The wetting behaviour and dispersion rate of cocoa powder in water

The efficient dispersion of powders in liquids is required in many fields. However, there are only a few studies on the physicochemical properties of the powders and the dispersion rate. The process of dispersing an agglomerated powder is mainly controlled by the forces acting between the primary particles, and between particles and liquid. In this paper, we present an experimental study of the dispersion kinetics of a hydrophobic powder (cocoa) in water. We firstly determined the surface free energy of the powder using several methods (static wettability, dynamic wettability). Interpretation of calculated values of spreading coefficients and interaction parameters revealed no energetically favoured cocoa-water interactions. A series of dispersion experiments were conducted in a stirred vessel to investigate the influence of stirring speed, temperature and concentration of powder in water. The dispersion concentration was measured using an optical scattering method, which was shown to give good information for evaluating the dispersion process. The experimental data fit an exponential mathematical model with two parameters (A, alpha): X(t) =A[ 1 - exp(-alphat)]. It was found that the rate of dispersion depends on the agitation speed with a critical speed 630 rpm. All results are discussed as a function of the agitation speed and temperature.