Crystallization kinetics, polymer crystal nucleation

An alternative possibility arises from considerations related to the development of crystalline structure in polyethylene [22], The main feature of this structure is the periodic folding of the polymer chains in the crystal. Theoretically this is explained within the context of the kinetics of crystal nucleation and growth from solution. According to Cormia, Price, and Turnbull [22], the fold-surface energy in polyethylene crystals is comparable to the end-interfacial energy of rodshaped nuclei. These surface free energies are of the order of 10 to... 

The details of the polymer crystallization process can be quite complicated. Practically, one may not care about the details of crystal nucleation and the linear crystal growth rates, but just want to characterize the overall crystallization kinetics. The degree of crystallization process can be roughly defined as crystallinity, regardless of their detailed crystal morphologies. The conventional methods to characterize the crystallinity include DSC, X-ray diffraction and dilatometer. Depending on the measured quantity, crystallinity is also separated into the weight crystallinity... 

The interplay of phase separation and polymer crystallization in the multi-component systems influences not only the thermodynamics of phase transitions, but also their kinetics. This provides an opportunity to tune the complex morphology of multi-phase structures via the interplay. In the following, we further introduce three aspects of theoretical and simulation progresses enhanced phase separation in the blends containing crystallizable polymers accelerated crystal nucleation separately in the bulk phase of concentrated solutions, at interfaces of immiscible blends and of solutions, and in single-chain systems and interplay in diblock copolymers. In the end, we introduce the implication of interplay in understanding biological systems. 

Fig. 11.4 Comparison in the theoretical phase diagrams of phase separation and polymer crystallization in polymer solutions, and the kinetic phase diagrams of crystal nucleation. The energy parameters are set as EpIEc =1.0 and BlEc = 0.076 for the labeled Cl curves, EpjE = 1.072 and BjEc = 0.03 for C2, and EpjEc = 1.275 and BjEc = —0.1 for C3. Three solution series share the same melting points (solid lines) at polymer concentration ( = 0.125, but different depths of critical points for phase separation. The dashed lines are binodals, and the dotted lines are spinodals. The data points are the onset temperatures for the uprising of crystallite numbers on isothermal crystallization. The straight lines are drawn to guide the eyes (Zha and Hu2007) (Reprinted with permission)...

Ellis RJ (1997) Molecular chaperones avoiding the crowd. Curr Biol 7 R531-R533 Flory PJ (1953) Principles of polymer chemistry. Cornell University Press, Ithaca Graham PD, McHugh AJ (1998) Kinetics of thermally induced phase separation in a crystallizable polymer solution. Macromolecules 31 2565-2568 Hu WB, Frenkel D (2005) Oriented primary crystal nucleation in lamellar diblock copolymer systems. Faraday Discuss 128 253-260... 

Androsch, R. and Di Lorenzo, M.L. (2013) Kinetics of crystal nucleation of poly(L-lactic acid). Polymer, 54, 6882-6885. 

Fig. 3.1. Illustration to the chain-folding principle of pol5mier crystallization. The metastable chain-folding is a favorite pathway in the kinetic selections of polymer crystal nucleation...

Abstract. Kinetic theory of crystal nucleation is proposed for flexible chain polymers subjected to flow deformation with transient molecular deformation and orientation. Significant transient effects in the kinetics of oriented nucleation are expected in melt processing involving high deformation rates, like in high-speed melt spinning. 

In the present paper a kinetic theory of crystal nucleation is considered for the polymers subjected to time-dependent deformation rates, with transient effects of the chain relaxation. The considerations provide a theory useful in modelling fast polymer processing with stress-induced crystallization, like high-speed melt spinning, melt blowing, electro-spinning, etc. 

Transient molecular deformation and orientation in the systems subjected to flow deformation results in transient and orientation dependent crystal nucleation. Quasi steady-state kinetic theory of crystal nucleation is proposed for the polymer systems exhibiting transient molecular deformation controlled by the chain relaxation time. Access time of individual kinetic elements taking part in the nucleation process is much shorter than the chain relaxation time, and a quasi steady-state distribution of clusters is considered. TVansient term of the continuity equations for the distribution of the clusters scales with much shorter characteristic time of an individual segment motion, and the distribution approaches quasi steady state at any moment of the time scaled with the chain relaxation time. Quasi steady-state kinetic theory of nucleation in transient polymer systems can be used for elongation rates in a wide range 0 < esT C N. ... 

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