WILHELMY PLATE CONTACT-ANGLE DATA ON POWDER COMPACTS - CONSIDERATIONSOF PLATE PERIMETER

A Wilhelmy plate method has been used to study the surface energies of spray-dried salbutamol sulphate. Scanning electron micrographs of com pacts, prepared for the measurement of contact angles, revealed that t he surfaces of the formed compacts were rough, and that the lowest com pression pressure left spheres of material over the surface of the com pact. As the perimeter of the plate is an essential measurement for us e in calculation of contact angles from Wilhelmy plates, estimates of the true perimeter have been made, and the results compared to those o btained by the use of the apparent external perimeter. On the basis of fractal geometry, the perimeter will increase in relation to the sens itivity of the measurement method, and in actual fact may be very sign ificantly greater than the perceived external measurement. The effecti ve perimeter must be considered for measurements of contact angle obta ined by the Wilhelmy plate technique; unfortunately this is not readil y estimated.