In this project funded by the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Steven Zimmerman of the University of Illinois will create a practical system of nanoscale adhesion promoters using the tools of supramolecular polymer chemistry. The approach is to further expand the toolkit of multiple hydrogen bonding units, and to develop general methods to functionalize polymers and surfaces with such units. The ability of the adhesion promoters to adhere two surfaces together at the macro-, micro- and nanoscopic levels will be assessed as will the reversibility and self-healing nature of the attraction. The broader impacts involve training undergraduate students, graduate students and postdoctoral researchers, broadening participation through the inclusion of women researchers on the project, and continuing to build a summer bridge program for URMs at the University of Illinois, Department of Chemistry.
This work will enhance our fundamental understanding about polymer adhesives and composite materials. Adhesives and composite materials have improved human life in innumerable ways, for example, the latter being found in a broad range of high performance products such as aircraft, Hummvees, and the Space Shuttle. There is a significant need for more advanced materials, including reversible glues, and composites with greater strength and resistance to delamination. For example, the fracturing of a composite material is what precipitated the Shuttle Columbia disaster. The results of these studies could have many important long term impacts on applications in which engineering adhesives are important, including automotive, packaging, and aerospace industries.
This NSF-sponsored project discovered and developed small molecules that resemble the DNA bases of double helical DNA. These DNA bases, which contain our genetic code, bind one another weakly and reversibly so that the code can be read. Inspired by DNA, we developed new DNA-like bases that bind one another significantly tighter and with even higher fidelity (selectivity) than seen in nature. The chemical synthesis of these single "sticky" bases was developed so that could be made easily and on a large scale for applications. We explored several applications for these sticky bases or nanoscale adhesion agents. First, these sticky bases were integrated into two polymers that ordinarily would not blend together. Polymer blends have important properties not found in the single polymers and they are used in a wide variety of materials including coffee cups and car bumpers. By incorporating the complementary or matched sticky bases into polystyrene and polybutylacrylate we were able to blend these normally immiscible polymers. Another application involved coating surfaces with one of the sticky bases and then reversibly gluing them together using a polymer with the complementary sticky base. One advantage of this approach, which uses reversible nanoscale adhesives or sticky bases is the ability to alter the adhesion with the appropriate stimulus. For example, these adhesive interactions become extremely weak or nonexistent in the presence of water or other highly polar solvents. Furthermore, we chemically synthesized a sticky base that could be turned on or off using oxidation and reduction processes. For example, oxygen with the appropriate catalyst was able to turn the sticky base off for low adhesion. Overall, this work suggests the possibility of creating extremely strong adhesives that are under appropriate conditions fully reversible. As part of this project a diverse group of undergraduate, graduate, and postdoctoral students were trained and several have entered the workforce making significant contributions to industrial and academic chemical research and education.
