City College will close today, January 26, 2015, at 3 p.m. due to inclement weather. Only essential personnel are expected to report to or remain at work for regular business hours. The college is closed Tuesday, January 27, 2015. Only essential personnel report to work.
Levich Institute Seminar
Tue, Apr 23
2:00 PM — 3:15 PM
Steinman Hall160 Convent Avenue
Steinman Hall, 312
Dr. Johannes M. Soulages SeminarTITLE: "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.