ASSESSMENT OF ADHESION AND AUTOADHESION FORCES BETWEEN PARTICLES AND SURFACES .1. THE INVESTIGATION OF AUTOADHESION PHENOMENA OF SALMETEROL XINAFOATE AND LACTOSE MONOHYDRATE PARTICLES USING COMPACTED POWDER SURFACES

A centrifuge technique has been used to investigate the autoadhesion force between particles and a plane surface of the same material compacted into a disk, which is resistant to the centrifugal force. When measured by profilemetry, these compact surfaces are rougher than metal or plastic surfaces used in previous studies. This results in a change of the detachment force distribution from a log-normal to a right-shifted distribution. The relationship between press-on force and median autoadhesion force depends on particle size, shape and particle surface morphology of the powder particles autoadhered. The lower the autoadhesion force, the greater the possibility that the substance can be used in a single-component powder application. The bulk properties of the powders such as cohesiveness or free powder flow were found to be related to the autoadhesion force. Estimation of the distance between the particles and surfaces has been made based on the Lifshitz-van der Waals constant derived from low frequency dielectric measurements. There was a decrease in distance of separation with increase in press-on force for both sets of particles. The contact between angular lactose monohydrate particles and a lactose monohydrate surface can be increased by more than that between irregular or spherical salmeterol xinafoate particles and their equivalent compact surface.