Crystal Growth of Urea and Its Modulation by Additives as Analyzed by All-Atom MD Simulation and Solution Theory

Abstract

The crystal growth of urea was analyzed with all-atom molecular dynamics (MD) simulation for the (001) and (110) faces in contact with aqueous solutions. The local environment of a crystallizing molecule was treated in terms of the numbers of crystalline neighbors and the orientation relative to the crystal surface, and the molecular-level inhomogeneity of a growing surface was addressed by decomposing the overall rate of growth into a sum of the contributions conditioned by the local structure and orientation mode. The contrast of the growth mechanism between the (001) and (110) faces was then evidenced by the local contributions, and the roles of the outer layers of the crystal toward the liquid region were pointed out for (001). The effect of the additive species in the liquid on the crystal growth of urea was investigated with biuret, N,N-dimethylformamide (DMF), and acetone. The growth was observed to be suppressed more strongly in the order of biuret > DMF > acetone, and it was found that the ordering of suppression by the additive is common irrespective of the local environment of a crystallizing urea. This finding implies that the additive’s effect on the crystal growth can be predicted by treating the flat surface, which is a convenient system for detailed analyses at atomic resolution. The correspondence to the free energy of adsorption of the additive was then examined for the additive-induced modulation of the growth rate. It was seen that the adsorption free energy correlates to the extent of modulation of the growth rate, and the interaction components that govern the adsorption propensity were identified.

Enhanced Predictability of Urea Crystallization by an Optimized Laser Repetition Rate

“…The assumed error of the induction time is 2 frames, which translates into 0.4 s. Within these 2 frames, the detection delay between the nucleation and a detectable crystal size is included. The growth rate of the (001) growth mode is simulated with 0.02 nm/ns . The detectable size with this setup is ≥ 1mm which is smaller than the size of a crystal growing for 0.4 s. From the distribution of the number of pulses required to induce crystallization, the probability of induction is extracted (see the Supporting Information for a detailed explanation of the evaluation).…”

“…The growth rate of the (001) growth mode is simulated with 0.02 nm/ ns. 27 The detectable size with this setup is ≥ 1mm which is smaller than the size of a crystal growing for 0.4 s. From the distribution of the number of pulses required to induce crystallization, the probability of induction is extracted (see the Supporting Information for a detailed explanation of the evaluation). The maximum illumination time was 10 min; if crystal induction was not observed in that time, then nucleation was deemed unsuccessful.…”

Crystal growth and morphology control of needle-shaped organic crystals

“…74,86 Recently reported all-atom MD simulations confirmed that the modulation of the growth rates of the (0 0 1) and (1 1 0) faces in the presence of biuret, acetone and dimethylformamide correlates with the adsorption free energy of the respective additive. 75 Rizvi et al studied the influence of biuret on the urea morphology as a function of supersaturation in ethanol. 87 Biuret suppresses the growth of the (1 1 1) face more strongly than the growth of (1 1 0) in line with its much stronger interaction with the former.…”