Fundamental studies aimed at understanding the mechanism of adsorption and desorption of contaminants in activated carbons is being pursued. This includes determining factors that control pore diameter, pore diameter distribution, and surface character (acidity vs. basicity). With this kind of basic knowledge it is anticipated that one can design greatly improved adsorption systems to control a wide range of atmospheric pollutants, including CO₂, freons, SO_x, and indoor air contaminants. Carbon particles measuring 130A to 1000A will be chemically functionalized and then reacted to form cross-linked structures. These macrostructural polymers will be examined in terms of their structural features, thermomechanical properties, and potential use as advanced filtration systems.

A new family of thermosetting resins based on aromatic copolyesters has been developed. These materials provide for the first time thermosets that retain 100% of their properties at 200C, are stable in air at 350C, and pick up minimal moisture. It has been shown that these polymers can be processed as adhesives, matrices for composites, and rigid foams with very low dielectric constants. The cured resins can also form strong adhesive bonds by interchain transesterification reactions at temperatures of 200 to 300C.

A broadly based program to develop improved matrices for advanced ceramic composites based on boron nitride is being pursued. The borozine oligomer used to form the boron nitride is also being examined as a precursor to BN in the form of a thin-film dielectric insulator as well as adhesion for high-temperature ceramics.

Single-crystal flakes of aluminum diboride in an epoxy matrix have been shown to yield outstanding planar mechanical properties far in excess of those achievable with graphite fiber epoxy composites. The current program is directed at exploring AlB₂ aluminum matrix composites to develop an understanding of the crystallization kinetics of the flakes, ability to process directly into shapes, and establishing the strength-limiting characteristics of such composites.

It has been shown for two families of flexible segment containing thermotropic main chain liquid crystal polymers, that chain-folded lamellae develop during crystallization from the liquid crystal state in quiescent and sheared thin films, annealed solution grown (folded chain) single crystals, and on the surfaces of bulk samples. Extended chain lamellae, when formed, are suggested as developing from a chain-folded morphology by sliding diffusion. Ultraquenching is being used to characterize the nematic state and the effect of crystallization from the glass. Electron diffraction has permitted characterization of the crystal structure, and transition behavior.

The morphology, crystal structure, and changes therein with temperature of a wide variety of homopolymer and both random and alternating copolymer lamellar (100A thickness) single crystals and single disclination domains have been characterized by electron microscopy and diffraction. Polymers include many rigid polyester LCPs, PET, PEN, Kevlar, Kapton, polyethers, and polyanhydrides. The high-temperature lattices for poly(p-oxybenzoate) and their relationship to the low-temperature lattices have been clarified. Crystal structures of many of the polymers have been determined by the use of electron diffraction aided by modeling. The polymers are prepared by a unique, low-temperature, confined, thin-film melt polymerization process.

Macrocrystals (up to 0.1 mm) of several liquid crystal homo- and copolymers have been prepared by a variation of the confined thin-film polymerization technique. They are composed of lamellae ca. 100A thick, presumably extended chain in nature, and all with a common alignment. Their chemical structure (alternating vs. random) and transition behavior are being characterized by infrared microscopy/thermal analysis for comparison with electron diffraction studies. Growth rates are being observed by hot-stage optical microscopy as a function of film thickness, temperature, and composition.

Polymerization of PpOBA in high-temperature solvents (300-350C) yields morphologies varying from single-crystal whiskers (up to 50 micro-m length) to hexagonal platelet crystals (2-5 micro-m thickness and up to 100 micro-m lateral size). Effects of time, temperature, concentration, and stirring have been characterized. The platelets are suggested to form by a mechanism similar to that described by Bassett (University of Reading) for extended chain platelets of linear polyethylene, i.e., transformation from a hexagonal columnar liquid-crystal state to an orthorhombic lattice. Electron diffraction is used to characterize the relative arrangement for the crystalline domains after the transformation.

The potential of using Illinois rapid growth wood stock and Kenaf as cellulose sources for a new pollution-free solvent-based spinning process is being examined. The molecular weight and crystallinity of alpha-cellulose purified from the various sources is being characterized. The morphology and properties of the solvent spun fiber is being compared to several current types of viscose rayons. Textile properties of fabrics prepared from the new and old rayons are being compared.

Electron diffraction patterns from the confined thin-film melt polymerized lamellar crystals and solution-grown whisker single crystals have been used for ab initio direct phasing crystal structure studies. Current emphasis is on poly(p-oxybenzoate) (phase I and II) and poly(terephthalate anhydride). Excellent agreement has been obtained for poly(p-oxybenzoate) in comparison to molecular Cerius² program.

It has, unexpectedly, been found possible to polymerize, e.g., poly(p-oxybenzoate) at temperatures as low as 130C, 70 degrees below the monomer melting point. The polymer formed consists of lamellae, ca. 100A thick, composed of extended chains. Rapid chain extension occurs on heating to the polymer's nominal T _k-m . Incorporation of glass fibers or polymer whiskers results in overgrowths with excellent adhesion; the molecules are normal to the plane, parallel to the whiskers. Applications as nanocomposites, normal composites, coatings, and adhesives are being explored.

Lamellar single crystals of PPTA (Kevlar) and several polyimides have been grown by our confined thin-film polymerization technique, permitting electron diffraction determination of the crystal structure ``correcting'' the unit cell described in the literature. The effect of temperature on this structure has been characterized by hot-stage electron diffraction, x-ray diffraction, and thermal analysis.

Electron microscopy and AFM are being used to examine the morphology of shape-persistent macrocycles based on phenylacetylene (PAMs). Solvent cast films consist of ribbons on the order of 1 micron in width and 200A thickness. Electron diffraction indicates the macrocycles pack normal to their plane parallel to the long axis of the ribbons, presumably forming nanotubular (8A diameter holes) parallel to the long axis, with a similar type of packing in Langmuir-Blodgett films. Phase changes and liquid crystal-line packing are being examined by hot-stage electron diffraction.

We have constructed a device for measuring forces be tween mica surfaces at controllable separations in the range of 0-5000A with a force resolution of ± 10µm and a distance resolution of ±1-2A, over a range of temperatures. Measurements can be made in liquid medium or in a controlled atmosphere. Intermolecular forces between a variety of surface-active polymers are being investigated. Recent experiments concern forces between polymers in shear.

A high polymer can adsorb tightly from solution to a surface even if its individual monomers do not, by virtue of a large aggregate free energy of sticking. The focus of experimental work has been to measure equilibrium effects. The dynamic aspects of polymer adsorption are not understood. In this work, polymer populations at a surface are measured by infrared spectroscopy. By measuring the kinetics of adsorption, desorption, and surface diffusion at well-characterized surfaces, our goal is to understand the dynamics of mass transfer in thin interfacial regions.

The objective of this research is to probe the tribology of polymer and surfactant boundary layers on a molecular level. We have developed new methods for measuring frictional forces between surfaces that are close to one another (a few angstroms), but not actually touching. With these methods, we measure the viscosity and static shear strength of liquids of thickness comparable to molecular dimensions.

When a high polymer is spread at a liquid surface to form a two-dimensional monolayer, a surface pressure exists that is analogous to the osmotic pressure characteristic of three-dimensional solutions. An oligomeric series of linear and cyclic polyphenylmethyl siloxanes with degrees of polymerization 30 to 300 has been prepared. An instance of two-dimensional phase separation at the water-air interface is being investigated, and comparison is being made with existing scaling theories.

The project revolves around the tribology of perfluoroether fluids under extreme but nonetheless well-defined conditions of shear rate and confinement. This will allow one to understand the surface chemical and rheological components of perfluoroether friction, as distinct from the classical ones that are rooted in the solid-solid contact. Interpretation from molecular viewpoints is emphasized.

This collaborative research between Exxon and the University of Illinois involves work in both laboratories. The conceptual objectives are to establish specific science connections beween microscopic observables and tribological properties of fluids at interfaces in chemically reactive environments. Specifically, we will integrate spectroscopic probes and rheological measurements in model asperity contacts.

Underway are systematic studies of surface-surface interactions based on the rational design of known protein and polymer interfaces. We are interested in the effects of peptide composition, electrostatic and hydrophobic properties, and especially conformations and specific interactions with polymers.

The adsorption of polymers with infrared-active vibrations in the skeletal backbone is studied by infrared spectroscopy in attenuated total reflection to give direct information about chain flattening through dichroic measurements. Of particular interest is the dependence of surface rearrangement rates on the surface coverage. History dependence is expected to be related to the high local density.

This work brings together two laboratories in university-industry cooperation to (1) employ a newly designed tribometer to examine energy dissipation at intermediate length scales, between molecularly thin films and the continuum limit and (2) integrated spectroscopic and newly designed tribological measurements to ``see'' what actually occurs at the interface while sliding takes place.

The goal is molecular-level understanding of fluid flow under extreme conditions of confinement. We are particularly interested in the case when the thickness of the confined film is so small that familiar bulk and continuum concepts no longer apply in the description of the equilibrium thermodynamic properties or in the dynamic re- sponse to shear. Of particular specific concern has been the linear shear response (in which measurement reflected the unperturbed dynamical structure) of aqueous electrolyte films of thickness <2nm, especially KCl and MgCl₂, and polyelectrolytes.

Microscopic statistical mechanical theories of diblock copolymer melts and solutions are being developed and applied to understand single-chain conformation, collective concentration fluctuations, small-angle neutron scattering measurements, and the molecular factors that control phase separation. The influence of chain branching, backbone stiffness, and intermolecular attractive forces on the order-disorder microphase separation transition of polyolefins have been determined. Excellent agreement with recent neutron scattering experiments has been demonstrated.

Microscopic theories of the dynamics of nonlinear macromolecular solutions and melts are being developed based on modern statistical dynamical methods. The mechanical response, diffusion, and conformational relaxation times of macromolecules modeled by fractal mass distributions are studied. Detailed applications to experimental systems such as polymer rods, macromolecular rings, and spherical microgel fluids are in progress.

M icroscopic integral equation theory methods are being developed to study the equilibrium properties of chain molecules near surfaces, between parallel plates, and in pores. A major goal is to understand the detailed influence of chain length, molecular architecture, and polymer-surface interaction in determining surface forces, density profiles, conformation, and intermolecular packing as a function of distance from the confining boundaries. Applications to solutions of rigid macrocycles have also been initiated. The unusual nonequilibrium and viscoelastic effects observed in confined fluids are also under investigation.

Microscopic theories for the conformation, structure, and dynamics of self-assembling multiblock copolymers and ionomers are being developed. The influence of block length and composition on long wavelength concentration fluctuations, microdomain formation, and phase separation temperature have been systematically explored. Application to address small-angle scattering and the microphase behavior of multiblock polyurethane melts have also been carried out.

Microscopic, off-lattice integral equation theories of dense p olymer mixtures are being developed and applied. The influence of density fluctuations, molecular architecture, and interchain forces on collective fluctuations, thermodynamic properties, interchain packing, and phase diagrams is being established via analytic and numerical approaches. Detailed applications to blends of hydrocarbon chains are being carried out and compared with small-angle neutron scattering measurements. The influence of concentration fluctuations on polymer conformation is also being studied.

A microphase theory of self and tracer diffusion in polymer blends and diblock copolymer solutions and melts has been developed. Long wavelength concentration fluctuations and microdomain formation are predicted to result in slowing down of diffusion and in enhanced entanglement coupling in a manner which depends on alloy composition, distance from the phase boundary, tracer and matrix poly mer molecular weight, and overall polymer density. Generalizations to treat chain dynamics, rheology, and dielectric response have been initiated.

This project investigates molecular conformation and phase structure in blends consisting of flexible polymers dissolved as guests in a liquid crystal polymer host. The experimental work involves measurements by broad-line proton NMR, polarized light microscopy, and differential scanning calorimetry. We have discovered that a number of polymers can acquire orientation parallel to the director axis of the liquid crystal polymer host. A very significant observation has been the guest's induction of liquid crystalline order in highly mobile (possibly isotropic) molecular segments of the host. This may be an example of liquid crystallinity induced by a binary interaction.

This project investigates the synthesis and properties of novel polymers containing paramagnetic organometallic structural units in their backbone structure. One of the systems synthesized is a copolymer of diamagnetic chemical sequences and paramagnetic units containing tetradentate copper II complexes. This system was found to form a liquid crystalline phase above its melting point and therefore acquires molecular orientation in the presence of an external magnetic field. At the present time we are studying both its orientation kinetics and solid-state structure. We are using the system's paramagnetic nature not only to study magnetic properties of organic polymers but also to probe cooperative phenomena.

This project investigates several systems that order spontaneously into specific microscopic patterns or molecular structures in the specific topologies. One system under investigation is the binary alloy of two chemically periodic nematic polymers. We are interested in this system's phase diagram and its microscopic patterns of phase separation. Other systems of interest are self-assembling monomers for the formation of molecular sheets, ladders, and combs.

This project investigates the synthesis of comb homopolymers and copolymers containing chiral centers in side chains. It is of interest here to study the ability of such polymers to form selective membranes for chiral separation. So far copolymers have been synthesized that exhibit smectic mesophases with phase transitions that can be controlled by achiral co-monomers.

Over the past few years our laboratory initiated research with the specific objective of focusing on the use of functionalized liquid crystal polymers as the molecular components on the interface. We succeeded in synthesizing a prototype system containing functions reactive toward surfaces and matrices. Interestingly, these self-ordering comb polymers were found to order spontaneously on the surfaces of carbon fibers over thousands of molecular layers. Very recently we have been able to place a ``single molecular layer'' of these polymers on a carbon surface and have observed the remarkable result that this mono molecular layer generates to macroscopic evidence of improved load transfer across a carbon fiber-epoxy interface.

This research focuses on the synthesis of new molecules and new molecular architectures of interest in the nonlinear optical phenomenon known as second harmonic generation (SHG). A system has been investigated that contains 2-D polymers synthesized in our laboratory. The 2-D architecture of polymer molecules in these films leads to excellent temporal stability of the noncentrosymmetric structure as required for SHG photonic materials. We have also discovered recently that a derivative of the precursor to these 2-D poly mers self-assembles into noncentro sym metric ``macroscopic'' films with remarkable second order susceptibility.

A synthetic pathway is described to construct ``in bulk'' 2-D polymers shaped as molecular sheets. A chiral oligometic precursor containing two reactive sites, a polymerizable group at one terminus and a reactive stereogenic center placed near the center of the molecule, is used. The 2-D molecular objects form through molecular recognition by the oligomers, which self organize into layers that place the reactive groups within specific planes. The oligomers become catenated by two different stitching reactions involving the reactive sites. This observation suggests that the transformation of common polymers from a 1-D to a 2-D architecture may produce generations of organic materials with improved properties.

We have synthesized a polymer consisting of a mono disperse, rod-like segment coupled to a monodisperse coil-like segment and have observed it to form microphase separated structures. The rod-like segment, an aperiodic sequence containing aromatic units, and the coil-like segment, polyisoprene, share the same molecular backbone. When not attached covalently to the coil, the aromatic rod-like segment forms a compound that melts into a liquid crystalline phase demonstrating the stiff segment's high aspect ratio. A film of the ``rodcoil'' polymer when cast from a selective solvent exhibits microphase separation, forming ribbons or strips as well as small aggregates that have dimensions in the range of the rod-like molecular segments.