| NSF Org: |
CBET Division of Chemical, Bioengineering, Environmental, and Transport Systems |
| Recipient: |
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| Initial Amendment Date: | August 12, 2009 |
| Latest Amendment Date: | July 7, 2011 |
| Award Number: | 0932311 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Eddie Chang
CBET Division of Chemical, Bioengineering, Environmental, and Transport Systems ENG Directorate for Engineering |
| Start Date: | August 15, 2009 |
| End Date: | December 31, 2012 (Estimated) |
| Total Intended Award Amount: | $195,861.00 |
| Total Awarded Amount to Date: | $195,861.00 |
| Funds Obligated to Date: |
FY 2010 = $68,334.00 FY 2011 = $69,407.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
1350 BEARDSHEAR HALL AMES IA US 50011-2103 (515)294-5225 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1350 BEARDSHEAR HALL AMES IA US 50011-2103 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | INTERFAC PROCESSES & THERMODYN |
| Primary Program Source: |
01001011DB NSF RESEARCH & RELATED ACTIVIT 01001112DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.041 |
ABSTRACT
0932311
Jeffries-EL
Intellectual Merit:
Nanoscale control of conjugated (conducting) polymers is especially important as the morphology of such functional materials plays a significant role in device performance, influencing properties such as conductivity, thermal stability, processability, and mechanical integrity. The goal of this proposal is to create new polymeric network materials for organic electronics devices, with improved performance due to the formation of well defined and continuous nanoscale conducting pathways. This goal will be achieved by combining the synthesis of near monodisperse conducting polymers (regioregular poly(3-alkylthiophenes) (rr-P3AT)s ), with the natural self assembly of block copolymers (BCPs) to create novel polymeric materials with the ability to form multiply continuous assemblies. There are two specific aims of this proposal. First, novel network forming ABC triblock copolymers containing an electrically conductive block will be synthesized. These materials will be designed such that they contain the block copolymer volume fractions necessary to generate the interfacial curvature and saddle surfaces, which are a hallmark of nanoscale networks. In addition, the chemical connectivity of the polymer will be designed such that crystallization of the conducting (rod) block is confined in order to maintain the network morphology. Next, membrane structures will be characterized by scattering, microscopy, and mechanical analysis techniques; membrane conductivity (and mobility) also will be examined using four point probe measurements, and dielectric spectroscopy. The proposed nanoscale network morphologies have superior mechanical attributes, relative to layers and cylindrical channels, and their percolating interconnected domains and large interfacial area present the opportunity to create conducting materials with tailored transport, chemical, and mechanical properties. These factors will lead to a dramatic improvement over polymer blend systems, where the creation of uniform-sized continuous pathways for conduction and transport is a key hurdle to improving the efficiency of polymeric devices.
Broader Impact:
The ability to create continuous nanoscale conducting pathways in organic thin films is crucial for further development and use of organic materials because poor electronic properties at domain boundaries often limit overall device properties. This is of particular concern for light emitting diodes (LEDs), thin-film transistors (TFTs), and photovoltaics (PVs), where improved transport is essential in the electronically active layers of these devices. While the synthesis of rr-P3AT BCPs has been reported in the literature, this work seeks to innovate their design. Specifically, the copolymers described above will contain one block that imparts toughness; a second block to provide confinement of the crystallizable block; and a third block that is crystallizable and conducting. A novel aspect of this work is that the chemistry of the conducting rr-P3AT block has been modified to lower the crystallization temperature, so that crystallization does not alter the overall self assembled block copolymer structure. The proposed research will provide new insights into the interplay between rod coil block copolymer composition, morphology and electronic properties. Collectively, this is expected to result in the optimization of CP morphology and electronic properties. Furthermore, this interdisciplinary project will train graduate and undergraduate students to address key scientific and engineering challenges in nanotechnology. Specific broader impact and educational initiatives are focused on increasing the participation of under represented groups. These include: providing summer research and mentorship opportunities through the PI's involvement with the ACS Diversity Partner Program and Minority Scholars Program. Additionally, the co-PI's involvement with several programs at Iowa State University [ISU] (AGEP, Freshman Honors, and NOBCChE) will be used to recruit graduate students from under represented groups to ISU. Finally, we propose the exchange of students between the University of Delaware, Chemical Engineering Department, and the ISU, Department of Chemistry, to broaden their research knowledge base.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The overall goal of the project was to develop strategies for controlling the assembly and organization of polymers on the nanoscale. The ability to form nanostructured films is beneficial as it can increase the charge carrier mobility within the material. This is of particular concern for light emitting diodes, thin-film transistors, and solar cells, where improved transport is essential in the electronically active layers of these devices. We investigated the synthesis of a series of rod-coil block copolymers containing a conjugated “rod” polymer block, poly(3-decylthiophene) (P3DT)and a coil block containing two units, polystyrene-b-polyisoprene (PS-PI). Each component of copolymer was selected to impart specific function into the material. The conjugated polymer, P3DT is an organic semiconductor with the ability to transport positive charges (holes). This material tends to be highly crystalline, but lacking is long-range order. In solution, molecules of P3DT retain their rigidity, thus are considered rod-like polymers. In contrast, PS and PI are both insulating polymers that form coils in solution. There are subtle differences in the thermal properties of these materials that make their coupling with P3DT desirable. Due to the differences in the behavior of the components, rod coil block copolymers are the polymeric equivalent of oil and water, they do not like to mix. However since they are chemically bonded, the chains must self-assemble in a way that is favorable for all components. By varying the ratios of the two components we can control the nanostructures that are formed.
Our group has evaluated several different approaches for the synthesis of these polymers. Initially we based our work on previous research of poly (3-hexylthiophene) block copolymers as the only difference between the two materials is the number of carbon and hydrogen atoms on the side chain. We have found that the chemical reactions to modify the thiophene block work well for the P3DT. The second aspect was the attachment of the PI-PS block. We were unique in this approach in that most other reported block copolymers contain only 2 blocks. During this project we found that while reactions to combine the polymer chains work well for shorter polymers (less than 20 repeating units), they often fail when longer polymers are utilized. As such we developed an approach to synthesize the units in sequential fashion. The project was performed in collaboration with Professor Thomas Epps at the University of Delaware. His group evaluated the properties of our materials.
In terms of broader impacts, this project has advanced the general understanding of the synthesis of block copolymers containing conjugated units. Furthermore, this interdisciplinary project has trained graduate and undergraduate students to address key scientific and engineering challenges in nanotechnology. Additionally, the PI’s involvement with several programs at Iowa State University was used to recruit students from under-represented groups to perform research in her lab.
Last Modified: 04/02/2013
Modified by: Malika Jeffries-El
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