Role of curvature elasticity in sectorization and ripple formation during melt crystallization of polymer single crystals

Abstract

The present article focuses on theoretical elucidation of possible effect of mechanical deformation on spatio-temporal emergence of unusual polymer morphology subjected to quiescent isothermal crystallization conditions. The present theory developed is based on a phase field model consisted of non-conserved time dependent Ginzburg-Landau equation having an asymmetric double well potential in the crystal order parameter signifying metastability for crystallization, coupled with the chain tilt angle involving curvature elasticity and strain recovery potentials. Under quiescent crystallization conditions, the curvature elasticity term is needed to discern the emergence of sectorized single crystals. Upon coupling with the strain recovery potential, the numerical calculation captures ripple formation running across the long lamellar growth front, which may be attributed to lamellar buckling caused by the volume shrinkage. Of particular interest is that these simulated topologies of the single crystals are in good accord with the growth character of syndiotactic polypropylene single crystals observed experimentally by us during isothermal crystallization from the melt.

Effect oftrans-cisphotoisomerization on phase equilibria and phase transition of liquid-crystalline azobenzene chromophore and its blends with reactive mesogenic diacrylate

“…The undulation on the LCAC crystal surface during the course of UV irradiation implied that the photoisomerization can take place even in the condensed phase, which may be attributed to the disparity of crystal density (or volume) of trans-and cis-isomeric states. This phenomenon is commonly found in other systems, such as the buckling phenomenon of syndiotactic polypropylene single crystals caused by a sudden volume change at the crystal-melt interface [31]. It should be emphasized that the present paper demonstrates the effect of trans-cis photoisomerization on the mesophase transitions of neat LCAC and the phase diagram of LCAC-RM257 as well as on the ripple formation (i.e., periodic undulation) on the azobenzene crystals.…”

“…6(a) and 6(b)]. A similar occurrence of periodic undulations on rectangular single crystals of syndiotactic polypropylene (sPP) was found to occur during thermal quenching from the melt [31]. This ripple formation has been attributed to the volumetric shrinkage driven by a sudden change of density at the solid-melt interface during sPP crystallization.…”

Morphology Development in Relation to the Ternary Phase Diagram of Biodegradable PDLLA/PCL/PEO Blends

“…Hence, c ¼ 0 corresponds to the isotropic melt, whereas c ¼ z 0 signifies the crystalline state. [14][15][16] The free energy of coupling interaction may be given as…”

Phase Field Modeling on Polymer Crystallization and Phase Separation in Crystalline Polymer Blends

“…In an attempt to generate such sectorized hexagons, Mehta and coworkers coupled two nonlinear differential equations, pertaining to a crystal order parameter and a chain tilt angle [51,52]. The process of chain tilting was described through the mechanical deformation field associated with a sudden change of density driven by volume shrinkage at the interface during the solid crystal-liquid melt transition.…”

“…liquid solid crystal region and the neat crystal region (Figure 4.10d). Although the FH interaction parameter controls the behavior of the UCST [52,61], the trend of liquidus and solidus lines at the high crystalline content compositions is not noticeably affected by the x parameter. It can be inferred that these phase diagrams of crystalline polymer blends are governed by the competition between the crystalline solid-amorphous melt phase transition and the liquid-liquid phase separation.…”