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Leveraging the Semiconducting Nature of Conjugated Polymers

Shrayesh N. Patel

    Conjugated semiconducting polymers are highly attractive for various organic electronic and energy storage and conversion applications due to tunable electronic properties, solution processibility, and mechanical flexibility. Due to advances in molecular design and improved processing techniques, the charge carrier mobility of semiconducting polymers in thin-film field-effect transistors are now approaching and exceeding amorphous silicon (> 1 cm2V-1s-1). For the first part of the talk, I will report on the structural characterization of a macroscopically aligned semiconducting polymer thin-film for field-effect transistors. This characterization reveals key design principles describing what limits and enhances charge transport in recent high mobility semiconducting polymers. Furthermore, the discussion will be extended to chemically doped semiconducting polymers where the interplay between local and long range order strongly govern the charge transport properties. For final part of the talk, I will present my work on conducting copolymers for lithium battery electrodes. A new electrode design was developed using a diblock copolymer consisting of semiconducting poly(3-hexylthiophene) (P3HT) for electronic transport and poly(ethylene oxide) (PEO) and LiTFSI mixture for lithium ion transport. This copolymer serves both as a binder and as an electronic and ionic charge transport medium essential for enabling redox reactions. By taking advantage of the semiconducting nature of P3HT, we can uniquely control the electronic charge carrier mobility in the electrode as function of potential.

    Dr. Shrayesh Patel is currently a postdoctoral research scientist at the University of California, Santa Barbara in the Materials Research Laboratory. His research expertise resides at the intersections of polymer science, organic electronic materials, and electrochemistry. Under the advisement of Prof. Michael Chabinyc, Dr. Patel’s postdoctoral research has focused on the structure-property relationships of high mobility semiconducting polymers for transistors and thermoelectrics. He received his Ph.D. at the University of California, Berkeley in Chemical Engineering under the advisement of Prof. Nitash Balsara. Dr. Patel’s dissertation topic was on simultaneous electronic and ionic conducting block copolymer for lithium battery electrodes. His Ph.D research was selected by AIChE as an Emerging Area in Polymer Science and Engineering and also part of the cover story for the May 2013 issue of Chemical & Engineering News. Dr. Patel received his B.S. degree in Chemical and Biomolecular Engineering at the Georgia Institute of Technology.

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     Drug adaptation in melanomas and other cancers driven by different oncogenic pathways limits therapeutic effectiveness and appears to promote the emergence of cells carrying resistance mutations resulting in resurgent disease. Understanding and effectively targeting resistance mechanisms is needed to increase the durability of therapeutic response. I will describe a systems pharmacology approach combining multiplex biochemical measurements, single-cell analysis and computational modeling to characterize drug-induced adaptive responses and their consequences for cancer cell fate. This approach identifies potential strategies to enhance drug maximal effect and to overcome drug resistance.

     Dr. Mohammad Fallahi-Sichani is a Life Sciences Research Foundation (LSRF) Postdoctoral Fellow, working with Prof. Peter Sorger in the Department of Systems Biology at Harvard Medical School. He received his Ph.D. in Chemical Engineering in 2012 from the University of Michigan under the joint supervision of Prof. Jennifer Linderman and Prof. Denise Kirschner. His postdoctoral research currently funded by an NCI K99 Pathway to Independence Award is focused on understanding mechanisms of adaptive resistance and fractional response of cancer cells to anti-cancer drugs. His doctoral thesis combined multi-scale modeling approaches with experiments on mouse models of tuberculosis to the study of mechanisms by which TNF signaling determines immunity to Mycobacterium tuberculosis infection. His postdoctoral and doctoral research were awarded the 2015 Scholar-in-Training Award from the American Association for Cancer Research and the 2011 Richard and Eleanor Towner Prize for Outstanding PhD Research from the University of Michigan.

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     Compartmentalization in cells is central to accomplishing diverse and simultaneous biomolecular interactions. In addition to membrane-bound organelles, cells organize many biochemical processes in membrane-less compartments. It has recently emerged that those membrane-less organelles are liquid droplets condensed from the cytoplasm/nucleoplasm through liquid-liquid demixing. It is however not clear what are the driving forces for phase transitions and how droplets maintain distinct functional and physical identities. With Whi3, an RNA-binding protein that contains a polyQ-expansion, we show that specific targeting RNAs can drive protein droplet formation at physiological conditions. RNAs can also alter the viscosity of droplets, their propensity to fuse, and the exchange rates of components with bulk solution. Different targeting transcripts impart distinct biophysical properties of droplets, indicating mRNA can bring individuality to assemblies. Furthermore, irreversible aggregates are observed in aged droplets indicating a mechanism that underlies the formation of pathological aggregates and are in line with the observation that RNA binding proteins with disordered prion-like domains are often associated with degenerative diseases such as Alzheimer's, Huntington's, and Parkinson's diseases.

     Dr. Huaiying Zhang has a longstanding interest in applying engineering principles to address biological issues. During her Ph.D. in chemical engineering at McGill University, she examined the diffusion and electrophoresis of lipopolymers in lipid bilayers with a combination of experimental and theoretical tools. During her post-doc at Dartmouth, she studied how principles of phase transition are applied in cells to create RNA granules, liquid droplets composed of RNAs and RNA-binding proteins. She discovered that instead of taking a free ride, RNAs actually drive RNA-binding proteins to form liquid droplets and tune droplet physical properties including viscosity, ability to fuse and exchange component with the surroundings. The focus of her independent research program will be intracellular phase transitions

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