Parsons, Gary Edward;
(1992)
Assessment of the surface energy of powders and its use in predicting the stability of nonpolar nonaqueous suspensions.
Doctoral thesis (Ph.D.), University College London.
Preview |
Text
Assessment_of_the_surface_ener.pdf Download (5MB) | Preview |
Abstract
The concept and application of solid surface energy values have been studied from a pharmaceutical perspective. The derivation of solid surface energy is usually based on the contact angle formed between a liquid of known surface energy and the test solid. Three commonly used methods of contact angle determination have been investigated, namely the Wilhelmy plate and sessile drop techniques (which utilise the sample in the form of a flat plate), and the liquid penetration technique which utilises a powdered sample of the solid. A system of model particles and plates has been used which allows systems of differing geometry to be studied, without altering the surface energy. Contact angles obtained by the Wilhelmy plate and sessile drop techniques were found to be in good agreement with, but consistently lower than, those obtained by liquid penetration experiments. A linear relationship was found to exist between the liquid penetration and Wilhelmy plate results, suggesting that the rate of liquid penetration through a packed powder bed is not adequately described by the Washburn model of a bundle of parallel capillaries. Surface energy values have been derived for the model systems studied by a variety of methods. The harmonic and geometric mean variants of the theory of surface energy components, the theory of non-additive surface energy components and an equation of state have been applied. The derived values of surface energy were comparable for the theoretical models studied. Values for individual components of surface energy were dependent upon both the theoretical model and liquid pair used. The stability of pharmaceutical nonaqueous nonpolar suspensions has been studied. The ease of dispersion, degree of aggregation and extent of powder adhesion to the container wall has been investigated for five solids (indomethacin, isoprenaline, aspirin, PTFE and beclomethasone) and related to surface energy data. Each phenomenon could be related to calculated surface and interfacial parameters.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D. |
| Title: | Assessment of the surface energy of powders and its use in predicting the stability of nonpolar nonaqueous suspensions. |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Thesis Digitised by Proquest. |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10122948 |
Archive Staff Only
 |
View Item |
