UIC Chemical Engineering

How Does a Polymer Network Break?

Thursday, April 3rd, at 11 AM
Engineering Innovation Building (EIB) Room 124

Bradley Olsen
Professor
Department of Chemical Engineering
Massachusetts Institute of Technology

ABSTRACT:
Polymer networks are one of the most ubiquitous categories of materials in the world today. From car tires to contact lenses to advanced biomedical and personal care materials, they enable our transportation, health, and quality of life in a critical way. However, networks are also one of the most mysterious categories of soft materials because they have both irregular spatial and topological structure, making them difficult to characterize with most structural techniques. Therefore, although it is known that the complex connectivity of polymer networks influences their material properties, we still lack a quantitative understanding of the relationship connecting structure and properties, and we cannot accurately predict the strength of these materials.

Classically, the strength of polymer networks is predicted using the Lake-Thomas theory which attempts to calculate the energy of a fracture by cleaving all of the chains crossing a single plane within the material. Recently, considerations of topology in polymer networks have led us to formulate the micronetwork fracture theory which postulates that network failure is triggered by depercolation of a crack volume rather than cleavage of a crack plane. This theory was tested quantitatively using model poly(ethylene glycol) gels with topological defects and of varying mechanophore strengths, and it is further qualitatively consistent with mechanophore studies which show delocalized activation around the crack tip.

Network simulations coarse-grained to the dumbbell chain level were also developed that enable modelling of fracture in these systems at relevant time scales, producing results that are consistent with experiment. The incorporation of excluded volume interactions into these simulations is necessary in order to produce the correct stress distribution within the material; these interactions are shown to have a stress-homogenizing impact on the network and to delay network failure at moderate elongations.

BIO:
Bradley Olsen is the Alexander and I. Michael (1960) Kasser Professor in the Department of Chemical Engineering at MIT. He earned his S.B. in Chemical Engineering at MIT, his Ph.D. in Chemical Engineering at the University of California – Berkeley, and was a postdoctoral scholar at the California Institute of Technology. He started as a professor at MIT in December 2009. Olsen’s research expertise is in materials chemistry and polymer physics, with focused activities in the areas of molecular self-assembly, polymer networks, natural and sustainable materials, and polymer informatics. He is a fellow of the American Chemical Society and the American Physical Society.

Zoom: Meeting ID: 992 0740 9473 Password: seminar4@

CHEMICAL ENGINEERING SEMINAR
Molecular Engineering of Field-Effect Transistor Water Sensors Based on 2D Nanomaterials

Thursday, February 20, at 11 a.m.
Engineering Innovation Building Room 124

Junhong Chen

Crown Family Professor
Pritzker School of Molecular Engineering
University of Chicago

Senior Scientist and Lead Water Strategist
Argonne National Laboratory, Lemont, Illinois

ABSTRACT:
The National Academy of Engineering identified “providing access to clean water” as one of the top ten grand challenges for engineering in the 21st century. A central requirement for safe drinking water is the availability of low-cost and real-time water quality monitoring. Current detection methods for critical analytes in water are often too expensive or unsuitable for in-situ and real-time detection. The unmet need is evidenced by the insufficient onsite water quality monitoring along the water distribution line and at the point of use that has led to major catastrophes such as the Flint Water Crisis due to the deterioration in water quality within water distribution systems. This talk will unveil a powerful approach to real-time water sensors through molecular engineering of 2D nanomaterials in a field-effect transistor platform. The working principle of the sensor is that the conductivity of 2D nanomaterial channel changes upon binding of chemical or biological species to molecular probes anchored on the nanomaterial surface. As such, the presence and the concentration of analytes (e.g., heavy metals, bacteria, and nutrients) can be determined by measuring the sensor resistance change. The patented technology allows for real-time detection of deadly contaminants with high sensitivity and selectivity in field settings for one-time testing or in-line continuous flow testing. The sensor signals can be wirelessly transmitted to a central control station so that the health status of the entire water distribution system could be monitored remotely in real time. The envisioned smart water distribution system can significantly mitigate risks to ensure a safe water supply. The talk will focus on the molecular engineering aspects of the sensor device (e.g., engineering nanomaterial channel, molecular probe, and device passivation) through both theoretical and experimental approaches. The talk will end with a brief introduction on the translation of the platform technology from concept to prototype product through partnership with industries.

BIO:
Junhong Chen is currently Crown Family Professor of Pritzker School of Molecular Engineering at the University of Chicago and Lead Water Strategist & Senior Scientist at Argonne National Laboratory. He also serves as the Science Leader for Argonne’s presence in the City of Chicago (Argonne in Chicago). Prior to coming to Chicago, Dr. Chen served as a program director for the Engineering Research Centers program of the US National Science Foundation (NSF) and the director of NSF Industry-University Cooperative Research Center (I/UCRC) on Water Equipment & Policy (WEP). He founded NanoAffix Science LLC to commercialize real-time water sensors based on 2D nanomaterials. Dr. Chen received his Ph.D. in mechanical engineering from University of Minnesota in 2002 and was a postdoctoral scholar in chemical engineering at California Institute of Technology from 2002 to 2003. His current research focuses on nanomaterial innovation for sustainable energy and environment. Dr. Chen has published 300 journal papers and has been listed as a highly cited researcher (top 1%) in materials science/cross-field by Clarivate Analytics. He is an elected fellow of Royal Society of Chemistry, National Academy of Inventors, and the American Society of Mechanical Engineers.

Zoom: Meeting ID: 992 0740 9473 Password: seminar4@

We are excited to announce a Town Hall meeting for the Department of Chemical Engineering!!
This is an excellent opportunity for you (faculty, staff, and students of all levels) to voice your concerns, ask questions, and engage in meaningful discussions about our program and its future.

Date: Tuesday, October 1
Time: 12 PM
Location: Seminar Room (Engineering Innovation Building Room 124)

During this meeting, we aim to address any concerns you may have and provide updates on department initiatives. Your input is invaluable as we strive to create an inclusive and supportive environment for all.
Please feel free to submit any questions or topics you would like to discuss in advance by filling out this survey:
https://uic.ca1.qualtrics.com/jfe/form/SV_3Db0X0i119PVXim

We look forward to seeing you there and fostering a constructive dialogue!

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