Crystallization seeds favour crystallization only during initial growth

TL;DR

This study uses a colloidal model to show that crystallization seeds promote initial growth but hinder further development once the crystal reaches a critical size, acting like impurities.

Contribution

It provides a detailed experimental and theoretical analysis of how heterogeneous seeds influence crystallization dynamics and structure.

Findings

Crystallization seeds only promote initial growth phase.

Crystals detach from seeds after reaching a critical size.

Seeds act as impurities hindering further growth.

Abstract

Crystallization represents the prime example of a disorder order transition. In realistic situations, however, container walls and impurities are frequently present and hence crystallization is heterogeneously seeded. Rarely the seeds are perfectly compatible with the thermodynamically favoured crystal structure and thus induce elastic distortions, which impede further crystal growth. Here we use a colloidal model system, which not only allows us to quantitatively control the induced distortions but also to visualize and follow heterogeneous crystallization with single-particle resolution. We determine the sequence of intermediate structures by confocal microscopy and computer simulations, and develop a theoretical model that describes our findings. The crystallite first grows on the seed but then, on reaching a critical size, detaches from the seed. The detached and relaxed crystallite continues to grow, except close to the seed, which now prevents crystallization. Hence, crystallization seeds facilitate crystallization only during initial growth and then act as impurities.