Supramolecular polymer networks possess versatile mechanical properties and a unique ability to respond to external stimuli. Understanding the rich dynamics of associative polymers is essential for tailoring user-defined properties in polymeric materials. In this talk we will examine the effect of varying associating chemistry, e.g. ionomers, hydrogen bonds, and hydrophilic-hydrophobic interactions, on linear viscoelasticity and nonlinear extensional rheology. The investigation of nonlinear extensional rheology is particularly of interest as such materials are questionably more solid than fluid on certain timescales. In general, associating polymers have two adjustable parameters: the interaction strength and the number of associating groups per chain. We will show that independent of chemistry there are three effects on linear viscoelasticity due to an increase in interaction strength and/or the number of associations per chain: (i) the longest relaxation time increases, (ii) the plateau modulus increases, and (iii) the power law scaling in the terminal regime deviates toward lower magnitudes for nonuniform distributions of association groups along the backbone. Increasing both interaction strength and number of interactions per chain has a profound effect on nonlinear extensional rheology. Throughout the discussion, effort will be made to make comparisons between associating and non-associating linear polymer melt rheology in order to contextualize our understanding of supramolecular polymer dynamics.  Lastly, we will tackle the “self-healing” dynamics of these networks in terms of their linear viscoelastic time scales.

BRIEF ACADEMIC/EMPLOYMENT HISTORY:

Nicolas J. Alvarez earned a BS in Chemical Engineering from the University of Florida in 2006 and a PhD in Chemical Engineering from Carnegie Mellon University in 2011. After three years of postdoctoral work at the Technical University of Denmark in Lyngby, he joined the Department of Chemical and Biological Engineering at Drexel as an Assistant Professor in 2014. Alvarez’s research interests involve development of unique experimental tools to understand and characterize the behavior of polymers and surfactants in nonlinear flows, at interfaces, and in bulk. These tools are used to understand how certain processing windows lead to advantageous material properties. One such tool, used for the characterization of extensional rheology, has been commercialized by Alvarez and colleagues.

MOST RECENT RESEARCH INTERESTS:

Supercritical Surfactant Dynamics and Equilibrium” AND “Extensional Rheology of Polymer Melts (Supramolecular Networks)” AND “Additive Manufacturing using Thermoset Chemistry”  AND “Fiber Spinning and Polymer Processing