneous crystallization, as the thin film crystallizes simultaneously if the interfacial interaction is relatively strong. We anticipate that this mechanism of stepwise crystallization of thin polymeric films will allow new insight into the chain organization in confined environments and permit independent manipulation of localized properties of nanomaterials.

Effect of Local Chain Conformation in Adsorbed Nanolayers on Confined Polymer Molecular Mobility

“…Napolitano et al [11][12][13][14] demonstrated that substrate effects on the glass transition temperature (T g ) and segmental dynamics, measured in thin films upon confinement, could be directly related to the degree of chain adsorption at the substrate. Koga et al [15], Wang et al [16][17][18] revealed that suppressed dynamics of ultrathin adsorbed layers could extend tens of nanometers away from the substrate, which could be related to the thickness or architecture of the adsorbed layer.…”

The role of the molecular weight of the adsorbed layer on a substrate in the suppressed dynamics of supported thin polystyrene films

“…The effect of the free surface on the T g of the supported film can be erased by irreversible adsorption. Koga et al 19 and Wang 6,20,21 found that by changing the thickness or structure of the adsorbed layer, the effect of suppressing the chain dynamics could propagate to distances of several tens of nanometers away from the substrate.…”

Glass transition temperature of single-chain polystyrene particles end-grafted to oxide-coated silicon

“…[4][5][6][7][8][9][10] Confinement effects, including the effects of the free surface and substrate interface, [11][12][13] finite size effect, 14,15 and chain confinement effect, [16][17][18] have commonly been employed to explain the unusual properties of polymer thin films. Many studies indicate that motions of polymer chains near the free surface are enhanced, 19,20 while those of the chains next to the substrate can usually be suppressed by polymer-substrate interactions. 21,22 It is noteworthy that the majority of these studies were carried out on polymer confined in thin films, with significantly fewer on polymer confined in nanoparticles.…”