Stability for Dispersions

Determining the effects of PVP upon sedimentation of clay suspensions Simona Schwarz* Gudrun Petzold Qaisar Abbas Bhatti The preparation of particle suspensions, which are widely used in different applications (such as paints, pharmaceuticals etc.) is known to be very difficult. Studies on the influences which are responsible for the stability of these particle dispersions are limited in number. But the stability and characterisation of nanoparticle systems is a central research issue, because knowledge about the stability of dispersions is important for their practical application. Pigments and their properties play an important role in the stability of paints. Properties of pigments such as particle charge, particle size and size distribution all influence the stability of dispersions. The pigments in a paint must be well dispersed in order to perform successfully. If the pigment agglomerates, then the paint will appear to have larger pigment particles and the colour quality may be degraded. The rate of agglomeration depends on many factors, including particle concentration, size distribution, velocity gradients, ionic strength, pH, the presence of polymers and what is termed the zeta potential the potential difference between the dispersion medium and the layer of fluid effectively attached to particles dispersed in it. In the work reported below, the stability of clay particles in aqueous dispersion and in the presence of the watersoluble polymer poly(vinylpyrrolidone) or PVP has been investigated. Various methods for particle characterisation such as zeta potential and particle charge determination, laser diffraction and separation analysis in a centrifugal field were used. The results will show how the particle size, particle size distribution and also the surface charge of particles and the stability of dispersions are influenced by the conditions of suspension preparation such as time of ultrasonication and the addition of PVP as a stabiliser.