The goal of our research is to understand on a molecular level a broad range of macroscopic properties of polymers. Owing to the tremendous diversity of their physical properties, polymeric materials find applications ranging from the most common to the most exotic products in the forms of fibers, plastics, elastomers, adhesives, and coatings. Inevitably, the final properties of the material depend not only on the chemical constitution of the polymer, but also on its physical structure or conformation. In our group we explore general aspects of the latter, relating the macromolecular structure and dynamics to the macroscopic properties. Present problems of interest include (1) the dynamics of polymer blends, (2) manipulation of the alignment of liquid-crystalline polymers and block-copolymers using flow, (3) controlling molecular alignment and microstructure in semicrystalline polymers and (4) physical aspects of the design of new biomedical materials.

Two examples that illustrate how we use fundamental physical insight to design functional materials for biotechnology are the development of switchable hydrogels and the creation of elastomers that can be reshaped using light. Using physiical associations, we have made biocompatible hydrogels that transform spontaneously from a low viscosity state to a gel state when they reach the implantation site. Applying basic understanding of elastomers and polymer dynamics, we have created biocompatible polymer gels that can be treated with light to change their shape, enabling, for example, intraocular lenses whose refractive properties can be non-invasively optimized to provide the correct lens power and astigmatic correction.

To obtain information on the desired molecular or microscopic scales, a range of techniques and model polymer systems is used. In some problems, it is necessary to use techniques that probe particular molecules in a multicomponent system or of specific parts of molecules in a topologically complex polymer. This is accomplished by using spectroscopic techniques, both infrared and nuclear magnetic resonance, that allow isotopically labeled components to be observed. In our laboratory, these methods are combined with dynamic mechanical testing, allowing us to measure directly the contribution of each species to the optical anisotropy and stress. To track meso-scale dynamics that are important in liquid crystals, ordered block copolymers and semicrystalline polymers, we combine polarimetry, optical and electron microscopy, light and X-ray scattering and rheological measurements.

In some cases it is necessary to develop new experimental techniques to access critical information. Recently we have developed new instruments that reveal the earliest stages of the effects of flow on polymer crystallization. For the first time, it is possible to observe chain conformation during transient flow of a sub-cooled melt and its relationship to the structure development during solidification after the cessation of flow. The results show the creation of dilute, long-lived aligned structures during flow that correlate with highly anisotropic crystal growth long after the flow has stopped. The molecular basis of the formation of these flow-induced nuclei is currently under investigation. Our group has also constructed a new instrument to visualize order in molecularly-thin polymer films. Toward the goal of producing uniform, highly aligned ultra-thin polymer films, it is necessary to image the degree and direction of alignment in such films. Therefore, we have developed a new microscope that integrates recent advances in laser-scanning microscopy with polarization-modulation polarimetry. This combination enables us to image molecular orientation with high spatial resolution, sensitivity and speed. We are using this unique capability to study orientational order in ultrathin Langmuir-Blodgett films of rodlike polymers.