National Science Foundation - Division of Chemical &Transport Systems ? Particulate & Multiphase Processes Program (1415)
Proposal Number: 0729967 Principal Investigators: Tilton, Robert Affiliation: Carnegie Mellon University Proposal Title: High Efficiency Nanoparticulate Emulsifiers
Intellectual Merit. Emulsions stabilized by colloidal particles adsorbed at the oil/water interface, commonly called Pickering emulsions, are distinguished by their superior stability against coalescence and sedimentation and by their ability to disperse high discontinuous phase volume fractions. We propose to develop novel nanoparticulate emulsifiers with extremely high emulsification efficiency. Atom transfer radical polymerization (ATRP) will be used to create nanoparticle-grafted, amphiphilic copolymer brushes with well-controlled architectures designed to drive particles to adsorb with high affinity and stabilize the oil/water interface. We will prepare two categories of nanoparticulate emulsifiers. The first type has a silica core with copolymer amphiphiles grafted from or to its surface. The second type are multi-arm miktoarm star polymers with dense polymer cores surrounded by two or more types of extended arms. These grafted brush particles have more degrees of freedom than conventional particulate emulsifiers that may allow for finer tuning of interfacial thermodynamic and mechanical properties. The conformation of the amphiphilic brushes will adapt to the local solvent environment as particles adsorb to the oil/water interface. In developing the most effective emulsifiers, the underlying mechanistic relationships between brush architecture and emulsification will be determined. The main technological goal is for the proposed nanoparticle-grafted brushes to stabilize emulsions at concentrations at least ten times smaller than are required for current particulate emulsifiers. Some of the proposed structures may be thermally responsive to de-emulsify in response to temperature cues.
Broader Impact. The proposed work will form the interdisciplinary training of a Chemical Engineering Ph.D. student and for part of a Chemistry Ph.D. student's training. Both will be trained in the design and physical characterization of functional materials as well as state-of-the-art controlled radical polymerization techniques. A secondary school outreach program will be developed on themes of interfacial engineering, whereby public school science teachers spend one or two summer months in the PI's lab to develop student lab modules and lesson plans on the role of interfaces in nature and materials. There will be an everyday materials theme involving vegetable oil/water Pickering emulsions and a ?novelties? theme that builds on the science of particle-stabilized interfaces to understand how so-called ?liquid marbles? (Aussillous, P.; Quearea, D., Nature 2001, 411, 924-927) work. The PI will provide the essentials of interfacial thermodynamics and help the teacher prepare lesson plans on capillary forces and their occurrence in nature. The PI will subsequently join the teacher as a guest in the classroom.
This research will deliver copolymer-grafted particulate emulsifiers that set the mark for emulsification efficiency, together with the brush design principles needed to meet new applications in any industry that relies on emulsions (agriculture, foods, personal care?). New applications may be made possible by significant improvements in particulate emulsifiers. For example, diesel emulsions combust more cleanly than conventional diesel fuel, and emulsifier formulation is a major challenge.
