Experiments were conducted in south Texas from 1983 to 1987 to evaluate clopyralid for huisache control using a carpeted roller. Huisache control with clopyralid applied as broadcast sprays or with a carpeted roller generally equaled that from the same rates of picloram or of 1:1 mixtures of clopyralid plus picloram. Applications of herbicides in the fall generally were more effective than in the spring, regardless of application method. In most cases, the herbicides at 48 to 60 g ae/L fall applied with a carpeted roller killed 70% or more of the huisache. Herbicide efficacy was not reduced when all huisache top growth was removed within 1 week after roller application of a 1:1 mixture of clopyralid and picloram at 60 g ae/L. The treat-and-cut sequence should improve the quality of hay from huisache-infested pastures.

Characterization of materials properties is critical for the understanding of materials behavior and performance under operating conditions. Tailoring materials properties, which are functions of the materials states, is essential for advanced product design. The need to characterize materials for a myriad of applications has spurred the development of many new methods and instruments. Unfortunately many of these characterization tools require destructive sectioning. Also many characterization techniques do not provide key information about material parameters in their operating environments. An ideal characterization tool would provide data about the material properties that are related to micro-and macrostructure without destructive sectioning. Such data can only be obtained using nondestructive-evaluation (NDE) methodologies. Therefore NDE is essential for almost any industrial product. Nondestructive evaluation has become an integral part of materials research because it enables the determination of material parameters (such as micro- and macrostructure, stress, physical properties, and defects) at nearly any point, line, surface, or volume element of interest and at nearly any state during the life of the material. Nondestructive evaluation is based on many different methods that rely on elastic waves, penetrating radiation, light, electric and magnetic fields, chemical sensing, etc. The large number of potential methods makes NDE not a single field but a synergism of many scientific and engineering disciplines. Since it would be impractical here to present all the new NDE methodologies with application to materials research, this issue of MRS Bulletin focuses exclusively on those ultrasonic techniques that are increasingly important in materials characterization.

“Fish-eye” particles consisting of metal clusters (Ag, Cu) a few nanometers in diameter encapsulated within a thin layer (-1 nm) of silica are produced using aerosol synthesis procedures. We present a method for predicting stable “fish-eye” nanostructures and describe synthesis techniques for producing significant quantities of silica-encapsulated metal nanoparticles.

For many metal/oxide pairs, gas phase formation of oxide encapsulated metal particles is thermodynamically favorable. Using known surface free energies and binary phase diagrams, it is possible to predict whether SiO2-encapsulated metal clusters will form in the gas phase. Two conditions which must be satisfied are: 1) that the surface free energy of the metal is higher than that of Si; and 2) that the metal composition in the particle is greater than the eutectic composition in the metal/Si phase diagram. Ag-SiO2 and Cu-SiO2 are two examples of systems which readily form “fish-eye” structures.

Two types of gas phase cluster sources are used at Purdue for producing encapsulated metal nanoparticles. The Multiple Expansion Cluster Source (MECS) is a well established apparatus which produces small quantities (- 50 mg/hr) of very uniform materials using resistive heating for evaporation. The new Arc Cluster Evaporation Source (ACES) offers much higher production rates (>1 g/hr) using DC arc evaporation. These two cluster sources make possible the study of a unique class of materials.

To develop optical power limiting thin films prepared from water-soluble materials, we have prepared chromophore-doped gelatin thin films. Thin films of gelatin were prepared by spin coating followed by annealing. We also prepared thin films doped with the water-soluble chromophore copper phthalocyanine sodium tetrasulfonate. The films were characterized by film profilometry and optical absorption spectroscopy. Optical power limiting measurements of these films, as well as comparisons with aqueous solution and gels were performed.

Series of molecules and polymeric systems are being evaluated as optical limiters for the design of a high second molecular hyperpolarizability γ. For example, results for a series of tolanes are discussed, as well as those of semi-flexible, stiff-chain polymers, including substituted biphenyl (X, Y = H, CH3, NO2, or a halogen atom) and benzo-bisthiazole moieties. The non-linear optical response was calculated using a finite field approach and compared for various derivatives.

To develop novel optical thin films, we have prepared self-assembled polypeptide films by an electrostatic process. The films were placed on a glass slide previously silanized by an amino silane and given a positive charge by immersion in aqueous acid. Subsequent immersion of the slide in aqueous anionic solutions of either poly(L-glutamic acid), congo red, copper phthalocyanine tetrasulfonic acid or p-nitroaniline-modified poly(L-glutamic acid) resulted in deposition of the anions on the surface. Following anionic immersion, the slides were dipped into a cationic poly(L-lysine) solution. Alternate dipping into anionic and cationic solutions yielded multilayers. The thin films were characterized by optical absorption and circular dichroism. The optical density increased with dipping cycles. Circular dichroism measurements of the thin films showed induced dichroism of the congo red and phthalocyanine-containing films, suggesting formation of a locally ordered dye-polypeptide complex. Solution circular dichroism measurements of the polypeptides indicated a coil conformation, while poly(Lglutamic acid)/poly(L-lysine) complexes showed circular dichroism spectrum characteristic of a β-sheet.

New polymers with exceptional properties are needed for applications in high-performance structures, novel electrical, optical and electro-optical devices, and for multi-functional smart materials. Concurrently, new computational capabilities and methods for properties prediction and analysis have enabled the study of a variety of polymer chain architectures to examine the principles that govern their high-performance properties. By semi-empirical and ab initio computational methods, flexible, stiff-chain, rigid-rod, and biological structures could be analyzed. Single chain molecular stress-strain curves for axial tension and compression were calculated, and the strain dependence of the molecular modulus and vibrational frequencies were compared to measurements of molecular deformation, such as IR and Raman spectroscopy. However, of special interest is the distinctly different response of alpha-helical biopolymer chains to strain. Indeed, in this study we compare on a theoretical basis the ‘spring-like’ microscopic mechanical response of alpha-helical biopolymers having a reinforcing intra-molecular hydrogen bonding network to analogous synthetic extended chain polymers, especially poly(para-phenylene terephthalamide) (PPTA) [KEVLARTM]. The theoretical verification of the absence of compressive buckling in alpha-helical biopolymer chains rationalizes the molecular elasticity and resistance to ‘kinking’ of those strands, manifested by the prevalence in Nature for coiled coils. The understanding of the structure-tofunction relationship in biopolymers explaining the role of the alpha-helix in these systems as a requirement for superior compressive mechanical properties, may enable new guidance for the synthesis of motifs consistent with molecular frameworks optimized by Nature.

In our continuing efforts towards the design of nonlinear (NLO) optical chromophore containing polypeptides we present an integrated computational approach, in which the design of biomolecular materials with defined secondary and tertiary structures is investigated by means of novel predictive tools, while the effects of the nonlinear optical chromophores are studied with molecular dynamics simulations. A neural network that was trained to predict the spatial proximity of Cα atoms that are less than a given threshold apart, is applied. The double-iterated Kalman filter (DIKF) technique is then employed with a constraints set that includes these pairwise atomic distances, and the distances and angles that define the structure as it is known from the protein's sequence. The results for test cases, particularly Crambin and genetically engineered Eglin-C, demonstrate that this integrated approach is useful for structure prediction at an intermediate resolution. Defined structural motifs of NLO chromophore containing polypeptides are investigated by using molecular dynamics techniques, particularly for the design of coil coiled amphiphatic biopolymers.

Results on the nonlinear properties of solutions of Buckminsterfullerene in toluene are reported. Optical limiting thresholds are as low as 15 mJ/cm2 with multiple pulse stability. Evidence for a different mechanism than that applicable in graphitic carbon black suspensions is presented. The calculated second hyperpolarizability agrees with experimentally reported values.

Molecular simulations that predict the molecular mechanical response of alpha-helical biopolymers with a reinforcing intra-molecular hydrogen bonding network, viz,, a ‘spring-like’ behavior, are presented in this study. Mechanical properties of extended biopolymer strands based on naturally occurring amino acids, namely poly(L-A1a) and for comparison poly(LGlu), versus synthetic PPTA containing an amide bond, are compared to those assuming alpha-helical structures. Thus, the pivotal role of such motifs in biological systems utilizing superior compressive mechanical properties can be inferred.

Recent advances in recombinant DNA technology have created the potential for engineering of protein molecules to specific uses beyond those normally considered for biomaterials. This research project has demonstrated the feasibility of producing polypeptides useful for narrow band filters and nonlinear optical applications.

Synthetic genes, ranging in size from 36 to 576 base pairs, have been constructed from oligonucleotides using a restriction doubling technique. The synthetic genes have been inserted into a Protein A fusion expression system. Fused polypeptides from induced cells have been purified by affinity chromatography (IGG), and analyzed by polyacrylamide gel electrophoresis.