DEVELOPMENT OF A FLOW MICROCALORIMETRY METHOD FOR THE ASSESSMENT OF SURFACE-PROPERTIES OF POWDERS

Purpose. This study describes the development of a microcalorimetric f low 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 c ell was constructed to mix two separate air streams (0% and 100% relat ive humidity respectively) to create any humidity at a standard flow r ate. 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 wa s 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. Concl usions. This technique offers a very sensitive and versatile method of obtaining a reliable indication of powder surface energetics and as s uch is a major advance in the field.