| NSF Org: |
DMR Division Of Materials Research |
| Recipient: |
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| Initial Amendment Date: | August 3, 2021 |
| Latest Amendment Date: | August 3, 2022 |
| Award Number: | 2132696 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Birgit Schwenzer
bschwenz@nsf.gov (703)292-4771 DMR Division Of Materials Research MPS Directorate for Mathematical and Physical Sciences |
| Start Date: | August 15, 2021 |
| End Date: | July 31, 2024 (Estimated) |
| Total Intended Award Amount: | $300,000.00 |
| Total Awarded Amount to Date: | $300,000.00 |
| Funds Obligated to Date: |
FY 2022 = $150,000.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
900 S CROUSE AVE SYRACUSE NY US 13244-4407 (315)443-2807 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
Office of Sponsored Programs Syracuse NY US 13244-1200 |
| 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): |
CONDENSED MATTER PHYSICS, DMR SHORT TERM SUPPORT, SOLID STATE & MATERIALS CHEMIS, CONDENSED MATTER & MAT THEORY |
| Primary Program Source: |
01002223DB 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): | 47.049 |
ABSTRACT
Non-technical Summary
Imagine a world with infinitely rechargeable batteries that are very light, store electrical energy without losses, power lines that lose no power, and portable medical imaging scanners ? these are a few of the transformative applications that could be realized by the development of room-temperature (RT), ambient pressure superconductors (materials that transport electricity without resistance). Theory predicts that linear molecular conductors, like polyacetylene (PA), whose chains of carbon atoms are connected by alternating double and single bonds, might be one such superconducting material. In the laboratory, PA is anything but linear when synthesized, becoming highly disordered (like a spaghetti) and prone to reacting with itself or neighboring molecules. Just as a winding road slows traffic, what starts as a straight PA chain can twist to produce bent and twisted geometries that significantly affect its conductivity ? this factor alone is a major experimental bottleneck in achieving RT superconductivity in this and other potential organic conducting polymers. With this project, supported by Division of Materials Research, Professor Michael Sponsler and his research group at Syracuse University will focus on preparing a completely new form of PA with separated and highly ordered single chains isolated in long, straight tunnels. To achieve a linear geometry capable of exhibiting potential RT superconductivity, the PA chains will be synthesized within the tunnels of honeycomb-like urea crystals, then studied to confirm their geometries and electrical behavior. If successful, the project will produce structurally ordered PA for the first time, result in a novel organic material that will have a significant impact on the theory and application of conducting polymers, and reveal the RT, ambient pressure superconductivity state, a long-standing elusive goal. Moreover, integrating a large arsenal of experimental efforts to characterize these chains and their behavior will serve to educate new chemists from undergraduate to post-doctoral levels, including women and underrepresented minorities in these interdisciplinary research projects.
Technical Summary
Polyacetylene (PA), the simplest conjugated polymer, is thought of as a long, straight-chain semiconductor exhibiting bond-length alternation (BLA). Based on foundational calculations predicting that PA chains cannot have BLA because the vibrational zero-point energy is above the Peierls barrier, the premise of the proposed study is that an individual, isolated chain of PA in its fully extended all-trans conformation will have a half-filled band electronic structure and thus will be a one-dimensional (1D) metallic polymer without doping. Further, the vibrational frequency of the carbon-carbon (C-C) bond alternation mode (1455 1/cm) associated with the 1D conductivity is ~7 times higher than thermal energy at room temperature (RT), precluding thermal excitation as a mechanism of electron scattering. Since there is no mechanism for resistance to the electron motion, high-temperature superconductivity in PA is a real possibility. This project, supported by the Division of Materials Research, will test the hypothesis that individual PA chains of sufficient length and isolation will show superconductivity by (1) synthesizing ordered, fully extended PA chains by encasing the polymer chains into structures with nanometer-sized diameters ? the parallel tunnels of a urea inclusion crystal; and (2) characterizing the structural and electronic properties of the long chains produced to demonstrate that they show no BLA and have no measurable electrical resistance to DC currents, showing that PA acts as an RT, ambient pressure superconductor. The PA/urea inclusion crystals will be made from urea and a photoreactive precursor molecule, (E,E,E)-1,6-diiodohexatriene (DIHT), through a new light-induced process called elimination-condensation inclusion polymerization. This unique approach employs photochemical bond scission of terminal carbon-iodine (C-I) bonds from a DIHT molecule with the formation of new C-C bonds and elimination of iodine from the tunnels of the urea host crystal. The photochemical process continues until all iodine has left the crystal and high molecular weight and fully-conjugated PA chains are made within the crystalline urea tunnels. The photochemical conversion of included DIHT to PA will be monitored by mass-loss measurements to track the stoichiometric amounts of iodine lost from the initial crystal and by Raman spectroscopy that monitors the growth and disappearance of features observed in the initial stages of the process. The resulting PA/urea crystals will be studied by high-resolution X-ray diffraction, Raman spectroscopy, inelastic neutron scattering spectroscopy, and conductivity measurements, both in bulk crystal measurements and by the use of conductive atomic force microscopy.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
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.
Intellectual Merit. Superconductors are highly useful, such as the superconducting electromagnets in Magnetic Resonance Imaging (MRI), but known superconductors require very low temperatures. Prior collaborators published calculations that predicted that a sample with long and well-ordered, isolated chains of polyacetylene should be superconducting at room temperature or higher. In this project, we have aimed to make such samples and to show that they display conductivity and superconductivity.
Polyacetylene (PA) was shown in the 1970’s to be electrically conducting when it is doped, (treated with oxidizing or reducing agents) and this work was recognized with the 2000 Nobel Prize. PA was the first organic conducting polymer to be discovered. Without doping, PA does not conduct electricity, but the above-mentioned calculation showed that a high-quality PA with isolated chains is predicted to be a conductor without doping and to be superconducting. We reason that the many known ways to make PA all give samples with many defects, including cross-linking, and the chains are not isolated from each other.
In prior work, we showed that we could make urea inclusion crystals that have parallel channels that each contain a chain of PA. This was done by growing precursor crystals that had the channels filled with either DIBD or DIHT. By irradiating the precursor crystals with UV/vis light, chains of PA were formed in the channels. In the work of this current grant, much progress was made in gaining control over the crystallization of several polymorphs of DIBD/urea and DIHT/urea and in X-ray diffraction characterization of these crystals. We also developed better photopolymerization procedures that promote uniform and high-conversion results.
In our crystallization studies, we made an unexpected and interesting discovery. When either DIBD or DIHT crystals (without urea) were left at room temperature in the dark for about three days, polyacetylene and iodine (I2) were formed. The DIHT crystals turned black, and the iodine was able to be removed by extraction, changing the crystals to red or brown. The black crystals are clearly I2-doped PA, and they were observed to conduct electricity. The DIBD crystals darkened only a little, suggesting that the iodine was able to escape from these crystals. Raman spectroscopy showed that PA was formed in both cases. Thus, the photochemical process in the urea inclusion crystals happens thermally without the urea. With the urea, light is needed.
Conductivity measurement of PA chains inside an inclusion crystal is not simple. Relatively simple experiments, done by breaking the ends from irradiated crystals (to remove crystal portions that no longer have guest, due to the loss of iodine) and connecting wires to each end with a drop of gallium metal, gave no observation of conductivity. While this might be interpreted as showing that PA in the crystal is not conductive, we recognized two other explanations: that the gallium is not making good electrical contact with the PA, and that the PA chain lengths are shorter than the crystal. Both explanations are reasonable, given that simply breaking the crystal likely does not have PA going all the way to the ends of the crystals, and about 1 million connected C=C units are needed to span a crystal of 0.25 mm length.
We addressed the first of these concerns by using the strategy outlined in Figure 1. The center of an irradiated crystal is glued to a glass slide using epoxy, which also covers the center portion of the crystal. The urea in the ends of the crystal is then dissolved with 1-µL portions of iodine-containing methanol. The methanol dissolves the urea, and the iodine dopes the PA that is left behind. This doped PA now serves as an electrical contact for the included PA in the center crystal portion. We have found that silver paint serves well to make this electrical contact.
Using this method (Figure 2), we have made measurements of crystal centers down to 0.25 mm length. We have not yet detected conductivity in the crystals, but the need for defect-free conjugation lengths of 1 million monomers is likely the explanation for this. In using this method, we have made many improvements, and further improvements are expected and planned, including both more complete photochemical conversion to PA in the crystals and the measurement of shorter crystal centers, down into the um range.
Broader impacts. Clearly, micron-sized crystals that are superconductive will not be readily useable in many applications. But our goal at this stage is to demonstrate the properties in a proof-of-concept result. With such a result in hand, then further improvements both in the chemistry and in the engineering can be pursued. And this result will force much rethinking about the nature of this very important polymer, PA.
In addition, this project has provided education and training to new chemists from post-doctoral to undergraduate levels and including women and underrepresented minorities.
Last Modified: 11/28/2024
Modified by: Michael B Sponsler
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