| The amorphous solids can be used in a number of applications such as food, bio-preservation, organic electronics, and drugs. In pharmaceutical systems, amorphous drugs have greater solubility and bioavailability than their crystalline counterparts, giving them an important function in drug delivery formulation.;Recent studies have compared surface-enhanced crystallization to bulk crystal growth. The surface crystal growth rate can be orders of magnitude faster than growth rate in the bulk. It has been shown that surface-enhanced crystallization is a common phenomenon on molecular glasses. Thus, it is significant to understand the mechanism of fast surface crystallization on molecular glasses.;We report that the onset of fluidity generally disrupts fast surface crystal growth in indomethacin(alpha IMC), nifedipine (NIF), and o-terphenyl (OTP). The severity of this inhibition depends on crystal morphology. Segregated needles are more susceptible to the liquid flow than crystals that grow in compact domains. With scanning electron microscopy (SEM) and atomic force microscopy (AFM), we characterize the surface evolution of depletion zones around growing a crystal. We find that the observed depletion zones are well reproduced by the known coefficients of surface diffusion and crystal growth rate. Finally, the effect of special confinement on surface crystal growth was performed. Surface crystal growth was disrupted if the width is reduced to below several micrometers or if the glass film is thinner than the depth of depletion zones. Similarly, surface crystallization kinetics is affected by glass thickness or substrate. Surface crystal growth is initially fast, but slows over time if the glass film is thinner than approximately 10 mum. All these effects reflect the environmental perturbation of surface crystal growth. The slowdown of surface crystal growth in microns-thick films may be caused by the propagation of cracks created by a fracture in the bulk.;These results are relevant to understand the stability of amorphous solids against surface crystallization in formulations and product development. |
