| Start Date: | 11/12/2015 | Start Time: | 4:30 PM |
| End Date: | 11/12/2015 | End Time: | 5:30 PM |
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Event Description
Nicolas J. Alvarez, PhD, chemical and biological engineering, Drexel University
“The Importance of Chemical Structure (Hydrogen Bonding) in Extensional Rheology of Polymer Melts”
Over the past forty years, the big challenge in polymer physics is a model(s) that can capture and predict polymer dynamics in shear, extensional, and mixed flows. Although such a model is still out of reach, the model with the most potential is known as the tube model. The tube model has shown success in predicting and modeling linear viscoelastic responses, but fails to capture the nonlinear response of the simplest polymeric melts (i.e., linear polymers). There are considerable efforts in improving the tube model, however, recent experimental data using our novel filament stretching rheometer, brings into question the fundamental principles underlying the theory. For example, the tube model predicts that for a given number of entanglements and maximum stretch ratio, different polymers (i.e. polymers with different chemical structures) exhibit identical normalized nonlinear behavior. This is the concept known as universality in polymer physics. Recent nonlinear extensional measurements involving polymer solutions and polymer melts with different chemistry show that universality in polymer dynamics is not experimentally supported. The data instead supports the conclusion that each chemical structure will give rise to a unique nonlinear response that depends on a yet determined parameter. To continue our exploration on the importance of chemical structure, we will also examine the effect of introducing hydrogen bonding groups along the backbone of an entangled linear polymer chain. Hydrogen bonding groups induce reversible network formation, commonly referred to as supramolecular networks. Using a novel system, the chain backbone length is kept constant, but the number of hydrogen bonding groups along the chain is systematically increased. By taking into account changes in chemistry, we show that hydrogen bonds play a fundamental role. |
Contact Information:
Name: Prof. Frank Ji
Phone: 215.895.2562
Email: hj56@drexel.edu |
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Location:
Disque Hall, Room 109, 32 South 32nd Street, Philadelphia, PA 19104 |
Audience:
Undergraduate StudentsGraduate StudentsFacultyStaff |
Special Features:
Free Food |
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