Properties of the Crystal-Melt Interface

Much of the interesting physics in semicrystaUine materials is hidden in the transition region between the crystalline domain and the melt-like domain. In particular in polymeric systems with a certain degree of stiffness of the backbone, the chain connectivity between both phases results in a rather wide transition region. In the following, we focus on the characterization of the crystal-melt interface by invoking the Gibbs construction of a sharp 

The calculation of the interface properties as described in Sect. 14.2.4 requires determination of the position of the Gibbs dividing surface, z. We calculated the mass density profiles p z), and then used the criterion = 0 with (14.9). The resulting values are reported in Fig. 14.8. There, the position of the Gibbs dividing surface is measured with respect to the real crystal surface, which is defined midway between the top layer of united atoms in the crystal and the first layer of mobile atoms bonded to it. The thickness of the interface (approx, equal to 2 div) decreases for the higher temperatmes as a result of weakened chain stiffness and entropic effects, in accord with previous results [26]. 

The error bars in Fig. 14.8 (as also for Figs. 14.9 and 14.10) are calculated by splitting the entire Monte Carlo simulation in ten blocks, from which 

Solid bars indicate the ranges of values given in [16 18] for n-paraffin at T = 296 K (dark grey), and melt-crystaUized polyethylene at T = 298K (light grey). Reprinted from [30] with written permission from Elsevier 

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Since a substantial amount of material is contained in the interlamellar region, the properties of the latter give significant contributions to the overall material behavior. The properties of the interlamellar material he between those of the unconstrained amorphous melt and those of the crystalline phase [9-11], and the influence of the crystalline constraints can be addressed experimentally [12-14]. Furthermore, the properties of the crystal-melt interface have various ramifications that can be observed experimentally [15], e.g., interface stresses lead to distortion of the crystal lattice spacing [16-18], and they are possibly responsible for lamella twisting [19]. In addition, the surface tension enters in theoretical models for crystallization rates [20,21]. 

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