Activated Carbon Fibers
J. Economy,* C. Mangun, K. Benak, L. Dominguez, Z. Yue
National Science Foundation, DMR 92-08545

Fundamental studies aimed at understanding the mechanism of adsorption and desorption of contaminants in activated carbons are being pursued. These include 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, SOx, and indoor air contaminants. Use of such fibers as substrates for a wide range of catalytic processes is actively being explored. Design of new kinds of fibers such as high surface area SiC fiber and ion exchange fibers is being pursued.Under a DARPA grant, DABT-63-98-C-0053, fabrication of specially tailored activated carbon fiber assemblies is underway with the goal of removing highly toxic materials from drinking water.

High-Temperature Adhesives and Matrices
J. Economy,* A. Hall, K. Xu, A. Lopez
Motorola/Morton/DARPA/Allied Signal

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 200°C, are stable in air at 350°C, 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 solid-state interchain transesterification reactions at temperatures of 200° to 300°C. It has been shown that composites can be fabricated by solid-state processing techniques, greatly simplifying current processes for preparing components. A new approach to a low-cost, high-module polyester fiber has been devised.

Improved Ceramic Composites
J. Economy,* S. Seghi
National Science Foundation, DMR 95-25735

A broadly based program to develop improved matrices for advanced ceramic composites based on boron nitride is being pursued. The borazine 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.

Metal Matrix Single-Crystal Flake Composites
J. Economy,* A. Hall
University of Illinois

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.

Structure of Condensation Polymers
P. H. Geil,* G. Sidoti, J. Yang, A. Pederson, J.-I. Jin* (Korea Univ.); F. Rybnikar* (Univ. of Brno, Czech Rep.)
National Science Foundation, DMR 96-16255; Kosef; GACR

The morphology, crystal structure, and changes therein with temperature of a wide variety of homopolymer and both random and alternating copolymer lamellar (100Å thickness) single crystals and single disclination domains have been characterized by electron microscopy and diffraction. Polymers include many rigid polyester LCPs, PET, PBT, 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.

Morphology of Nascent Polytetrafluoroethylene Dispersion Particles and the Effects of Melt Time and Temperature
P. H. Geil,* J. Yang
W. L. Gore and Associates, Inc.

The morphology of PTFE dispersion particles, prepared by different polymerization schemes, is being characterized by bright and dark field transmission electron microscopy. Examination of the effects of melt time and temperature on the development of folded chain single crystals from dispersed dispersion particles on glass and mica substrates indicates an intermediate step of the formation of "large" angular crystals. Significant molecular motion on the substrate occurs in the melt state.

Phase I-Phase II Compositions of Melt and Solution Polymerized Poly(p-oxybenzoate)
P. H. Geil,* B. L. Yuan; F. Rybnikar and P. Saha (Univ. of Brno)
National Science Foundation, DMR 96-16255; Granting Agency of the Czech Republic

Polymerization of PpOBA in high-temperature solvents (300-350°C) yields morphologies varying from single-crystal whiskers (up to 50 mm length, 360°C Tk-m) to hexagonal platelet crystals (2-5 mm thickness, up to 100 mm lateral size, 320°C Tk-m). Effects of time, temperature, and concentration on the morphology and the phase I-phase II crystal structure ratio have been determined; the variation in Tk-m cannot be attributed to the phase composition. The composition of PpOBA melt polymerized in thin films is affected by the substrate; base treatment of both mica and glass result predominantly in phase II.

Processing and Structural Characterization of Zein-Base Films
P. H. Geil,* G. Padua (Food Science), M.-C. N'Guyen
Illinois Council on Food and Agriculture Research

Zein, a protein from corn, plasticized with oleic acid has been shown to be suitable for the production of thin films of potential application as packaging. Optimization of the properties is being sought by variations in processing techniques (including protein unfolding, orientation, and crosslinking as well as typical plastics film production processes). Structural characterization by WAXS and SAXS of orientation, molecular conformation, and morphology is being carried out to aid in the process improvement.

Collagen Fibril Characterization
P. H. Geil,* A. Pederson
Industrial Technology Research Institute, Taiwan

The morphology, molecular packing, and orientation of collagen fibrils in samples of potential use in and as artificial skins is being characterized by transmission electron microscopy and WAXS and SAXS.

Molecular Tribology of Perfluoropolyether Films
S. Granick,* T. Dellinger
U.S. Air Force Office of Scientific Research, F49620-97-1-0432

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.

Molecular Tribology of Confined Hydrocarbons and Lubrication Additives
S. Granick,* M. Drake, M. Ruths
Exxon Research and Engineering Corp.

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.

Polymer-Peptide Interactions for Biocompatibility Applications
S. Granick,* S. Sukhishvili
Engineering Foundation

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.

Nanorheology in Fine Powder Flow
S. Granick,* S. Sukhishvili
International Fine Particle Research Institute

Systematic studies are underway of particle-particle nanorheology based on the concurrent measurement of static and dynamic forces in both the shear and normal directions. This is relevant to an enormous range of fine powder applications based on rheological properties in an environment that is not dry (among them fluidization and rapid shear flow in riser reactors, segregation processes, and mixing and pneumatic conveying).

Molecular Tribology in the Biomaterials Environment
S. Granick,* T. Dellinger
National Science Foundation (Tribology Program)

Nanotechnology with Emphasis on Tribology
S. Granick,* Y. Zhu, M. Ruths
National Science Foundation, subgrant R9915-.01.01 from University of Tennessee

This multidisciplinary, multi-institutional collaboration (University of Illinois, University of Tennessee, Sandia National Laboratory) has several goals. The first is to achieve overlap in shear rate between experiments and simulations with the same systems. The second is to expend experimental and computational study to surfaces with chemical and topographical heterogeneity.

Polymer Fillers and the Role of Interfacial Rheology
S. Granick,* A. L. Demirel
National Science Foundation (International Programs)

In this collaborative effort, we study the role of polymer-solid interfacial interactions by relating measurements on model systems (at the University of Illinois) with measurements of systems of immediate practical importance (Koc University, Istanbul, Turkey). Variables of interest include polymer molecular weight, degree of crystallinity, and intensity of polymer-filler interaction.

Molecular Studies of Boundary Layer Lubrication
S. Granick,* H. Ohtani
Ford Motor Co.

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 effective viscosity and shear strength of liquids of thickness comparable to molecular dimensions.

Studies of Perfluoropolyalkylether Lubrication
S. Granick,* A. Koike, M. Ruths
Hitachi Corp.

The hard disc drives used for information storage are lubricated by perfluoropolyalkylether molecules of various molecular weights and chain-end functionality. In this university-industry collaborative project, we study systematically the role of chain-end functionality, especially polarity and surface packing.

Dielectric Studies of Confined Polymers
S. Granick,* Y.-K. Cho, S. Jeon
Petroleum Research Fund, American Chemical Society

This research focuses upon dielectric relaxation of high polymer chains confined to molecularly thin spacings. In situ dielectric measurements of normal-mode relaxation are made for homopolymer melts and diblock copolymer adsorbed brushes. The significance is to provide, by measurements of a kind that have not been made previously, a valuable perspective from which to understand the motions and relaxations of confined polymers.

Structure of Multiblock Copolymers and Ionomers
K. S. Schweizer,* K. Kolbet
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

Microscopic theories for the conformation and structure 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 and ionomer melts have been carried out. The role of water, nonpolar solvents, and blending with homopolymers on ionomer structure physical clustering and bulk properties are of interest.

Equilibrium Theory of Polymer Blends and Solutions
K. S. Schweizer,* A. P. Chatterjee, T. M. Chang
U.S. Department of Energy, Basic Energy Sciences; Oak Ridge National Laboratory (In cooperation with the Materials Research Laboratory)

Microscopic, off-lattice integral equation theories of dense polymer mixtures are being developed and applied. Detailed applications to blends of hydrocarbon chains are being carried out and compared with small-angle neutron scattering measurements. Generalizations of the theory to treat specific interactions, lower critical solution type phase separation, and the blend equation-of-state are being pursued. Multicomponent alloys consisting of both homopolymer and block copolymers are being studied with the goal of understanding the role of local chain stiffness and cohesive forces on the competition between macrophase and microphase separation.

Dynamics of Self-Assembling Polymer Alloys
K. S. Schweizer,* M. Guenza
U.S. Department of Energy DE-FG02-96ER45439; University of Oregon (In cooperation with the Materials Research Laboratory)

A microscopic statistical dynamical theory of self and tracer diffusion in 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 polymer molecular weight, and overall polymer density. Generalizations to treat chain dynamics, rheology, and dielectric response are also under study.

Structure and Phase Behavior of Polymer-Colloid Suspensions
K. S. Schweizer,* M. Fuchs
German National Science Foundation, DFG

Microscopic liquid state theories of mixtures of polymers and colloids are being developed. The role of macromolecular structure, colloid size, composition, and intermolecular interactions on equilibrium properties are being systematically explored. Polymer-induced crystallization of colloidal suspensions is being addressed with thermodynamic density functional methods. The influence of polymer/particle size asymmetry and solvent quality on liquid-gas type phase separation and the particle percolation transition are also under study.

Macromolecule-induced Interactions between Spherical Particles
K. S. Schweizer,* A. P. Chatterjee
U.S. Department of Energy, DE-FG02-96ER45439; Oak Ridge National Laboratory (In cooperation with the Materials Research Laboratory)

Microscopic statistical mechanical theories of the structure and thermodynamics, dilute suspensions of spherical particles in polymers solutions are being developed. The particles may be nanometer-sized proteins or micelles, larger objects such as dendrimers, or micron-sized colloids. The complex influences of particle size, polymer concentration and molecular weight, and steric and specific attractive forces on equilibrium properties are under study. Specific applications to protein-water soluble polymer suspensions and rigid rod polymer solutions are of particular present interest.

Liquids of Branched Marcomolecules
K. S. Schweizer,* T. M. Chang
U.S. Department of Energy, DE-FG02-96ER45439; Oak Ridge National Laboratory (In cooperation with the Materials Research Laboratory)

The structure and thermodynamic properties of many arm star, "core-shell" soft colloids and other highly branched macromolecular fluids are being studied with microscopic statistical mechanical theory. Such systems display unusual equilibrium and dynamic behavior because of the intermediate degree of interpenetration of different macromolecules. Understanding the phase behavior of alloys of such highly branched macromolecules with linear chains is also under study in order to provide molecular-level guidelines for controlling miscibility.

Anisotropic Polymer Fluids
K. S. Schweizer,* G. T. Pickett
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

Novel liquid state integral equation theories of fluids composed of polymers with spatially anisotropic conformations are being developed. A new mechanism for nematic and dissotic liquid crystal formation in flexible and semiflexible polymer fluids has been discovered. Generalizations to treat the influence of attractive cohesive forces and rigid rod polymers are underway. Predicting the anisotropic structure of confined polymer thin films is also possible with the new approach.

Molecular Reinforcement of Polymers
S. I. Stupp*
3M Co.

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.

Paramagnetic Organometallic Polymers
S. I. Stupp,* W. Mahoney
U.S. Department of Energy, DE-FG02-96ER01198 (In cooperation with the Materials Research Laboratory)

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.

Self-ordering Polymers
S. I. Stupp,* M. Osuga
University of Illinois

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.

Chiral Polymers
S. I. Stupp*
Monsanto Co.

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.

Molecularly Engineered Composite Interfaces
S. I. Stupp,* V. LeBonheur
Center for Composite Materials Research, ONR N00014-86-K-0799

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 monomolecular layer generates to macroscopic evidence of improved load transfer across a carbon fiber-epoxy interface.

Nonlinear Optical Polymers
S. I. Stupp,* L. S. Li, H. C. Lin, S. Son, K. Huggins
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

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 polymers self-assembles into noncentrosymmetric "macroscopic" films with remarkable second order susceptibility.

Synthesis of Two-dimensional Polymers
S. I. Stupp,* M. S. Lee, L. S. Li, M. Keser
National Science Foundation, NSF 93-12601; Monsanto Corp.

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.

Rodcoil Polymers
S. I. Stupp,* L. H. Radsilowski, J. L. Wu, K. Walker
National Science Foundation, NSF 15-30799 (In cooperation with the Materials Research Laboratory)

We have synthesized a polymer consisting of a monodisperse, 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.