Levich Institute Seminar Announcement, 04/23/2013
Tuesday, 04/23/2013
2:00 PM
Steinman Hall, Room #312
(Chemical Engineering Conference Room)

Dr. Johannes M. Soulages
Exxon Mobil Research and Engineering Company

"Long Chain Branching Characterization by Large Amplitude Oscillatory Shear Rheology"

ABSTRACT


Long chain branching (LCB) has long been recognized to play a central role for many commercial products (polyolefins, elastomers, lubricants) and processes (extrusion, film blowing, fiber spinning). Nonetheless, identification of specific LCB topology has remained a challenging task to date. Recent research efforts have allowed for qualitative differentiation between different families of long chain branched molecules, such as combs, stars, dendrimers, or pompom architectures. However, a current challenge is to find a quantitative analytical technique capable of differentiating the geometrical details of the branching topology, such as the number and length of dangling arms, density of branch points, or quantity of branched molecules present.

In this talk, we study the use of nonlinear shear rheometry to characterize molecular topology and microstructural architecture. We use an inventory of well-defined branched model polyethylenes with unique molecular architectures. These branched polyethylenes are blended into an essentially linear polyethylene matrix. We study the non-linear rheological response using deformation-controlled Large-Amplitude Oscillatory Shear Strain (LAOStrain). The LAOStrain technique probes the nonlinear viscoelastic response as a function of frequency and strain amplitude, systematically surveying a broad range of deformation timescales and amplitudes. We make use of higher-harmonic Chebyshev coefficients in the nonlinear shear stress response to show the potential of LAOS as an analytical tool for fingerprinting the nonlinear behavior of viscoelastic materials and thereby probing the molecular topology and microstructural architecture of LCB systems.

BRIEF ACADEMIC/EMPLOYMENT HISTORY

  • PhD at ETH Zurich (with Hans Christian Oettinger)
  • Post-doc at MIT with Gareth McKinley
  • Researcher at ExxonMobil since June 2010

RECENT RESEARCH INTERESTS:

Structure-property relationships for polymer melts and solutions.



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