Homogenous crystal nucleation and growth in polyamide 66 (PA66) are followed in situ by means of a combination of FTIR spectroscopy and fast scanning chip calorimetry (FSC). Therefore, a novel setup with a calorimetry chip equipped with an IR-transparent SiN membrane was developed, which enables to examine IR spectroscopic and FSC experiments on the identical specimen. Because of the small amount of sample material (~ 100 ng), it is possible to achieve heating and cooling rates up to 5000 Ks⁻¹, and hence to quench the sample into a fully amorphous state without quenched-in homogeneous crystal nuclei. Annealing the film then allows to determine the onset of homogenous nucleation and crystal growth by means of FSC, whereas molecular interactions are unraveled by FTIR spectroscopy. It is demonstrated that different moieties of PA66 respond distinctly during crystallization; far-reaching interactions such as hydrogen bonding are established prior to onset of short-range steric hindrance.

The specific features of crystal nucleation widely determine the morphology of the evolving crystalline material. Crystal nucleation is, as a rule, not accessible by direct observation of the nuclei, which develop with time. This limitation is caused by the small size (nanometer scale) of the critical nuclei and the stochastic nature of their formation. We describe an experimental approach to the determination of specific features of the cluster size distribution employing fast scanning calorimetry (FSC) at scanning rates up to 10,000 K s^‑1. The surviving cluster fraction is determined by selectively melting/dissolving clusters smaller than the critical size corresponding to the highest temperature of a short spike positioned between the nucleation and the development stage in Tammann's two-stage method. This approach allows for estimating the time evolution of the radius of the largest detectable clusters in the distribution. Knowing this radius as a function of nucleation time allows for determining a radial growth rate. On the example of poly(l-lactic acid) (PLLA), the order of magnitude estimate of radial growth rates of clusters of about 2 to 5 nm yields values between 10^-5 and 10^‑3 nm s^‑1. The radial growth rate of micrometer-sized spherulites is available from optical microscopy. The corresponding values are about three orders of magnitude higher than the values for the nanometer-sized clusters. This difference is explainable by stochastic effects, transient features and the size dependence of the growth processes on the nanometer scale. The experimental and (order of magnitude) classical nucleation theory (CNT) estimates, agree well.

Supercooled tolbutamide melt was studied revealing nucleation and growth kinetics, nuclei stability and growth rate, and factors guiding polymorph selection.