(558g) Probing Self-Assembly & Gelation in Complex Fluids through Combined Low Frequency Raman Spectroscopy and DLS Based Optical Microrheology

A great variety of complex fluids including but not limited to polymers, gels, colloidal fluids, suspensions, emulsions, foams, micellar and liquid crystal phases etc. are being widely used across a range of industrial and consumer sectors like plastic and rubber industries, ceramic, food, biochemical and pharmaceutical industries, cosmetic, detergent, paints, lubricants, inks, etc. In many instances, the final product format of these complex fluids are gels or soft solids and the processing and product functionality attributes of such materials are often dependent on their rheological response and viscosity. The rheology evolution in such complex fluid systems under various formulation conditions (pH, ionic strength, buffer salts, temperature) must be well-understood, characterized, and controlled. Most insights developed into understanding the self-assembly and rheology evolution process in such systems has primarily focused on elucidating the associated micro- and mesostructural changes through various scattering (light, x-ray, neutron) and imaging techniques (cryo-TEM, SEM, AFM). Detailed insights into the associated chemical conformational/structural changes and various non-covalent interactions (e.g. H-bonds, hydrophobic interactions) leading to the self-assembly process have been very limited. An understanding of the changes in the molecular level structural changes as self-assembly and gelation progresses will provide new mechanistic insights that will allow better optimization and control over performance controlling formulation design rules in industrial complex fluids. In this presentation, we provide new structural/interaction insights into the self-assembly and gelation mechanism of complex fluids through combination of a number of well-established analytical techniques namely optical probe microrheology, dynamic light scattering (DLS) & Raman spectroscopy. The talk will illustrate the utility of the combination of mesoscale structure-property elucidation techniques such as DLS/microrheology with the high resolution chemical structure/conformation elucidation techniques such as Raman spectroscopy in generating novel mechanistic insights that will allow the performance engineering of complex fluids and soft matter systems. This will be exemplified through studies into the self-assembly/gelation mechanisms in three very different complex fluids-mixed anionic/zwitterionic surfactant wormlike micelles, polyvinyl alcohol and a thermo-reversible, gel-forming agarose biopolymer.