“Kinematic” analysis of growth and coalescence of spherulites for predictions on spherulitic morphology and on the crystallization mechanism

Estimation of polymer nucleation and growth rates by overall DSC crystallization rates

“…Knowing 1/t tot , it is necessary to know h to obtain G 0 or, vice versa, to know G 0 to obtain h. The value of h cannot be accurately estimated by measuring the radius of spherulites in actual polymer samples because crystallization occurs from multiple nucleation sites; the collision between spherulites, according to their distance and growth rates, 5 causes the cessation of their growth and the generation of a tessellated structure with polyhedral tessellations. However, because the impingement between a number of spherulites nucleated far from the cooling source can be considered to occur only during the final stage of crystallization, a good approximation of h is obtained by using in h¼1/r the maximum radial dimension of spherulites visible on the top surface of a crystallized sample.…”

“…Impingement begins when adjacent spherulites touch each other at a point and causes the cessation of the growth at the contact region between spherulites with a progressive reduction of the length of the growth fronts relative to separate spherulites. 5 Therefore, the function N(t) has values in the range of rational numbers and accounts for the decrease of the fraction of the growth front of coalescing spherulites. For instance, the contribution to N(t) of z spherulites is z until they remain separate, but once they begin to coalesce, their contribution to N(t) is a fractional number that becomes progressively smaller than z, according to the increasing fraction of the contour that ceases to grow.…”

“…The visual observation of solids by means of high-resolution microscopes, as opposed to monitoring during solidification, has already been proved to be very useful in obtaining information on the crystallization mechanism. 5 Indeed, the shape of the interface between spherulites gives an indication of the relative instances of nucleation and growth rates of the spherulites. 5 Growth parameters have also been obtained from the overall crystallization rate of previously self-nucleated samples at an ideal temperature.…”

“…5 Indeed, the shape of the interface between spherulites gives an indication of the relative instances of nucleation and growth rates of the spherulites. 5 Growth parameters have also been obtained from the overall crystallization rate of previously self-nucleated samples at an ideal temperature. 3,6 This method requires preliminary differential scanning calorimeter (DSC) scans to identify the self-nucleation temperatures of polymers.…”

Growth of spherulites: foundation of the DSC analysis of solidification

“…This is why crystallization is conducted industrially by continuous cooling (non-isothermal crystallization), whereas enquires on solidification are based on observations at a constant temperature (isothermal crystallization), which ensures accurate results. The mechanisms of the so-called non-isothermal and isothermal solidification are essentially the same, as proved by the shape of interfaces between the grains [13]. The only differences regarding the dynamics of the solidification mechanism result in a time dependence of nucleation and in a highly accelerated growth which lead to a much higher rate during crystallization at variable temperature.…”