We will discuss the origins of the stabilization in a range of novel particle-stabilized (Pickering) foams as well as strategies for making triggerable foam systems. Our group has shown how particles with anisotropic shape and engineered properties can serve as excellent by-design stabilizers of Pickering foams and emulsions. These particles are made by “liquid nanofabrication” in biphasic liquids under shear. Polymer microrods and irregular particles from hydrophobically modified cellulose (HMC) made by this method can serve as superstabilizers of foams and emulsions. The HMC particles can also serve as a facile platform to enrich the Pickering foams and emulsions with additional features such as color, specific rheological response, stability against drying, controlled destabilization and controlled release. The inclusion of magnetic particles in the HMC matrix allows making “magneto-Pickering” foams, which exhibit excellent stability in the absence of a magnetic field, but can be rapidly destroyed on-demand by a threshold field. We will also present stimuli-responsive Pickering foams containing molecular assemblies of thermo-responsive fatty acids and carbon black or carbonyl iron particles. These Pickering systems can be made photo-, thermally, as well as magnetically responsive. They provide fundamental insights on the properties of particle-containing foams and could find applications in processes requiring immediate non-contact defoaming. The need for such efficient breakdown of Pickering foams is encountered in modern bioreactor operations. In the second part of the talk, we will discuss the mechanisms by which foams are stabilized by particles of biological origin during cell culture proliferation in bioreactors. We found that Pickering stabilization of the foam head in bioreactors is present in the later stages of cell growth, causing the traditional remediation strategy of antifoam addition to be less effective. Data for bioparticle adsorption, entrapment in the thin liquid films and Plateau borders and accumulation in real bioreactor foams will be discussed. We evaluate how the bioparticles and surface-active agents contribute to bioreactor foam formation and discuss the controversial role of added antifoam on the lifetime of these bioparticle-containing foams. The physical understanding of new types of Pickering foams and developing means for their destabilization remains an ongoing challenge in emerging fields of science and technology.

New directions in the science and engineering of particle-containing foams: Responsive materials and bioreactor operations

254th National Meeting (2017)

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