The Formation Mechanism of the Crystal Morphology of Guanidinoacetic Acid: Selective Adsorption of Additives and Solute Diffusion

Guanidinoacetic acid (GAA), an important feed additive, shows poor powder properties due to its morphological characteristics. In this study, GAA was employed as a model compound to investigate the regulatory effects of polymeric additives (hydroxypropyl methyl cellulose, hydroxypropyl cellulose, and polyacrylamide) on its crystal growth and powder properties through integrated experimental and molecular simulation approaches. In situ single-crystal growth experiments reveal that hydroxypropyl methyl cellulose (HPMC) and hydroxypropyl cellulose (HPC) can selectively suppress the growth of the (11–1) crystal face while slightly promoting the growth of the (011) crystal face, thereby altering the relative growth rates and modifying the final crystal morphology. However, polyacrylamide (PAM) inhibits the growth of both the (11–1) and (011) crystal faces, resulting in negligible alteration of GAA crystal morphology. Growth kinetic analysis indicates that crystal growth is governed by a surface integration-controlled mechanism. Molecular dynamics simulations further demonstrate that the additive preferentially adsorbs onto specific crystal faces, reducing interfacial solute accumulation and inhibiting molecular diffusion. Collectively, these findings demonstrate that additives exert synergistic control over crystal morphology and particle size distribution through selective adsorption and modulation of interfacial mass transfer. This research provides mechanistic insights and theoretical guidance for the regulation of crystallization processes via additive intervention.