Salt Whisker Growth through Macromolecular Crowding Matrix Regulation

The stable and controlled substance transportation regulated by intricate mechanisms in nature enables the growth of an elaborate crystal structure under diffusion control, exemplified by many biological behaviors such as biomineralization. Crystal growth in oversaturated solutions often faces challenges in controlling the growth direction and morphologies, especially within unregulated, simple artificial environments. In this study, polyampholyte (PA) hydrogels synthesized through the random copolymerization of cationic and anionic monomers were employed as a matrix for directional salt crystal growth. This approach successfully facilitated the large-scale growth of sodium chloride salt whiskers (SWs) on the surface of the PA substrate. Real-time observation of the growth process and surface morphology evolution of SWs on the PA substrate revealed two distinct SW morphologies, suggesting that multiple mechanisms are involved in their development. The demonstration of growing SWs using a PA gel matrix offers a scalable and practical approach for one-dimensional salt crystal synthesis. PA, as a representative hydrogel matrix with a tunable charged macromolecular crowding environment, serves as a promising model for investigating biomineralization, encompassing substance transport and crystal growth.