(334h) Revealing the Flow Properties of Polysaccharide-Based Nanostructured Fluids By Microfluidics

Consumer product attributes are often conflicting, such that molecular engineering can be necessary to yield a successful commercial product. A common example of conflicting attributes is the need for shelf and transportation stability in products comprised of suspensions of emulsions and/or colloids along with good portability, high shear stability, and sprayability. Nanostructured fluids where physical interactions provide both this desired yield-stress feature as well as strong shear-thinning behavior are required, and are often comprised of self-assembled wormlike micelles, clay gels, or microgels. Critically, after the mixing or flowing of the materials, the thixotropic properties of the fluids allow subsequent recovery of the structure either in the product container or during scale-up and packaging processing. Design such systems requires understanding of the history of the applied strain, shear and extensional properties, and flow-induced alteration in these fluids. Here we explore the mechanisms by which tailored suspensions of mixed polymer gums create self-healing and yield-stress structured fluids.

Novel microfluidic flow channels with pressure measurements comprised of shear, sudden contraction and hyperbolic contraction are created to enable probing both shear and extensional rheology relevant for designing advanced materials of interest. Simultaneous microscopy enables flow velocimetry, and rheology with small angle neutron scattering (SANS) quantifies the flow-induced structural alteration, which provides important insights into molecular engineering process. Polysaccharide-based nanostructured fluids (xanthan-konjac-based mixture) and polyethylene oxide solution are investigated. Stress created by deformed structure and molecules determines the flow behavior especially for extensional flow (through the contraction). Generalized Newtonian model, viscoelastic model, and thixotropic structure kinetic models are used to reveal the flow properties of the fluids. Semi-quantitative connections are made between molecular architecture and the transient and steady shear and extensional properties, providing new insights valuable for successful design of advanced materials.