Controlled spherulitic crystal growth from salt mixtures

Abstract

For the first time, we present data on the actual growth rate, supersaturation, viscosity, and growth mechanism that lead to spherulitic growth. So far, fundamental questions regarding the growth conditions, mechanisms, and the necessity of a viscous growth medium have remained unresolved. Surprisingly, we observed a sol-gel transition in evaporating silica-free sulfate mixtures, followed by the growth
of sodium sulfate spherulites. We characterized the spherulites’ morphological evolution and chemical/structural composition using various microscopy techniques and Raman Spectroscopy. The study reveals that faceted crystals, during their morphological evolution, can transiently exhibit a spherulitic morphology before attaining their final shape. We demonstrate that adding bivalent ions to sulfate solutions can create the conditions required for the spherulitic growth of the crystal phase. We show how to obtain perfectly developed spherulites through an in-depth experimental investigation of ion concentrations, evaporation rate, and geometric constraints. Moreover, quantifying the growth conditions enables a precise understanding and facilitates a comprehensive discussion on a general approach for
cultivating spherulites through solvent evaporation that is imperative for innovative purposes.