University of Kentucky

Investigation of Surface Energy of Aspirin Crystals Using a Contact Angle System

Institution

University of Kentucky

Abstract

Almost 90% of pharmaceutical materials are in a solid dosage form. A major hurdle during the development and manufacturing of these compounds is being able to characterize the best morphology and stable polymorph. An essential parameter that is being used to help elucidate the differences in surface characteristics is surface free energy. The conventional method for obtaining surface energy is through measuring contact angles and applying an indirect model to derive surface energies between various interfaces. The objective of this study is to measure the contact angles on the (100) and (001) faces of aspirin and observe how each face interacts differently with a specific solvent. A video-based contact angle device is used to record and measure contact angles. The sessile drop method was employed with three solvents (water, glycerol, and diiodomethane) on each major face. Results of this investigation reveals the (100) aspirin growth face having the larger contact angle in all three solvents water, glycerol, and diiodomethane, 66.9 ± 1.2, 65.1 ± 1.1, and 41.2 ± 1.1 respectively. The smaller contact angle results seen on the (001) aspirin face in water, glycerol, and diiodomethane were: 56.4 ± 1.4, 56.5 ± 0.9, and 36.2 ± 1.2 respectively. These results suggest cleavage of the (100) face does not expose the carboxylic group which would cause a stronger interaction between the crystal surface and the solvent. Therefore, the stronger interaction between the solid surface and liquid is seen on the (001) face.

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Investigation of Surface Energy of Aspirin Crystals Using a Contact Angle System

Almost 90% of pharmaceutical materials are in a solid dosage form. A major hurdle during the development and manufacturing of these compounds is being able to characterize the best morphology and stable polymorph. An essential parameter that is being used to help elucidate the differences in surface characteristics is surface free energy. The conventional method for obtaining surface energy is through measuring contact angles and applying an indirect model to derive surface energies between various interfaces. The objective of this study is to measure the contact angles on the (100) and (001) faces of aspirin and observe how each face interacts differently with a specific solvent. A video-based contact angle device is used to record and measure contact angles. The sessile drop method was employed with three solvents (water, glycerol, and diiodomethane) on each major face. Results of this investigation reveals the (100) aspirin growth face having the larger contact angle in all three solvents water, glycerol, and diiodomethane, 66.9 ± 1.2, 65.1 ± 1.1, and 41.2 ± 1.1 respectively. The smaller contact angle results seen on the (001) aspirin face in water, glycerol, and diiodomethane were: 56.4 ± 1.4, 56.5 ± 0.9, and 36.2 ± 1.2 respectively. These results suggest cleavage of the (100) face does not expose the carboxylic group which would cause a stronger interaction between the crystal surface and the solvent. Therefore, the stronger interaction between the solid surface and liquid is seen on the (001) face.