Influence of fatty alcohol antifoam suspensions on foam stability

Water-based antifoams are investigated extensively for their effectiveness in reducing the total volume of air in froth and foam by enhancing bubble coalescence. These are suspensions of fatty alcohol particles in an aqueous phase containing essentially a non-ionic surfactant and polysaccharides. The time dependent total volumes of air in froth and foam are recorded in a glass column in which air is continuously bubbled through a pool of surfactant solution. An optimum mean particle diameter is found to exist for maximum antifoaming efficiency. The % reduction in air content due to the antifoam with an optimum particle size increased with temperature until a maximum is reached. Correspondingly, the solid fatty alcohol content in the antifoam suspension has been measured to be about half of the initial value. The % reduction in air subsequently decreased to a negligible value as the fatty alcohols melted completely at a higher temperature. When the low melting fatty alcohol particles are replaced by a high melting fraction, the efficiency at higher temperature is restored. A model is presented, which characterizes the measured kinetics of foaming and bubble coalescence for different antifoams. The observed antifoaming efficiencies are related to the local conditions prevailing at the air-water-solid contact region. Scanning electron microscope images show the fatty alcohol particles to be almost spherical at room temperature. Advancing contact angles measured within the aqueous phase using the Wilhelmy plate tensiometry exceeded 90°, which is the critical angle for initiating film drainage for a smooth spherical particle.