Polydimethylsiloxane (PDMS)-based antifoams

The most widely used industrial antifoams are based on polydimethylsiloxane (PDMS) oils, yet very little fundamental information exists for these products. In most formulations hydrophobically modified particles are dispersed in the oil to increase antifoam efficiency but the primary mechanism responsible for this effect has remained unclear. To address these needs, we provide a systematic study on PDMS-based antifoams for a wide range of common surfactant solutions. By measuring surface and interfacial tensions, contact angles, oil spreading rates, particle size distributions and individual film stability characteristics, in parallel with foam stability measurements, we are able to quantitatively evaluate the parameters believed important for PDMS-based antifoam action. We find that a significant loss of antifoam performance (based on a 60 s foam-life criterion) correlates with an antifoam globule size reduction to less than 6 mu m. Furthermore, we provide direct evidence that hydrophobically modified particles, situated at the oil/water interface, puncture the aqueous interface as antifoam globules approach, thereby accelerating oil entry and antifoam efficiency.