Exploring the crystallization preference for NaCl in solvent mixtures by Nanoprecipitation

Nanoprecipitation is a powerful method for synthesizing nanoparticles with controllable morphologies and well-defined crystallographic facets, offering broad utility in materials science, pharmaceuticals, and nanotechnology. Sodium chloride (NaCl) serves as an ideal model system to investigate solvent effects in nanoprecipitation. Herein, we investigate the influence of protic and aprotic solvents, as well as their mixtures, on the morphology and facet distribution of NaCl nanoparticles through a combination of experimental and theoretical approaches. Experimental results show that the ratio between isopropanol and tetrahydrofuran significantly affects the ratio of {110} to {100} crystal faces, leading to a morphology transformation from cubes dominated by {100} facets to hexapods with a mixture of {100} and {110} facets, and finally to rhombic dodecahedra enclosed by {110} facets. This transition represent a novel facet evolution mechanism. Complementary theoretical simulations of crystal formation free energy calculations provide further insight into the role of solvent molecules in stabilizing specific crystal facets, with protic solvents exhibiting varying preferences for {110} facets in the order ethanol > n-propanol > isopropanol > n-butanol > n-pentanol. These findings provide deeper insights on the interplay between solvent composition and crystal facet formation, offering new possibilities for tailoring the properties of ionic nanoparticles.