Suppressing Barium Sulfate Crystallization with Hydroxycitrate: A Dual Nucleation and Growth Inhibitor

Designing (macro)­molecules that can suppress crystallization is advantageous in natural, pathological, and commercial processes where mineralization has a detrimental impact. Control over this phase transformation is often one-dimensional, meaning that modifiers either block nucleation or impede crystal growth. Inhibitors of mineralization are predominantly composed of either phosphate or carboxylate moieties. It is less common to observe a modifier with only carboxylate functionality inhibit both nucleation and growth. Here, we explore a series of homologous poly­(carboxylic acid)­s as crystallization inhibitors of barium sulfate (barite), a pervasive and undesirable mineral scale in many industrial processes. Through bulk crystallization, time-resolved microscopy, and scattering measurements, we show that hydroxycitrate (a naturally derived small molecule) effectively inhibits barite nucleation. Moreover, combined microfluidics and atomic force microscopy measurements reveal that hydroxycitrate fully suppresses growth via the formation of a disordered layer on barite surfaces. The rate of barite growth prior to hydroxycitrate exposure could not be recovered over 12 h after removal of the modifier, indicating that growth was sustainably (and irreversibly) altered by exposure to hydroxycitrate. Thus, hydroxycitrate is a barite crystallization modifier capable of suppressing nucleation and irreversibly inhibiting surface growth