Intelectual Merit: The proposed work seeks our understanding and establishes applications of the properties of aggregation, self-assembly and chaining of small particles in flows of polymer solutions (viscoelastic fluids). Particle-particle interactions in viscoelastic fluids are dramatically different than in Newtonian fluids: particles disperse in the flow of Newtonian fluids and they aggregate in the flow of viscolastic fluids. We have done analyses which suggest that the chaining of the particles in viscoelastic liquids is local and based on two pillars; the first is a viscoelastic ?pressure? generated by normal stresses due to shear. The second is due to the change in the sign of the normal stress which we compute in the second-order order fluid. Different numerical and experimental experiments will be carried out to validate this theory. We will establish the limits of particle size, concentration, particle to fluid density ratio, liquid rheological parameters, flow field etc for which particles aggregate in viscoelastic fluids. The basic assumption of particle image velocimetry (PIV) is that small particles seeded in fluid will not interact in flow. This assumption is valid for Newtonian fluids where tracer particles disperse, but it will not work in viscoelastic fluids in situations in which particles aggregate. This study will determine the conditions under which small particles track the flow, as is assumed in studies of PIV. Understanding the rage of parameters at which interaction and chaining of particles occurs will benefit several other applications in oil, composite, food, and pharmaceutical industries.
Broader Impacts: The participation of women and individuals of underrepresented groups in the proposed effort will be encouraged by coordinating recruitment of new graduate students through established programs at UC Irvine. These student oriented programs are designed to encourage the participation of women and minorities in the science and engineering fields and include the Center for Opportunities and Diversity in Engineering (CODE) and the California NSF Louis Stokes Alliance for Minority Participation (CAMP). One of the coPIs is the UCI Division Director for CAMP and he will provide a connection between this project and the underrepresented STEM students on campus interested in research. The research team includes two female graduate students. In 2005, female graduate students comprised 150 out of a total number of 630 graduate students enrolled in the Henry Samueli School of Engineering at UCI, representing 24% of the student body. The graduate level research opportunities generated by this effort will be used to support these underrepresented graduate students in engineering and provide a solid base for advancement to the postdoctoral level and future achievement in academia. The project will also provide research opportunities for undergraduate students through the Undergraduate Research Opportunities Program (UROP) at UCI. The investigators have a long history of involvement in this program and will ensure the participation of undergraduates, particularly in the experimental aspects of the project.
