(374u) From Theoretical Models to Practical Solutions in Crystal Growth Inhibition: Role of Adaptive Kinetic Monte Carlo Simulations in Understanding Modifier Binding and Etch Pits

The regulation of crystal growth across biogenic, synthetic, and natural matrices can be significantly influenced by the presence of modifiers, including inhibitors ranging from small ions to large macromolecules. Consequently, understanding the complex mechanisms of non-ideal crystallization processes modulated by these growth modifiers is pivotal for the design of therapeutics to treat human diseases, such as kidney stones [1] and malaria [2], and to prevent scaling (mineral buildup) in oil and gas recovery [3]. Modifier interactions with surfaces of crystals reduce the rate of step advancement by increasing the rate of dissolution [1]. The main mechanistic model for dissolution posits a monomer detachment (e.g., atom-by-atom or ion-by-ion) process, articulated through the terrace-ledge-kink framework for crystallization [4]. This theoretical model has been used to understand most dissolution phenomena as a sequence of ion removal from critical sites such as step edges, commonly within etch pits, and along strained defects like dislocations or grain boundaries [5]. Advanced computational predictive tools like kinetic Monte Carlo (kMC) methods can be used to study the interactions between surface modifiers and dissolution phenomena encompassing crystallization processes [6], [7] to bridge the theoretical models with computational tools facilitating a deeper comprehension of crystal surface dynamics.

Motivated by this need, we introduce an integrative model that adeptly predicts the growth and surface morphology alterations in crystals subject to modifiers, through the amalgamation of theoretical dissolution framework based on stress induced dissolution kinetics. This framework was integrated with kMC using microkinetic steps namely (a) adsorption, (b) dissolution, and (c) diffusion of crystal growth unit cells on the lattice surface to elucidate the effects of modifiers on crystal growth based on previous theoretical studies on thermodynamics of modifier effects on dissolution. These modifiers exert strain energy on the crystal structure, acting as a catalyst for etch pit formation and, consequently, altering crystal growth dynamics.

This model encapsulates transitional state kinetics, governed by the intrinsic characteristics of the modifiers, to determine the thermodynamically favored state at each simulation step. The predictive capacity of this kMC model, particularly concerning crystal morphology and growth patterns, was corroborated through Transmission Electron Microscopy (TEM) analysis of calcium oxalate monohydrate (COM) crystals in the presence of citrate (CA) and hydroxycitrate (HCA) modifiers [1]. Particularly for the dissolution phase, modifier-induced lattice stress modulates the dissolution rates of COM crystals. Accordingly, our kMC simulations reveal a seamless transition between unimpeded COM crystal growth and growth inhibition due to the addition of CA and HCA modifiers marked by etch pit development on COM crystals, an achievement beyond the reach of prior models.

References

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