bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluation of thin film Capacitors Fabricated from Heterogeneous Polypyrrole Based Langmuir-Blodgett Films
Authors: Rosner R. B. , Rubner M.F. 
Published: March 2011

ABSTRACTThe electrical properties of Langmuir-Blodgett films of conducting polypyrrole were investigated in an effort to illucidate the molecular architecture of these multilayer films and determine the mechanism of conduction. Values of the dielectric constant and transverse conductivity recorded as a function of frequency were determined from electrical measurements performed on devices made with the conductive polymer. The highly anisotropic nature of the conductivity as well as the frequency dependence demonstrated by both the conductivity and dielectric constant provide evidence for a highly ordered molecular structure in which the conductive and insulative components of the multilayer film form an organized, layered structure. Even greater control of the electrical and structural properties has been achieved through the fabrication of a thin film superlattice in which the conducting polymer and an insulating derivative were deposited as alternating bilayers. The properties of the superlattice were close to those predicted for an inhomogeneous, mixed media.
Heterocyclic Polymers and Copolymers with Controlled Optoelectronic Properties
Authors: Ruiz Jose P. , Nayak Kasinath , Child Andrew D. , Marynick Dennis , Reynolds John 
Published: March 2011

ABSTRACTA series of aromatic polymers and copolymers have been investigated that contain a combination of 2,5-thienylene and 1,4-phenylene linkages. l,4-Bis-(2-thienyl)phenylene monomers have been prepared with a variety of substituents on the 2,5-phenylene positions. Subsequent oxidative polymerization of these monomers, both chemically and electrochemically, yield a family of polymers containing a thiophene-phenylene-thiophene repeat unit. Theoretical modeling, using both PRDDO and ab initio methods, has been used to correlate the thiophene-phenylene torsional angles with band gaps. In addition, polymer band structure has been investigated using the Extended Hiickel method.
Optical Spectroscopy of the Charge Accumulation Layer in Mis Structures with Polymeric Insulator and Semiconductor Layers
Authors: Burroughes J. H. , Friend R. H. 
Published: March 2011

ABSTRACTMetal-Insulator-Semiconductor (MIS) and MISFET structures constructed with polyacetylene prepared by the Durham precursor route provide convenient systems for the investigation of charge storage and transport in this polymer. The charge accumulation layer is particularly easy to form, and is of particular interest because charge is introduced into the polymer without compensation by chemical dopants. Charge is stored in soliton-like excitations of the chain, and we are able to characterise these from optical measurements of their electronic excitations. We find that the nature of the soliton-like states is very sensitive to the structure of the polyacetylene at the interface between the insulator and polyacetylene, and we report here the properties of devices formed with various organic polymers as the insulator layers which we contrast with those formed with silicon dioxide.
The Effects of Conjugation Length and Substituents on the Conductivity of Oxidatively Doped p,p’-Disubstituted Diphenylpolyenes
Authors: Sapochak Linda S. , Polis David W. , Bain Art N. , Bryson Paul , Dalton Larry R. , Spangler C. W. 
Published: March 2011

ABSTRACTIt has been demonstrated that the oxidative doping of a.oo-diphenylpolyenes generates polaronic and/or bipolaronic intermediates which can be directly observed by optical spectroscopy. Furthermore, the absorption frequencies have been shown to correlate with conjugation length and the nature of the substituents. Species are stabilized by donor substituents and destabilized by acceptor substituents. We now report conductivity and ESR studies on iodine doped α,ω-diphenylpolyenes, containing donor p,p’-disubstituents. The implications of these studies can provide insight into electrical conductivity and optical nonlinearity of doped organic materials.
The Doping of Poly-P-Phenylene Sulfide and its Oligomers: a Spectroscopical Study
Authors: Piaggio P. , Giribone D. , Cuniberti C. , Dellepiane G. 
Published: March 2011

ABSTRACTIt is shown that the spectra of poly-p-phenylene sulfide doped at low doping level with different doping agents exhibit features similar to those already observed in polyacetylene and can be qualitatively interpreted in terms of the Amplitude Mode Theory.
Ferroelectricity of Chiral Compounds in Highly Ordered Smectic Phases
Authors: Wróbel Stanisław , Pfeiffer Matthias , Biradar Ashók M. , Haase Wolfgang 
Published: March 2011

ABSTRACTMeasurements of the complex electric permitttivity for the Sm C* and for three highly ordered smectic phases: Sm I*, Sm J* and Sm K* of 4- (2 - methylbutyl)-phenyl-4′-(octyloxy)-(1,1′)-biphenyl-4-carboxylate (8 OSI) have been done in the frequency range from 5 Hz to 13 MHz. For the first three chiral phases the Goldstone mode was found with temperature independent critical frequencies, νc = 1.5kHz and the relaxation time τG = 106 μs - for the Sm C* phase, and νc = 1 kHz and τG - 160 μs - for the Sm I* one. In two highly ordered smectics, i.e. Sm J* and Sm K* with inter-layer correlations, the Goldstone mode seems to be suppressed. By applying a D.C. bias field of 1.4 kV/cm the Goldstone mode has been suppressed and shifted towards higher frequencies in both the Sm C* and Sm I* phase. For the Sm J* phase the Goldstone mode is very weak and practically insensitive to the bias field used. In the Sm K* phase there is no Goldstone mode like relaxation, and the only contribution to electric permittivity comes from the fast molecular motion connected with reorientation of molecules about their long axis.
Langmuir-Blodgett Films of Potential Unidimensional Organic Rectifiers
Authors: Metzger Robert M. , Panetta Charles A. 
Published: March 2011

ABSTRACTThe progress of the Organic Rectifier Project (ORP) is reviewed. Several molecules of the type D-σ-A (D=organic one-electron donor, σ = covalent saturated bridge, A = organic one-electron acceptor) have been synthesized, to test the Aviram-Ratner Ansatz that they could be one-molecule thick rectifiers of electrical current. Many of these molecules (σ= urethane) self-assemble as Langmuir-Blodgett films; the cyclic voltammetry peaks confirm that these molecules preserve the good D and A characteristics. Calculations confirm that the zwitterionic state D+-σ-A- is much below the state D-σ-A+, as expected. Preliminary tests of electrical rectification have failed. With the installation of a new scanning electron microscope, the Aviram-Ratner Ansatz will soon be put to a final and definitive test
Effects of Molecular Rigidity on Electric Field Induced Alignment and Orientational Stability of Dipolar Chromophore Composites
Authors: Katz H. E. , Schilling M. L. , Washington G. , Dirk C. W. , Holland W. R. , Fang T. , Singer K. D. 
Published: March 2011

ABSTRACTThe relationship between the supramolecular conformational structure of assembled chromophores and their susceptibility to electric field poling is of interest for maximizing the bulk alignment achievable in an electro-optic material. We have employed solution phase dielectric constant measurements to investigate possible enhancements in dipolar susceptibility as a function of connectivity and state of aggregation in rationally synthesized chromophore assemblies, including conformationally defined head-to-tail oligomers. On the other hand, conformationally unrestricted, highly dipolar azo dyes behave as relatively isolated molecules even when present in supersaturated solutions and in close proximity on polymer chains.
Investigations of a New Reversible Strain Induced Chromic Transition in Polydiacetylene Elastomers
Authors: Nallicheri R. A. , Rubner M. F. 
Published: March 2011

ABSTRACTIn-situ visible dichroism/tensile elongation studies of segmented polyurethanes containing conjugated polydiacetylene chains within their hard segment domains have revealed a new reversible mechanochromic transition that manifests itself as a color change from blue to yellow during tensile elongation. This unusual strain induced transition, found in an elastomer whose hard segment structure is derived from hexamethylene diisocyanate and 5,7-dodecadiyne-l,12 diol, closely resembles the thermochromic transition also exhibited by this same material. The color change and the associated shift in the position of the polydiacetylene absorption band to higher energies is not simply an order-disorder transition but reflects a strain induced reorganization of the hard domain structure. It has been found that this blue to yellow transition is reversible as long as the material is not strained beyond about 300%. This represents the first reversible, mechanically induced chromic transition in a cross-polymerized diacetylene containing polymer.
Electronic Structures and Nonlinear Optical Properties for Cross-Conjugated Polyene
Authors: Mori Yuhei , Okano Yoshimichi 
Published: March 2011

ABSTRACTFor several cross-conjugated molecules, molecular excited states and third-order nonlinear susceptibilities γ are calculated by semi-empirical molecular orbital method. The calculated γ are compared with each other and the reason for the differences are discussed in terms of the orbital shapes which contribute mainly to γ. The reason that long polyene chains have large γ, is ascribed to the large transition moment which is explained by the signs of the LCAO coefficients. On the other hand, it is found that the cross-conjugated molecules in which two similar-length chain cross at the center is not good for large third-order susceptibility.
Ontogenetic and Phylogenetic Variation of Form and Function of the Ocular Lens
Authors: Sivak J. G. 
Published: March 2011

AbstractThe crystalline lens of the eye is a unique optical structure that continues to develop within the eye throughout life. This process of development results in the formation of a lens with a gradient refractive index that has important optical consequences, particularly in the control of spherical aberration. The optical characteristics of the vertebrate crystalline lens are reviewed in terms of environmental concerns and spherical aberration. Lens shape and relative size are determined by such factors as whether the eye is to be used in air or water and whether it is to be used under scotopic or photopic conditions. The continued growth of the lens through life can be related to whether the lens exhibits positive or negative spherical aberration. In general, spherical aberration, as measured using a split laser beam method with excised lenses, is minimized in species with life histories indicating superior resolution ability. In addition, lens optical quality, as indicated by zonular differences in focal length, deteriorates with lens age. While the embryonic and post-embryonic lens undergoes significant change in size, shape and refractive index distribution, it appears that focal constancy is maintained, at least in certain species. This finding may indicate a means of simplifying the process of emmetropization.
Bending, Folding, and Buckling Processes During Bacterial Macrofiber Morphogenesis
Authors: Mendelson Neil H. , Thwaites John J. 
Published: March 2011

AbstractBacterial macrofibers are multicellular structures produced by certain cultures of rod-shaped cells when cells do not separate from one another after septation. Chains of cells arise that twist as they grow. This twisting is thought to reflect either the geometry of assembly of the cell wall polymers or some aspect of their anisotropic behaviour after insertion into the wall. The degree and direction of twisting is controlled by genetic and physiological factors such as growth temperature and the concentration of certain ions and other compounds in the growth medium. Twisting is ultimately responsible for a shape deformation of the cells into double-strand helical forms. The mechanical basis for shape determination and eventually macrofiber morphogenesis involves a folding process, the touching of elongating structures to themselves, blocked rotation, and shape deformation. In normal growth medium, time-lapse films reveal that writhing motions which lead to increased bending result in touching. In media of increased viscosity, bending is suppressed although elongation and rotation are unaffected. Folding occurs but now as a result of buckling. The forces responsible for both processes derive from g–, wth and interaction of the cell surface with the growth medium. The helical shape, once established, is heritable. Whether the shape becomes “set” by cross-linking or other modification of the peptidoglycan remains to be determined. From the perspective of materials science, macrofibers represent a new biodegradable fiber, the mechanical properties of which are governed by cell wall peptidoglycan. Both peptidoglycan and the other major cell wall polymer, teichoic acid, contain many reactive groups to which new constituents can be attached. Thus, there is now the potential to create a range of new materials using bacterial cells as the structural backbone.
Enzymatic Synthesis of Alkyds
Authors: Geresh Shimona 
Published: March 2011

AbstractThis paper describes the application of lipase-catalyzed polytransesterification to the preparation of two series of unsaturated “all trans” polyesters (alkyds): in the first series the starting materials were diesters of fumaric acid and 1,4-butane diol, and in the second, bischloroethyl fumarate and aromatic diols (benzene dimethanol and derivatives of bisphenol A). Most of the reactions were carried out in tetrahydrofuran and acetonitrile. As opposed to the extensive isomerization which occurs during the synthesis of unsaturated polyesters by chemical polycondensation, no isomerization of the double bond was found under the mild conditions of enzymatic catalysis. The “all trans” character of our alkyds was determined by nmr spectroscopy, and average molecular weights and dispersivity were measured by gel permeation chromatography. The average molecular weight was found to vary with the solvent. In acetonitrile a relatively high-melting point alkyd was obtained (m.p. 106–108°C), with low solubility in conventional solvents. Powder X-ray diffraction and SEM analyses revealed crystaUinity and layer-type structures.
Characterization and Structure of Mussel Adhesive Proteins
Authors: Laursen Richard A. , Ou Jung-Jung , Shen Xiao-Tong , Connors Michael J. 
Published: March 2011

AbstractMany marine animals such as mussels and barnacles are able to anchor themselves to surfaces through the use of proteinaceous adhesives, which have the unique ability to form strong bonds in a wet environment. With eventual goal of developing wet-surface adhesives, we have carried out gene sequencing studies, using three species of mussel, in order to learn what structural characteristics give these proteins their special properties. Two classes of protein are revealed. Both are characterized by containing about 20% each of lysine and of tyrosine (or DOPA). However, the proteins fromMytilus edulis and Mytilus californianusconsist primarily of tandem repeats of variations of the proline-rich decapeptide sequence, AKPSYPPTYK, while the protein fromGeukensia demissais rich in glycine and glutamine and is comprised of 11- and 13-residue variants, e.g., GKPTITYDAGYK, GQQKQTGYDTGYK and GGVQKTGYSAGYK. We propose that the repeat domains have definite folded structures, if not in solution, at least in the condensed (crosslinked) state that gives them their distinctive properties. In this respect, the mussel proteins may resemble collagen, which has both secondary structure and adhesive properties.
New Carbohydrate-Based Materials
Authors: Callstrom Matthew R. , Bednarski Mark D. , Hill Tara G. , Oehler Lynn M. , Gruber Patrick 
Published: March 2011

AbstractThe polymerization of a series of new monomers composed of carbohydrates functionalized with polymerizable side-groups gave high molecular weight water-soluble materials. The preparation of the monomers using both chemical and enzymatic methods allowed complete stereo- and regiochemical control of the composition of the monomers.
The Genetic Production of Synthetic Crystalline Protein Polymers
Authors: Cappello Joseph , Crissman J. , Dorman M. , Mikolajczak M. , Textor G. , Marquet M. , Ferrari F. A. 
Published: March 2011

AbstractGenetic and protein engineering are components of a new polymer chemistry which provide the tools for producing macromolecular polyamide copolymers of diversity and precision far beyond the current capabilities of synthetic polymer chemistry. The genetic machinery allows molecular control of chemical and physical chain properties. Nature utilizes this control to formulate protein polymers into materials with extraordinary mechanical properties such as the strength and toughness of silk and the elasticity and resilience of mammalian elastin. The protein chains which make up these fibers consist of extensive repeating oligopeptide sequences. By producing synthetically designed protein chains containing many tandem repeats of only one repetitive sequence block (homoblock polymers), we are able to evaluate the inherent contribution of each repeat to the overall material properties. Using biotechnology, we produced homoblock protein polymers consisting exclusively of silklike crystalline blocks in quantities sufficient for material evaluation studies (10–100 grams). Silk-like homoblock polymers, as produced by microbial fermentation, exhibited measurable crystallinity both in solution and in solid state. The chain properties of the homoblock polymer were changed by adding blocks of amino acids designed to contribute different structural or functional properties. We produced alternating copolymers of various amounts of silk-like and elastin-like blocks ranging from a ratio of 1:4 to 2:1, respectively. The crystallinity of each copolymer varied with the extent of crystalline block interruption. The substitution of the elastin block with one containing the amino acids from human fibronectin responsible for mammalian cell attachment, produced a highly active silk-like copolymer with biological activity. The ability to specifically engineer the mechanical and functional properties of a fiber material is a potential outcome of this technology.
High Compressive Strength Ordered Polymer Fibers and Films Via Sol Gel Microcomposite Processing
Authors: Kovar Robert F. , Lusignea Richard W. , Haghighat R. Ross , Pantano Carlo , Thomas Edwin L. 
Published: March 2011

AbstractSol-gel glass microcomposite processing of polybenzobisthiazole (PBZT) films increased the compressive strength of PBZT/PEEK film laminates by more than four times. The presence of glass within microfibrillar regions of PBZT/sol-gel glass microcomposite films inhibited microbuckling during compression and greatly increased resistance to compressive failure.Studies of PBZT/sol-gel glass microcomposite film morphology conducted at UMass by E.L. Thomas and at Penn State by C. Pantano indicated sol-gel glass precursor solutions had condensed within PBZT to produce a fine-scale (100 to 300Å) granular structure, homogeneously distributed throughout PBZT lamellae of microfibrils.In a parallel effort, we have successfully extended sol-gel microcomposite processing technology for the improvement of compressive strength in ordered polymer fibers. Details concerning our results will be discussed.
The Influence of Sol-gel Glass Technology on Coherent and Partially Coherent Optical Imaging Systems
Authors: Phillips Nicholas J. 
Published: March 2011

AbstractThis paper addresses developments in the understanding of intra-cavity elements in ion lasers using sol-gel prepared silica. Growing interest centres around the generation of coherent light in the near u.v. spectrum. Sol-gel silica offers unprecedented levels of purity and homogeneity for critical intra-cavity applications and may well solve the problem of creating colour-centre free Brewster windows for use in the u.v.We also report new work which makes use of the porous phase of such material and show how it is directed at one of the early bastions of photographic science – Lippmann's photography.
Multifunctional Silica Optics
Authors: Hench L. L. , Fosmoe A. 
Published: March 2011

AbstractThe sol-gel chemical processing method of producing fully dense silica optics provides an intermediate product termed Type VI silica ideally suited for use in engineering multifunctional silica optics. This paper reviews the sol-gel process, the Type V dense gel-silica produced by this process and the Type VI ultraporous gel-silica intermediate product. Included is a comparison of two different porous ultrastructures with 1.2 nm and 8.0 nm average pore radii. Two uses of the porous gel-silica components as multifunctional optics are described. The first is for use in transpiration cooled windows in highspeed rocket guidance systems. Flow rates of He and N2 through the 1.2 nm and 8.0 nm ultrastructures are as high as 0.9 m/min at 0.75 MPa. High temperature UV transmission in contact with an impinging oxy-acetylene flame is demonstrated. Use of Type VI gel-silica as a host matrix for fast radiationhard scintillating detectors is also reviewed.
Magnetic Properties of Liquid Crystals Incorporating Metal Centres
Authors: Haase Wolfgang , Gehring Stefan , Borchers Bettina 
Published: March 2011

AbstractMagnetic susceptibility data (300–520 K) of monomeric and dimeric mesogenic copper(II) compounds are presented. Different magnetic effects arising from the paramagnetic Cu(II)-centres and the diamagnetic anisotropy of the mesogenic groups are observed and discussed with respect to possible inter molecular interactions.
Microstructural Control in Side Chain Polymers for Optical Applications
Authors: Findlay Rob , Lemmon Tim , Windle Alan 
Published: March 2011

AbstractCharacterisations of side chain liquid crystalline polymers point towards chemical structures and processing techniques which optimise their suitablility for non-linear optical (NLO) applications. Techniques used are thermal analysis, X-ray and hotstage polarised light microscopy (orthoscopic and conoscopic).
Behavior of Superconducting Ceramic-Polymer Composite
Authors: Vipulanandan C. , Salib S. 
Published: March 2011

AbstractPoly (methyl methacrylate) (PMMA) was used to improve the flexural properties of the high temperature superconducting ceramics (YBa 2Cu3O7-x). The organic polymer was impregnated into the porous ceramic at room temperature. The flexural properties were evaluated using disk specimens. The interaction between the PMMA and ceramic was studied using electron probe microanalysis (EPMA). Poly (methyl methacrylate) polymer increased the flexural strength of the superconducting ceramic without affecting its electrical properties. Flexural strength relationships have been developed for the superconducting ceramic with and without polymer. Performance of the ceramic-polymer composite was also evaluated by thermocycling between 77k and 300k.