Lamellar Growth Rate

The growth rate is important for any kinetic study. Many studies have been performed to measure the growth rate of spherulites using OM and recently 

To explore the effect of temperature on the growth rate of the lamellae, the length of the lamellae was measured at two other temperatures (16 and 28 °C) and the results are shown in Fig. 26. The growth rate of the lamellae at 16 and 28 °C was measured to be 8.2 and 32.4 nm/min, respectively. The rate increases significantly as the temperature increases indicating that the growth rate of the lamellae at this temperature range is limited by the diffusion of the polymer chains. 

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Fig. 18 Lamellar growth rate of BA-C10 as a function of crystallization temperature, determined by AFM [64]...

The Effect of Film Thickness on Lamellar Growth Rate and Morphology... 

Fig. 4.29 (a) Lamellar growth rates for PEO as function of crystallization temperature Tc (inset lamellar dimensions vs. crystallization time) and (b) lamellar thickness plotted against inverse undercooling. The linear fit of the lamellar thickness vs. inverse undercooling plot with the boundary condition (0,0) yields a satisfactory result. Adapted with permission from [52]. Copyright 2002. American Chemical Society... 

The crystallization of PEO was also unveiled at the level of individual lamellae in ultrathin films (278-280). It was observed that although lamellar growth rates were retarded in films thinner than 200 nm because of interfacial interactions, SFM provided the same qualitative and quantitative information as typically applied bulk characterization techniques on lamellar growth rates, lamellar thicknesses, and melting points. The Hoffman-Weeks extrapolation, the Gihhs-Thompson equation, and the Hoffman-Lauritzen theory were apphed and the results compared favorably to the corresponding hulk data. 

Preferential absorption of OSO4 has been shown [115] to reveal spherulites in semicrystalline PET. Stefan and Williams [116] work on ABS-poly-carbonate blends also showed contrast by selective absorption. The dark SAN polymer, in this latter study, contains the osmium stained rubber particles while the polycarbonate was not stained. Niimoni et al. [117] found that there is often enough phase contrast in stained copolymers which have different degrees of unsaturation or functional groups like -OH, -0-, or as they each vary in reactivity with the stain. A specially constructed pressure bomb was developed by Edwards and Phillips [118] in order to terminate crystallization and fix polymers with OSO4 at elevated pressure. This method has permitted determination of lamellar growth rates and the observation of developments in crystalline morphology. 

Fig. 12.14 Plot of lamellar growth rate, G, as a function of temperature for cross-linked natural rubber at indicated strains. (Adapted from Andrews et al. (60))...

Growth rate measurements can also be made on systems crystallizing under deformation. Andrews et al. have in fact carried out studies of the lamellar growth rate in cross-linked natural rubber at relatively low strains.(60) The study was limited to two extension ratios and one network. A summary of the results is given in Fig. 12.14. A maximum in the growth rate with temperature is observed in each of the deformed samples, similar to that reported for undeformed natural rubber. The magnitudes of the two growth rates at the maxima are comparable to one another. However, there is an increase of about 15 °C between the two maxima. 

Investigations of the crystalUzation kinetics of polymers from dilute solution are of particular interest WeU-defined lamellar-Uke crystallites are formed in this concentration region. Moreover, in contrast to crystallization from the pure melt, or concentrated solution, the chains are relatively isolated from one another. Both the overall crystallization and lamellar growth rates have been studied in this concentration range. Attention will initially be given here to the overall crystallization studies and the analysis of the data obtained. 

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