Influence of Polar Protic Solvents on Urea Morphology: A Combination of Experimental and Molecular Modeling

This work reports the solvent effectson the crystal ureamorphology through experimental and molecular modeling approaches. The modification of crystal shapesis used intensivelyin designingparticles with desired properties to ensure the efficiency of themanufacturing processes. In this work, urea crystals grew in variouspolar protic solvents by cooling crystallization that produced alpha-formurea. The aspect ratios of the crystals were found to be in the rangefrom 14.77 to 1.44, grown in the following solvents: water > methanol> ethanol > isopentanol > isobutanol > pentanol > butanol> propanol> isopropanol. An attempt to establish a correlation between thenonbondedenergy, solvent molecule size, binding energy, and the change in morphologyrevealed that the aforementioned factors could not accurately predictthe aspect ratios of the urea crystals. The solvent-surface bindingenergy showed the {111} and {001} capping facets recorded the higheststrength (most negative energy), while the {110} facet was the lowest.The inhibition of the solvent molecules on the {001} and polar {111}facets stopped the growth along the c-axis by stoppingthe formation of synthon A and synthon B, while the growth along the a-axis was halted by stopping the formation of synthon B.The transformation from elongated cuboid to prismoidal shape of ureawas governed by the {111}/{110} energy ratio, i.e., it must be <1.78.

Automated summary

This work investigates the impact of solvents on the morphology of urea crystals through experimental and molecular modeling approaches. The research finds that the aspect ratios of urea crystals grown in different polar protic solvents vary significantly. The study attempts to establish a correlation between various factors and crystal morphology but finds that these factors cannot accurately predict the aspect ratios of the crystals.