Development of a 2D-FTIR/Dielectric Spectrometer for Materials Research

0079432

Painter

This grant will help develop a new instrument for polymer characterization that will combine dielectric relaxation and two-dimensional (2D) infrared spectroscopic measurements. Dielectric relaxation measurements have been used for many years as a probe of the dynamics of polymer chains, through the detection of the transitions and relaxations that are a result of various types of coupled or local motions. Infrared spectroscopy provides a probe of molecular level structure and, in certain systems, intermolecular interactions. Clearly, a technique (or, more accurately, a hybrid-technique) that can measure the temperature and frequency range of various transitions and relaxations, while simultaneously probing the functional groups involved and the degree to which their motions are coupled, would be an extremely powerful analytical tool. Essentially, we will use a dielectric spectrometer to provide an oscillating electric field to modulate the dipoles of a sample. This modulation can be probed by infrared spectroscopy. Applying standard methods of cross-correlation analysis, the resulting in-phase and out-of-phase signals can be used to construct two dimensional plots, which, amongst other things, allow an identification of the functional groups whose motions are coupled. By varying the oscillatory frequency applied to the sample and its temperature, the molecular basis of the relaxations and transitions that occur in polymer (and other) materials can be investigated, providing a new and powerful probe of structure and dynamics. The new instrument will be initially applied to the range of problems facing our research groups, including the identification of the functional groups involved in specific interactions in polymer blends, the dynamics of functional groups and chain segments in such mixtures, the relaxation phenomena that occur in crystallizable miscible blends, relaxations in polymer liquid crystals and polymer dispersed liquid crystals, and so on.

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When a polymer chain is subjected to some external force, such as stretching or other types of mechanical deformation, the chains take time to adjust or 'relax' to a new conformation. Relaxation processes in polymers are complex and depend upon factors such as the flexibility of the individual chains in a sample and how much different chains are tangled up with one another. Relaxation processes have a profound effect on the properties of polymers and hence their uses, ranging from applications in everyday life to their incorporation into advanced devices. An understanding of the molecular mechanisms involved in such relaxations is therefore important in not only understanding the behaviour of polymers presently in use, but designing materials for new applications. Unfortunately, this information is not easily obtained, as certain techniques can measure relaxation processes, but give no information on the molecular mechanisms involved, while others probe the molecules themselves, but give no information on relaxations.

To solve this problem we are proposing to build a new hybrid instrument that will simultaneously probe molecular relaxations (or polymer dynamics) and molecular level structure. Dielectric spectroscopy and infrared spectroscopy, respectively, are the two techniques that will be combined and the new instrument will be called a 2D-FTIR/Dielectric Spectrometer. The two techniques are both standard tools for analysis and our task is to construct a sample cell that will allow these to work together.

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