Many complex fluids are emulsions or dispersions, i.e., multicomponent systems where the “particles” or “droplets” of a dispersed phase are distributed within the continuous-phase matrix. (If the “matrix” is “solid”, we usually talk about “composites” and use composite mechanics models). These fluids have variety of applications (Food industry, Pharmaceutical industry, Electronics, Water desalination, Agriculture, Paints and Coatings, and many others). Materials scientists and chemical engineers need to develop complex, multiscale models to predict the rheology and mechanics of such fluids at different temperatures and frequencies or shear rates.
Here, I discuss two examples. One (with Prof. Ron Larson, University of Michigan, and other collaborators) is related to waterborne paints with associative thickeners called HEUR
(hydrophobically ethoxylated urethanes). The latex/water/HEUR dispersions are characterized by rheological measurements and described by multiscale computer models. The viscosity and shear moduli (storage and loss) are strongly non-Maxwellian. Such a behavior is due to formation and breakage of polymer “bridges” between particles, leading to the formation of transient network of bridged particles (TNBP). These hybrid networks typically are characterized by power-law relaxation time spectra that recently gave rise to new mathematical approach known as Fractional Calculus (FC). Thus, my second example (with Prof. Mohsen Zayernouri, Michigan State University, and other collaborators), deals with the use of FC modeling to characterize the rheology of segmented polyurethanes (PU) and their nanocomposites with graphene nanoplatelets. We show that the use of fractional Maxwell models (FMM) allows us to successfully describe the linear rheology of PU materials over wide ranges of frequency and temperature. As the use of FC becomes more widespread, I conclude by discussing potential opportunities for its application in various emulsion and dispersion fluids.
