This research involves studies of specific interactions in polymer systems. One part of the proposed work seeks to obtain a fundamental understanding of the interplay between microstructure and the fraction of same chain contacts, or self-concentration, in hydrogen bonded polymer blends. Measurements of the fraction of hydrogen-bonded groups in these mixtures will also be used to determine the effect of hydrogen bonding on rheological properties. This work will be complemented by the second part of the proposed research, which involves studies of the shapes and widths of bands in these strongly interacting systems and how these are affected by interactions and relaxation processes. Infrared bands and Raman lines are sensitive to local environment and picosecond scale dynamics. The extent to which useful information can be obtained from the spectra of polymers will be evaluated by comparing the results of band shape analysis to those obtained by applying ultrafast two-dimensional infrared spectroscopic (2D-IR) techniques.
NON-TECHNICAL SUMMARY
The factors that govern both the mixing of polymer materials and so-called relaxation phenomena (which govern their mechanical and rheological behavior) is of considerable practical importance. Finding polymers that mix at the molecular level (most do not) can lead to materials with novel properties. Even polymers that phase-separate can have important properties, such as enhanced impact resistance, providing that the size of the phase separated domains are controlled. This research will use infrared spectroscopy to study both specific interactions and relaxation behavior in polymers and their mixtures. The work will also contribute to education through the mechanism of involving both undergraduate and graduate students in laboratory work, thus teaching them the fundamentals of spectroscopic and other techniques. More uniquely, work supported on previous NSF awards that resulted in CD based monographs, complete with animations and interactive programs, will be extended to produce sets of lectures that will be freely accessible over the web.
. Many commercial polymers are non-polar and the segments of the chains interact only weakly. However, polymer chains containing certain types of polar chemical groups can interact more strongly, through hydrogen bonds, for example. Even stronger interactions occur in polymers containing ionic groups. The presence of such strong interactions has a profound influence on properties and an understanding of their nature can lead to materials with new or enhanced properties. The intellectual merit of this work is based on the use of techniques that can study structure and concentration of the molecular arrangements or complexes formed by materials that interact strongly, in combination with techniques for studying important physical properties, such as relaxation behavior (mechanical properties) or electrical conductivity. Infrared spectroscopy was used to determine the number and type of hydrogen bonds in mixtures or blends of polymers. Most non-polar polymers do not mix with one another, but if complementary hydrogen bonding groups are placed along a chain, miscible mixtures can be formed. There are some complexities, polymer chains have "self-contacts" – they "see" more of themselves as a result of the flexible chains being able to bend back on themselves locally. This affects properties and mixing. A careful study of low and high molecular weight materials with the same chemical groups can sort this out, however. In polymers with ionic groups, infrared spectroscopy can be used to characterize the structure of the aggregates that may be present. Conductivity in these materials depends on both the number of charge carriers and their mobility, which in turn depends on complex relationships between the types of ionic groups present (e.g., single or "free" ions, triplets. etc.), how they are coordinated to polymer functional groups and how ion motion is coupled to chain dynamics. The research performed during the last four years achieved a number of goals. Methods for infrared band shape analysis in polymer materials were developed and applied to measuring relaxation phenomena in polymers. Local structure in hydrogen bonded mixtures and their relationship to the glass transition temperature were probed. The state of aggregation in ion containing polymers and various polymer mixtures was also studied and the results correlated to conductivity measurements. It was a combination of work on ion containing materials that also hydrogen bond strongly that may lead to the broadest impact, however. We were studying mixtures of ionic liquids (ILs – materials consisting of ionic groups that are liquid below 100?C) with polymers when we stumbled across a story in the New York Times Science Edition on the huge environmental problems with the processing of tar or oil sands with water. So, out of curiosity, we obtained some Canadian tar sands and examined how they would interact with ILs. We found that ILs used in conjunction with a non-polar solvent would drive a phase separation as a result of their strong interactions with mineral surfaces. The separation occurs at room temperature and does not require the use of water in the initial separation process. Almost all of the bitumen is recovered in a very clean form. This work led a patent application. Finally, this excursion also led us back to our polymer/strong interactions roots and the final work on this grant involved deep eutectic mixtures involving components that both hydrogen bond and have ionic interactions. Both low molecular weight analogues and polymer/IL mixtures were studied. We found that ions do not appear to aggregate in these systems and these mixtures should be explored for use in electronic devices.
