Michelle Seitz
PhD Candidate
B.S. MSE, 2004, Massachusetts Institute of Technology
Cook Hall 2009, 1-3675
m-seitz at northwestern dot edu
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The Shull Group |
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Michelle SeitzPhD Candidate |
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Poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) triblock copolymers in 2-ethylhexanol self-assemble into thermoreversible gels with endblock aggregates linked by well-solvated midblocks. A description of these materials can be found here.
My work has focused on how gel behavior is influenced by changes in block length and fraction.
Self-Assembly and Stress Relaxation [1] :
These gels are unique because of the extremely strong temperature dependence of their relaxation behavior with relaxation times varying by 10 orders of magnitude over 40 degrees C. Fundamental studies using small angle X-ray scattering and shear rheology have been used to investigate the correlation between gel structure and relaxation behavior. The swelling behavior of gels in pure solvent depends on the degree of midblock stretching and can be controlled by changing gel concentration and endblock fraction. Gel moduli, swelling behavior, and thermostability can be tuned via PMMA homopolymer additions with additions of isotactic PMMA homopolyers can extend a gel’s elastic behavior by over 70 degrees C.
Fracture:
The behavior of soft model systems can be used to help understand the behavior of much more complex biological systems. Unlike stiff materials which fail at small elongations, elastic polymer gels can sustain very large elongations before failing in a brittle manner. Acrylic triblock copolymer gels are ideal model elastic gels for fracture studies because their mechanical response of is reproducible and their structure is well understood. We are collaborating with Tristan Baumberger at the Institut des Nanosciences Paris/Université Paris 6 to study the fracture behavior of these materials.
Application to Ceramic Processing:
Thermoreversible gelcasting (TRG) is a forming technique that utilizes the rapid, reversible gel formation of acrylic triblock copolymers in which ceramic or metallic powders are dispersed. An understanding of gel relaxation is crucial to designing triblocks that achieve excellent detail replication and low slurry viscosity. Additionally, the strength and toughness of dried green bodies is dependent on the relative block ratio and whether the midblock is rubbery poly(n-butyl acrylate) or glassy poly(tert-butyl acrylate).
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A schematic of the temperature dependent structure of an acrylic triblock copolymer gel |
An acrylic triblock copolymer gel filled with aluminum oxide particles in the gel's viscoelastic regime illustrating the thermoreversible nature of the gel transition.. |
Biaxial strength specimans after testing. Sample on the left contains triblock copolymer with a rubbery midblock and exhibits significant toughness while sample on the right has a glassy midblock and failed in a brittle manner. |
I am jointly advised with Professor Kathy Faber for the thermoreversible gelcasting work. This work is supported by a National Science Foundation Graduate Research Fellowship and NU-MRSEC.
References: