Studies of dispersions of organic and inorganic pigments in non-aqueous media

The behaviour of pigment dispersions containing high solid concentrations has been studied when the dispersions settled in such a manner that the classical Stokes' Law was inoperative. The sedimentation of the solid particles in such suspensions occurs with the movement of an interface, and this is termed "hindered settling" when above the interface is tne clear supernatant liquid and below the interface is the suspended solid. The properties of the suspensions were judged in terms of the interface's behaviour as a function of time.The observation of the interface's behaviour as a function of time, was used to determine the effect of adsorbed alKyd resin [a polyester) from xylene onto the surface of iron oxide, titanium dioxide and alpha copper phthalocyanine had on hindered settling parameters. The measurement of tne mass of polymer absorbed was undertaken by infrared spectroscopy and a radio-active tracer method.The work was concerned witn tne inorganic and organic pigments i,i the same bulk solution and provided information about eacn pigment in tne same solution. The hindered settling exneriments took place at specific points on each pigtrant's alkyd resin adsorption isotherm to provide an understanding of Darameters involved in sedimentation equations in chemical and physical terms.Complementary experimental techniques were necessary, microelectrophoresis, optical and scanning electron microscopy, which enabled a more concise understanding of changing parameters involved in hindered settling equations. This provided information on the effect of adsorbed alKyd resin on the stabilisation/destabilisation of the pigment particles.The experimental results indicated that the adsorbed alkyd resin stabilised iron oxide by an electrical double layer mechanism, the titanium dioxide by a ster % ic barrier mechanism and the copper phthalocyanine was destabilised. These conclusions are for each pigment dispersed in solutions of alKyd resin in xylene, compared to the pigments dispersed in xylene only.The particle diameter and particle diameter distribution of the pigments in the settling suspensions were seen to have the greatest effect on parameters involved in hindered equations