| NSF Org: |
DMR Division Of Materials Research |
| Recipient: |
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| Initial Amendment Date: | January 3, 2011 |
| Latest Amendment Date: | March 6, 2015 |
| Award Number: | 1049706 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Andrew Lovinger
alovinge@nsf.gov (703)292-4933 DMR Division Of Materials Research MPS Directorate for Mathematical and Physical Sciences |
| Start Date: | March 1, 2011 |
| End Date: | February 28, 2017 (Estimated) |
| Total Intended Award Amount: | $500,000.00 |
| Total Awarded Amount to Date: | $506,250.00 |
| Funds Obligated to Date: |
FY 2012 = $106,250.00 FY 2013 = $100,000.00 FY 2014 = $100,000.00 FY 2015 = $100,000.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
3124 TAMU COLLEGE STATION TX US 77843-3124 (979)862-6777 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
3124 TAMU COLLEGE STATION TX US 77843-3124 |
| 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): | POLYMERS |
| Primary Program Source: |
01001213DB NSF RESEARCH & RELATED ACTIVIT 01001314DB NSF RESEARCH & RELATED ACTIVIT 01001415DB NSF RESEARCH & RELATED ACTIVIT 01001516DB 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
TECHNICAL SUMMARY:
Layer-by-layer (LbL) assemblies represent a novel and revolutionary class of materials with potential applications ranging from biological and energy systems to smart surfaces and sensors. However, their internal structure and materials properties are challenging to discern because they are often ultra thin or confined to their substrate. As shown for many neutral polymers, the materials properties (such as the glass transition temperature) significantly depart from bulk behavior as the film thickness deceases. The aim of this work is (i) to discern physical and structural differences within LbL assemblies of varying thickness, curvature (in the form of polymer nanotubes), and components using calorimetry, ellipsometry, and electrochemistry and (ii) to relate that information to how LbL films grow and perform. Bulk free-standing LbL films will be compared to LbL-coated porous templates. LbL thickness and pore diameter will be varied to isolate the influence of confinement and curvature, respectively. The assembly and adsorption of polyelectrolytes within small pores will also be explored for polyelectrolyte solutions of varying pH and ionic strength. Layer-structure and properties of composite LbL films containing nanoparticles will be compared to those without to determine the influence of hard inorganic materials within some of the layers. Calorimetry will access thermal fluctuations and ellipsometry will access density fluctuations related to phase transitions within the film. Electrochemical permeability measurements will qualitatively determine structure and free volume within the films using redox-active probes. Together, these techniques will give new knowledge regarding layer mixing, polyelectrolyte complexation, and confinement for LbL assemblies.
NON-TECHNICAL SUMMARY:
Layer-by-layer (LbL) assemblies represent an exciting new class of polymer coatings and films. Made from the alternating layers of oppositely charged molecules, LbL films have applications in energy storage and production, biomaterials, self-cleaning surfaces, and more. However, little is known regarding whether these films melt, soften, or crosslink at a given temperature; such knowledge is important to discern if LbL assemblies are to be commercialized. In this program, the thermal properties of LbL films and LbL nanotubes will be determined. The aim is to understand how thickness, curvature, and components influence film structure and properties. If successful, acquired knowledge could be used to manipulate and design thin films for organic energy storage and other applications. The major impact of this program would be in the acquisition of new knowledge and mentoring of individuals in STEM disciplines. Participants will learn state-of-the-art characterization and processing techniques as well as valuable professional skills. One graduate student will be supported. Community outreach is planned via online video demonstrations, Texas A&M University?s E3 program for high school teachers, Texas A&M University?s Women Explore Engineering program for young women, and other outlets.
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 major focus of this project was on the thermal properties of layer-by-layer assemblies and how they might exhibit confinement effects. Layer-by-layer assemblies are thin layers of oppositely charged polymers or other species that assemble into a coating. The general idea is that a material’s melting point, glass transition, or cross-linking temperature could be affected by film thickness, the underlying substrate, curvature, or other factors.
The intellectual merit of this project was that several new methods to measure the thermal properties of layer-by-layer assemblies were established and verified. New methods were needed because the thin nature of the films complicated traditional bulk-scale measurements. This led to the new knowledge that these materials exhibited a glass transition that was strongly affected by its surrounding environment. A glass transition describes the temperature at which a polymer softens from a brittle to a rubbery state. It was shown that the glass transition was most strongly affected by water, but also affected by pH and by salt. The effect of curvature and nanoparticle content was also investigated. The confinement effect manifested generally by an increase in the glass transition temperature and cross-linking temperature (if present for that system). This was attributed to substrate effects, in which attractive interactions with the substrate increased the glass transition temperature. It was found to be generally true for both layer-by-layer systems made by electrostatic and by hydrogen bonding interactions. The general effect of nanoparticles was not as clear. In some cases, a second higher glass transition appeared, but in other cases no strong effect was observed, depending on the system and the nanoparticle type.
The broader impact of this project was that the thermal properties of layer-by-layer assemblies were revealed and that new methods to do so were presented. This provides tools for others that might envision implementing these materials in thermally responsive or sensitive applications ranging from energy to health. Several participants received mentoring and skill development directly or indirectly through this project, including one post-doctoral researcher, five graduate students, and eight undergraduates, and two high school teachers. Of these, nine of the seventeen participants were female or from an underrepresented group in science and engineering. This work was disseminated through 12 peer reviewed publications, student dissertations, presentations at national and international conferences as well as universities, a Youtube video, and Texas A&M’s Chemistry Open House.
Last Modified: 06/12/2017
Modified by: Jodie Lutkenhaus
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