Understanding polymer nucleation by studying droplets crystallization in immiscible polymer blends

Abstract

This Feature Article reviews our recent work on the nucleation and crystallization of finely dispersed semicrystalline polymeric droplets in immiscible matrices. Droplets dispersions can be used as a toolbox to investigate polymer nucleation. Studying the overall crystallization kinetics of the droplets can be a way to separate the contributions of nucleation and growth rates depending on the sample. To characterize the relative importance of nucleation versus growth, we have defined a dimensionless parameter named the “Turnbull number”. This number equals the ratio of the time needed for a crystal to grow inside the average droplet volume, divided by the required time for nucleation to occur in the same droplet. We show examples for Turnbull numbers close to unity, where the overall crystallization kinetics of the droplets is dominated by crystal growth, and a sigmoidal (second or third order) kinetics is obtained. On the other hand, when the overall crystallization of the droplets is controlled by nucleation, very low Turnbull numbers are obtained (e.g., 0.1–0.01) with concomitant first-order kinetics. We also show how the nucleation step in the droplets can be skipped through the strategic use of self-nucleation. In the case of double crystalline polymer blends, the self-nucleation of the matrix can be used to study the surface nucleation of the droplets at the interface. The role of interfacial roughness in promoting droplet nucleation is also addressed, together with the addition of heterogeneous nucleating agents. Considering all the body of information, we demonstrate that studying the overall kinetics of different droplet dispersions can contribute to the fundamental understanding of polymer nucleation.