CAREER: Morphological Control in Polymer Blends Using Polymeric Surfactants

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

ABSTRACT - 0448845 Motivation: Blending of immiscible polymers is an effective and efficient strategy to obtain materials with unusual properties. Often the desired properties are realized only if the blend has a specific morphology, e.g. a diffusion-barrier material requires that the low-diffusivity component be in the form of lamellae or platelets. An ability to control the morphology is therefore crucial for design of new polymeric materials. The hypothesis of this proposal is that the morphology of immiscible polymer blends can be controlled by addition of polymeric surfactants. Specifically, we propose to exploit the coupling between interfacial flow and surfactant concentration to manipulate the morphology. Research Proposal: The structure obtained from a two-phase blending operation is a result of the interplay between hydrodynamic stresses due to blending, and interfacial stresses due to interfacial tension. The latter make it difficult to obtain small-scale anisotropic morphologies in blends. A well-known effect of added surfactant is to reduce these interfacial stresses by decreasing the equilibrium interfacial tension between the immiscible phases. Less obviously, a coupling between the flow and the concentration of the surfactant on the interface causes deviations of the interfacial tension from its equilibrium value, as well as interfacial tension gradients, along the interface. The focus of this proposal is to quantify these nonequilibrium surfactant effects, and exploit them to control structural evolution. Key elements of the methodology are simple materials and flow fields to help highlight interfacial phenomena, and a surfactant that is generated by an interfacial coupling reaction. The latter ensures that most of the surfactant remains at the interface, and very little dissolves in the bulk. A crucial innovation is the use of fluorescently-tagged surfactants, which allows locating the surfactant in the blend, and measuring the local interfacial tension, by confocal laser scanning microscopy. The mechanisms by which surfactants can achieve unusual morphologies such as dispersed plates, dispersed ribbons, or dual-phase continuity, will be elucidated. Rheological methods to determine the viscoelastic properties of surfactant-laden interfaces will be explored. Education Plan: The education plan addresses the need to shift the undergraduate Chemical Engineering curriculum towards Chemical Product Design. The central educational goal is to introduce product design ideas throughout the curriculum, and not only as an add-on Product Design course. Short modules that can be incorporated into existing classes in Chemical Engineering will be designed to facilitate a curriculum-wide introduction to Chemical Product Design. These will culminate in a newly developed capstone course on Chemical Product Design. In the modules as well as in the course, all case studies will be chosen to emphasize core Chemical Engineering disciplines such as Transport Phenomena and Thermodynamics. Intellectual merit: Polymeric surfactants, (more commonly referred to as "compatibilizers") are routinely used to facilitate blending of immiscible polymers. This proposal is based on the idea that the same surfactants can also be used to manipulate the morphology. The chief scientific advances over past research in this area are that the anisotropy of the structure, and the coupling between the flow and the surfactant on the interface, will be quantified for the first time. This research will offer fundamental insights into the fluid mechanics of multiphase flow and will lay guidelines for using surfactants to control structure in immiscible polymer blends. Broader impact: While the research will be conducted on polymeric systems, the results are applicable to all liquid-liquid emulsions with surfactants, such as those encountered in the foods, personal care products, or oil industries. The rheological properties obtained in this research will guide the design of processing equipment for polymer blends. A significant portion of the research will be performed by undergraduate students. The product design modules, to be made available to instructors everywhere, is likely to influence the pedagogy of product design in other Chemical Engineering departments. Feasibility: The PI has extensive knowledge and experimental skills in the research topics covered here. All necessary experimental resources are either available, or will be purchased during this research. The Department whole-heartedly supports the curricular changes proposed in the education plan.