| NSF Org: |
CMMI Division of Civil, Mechanical, and Manufacturing Innovation |
| Recipient: |
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| Initial Amendment Date: | August 9, 2018 |
| Latest Amendment Date: | August 9, 2018 |
| Award Number: | 1762567 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Siddiq Qidwai
sqidwai@nsf.gov (703)292-2211 CMMI Division of Civil, Mechanical, and Manufacturing Innovation ENG Directorate for Engineering |
| Start Date: | August 15, 2018 |
| End Date: | July 31, 2021 (Estimated) |
| Total Intended Award Amount: | $270,354.00 |
| Total Awarded Amount to Date: | $270,354.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
3720 S FLOWER ST FL 3 LOS ANGELES CA US 90033 (213)740-7762 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
3720 S. Flower St. Los Angeles CA US 90089-0001 |
| 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): | Mechanics of Materials and Str |
| Primary Program Source: |
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| 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
Self-healing polymers are synthetic materials capable of autonomously repairing damages without human intervention. They have shown great potentials for sustainable technologies in diverse engineering applications, including artificial muscles and skins, flexible electronics, soft robotics and many others. Nevertheless, the state-of-the-art design of self-healing polymers remains at the trial-and-error stage with insufficient theoretical guidance. This award supports fundamental research to elucidate the self-healing mechanics of nanocomposite hydrogels that consist of water-mediated polymer networks crosslinked by nanoparticles. The knowledge obtained from this project will provide mechanistic insights into self-healing polymers that are able to restore their functionality after damage. The research will not only promote the fundamental science of self-healing mechanics, but also advance the national health, prosperity, and welfare through further development and enhancement of soft-materials based sustainable technologies. This project will also train a diverse group of students in the areas of solid mechanics, polymer science, mechanical engineering, and high-performance computing for next-generation workforce development. The educational objectives of the project will be realized through curriculum development, undergraduate research opportunities, summer research program for high school students, research experience for K-12 teachers program, and K-12 outreach program. Special efforts will be made to involve underrepresented students in this project.
Despite extensive studies in the syntheses and applications of self-healing polymers, constructing the mechanistic relationship between self-healing properties and material/healing settings remains challenging. The key technical barrier is how to physically model the microstructure evolution of the polymer networks during the self-healing process. The central hypothesis of this project is that the self-healing strength of nanocomposite hydrogel is governed by the diffusion of polymer chains across the fractured interface and subsequent crosslinks formed with nanoparticles. To test this hypothesis, the project integrates molecular dynamics simulations and analytical theories to study microscopic diffusion-reaction behaviors of polymer chains during self-healing process and macroscopic interfacial strengths after self-healing. The computational and theoretical predictions will be systematically validated with experimental studies of nanocomposite hydrogels composed of several material compositions, such as particle concentration, particle size, and water fraction, and under various external healing controls, such as temperature and delaying time. The interdisciplinary effort will open promising avenues for quantitatively understanding the multiscale mechanics of self-healing polymers and providing fundamental design principles of high-performance self-healing polymers.
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.
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 following outcomes have been achieved to address the intellectual merit and broader impacts of this project:
First, a diffusion-reaction model and systematic molecular simulations have been integrated to understand the interpenetration behavior of polymer chains across the healing interface during the self-healing process of nanocomposite hydrogels. The results reveal that the interpenetration behavior across the healing interface is governed by the reaction-driven chain-length-dependent diffusion of polymer chains. The understanding of the interpenetration behavior of polymer chains may significantly benefit the understanding of polymer-particle interactions and polymer chain dynamics at various surfaces and interfaces.
Second, systematic experiments and a healing mechanics model have been integrated to understand the interfacial healing strength of nanocomposite hydrogels. The results reveal that the healing strength of nanocomposite hydrogels increases with healing time until reaching a plateau. The quantitative understanding of the healing mechanism and strength of nanocomposite hydrogels may provide useful implications for understanding the constitutive and healing behaviors of novel self-healing polymers with unconventional network topologies and crosslinkers.
Third, systematic experiments and healing mechanics models have been integrated to understand the effects of material compositions and external stimuli on the healing behavior of nanocomposite hydrogels. The results reveal that the healing strengths of nanocomposite hydrogels can be drastically affected by nanoparticle concentration, nanoparticle size, and temperature. The understanding of the composition- and stimuli-dependent self-healing behaviors may provide new knowledge for understanding stimuli-responsive interfacial mechanics of future novel polymers.
Finally, the project has provided a platform to educate and train next-generation researchers and engineers including graduate students, undergraduate students, and K-12 students. Students of underrepresented minorities were actively involved in the project through close interactions with the University of Southern California VAST outreach office, Orthopaedic Medical Magnet High School, and The Los Angeles Chamber of Commerce. A graduate-level course Mechanics of Soft Materials and 3D printing was offered in fall 2018 and 2019. The new knowledge of self-healing mechanics of nanocomposite hydrogels was introduced, and the ongoing progress of the project was shared with more than 40 graduate students including ~20 female students. Besides, 7 underrepresented graduate and undergraduate students including 6 females and 1 African American have been involved in this project. They received careful mentoring and guidance through the research experience which prepared 5 of them to be successfully admitted to graduate programs. Moreover, the students from the PI lab exhibited smart materials including self-healing nanocomposite hydrogels to K-12 students and their parents at the USC Robotics Open House and USC Game Expo outreach event. K-12 students and their parents had hands-on experience with the synthesized self-healing nanocomposite hydrogels in this project. Furthermore, together with other co-organizers, the PI organized the first Southern California Mechanics Workshop in January of 2020. This workshop was to promote idea exchange and collaboration among different research groups from Southern California and other areas of the USA who are working on solid mechanics, including self-healing mechanics of smart materials. The total enrollment was over 130, including faculties, postdocs, and graduate students working on solid mechanics, robotics, and artificial intelligence.
Last Modified: 12/28/2021
Modified by: Qiming Wang
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