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Development of a flow microcalorimetry method for the assessment of surface properties of powders
P L Sheridan1, G Buckton, D E Storey
1Centre for Materials Science, School of Pharmacy, University of London.
Purpose:
This study describes the development of a microcalorimetric flow cell which allows powder surface energetics to be probed my means of measuring their interaction with water vapour.
Methods:
A flow cell has been constructed and tested in an isothermal microcalorimeter to assess the interaction between water vapour and powder surfaces. The cell was constructed to mix two separate air streams (0% and 100% relative humidity respectively) to create any humidity at a standard flow rate. The powder sample was equilibrated in dry air and then exposed to sequential increments in humidity.
Results:
Adsorption isotherms were constructed from the cumulative heat as a function of humidity. It was possible to differentiate between different samples of alpha-lactose monohydrate (which appeared identical by contact angle determination). It was also possible to measure adsorption to two different alkyl p-hydroxybenzoates which were hydrophobic and of low surface area.
Conclusions:
This technique offers a very sensitive and versatile method of obtaining a reliable indication of powder surface energetics and as such is a major advance in the field.