Differential scanning calorimetry crystal growth kinetics

There are several methods available for the study of bulk crystallization, including dilatometry, differential scanning calorimetry, and x-ray diffraction. Optical microscopy is the most versatile method for the study of crystallization since the use of a trinocular permits the simultaneous measurement of bulk crystallization (using transmitted light intensity) and of crystal growth kinetics using direct observation. 

Differential scanning calorimetry (DSC) can be used to study the crystal growth kinetics. The nature of the experiment leads to data that are defined in terms of mass rather than volume. In order to convert the data the following expression is used to relate the mass crystallinity (wc) to a volume fraction (vc) ... 

The kinetics of crystallization has been simulated by many models, including the Avrami model (House 2007). The rate of conversion from amorphous to crystalline states can be measured by using thermal analysis (differential scanning calorimetry, DSC) and/or X-ray diffraction. The rate of conversion from amorphous to crystalline form depends on a number of factors. The process occurs in two steps, nucleation and growth (Mullin 2001), which are affected by various factors and occur at different rates. Specifically, for crystallization to occur, a seed or nucleus must form, on which subsequent growth will occur. Thus, the rate of nucleation is of primary interest. By analogy with Arrhenius-type processes, the nucleation rate can be written as... 

Mohan, R. Boateng, K. A. Myerson, A. S. Estimation of crystal growth kinetics using differential scanning calorimetry, J. Cryst. Growth 2000, 212,489-499. See in this paper a brief review of some key references to analysis and control of crystallization processes in industrial applications. 

In this chapter, we take a practical approach to briefly explain how to experimentally determine both spherulitic growth rates by polarized light optical Microscopy (PLOM) and overall isothermal crystallization kinetics by differential scanning calorimetry (DSC). We give examples on how to fit the data using both the Avrami theory and the Lauritzen and Hoffman theory. Both theories provide useful analytical equations that when properly handled represent valuable tools to understand crystallization kinetics and its relationship with morphology. They also have several shortcomings that are pointed out. 

In order to evaluate the application of modulated-temperature differential scanning calorimetry (M-TDSC) to the study of the crystallisation kinetics of semicrystalline polymers, isothermal crystallisation kinetics in poly(e-caprolactone)-SAN blends are investigated. The temperature dependence of d In G/dT (G =crystal growth rate), determined by M-TDSC agrees approximately with previous experimental data and theoretical values. These were obtained from direct measurements of spherulite growth rate by optical microscopy. Here, theoretical and M-TDSC experimental results show that the d In G/dT versus temperature plots are not sensitive to the noncrystalline component in the poly(e-caprolactone)-SAN blends. 15 refs. 

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