Polymer crystallization, nucleation simulations

Hu W, Cai T (2008) Regime transitions of polymer crystal growth rates molecular simulations and interpretation beyond Lauritzen-Hoffman model. Macromolecules 41(6) 2049-2061 Hu W, Frenkel D (2004) Effect of metastable liquid-liquid demixing on the morphology of nucleated polymer crystals. Macromolecules 37(12) 4336-4338 Hu W, Frenkel D (2005) Polymer crystallization driven by anisotropic interactions. Adv Polym Sci 191 1-35... 

Several significant developments in polymer crystallization theory have been made more recently, e.g., the two-dimensional nucleation and sliding diffusion theory of Hikosaka,231 the two-stage crystallization model by Strobl,232 and a number of simulation studies have been carried out and are in progress. Past and future experiments on model compounds will undoubtedly benefit these developments. 

Hu WB, Mathot VBF, Frenkel D (2003a) Lattice model study of the thermodynamic interplay of polymer crystallization and liquid-liquid demixing. J Chem Phys 118 10343-10348 Hu WB, Frenkel D, Mathot VBF (2003b) Sectorization of a lamellar polymer crystal studied by dynamic Monte Carlo simulations. Macromolecules 36 549-552 Hu WB, Frenkel D, Mathot VBF (2003c) Intramolecular nucleation model for polymer crystallization. Macromolecules 36 8178-8183... 

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. 

Polymer crystallization theory is a mature area, and there are several review articles available that present and discuss the different theories in great detail (eg, 103,104). Having said that, over the last 5 years or so there has been a flurry of new interest becanse of the increase in computational power, which has the potential to decisively enter the debate in some areas. In the following the underlying themes of the two principle theories of polymer crystallization, secondary nucleation theory and rough-surface or entropic barrier theory, are outlined. The results of more recent simulations are then briefly discussed, in which the constraints of the above theories, introduced to provide analytical solutions, have been relaxed. Finally, some of the more fundamentally different ideas that have recently appeared are discussed. 

Although secondary nucleation theory was, for a period, widely accepted, it is now coming under increasing pressure, from experimental data, from computer simulation, and from new approaches to the fundamental process of crystalhzation. It is not clear at this stage whether all that is required is a few adjustments to the theory, or whether the idea of a nucleation barrier is flawed, or even if the idea that the crystal thickness seen is the fastest growing is correct. With the development of new theoretical tools, and the increased integration of theory with computer simulation, it is hoped that a more complete model for polymer crystallization can be developed. 

Hu W (1998) Structural transformation in the collapse transition of the single flexible homopolymer model. J Chem Phys 109(9) 3686-3690 Hu W (20(X)) The melting point of chain polymers. J Chem Phys 113(9) 3901-3908 Hu W (2005) Molecular segregation in polymer melt crystallization simulation evidence and unified-scheme interpretation. Macromolecules 38(21) 8712-8718 Hu W (2007) Intramolecular crystal nucleation. In Reiter G, Strobl GR (eds) Lecture notes in physics progress in understanding of polymer crystallization. Springer, Berlin, pp 47-63 Hu W (2013) Polymer physics a molecular approach. Springer, Wien... 

Polymer crystallization is of great theoretical and practical significance and an extensive literature has been published that spans many decades. Some of the classic textbooks that have reviewed fundamental aspects of polymer crystallization are those by Wunderlich [1-3], Mandelkern [4,5], Schultz [6], Gedde [7], and Hiemenz and Lodge [8]. More specialized books review recent literature highlight controversies on polymer nucleation, crystallization theories, and simulation and also present new experimental results on multiphasic materials [9-13]. 

The present chapter has centered on experimental efforts performed to study confined polymer crystallization. However, molecular dynamics simulations and dynamic Monte Carlo simulations have also been recently employed to study confined nucleation and crystallization of polymeric systems [99, 147]. These methods and their application to polymer crystallization are discussed in detail in Chapter 6. A recent reference by Hu et al. reviews the efforts performed by these researchers in trying to understand the effects of nanoconfinement on polymer crystallization mainly through dynamic Monte Carlo simulations of lattice polymers [147, 311]. The authors have performed such types of simulations in order to study homopolymers confined in ultrathin films [282], nanorods [312] and nanodroplets [147], and crystallizable block components within diblock copolymers confined in lamellar [313, 314], cylindrical [70,315], and spherical [148] MDs. 

A drastic departure from nucleation theory was made by Sadler [44] who proposed that the crystal surface was thermodynamically rough and a barrier term arises from the possible paths a polymer may take before crystallizing in a favourable configuration. His simulation and models have shown that this would give results consistent with experiments. The two-dimensional row model is not far removed from Point s initial nucleation barrier, and is practically identical to a model investigated by Dupire [35]. Further comparison between the two theories would be beneficial. 

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