FOAM BREAKDOWN BY HYDROPHOBIC PARTICLES AND NONPOLAR OIL

Foam breaking and the inhibition of foam formation are important processes industrially. Foam reduction is often achieved by the addition of a dispersion of hydrophobic particles in nonpolar oil to potentially foaming systems. Both particles and oil alone may be capable of foam breaking, but they act synergistically when present in combination. A number of possible mechanisms for foam breaking have been proposed in the literature involving, variously, surfactant adsorption by particles, particles acting as supports for oil droplets, oil acting as a medium to distribute particles along lamellae surfaces, and effects involving contact angles between surfactant solutions and solid particles. The overall aim of the present work has been to assess in a methodical way, and for a range of systems, the likely applicability of a number of the possible mechanisms for foam breaking in the systems investigated. We have studied foaming behavior of aqueous solutions of three surfactants (SDS, CTAB, and AOT) in the presence and absence of hydrophobic particles (paraffin wax, PTFE, and ethylenebis(stearamide)) and dodecane. The effectiveness of oil alone on reducing foaming and single film lifetimes is discussed in terms of entry and bridging coefficients for dodecane with the surfactant solutions. The role of contact angles of surfactant with the solids, with and without dodecane present in the system, is assessed, and the effect of surfactant adsorption by the particles on their effectiveness in foam reduction is also probed.