On the origin of surface imposed anisotropic growth of salicylic and acetylsalicylic acids crystals during droplet evaporation

Abstract

In this paper droplet evaporative crystallization of salicylic acid (SA) and acetylsalicylic acid (ASA) crystals on different surfaces, such as glass, polyvinyl alcohol (PVA), and paraffin was studied. The obtained crystals were analyzed using powder X-ray diffraction (PXRD) technique. In order to better understand the effect of the surface on evaporative crystallization, crystals deposited on glass were scraped off. Moreover, evaporative crystallization of a large volume of solution was performed. As we found, paraffin which is non-polar surface promotes formation of crystals morphologically similar to those obtained via bulk evaporative crystallization. On the other hand, when crystallization is carried out on the polar surfaces (glass and PVA), there is a significant orientation effect. This phenomenon is manifested by the reduction of the number of peaks in PXRD spectrum recorded for deposited on the surface crystals. Noteworthy, reduction of PXRD signals is not observed for powder samples obtained after scraping crystals off the glass. In order to explain the mechanism of carboxylic crystals growth on the polar surfaces, quantum-chemical computations were performed. It has been found that crystal faces of the strongest orientation effect can be characterized by the highest surface densities of intermolecular interactions energy (IIE). In case of SA and ASA crystals formed on the polar surfaces the most dominant faces are characterized by the highest adhesive and cohesive properties. This suggests that the selection rules of the orientation effect comes directly from surface IIE densities.

The Self-Assembly Phenomenon of Poloxamers and Its Effect on the Dissolution of a Poorly Soluble Drug from Solid Dispersions Obtained by Solvent Methods

“…The common feature of evaporation approaches is the removal of small droplets or thin layers of the solvent from different surfaces. It may lead to the crystal growth of oriented morphology as described for droplet evaporative crystallization or microwave-accelerated evaporative crystallization [38,39,40]. The crystallization of the celocoxib–PVP mixture was found to generate drug crystals of improved dissolution characteristics [41].…”

Role of Self-Assembled Surface Functionalization on Nucleation Kinetics and Oriented Crystallization of a Small-Molecule Drug: Batch and Thin-Film Growth of Aspirin as a Case Study

“…ASA dimeric synthon involves intra-molecular HB between −OH/–COOH and two −COOH groups. 47 , 48 We hypothesized that the interaction with the superficial methacrylate groups could favor its formation because of molecular mimicking. Overall, ACR SAMs were extremely active in reducing the entropic penalty required for ASA nucleation.…”

Calcium Carbonate Mineralization in a Surface-Tension-Confined Droplets Array

“…Compared with the synthesis of CaCO 3 crystals in the bulk phase (Figure 4d), the synthesis of CaCO 3 crystals in microdroplets has a greater chance of producing crystal surface defects. The effect of evaporation of droplets generated on the surface on the crystallization of materials has been studied in previous researchers' work, and we analyzed the causes of defects on the surface of calcium carbonate crystals based on their conclusions [33][34][35]. We supposed that the growth of crystals in microdroplets coexists with the volatilization of solution, which makes the evaporation rate of the microdroplets have a large effect on the crystal growth.…”