Influence of surfactant–cosurfactant ratios on the morphology of vaterite microparticles in Inverse microemulsions

The controlled growth of calcium carbonate microcrystals is essential for their use in various industries such as construction, plastics, and textiles, where specific mineral forms and morphologies are required. A common method to achieve desired morphologies involves the use of surfactants to encapsulate calcium salts in a microemulsion environment (for instance, water in oil) to facilitate the growth of the microcrystals. In our work, we employed a system comprising octyl phenol ether-10 as the surfactant and n-heptanol as the co-surfactant. This mixing approach effectively fine-tuned the shape formation of vaterite calcium carbonate microcrystals. The study emphasizes the crucial role of surfactant and cosurfactant ratios in oil-in-water inverse emulsions for the generation of microparticles in diverse shapes. It was found that a higher ratio of octyl phenol ether-10 to n-heptanol (4:1) results in the formation of needle-shaped vaterite microparticles, whereas a lower ratio (1:1) leads to coral-shaped structures, together with a variety of shapes observed at intermediate ratios. Theoretical calculations, based on improved critical packing parameter theory, were conducted to shed light on the mechanisms behind these morphological variations. This method opened new avenues in mineral crystal growth and surface engineering.