CAREER: Self-Assembled Light-Sensitive Fluids with Tunable Rheological Properties

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Raghavan, SirnivasaU of Maryland - College Park"CAREER: Self-Assembled Light-Sensitive Fluids With Tunable Rheological Properties" The principle underlying "smart" tunable fluids is that one can tune the self-assembly of amphiphilic systems containing a photoactive component by light irradiation in the UV or visible range. The PI proposes to use this concept to cause reversible and dramatic changes in the rheological properties of the fluid. Rheological transitions include: (a) switching the low-shear viscosity by a factor of 1000 or higher; (b) switching the type of rheological behavior from shear-thinning to shear thickening; and (c) switching sample response from elastic solid to viscous liquid.The PI proposes three strategies for engineering such photorheological (PR) fluids. The first two strategies involve the self-assembly of wormlike micelles from surfactants. In these cases, a photochemical transformation decreases the micellar contour length or induces a transition from linear to branched micelles, both of which serve to dramatically reduce the fluid viscosity. The third strategy involves the formation of a vesicle gel, i.e., aself-assembled network of vesicles, upon addition of a telechelic associating polymer.Light irradiation disrupts the vesicles into spherical micelles, thus converting the sampleinto a low-viscosity liquid. The fundamental goals in this study are to closely investigatethe correlation between self-assembly, microstructure, and rheology in all these fluids.The use of light to tune self-assembly will permit novel experimental studies into thesemechanistic issues.Broader Impact:Photorheological (PR) fluids offer a new alternative for tunable rheology and are likely to have practical applications. Their nanoscale structure and homogeneous nature will make them especially suitable for exploitation in microfluidics or other emerging microscale technologies. The use of light to tune rheology will provide a degree of spatial control on submillimeter length scales that is difficult to achieve by other means.The research also will be integrated with educational, mentoring and outreach activities centered on the subject of complex fluids. The PI proposes to develop a new elective course on Complex Fluids, Self-Assembly and Soft Nanostructures, with the aim of unifying concepts from traditional subjects like polymers and colloids. In this course, he will attempt to impart an understanding of complex fluids based on their inherentmesoscopic structure, and he will highlight the links between chemical and biological systems. The mentoring activities will target talented undergraduate chemical engineers, especially women and minorities, to work with graduate students in studying the self-assembled PR fluids. The diverse student body in the department will facilitate such recruitment efforts. The PI also proposes to create simple and appealing demonstrations using various complex fluids, both household materials as well as the tunable PR systems, that can be taken to K-12 science classrooms in Maryland public schools. Pictures and movies of these demonstrations will also be featured on an interactive web page.