Growth Rate of Spherulites

Adamski, P. and Czyzewski, R. Activation energy and growth rate of spherulites of cholesterol liquid crystals. Soc. Phys. Crystallogr. 23, 725 (1978)... 

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... 

Figure 10-10. Plot of the natural logarithm of the reduced growth rate of spherulites of different polymers as a function of a reduced temperature. Tch is the characteristic temperature, about 50 K below the glass transition temperature, at which all molecular motion ceases. Tm is the thermodynamic melting point (after A. Gandica and J. H. Magill).

The spheruhte growth may be initiated by either heterogeneous nucleation by foreign particles or homogeneous spontaneous nucleation. The growth rate of spherulites from the polymer melt increases as the temperature decreases. It reaches a maximum in the temperature range of 140-150°C, and then decreases upon further decrease of temperature. The time dependency of the primary crystallization can be described by the known Avrami equation [282]. 

Shear flow greatly influences the kinetics of crystallization of PPS. A higher shear rate and a long shear time may decrease the growth rate of spherulites in PPS. 

As mentioned above, PLA should be addressed as a random copolymer rather than as a homopolymer the properties of the former depend on the ratio between L-lactic acid and D-lactic acid units. A few studies describe the influence of the concentration of D-lactic acid co-units in the PLLA macromolecule on the crystallization kinetics [15, 37, 77-79]. The incorporation of D-lactic acid co-units reduces the radial growth rate of spherulites and increases the induction period of spherulite formation, as is typical for random copolymers. In a recent work, the influence of the chain structure on the crystal polymorphism of PL A was detailed [15], with the results summarized in Figure 5.13. It shows the influence of D-lactic acid units on spherulite growth rates and crystal polymorphism of PLA for two selected molar mass ranges. 

The overall crystallization rate is used to follow the course of solidification of iPP. Differential scanning calorimetry (DSC), dilatometry, dynamic X-ray diffraction and light depolarization microscopy are then the most useful methods. The overall crystallization rate depends on the nucleation rate, 1(0 and the growth rate of spherulites, G(0. The probabilistic approach to the description of spherulite patterns provides a convenient tool for the description of the conversion of melt to spherulites. The conversion of melt to spherulites in the most general case of nonisothermal crystallization is described by the Avrami equation ... 

Figure 16.9 Radial growth rates of spherulites and the induction periods for spherulite growth of pure phase and blends of stereocomplexationable polymers as estimated from the respective POM images. Reprinted with permission from Ref [79] 2011, Nature Publishing Group.

This is the functional dependence expected for a growth with constant growth rate of spherulites with a constant inner structure. The agreement in the kinetics recorded in terms of P and in terms of Sp implies that the density in the growing lamellar crystallites does not change. The different functional dependencies of 6p and P on Ac , linear and quadratic ones, respectively, would result in different isotherms for P and Sp if Ac would vary in time. 

Fig. 5.38. Temperature dependence of the radial growth rate of spherulites of PeCL as measured in a polarizing microscope. Representation by Eq. (5.24) with Ta = 1350K, Tv = —110°C and Tg = 443K the zero growth temperature is T,g = (77 1)°C [57]...

Hoffmann ID, Frolen LT, Ross GS, Lauritzen 11. On the growth rate of spherulites and axialites from the melt in polyethylene fractions regime I and regime II crystallization. J Res Natl Bur Stand Sect A 1975 79 671. 

Example 11.3 Kennedy and co-workers used photomicroscopy to measure the radial growth rate of spherulites of isotactic polystyrene at a variety of constant temperatures [11]. These data are shown in Figure 11.10. Show that the results are consistent with Eq. (11.3.9). 

Figure 11.10 Comparison of experimentally determined growth rates of spherulites of i-polystyrene with ( ) experimental (— ) theoretical values. (From J. Polym. Sci. Polym. Phys. Ed., 21, Kennedy, M. A., G. Turturro, G. R. Brown, and L. E. St.-Pierre Retardation of spheralitic growth rate in the crystallization of isotatic polystyrene due to the presence of a nucleant, Copyright 1983 hy John Wiley Sons, Inc. Reprinted by permission of John Wiley Sons, Inc.)...

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