Bradford Scholars -how to deposit your paper
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Polar crystals are characterized by an axis that has a nonzero dipole due to the nature of the molecular packing. For these crystals, the growth rates of the faces delineating the polar axis are generally expected to be equal. Recent experiments, however, have revealed a few exceptions where the growth of these faces from the vapor phase is asymmetric, a notable case being crystals of resorcinol. Here, we present the mechanics of resorcinol crystal growth from the melt for the hemihedral faces (011) and (01̅ 1̅ ) delineating the polar axis as revealed by molecular dynamics simulations. The simulations reveal asymmetric growth consistent with experiment. The asymmetry is attributed to the slow-growing (011) face being less able to direct the correct alignment of the oncoming molecules and the presence of an alternate resorcinol conformation that readily incorporates into the lattice at this surface, serving to poison and retard subsequent growth. Putting the issue of the rogue conformation aside, the identified factors that influence molecular recognition are considered to be applicable to other polar crystals, which suggest asymmetric growth along the polar axis to be a common feature.
■ SIGNIFICANCE STATEMENTPolar crystals form the basis for important functional materials. For these crystals, we do not understand the nature and mechanism of crystal growth along the polar axis, which is considered to be identical at both ends. Recent experiments have revealed a few exceptions where the growth of these faces from the vapor phase is asymmetric. We have carried out molecular dynamics simulations on one of these exceptional cases, resorcinol. The simulations reveal the molecular processes involved and explain the asymmetric growth. The molecular recognition processes at play and the associated dynamics of molecule alignment during crystal growth suggest asymmetric growth along the polar axis to be a common feature.
Raman spectroscopy was shown to be a useful technique in classifying miscibility levels based on the hydrophobic interaction between the drug and the polymer. Different drug loadings showed varying degrees of drug-polymer interaction, and hence variable solid state stability of the solid dispersion.
Bradford Scholars -how to deposit your paper
Overview
Copyright check• Check if your publisher allows submission to a repository.• Use the Sherpa RoMEO database if you are not sure about your publisher's position or email openaccess@bradford.ac.uk.
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