Thesis (M.Sc. in Pharm)--Chulalongkorn University, 2013

Crystals of α-resorcinol exhibit asymmetry during crystal growth, both from vapour and solution, and dissolution, that is, the two faces at the ends of the polar axis grow or dissolve at different rates. Molecular dynamics (MD) simulations were carried out to understand this extra-ordinary behavior of α-resorcinol in terms of dissolution and growth on (0͞1͞1) and (011) faces. Four investigations were carried out: (i) dissolution of α-resorcinol in water at a number of temperatures; (ii) crystal growth from solutions at three supersaturation levels; (iii) crystal growth from vapour and (iv) crystal growth from melt at various temperatures. The results showed that dissolution and crystal growth rates were faster on the (0͞1͞1) face, the polar face, which is consistent with experimental observations. The dissolution and crystal growth were more marked at higher temperatures where the molecules have higher energy and able to diffuse much more rapidly. However, too high a temperature caused surface reconstruction in the simulation of crystal growth from vapour. The supersaturation levels influenced the crystal growth in solution. The higher supersaturation level caused faster growth rate as expected, in particular on the (0͞1͞1) face. The simulations clearly reveal the distinct molecular behavior of the molecules that gives rise to the asymmetry in crystal growth and dissolution. However, it is not apparent as to what exactly is the origin of the behavior. For dissolution and crystal growth from solution, the water (solvent) may have a preferential role in deciding the relative dissolution rate and growth at the respective surfaces.