Nucleation polymer crystal growth

Polymers crystallize from the molten state by the two-step process of nucleation and crystal growth. Nucleation initiates crystallization, followed by the addition of linear chain segments to the crystal nucleus. 

Polymer crystallization is usually divided into two separate processes primary nucleation and crystal growth [1]. The primary nucleation typically occurs in three-dimensional (3D) homogeneous disordered phases such as the melt or solution. The elementary process involved is a molecular transformation from a random-coil to a compact chain-folded crystallite induced by the changes in ambient temperature, pH, etc. Many uncertainties (the presence of various contaminations) and experimental difficulties have long hindered quantitative investigation of the primary nucleation. However, there are many works in the literature on the early events of crystallization by var-... 

Polymer crystal growth is predominantly in the lateral direction, because folds and surface entanglements inhibit crystalliza- 4 don in the thickness direction. Neverthe-1 less, there is a considerable increase in the fold period behind the lamellar front during crystallization from the melt and, as we have j seen, polymers annealed above their crys-tallization temperature but below Tm also irreversibly thicken. Nevertheless, in most theories of secondary nucleation, the most i widely used being the theory of Lauritzen and Hoffman,28 it is assumed that once a part of a chain is added to the growing crystal, its. fold period remains unchanged. 

Avrami Analysis The Avrami equation, a general approach for description of isothermal phase transformation kinetics originally developed for polymers (46), is often used for describing nucleation and crystal growth in fats. The Avrami equation is given as... 

The local resolution of laser-induced reactions depends on primary effects, i.e., the laser light, and secondary effects induced by the system. Laser-induced metal nucleation and crystal growth and the relevant mechanisms depend mainly on the electronic properties of the substrate, but also on interfacial and electrolyte properties. Depending on the system parameters, focused laser light can influence overvoltage-dependent terms particularly by local heat formation or by local activation of the solid state/electrolyte interface. As the electric properties of the substrate material is of strong influence, the effects will briefly be discussed for metal, semiconductor and polymer substrates. 

Wolkowicz, M., Nucleation and crystal growth in sheared poly(l -butene) melts, /. Polym. Sci. Polym. Symp., 63, 365,1978. 

Hu WB (2005) Molecular segregation in polymer melt crystallization simulation evidence and unified-scheme interpretation. Macromolecules 38 8712-8718 Hu WB, Cai T (2008) Regime transitions of polymer crystal growth rates molecular simulations and interpretation beyond Lauritzen-Hoffman model. Macromolecules 41 2049-2061 Jeziomy A (1971) Parameters characterizing the kinetics of the non-isothermal crystallization of poly(ethylene terephthalate) determined by DSC. Polymer 12 150-158 Johnson WA, Mehl RT (1939) Reaction kinetics in processes of nucleation and growth. Trans Am Inst Min Pet Eng 135 416-441... 

Zhang ZY, Zeng HM, Nucleation and crystal-growth of PEEK on carbon-fiber, J Appl Polym Sci, 48(11), 1987-1995, 1993. 

The scientific literature on crystallization in polymer blends clearly indicates that the crystallization behavior and the semicrystalline morphology of a polymer are significantly modified by the presence of the second component even when both phases are physically separated due to their immiscibility. The presence of the second component, either in the molten or solid state, can affect both nucleation and crystal growth of the crystallizing polymer. The effect of blending on the overall crystallization rate is the net combined effect on nucleation and growth. 

Abstract. We review how the nucleation mechanism of polymer crystallization could be assigned to intramolecular processes and what are the preliminary benefits for understanding some fundamental crystallization behaviors. The speculative concept of molecular nucleation and the theoretical model of intramolecular nucleation have been elucidated in a broad context of classical nucleation theory. The focus is on explaining the phenomenon of molecular segregation caused by polymer crystal growth. 

The regime-transition phenomena of polymer crystal growth have been well explained on the basis of the Lauritzen-Hoffman model [14,15]. Nevertheless, the assumptions about the details of secondary crystal nucleation can be replaced by the intramolecular crystal nucleation, without a substantial loss of semi-quantitative predictions about regime transitions. 

Abstract. Crystallization behavionrs are characterized with the nucleation and crystal growth rates, which are strongly dependent on temperature and molecular weight in polymeric materiak. Their rates show the beU-shape temperature dependence with maximum rates. The maximum rates are characteristic intrinsic values in polymer crystallization mechanism. Temperature and molecular weight dependencies are discussed. 

Crystallization is the competition between two processes nucleation and crystal growth. Nucleation is the formation of small sites (nuclei) from which crystallites can grow. Primary nucleation creates the initial nuclei. Crystallites develop aroimd these nuclei. Then in secondary nucleation, the surfaces of the crystallites are nucleated. More polymer chains diffuse to the crystallite surfaces and growth continues. 

The changes in the rate are a consequence of the change in balance between free energy of the melt and that of the solid and its influence on the nucleation processes. The LH theory has been used extensively to analyse polymer crystal growth data and is able qualitatively to describe processes that occur in a number of polymer systems. Its success lies in its ability to describe the temperature dependence of both the initial crystal thickness (L ) and the linear growth rate (coj.). A large volume of data has been shown to fit the relationship ... 

For fiber reinforced composites based on semicrystalline matrix, the ultimate properties are determined in part by the crystalline morphology of the polymer matrix, which in turn depends on the rates of nucleation and crystal growth. Therefore, the knowledge and understanding of crystallization mechanisms are crucial for designing the tailored materials or products with the desirable properties. In this section, we would like to introduce the crystallization kinetics of PET/PP MRCs first, and then the crystaUine structures and aggregated morphology will be also presented. 

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