Cylindrical tube and surface tension viscous flow models in the assessment of capillary flow and liquid contact angles in pharmaceutical powders.
International Journal of Pharmaceutics
The validity of the cylindrical tube (CT) model for the estimation of contact angles of irregular porous media using liquid penetration data is based on the linearity of l vs t 1 2 plots which assumes the same geometric contribution for liquids exhibiting different contact angles in the same medium. In recent criticisms it was observed that conformation of penetration data to t 1 2 dependence has also been predicted for systems other than cylindrical tubes, and a method for obtaining contact angles based on surface tension viscous flow (STVF) model and scaling concepts was proposed. To assess the validity of these proposals, the rates of liquid penetration of a homologous series of alkanes, alcohol and carboxylic acids into fifteen pharmaceutical powders (Avicel PH101, Starch 1500, magnesium stearate, calcium carbonate, calcium phosphate, calcium formate, calcium acetate, calcium lactate, calcium gluconate, calcium stearate, p-hydroxybenzoic acid, methyl p-hydroxybenzoate, ethyl p-hydroxybenzoate, propyl p-hydroxybenzoate and butyl p-hydroxybenzoate) were determined. Contact angles were obtained according to the CT model. Plots of l vs t 1 2 were linear as predicted by the CT model. Plots of reduced distance travelled as a function of reduced time, based on the STVF scaling concepts, did not superimpose on a single curve, an indication that the systems studied were in dissimilar states, exhibiting differing contact angles. On the other hand, contact angles obtained from STVF scaling concepts were similar, thus indicating that the systems are in similar states. This contradicts the results from plots of reduced distance vs time. The inability of both approaches to reach the same conclusion questions the validity of the universal application of the STVF model. The STVF model does not adequately describe liquid-powder systems which display finite and differing contact angles when different liquids are used on the same powder. This may be due to the differences in wettability and surface energetics inherent in such systems and not necessarily because of geometric factors. © 1993.
|Title:||Cylindrical tube and surface tension viscous flow models in the assessment of capillary flow and liquid contact angles in pharmaceutical powders|
|UCL classification:||UCL > School of Life and Medical Sciences
UCL > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > School of Life and Medical Sciences > Faculty of Life Sciences > UCL School of Pharmacy
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