Synergy between hydrophilic silica nanoparticles and poly(vinylpyrrolidone) for long-term foam stabilization with little energy input

Abstract

The role of solid particles to act as foam and emulsion stabilizers is well known, providing long-term stability to the two-phase system. However, the ability for particles to generate large volumes of foam with little energy input (low agitation speeds and short agitation times) is difficult to achieve. Poor foamability is due to the slow particle adsorption dynamics and the high adsorption barrier at the air–water interface. In contrast, common surfactants and some surface active polymers which adsorb more readily at the air–water interface exhibit good foamability but often poor foam stability due to the mutual action of multiple destabilization mechanisms. In the current study, we reported a simple bi-component system of hydrophilic silica nanoparticles and poly(vinylpyrrolidone) (PVP) polymer to produce foams with both high foamability and foam stability via simply hand shaking for 1 min. Foams are stabilized by PVP coated silica composite nanoparticles (CPs) with a well-defined core–shell structure. The strong adsorption of PVP onto silica was demonstrated using Quartz Crystal Microbalance with Dissipation monitoring (QCM-D), confirming the formation of an irreversibly and robust adsorbed polymer layer. To better understand the mechanisms for enhanced foamability and foam stability, the interfacial dynamics and the 2-dimensional mechanical properties of the particle-polymer network partitioned at the air–water interface were assessed. The presence of the PVP polymer corona substantially enhanced the adsorption and retention of hydrophilic silica particles at the air/water interface, while the rigid interfacial network formed by the silica nanoparticles guaranteed long-term foam stability (excess of one week), with coarsening fund to be the dominating destabilization mechanism for foam. The enhanced performance is in stark contrast to the individual components, which could only provide good foamability other than foam stability.