Application note 17: Measurement of the Surface Energies of Pharmaceutical Powders using a Novel Vapour Adsorption Method

Author: Dr Daryl Williams, Surface Measurement Systems Ltd.

Introduction

This paper presents a novel method for determining the surface energy of powders by measuring the adsorption isotherm of organic vapours using an automated gravimetric vapour sorption analyser. This approach avoids the limitations inherent in many of the currently available methods.

The measurement of the surface properties of powders is of increasing importance to many industries, which depend upon powder processing or powder technology. If known, the surface energy of a powder may be used to predict a wide range of properties such as processing stability, adhesion, colloid stability, toughness, powder flow and product performance. In practice the measurement of the surface energy of powders is non-trivial and prone to potentially large errors or uncertainties despite a wide range of techniques being available.
Current methods for surface energy characterisation of powders include a number derived from classical wetting approaches for studying monolithic samples such as films and fibres. Additionally, various liquid penetration methods are used.

Graphs:

App17 Surface Energy 2

Figure 2 Sorption/desorption isotherms for octane on caffeine

Figure 1 Octane sorption/desorption kinetics on caffeine

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