bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies on the Formation of Switching and Memory Storage Materials Constructed from Metallo-Organic Charge-Transfer Complexes
Authors: Duan Hailing , Cowan Dwaine O. , Kruger Jerome
Published: March 2011

Electrochemical measurements have been employed to study the formation process of the charge-transfer complexes Cu+TCNQ−,a switching and memory material, in a saturated TCNQ/CH3CN solution. These studies show that the Cu/Cu+TCNQ−(s), TCNQo(CH3CN) system is an active-passive system corroding under diffusion control. A possible mechanism of localized corrosion-crystallization is proposed for the formation of a Cu+TCNQ− film in an acetonitrile solution
Physical Characterization of Organic Radicals by Low-Field Epr Spectrometry
Authors: Moussavi Mehdi , Beranger Marc , Duret Denis , Kernevez Nelly , Secourgeon Liliane
Published: March 2011

A low-field (0.6 Gauss, 2 MHz) EPR spectrometer providing quantitative parameters is described. It gives informations such as frequency dependence of the linewidth, anisotropy of inhomogeneous line and also the values of T1, T2 and the magnetic susceptibility using simple hypothesis.

The behaviour of different typical π-systems, as well metallic as semiconducting is compared to a radical anion salt, quinolinium bis tetracyano-quinodinemethane Qn(TCNQ)2 considered as a reference.

The materials physical characteristics will be provided by a new variable field (0.6–60 Gauss, 2–200 MHz) which is under realization, for an extended family of organic radicals.
New Electrically Conducting Solids based on Nickel (II) - Bis(1,3-Dithiole-2-Thione-4,5-Diselenolate)
Authors: Kini A. M. , Beno M. A. , Budz S. , Wang H. H. , Williams J. M.
Published: March 2011

Electrochemical oxidation of the metal-organic complex, nickel(II)–bis(1,3-dithiole-2-thione-4,5-diselenolate) or simply [Ni(dsit)2]2−, yields highly conducting salts, in which the stoichiometry and packing arrangement depends critically on the size of the counter-cations incorporated. Smaller counter-cations, e.g., tetramethylammonium and tetramethylphosphonium ions, yield salts with a 1:2 cation:[Ni(dsit)2] stoichiometry, while the larger tetraethylammonium ion yields a salt with 2:2 stoichiometry. In both these salts, the [Ni(dsit)2] units occur as tightly bound dimers, in which the coordination geometry of nickel is a unique, but not unprecedented square-pyramidal type. Moreover, the packing arrangement of [Ni(dsit)2]2 dimer units in both (Me4N)[Ni(dsit)2]2 and (Me4P) [Ni (dsit)2]2 is κ-type, similar to that found in the organic superconductor with the highest-known Tc (10.4 K), κ-(BEDT-TTF)2Cu(NCS)2. Both these salts possess good room temperature conductivities (σrt = 36 and 19 S.cm−1 respectively), but the temperature dependance of their conductivities is characteristic of semiconductors with small bandgaps (Eg = 0.11 and 0.13 eV, respectively). The 2:2 salt (Et4N)2[Ni(dsit)2]2, on the other hand, has a substantially lower room temperature conductivity, about six orders of magnitude smaller than that of the 1:2 salts. Its structure is characterized by [Ni(dsit)2]2 dimer units which are separated from each other by the tetraethylammonium cations, with no effective interaction between [Ni(dsit)2]2 dimers. It is suggested that dimeric metal-dithiolene and metal-diselenolene complexes may be potential building blocks in the structural design of κ-type organic conductors and superconductors.
Discotic Liquid Crystalline Porphyrins: Photophysical and Photoelectrical Properties of Large-Area Crystalline Films
Authors: Gregg Brian A. , Fox Marye Anne , Bard Allen J.
Published: March 2011

Porphyrins exhibiting discotic liquid crystalline phases have been developed in order to prepare thin, large-area, crystalline films of molecular conductors. A series of octaalkylporphyrins bearing different side chains have been synthesized including some with electron-withdrawing substituents at the meso positions. The photophysical properties of thin films of these compounds are a strong function of the film order (crystallinity). A substantial and persistent photovoltaic effect was achieved (e.g., Voc = 0.3 V, jsc = 0.4 mA/cm2 under white light, 150 mW/cm2) in capillary-filled symmetrical cells with indium-tin oxide electrodes. A model based on kinetically-controlled asymmetric exciton dissociation leading to photoinjection at the illuminated interface is presented to explain these results. This appears to be the first unambiguous example of a photovoltaic cell controlled entirely by interfacial kinetics. The predominance of the photoinjection process in these cells is attributed to the single-crystal-like character of the porphyrin films.
Sound Velocity Study of Bechgaard Salts (TMTSF)2PF6 and (TMTSF)2ClO4
Authors: Shi X. D. , Chiang L. , Upasani R. , Chaikin P. M.
Published: March 2011

We have studied the elastic properties of the Bechgaard salts (TMTSF)2PF6 and (TMTSF)2C104 through their Spin Density Wave (SDW) and anion ordering transitions. Using a vibrating reed technique to measure the sound velocity and attenuation, we observed a large softening of sound velocity immediately above the SDW transition temperature, 12K, of (TMTSF)2PF6 followed by a large hardening below the transition. The softening results from a strong dependence of Tc on stress in the most conducting direction, while the hardening results from the loss of screening from the conduction electrons and yields a value for the long wavelength electron-phonon coupling constant. The anion ordering transition at 24K in (TMTSF)2ClO4 is marked by a hardening of the lattice that is considerably larger than expected from the lattice constant changes. Our most interesting finding, however, is the observation of a series of steps in the sound velocity as the Field Induced Spin Density Wave (FISDW) transitions are crossed by increasing the magnetic field at low temperatures. The fact that the sound velocity steps are small at the beginning of the cascade of transitions and increase with field, even as extrapolated to low temperature, is an unexpected result from present theory and may indicate a more direct coupling of the lattice stiffness to the SDW order parameter.
Quantum Hall Effect and Rapid Oscillations in (Tmtsf)2Pf6 under Pressure
Authors: Hannahs S. T. , Brooks J. S. , Kang W. , Chaikin P. M. , Chiang L. Y. , Upasani R.
Published: March 2011

We present magnetotransport data and the phase diagram derived from them for (TMTSF)2PF6 under sufficient pressure that the zero field Spin Density Wave (SDW) is suppressed and the material is superconducting. Application of a large magnetic field perpendicular to the conducting plane then leads to the cascade of Field Induced Spin Density Wave (FISDW) transitions. The transitions are in good agreement with the Standard model for these transitions and in contrast to the more complicated behavior seen in the ClO4 salt. In addition Hall and longitudinal resistivity indicates a behavior much closer to that observed in conventional Quantum Hall devices than in the ClO4 salt or previous studies of PF6. We do observe the “rapid” Schubnikov de Haas like oscillations in magnetoresistance at high field similar to those seen in ClO4, even though in the present case there is no evidence for anion ordering as some theories would require.
Polyaniline: an Old Polymer with New Physics
Authors: Epstein A. J. , MacDiarmid A. G.
Published: March 2011

Polyanilines have been known for over one hundred years. Recent studies of this chemically flexible polymer have demonstrated unusual electronic phenomena in both the insulating forms and the conducting forms. Studies of both forms show that the origins of the electronic phenomena are substantially different than those observed in polyacetylene and related earlier studied conjugated carbon backbone polymers. Unusual aspects include the formation of massive polarons upon photoexcitation in the insulating forms. These polarons have unusual time dynamics associated with the roles of ring-flipping and ring-conformation in the polymer system. A new model for the effects of electron lattice coupling via ring rotation has been introduced. The “metallic” form of the polymer shows that the metallic state is associated with the ordered regions of the doped polymer. The roles of localization are important in leading to the formation of a textured, granular metal. At low temperatures for emeraldine salt, and at higher temperatures for derivatized polyanilines, localization is important. Potential new technologies based on the polyanilines, including optical information storage, controlled microwave absorption, and use of a self-protonating derivative that is soluble in aqueous media are noted.
Chemical and Physical Properties of Soluble Part of Emeraldine: Comparison with Insoluble Emeraldine
Authors: Laversanne R. , Vaca P.
Published: March 2011

A preliminary physical study of the soluble part of emeraldine is presented. The electrical and magnetic properties of this low weight material are very similar of those of the pristine emeraldine salt. These results emphazise the possible role of short chain species in the conduction mechanism of polyaniline. In order to clarify this point, previous magnetic investigations on insoluble emeraldine salts are revisited. It appears that the fit of the magnetic susceptibility temperature dependence of polyaniline with a Curie law plus a Pauli term might not be justified at
low temperature. A T−α law with a ≈ 0.75 gives a better fit suggesting a behavior similar to the one found in Random Exchange Heisenberg Antiferromagnetic Chain (REHAC)
Moisture Effects in the Conducting Polymer, Polyaniline
Authors: Travers J. P. , Menardo C. , Nechtschein M. , Manohar S. K. , MacDiarmid A. G.
Published: March 2011

Water content as well as conductivity have been measured as a function of water vapour pressure on polyaniline and poly-N-methylaniline samples. It is shown that i) absorption is governed by the acid protons of the polymers and ii) enhancement of conductivity needs the existence of protonated imines. It is concluded that moisture favours conductivity through an increase of the interchain transfers.
Evaluation of thin film Capacitors Fabricated from Heterogeneous Polypyrrole Based Langmuir-Blodgett Films
Authors: Rosner R. B. , Rubner M.F.
Published: March 2011

The 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

A 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

Metal-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

It 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

It 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

Measurements 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

The 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

The 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.
Semiorganics: A New Class of Nlo Materials
Authors: Newman P. R. , Warren L. F. , Cunningham P. , Chang T. Y. , Cooper D. E. , Burdge G. L. , Polak-Dingels P. , Lowe-Ma C. K.
Published: March 2011

Recent results indicate that certain organic molecules whose electronic structures are characterized by extended pi-molecular orbitals can exhibit significant second and third order nonlinear optical (NLO) effects [1]. Unfortunately, this same arrangement which leads to the NLO effects, can also result in essentially one-dimensional bonding coordination. This in turn means that crystals grown from these materials do not readily form good three-dimensional optical-quality crystals, but rather tend to form needles. In addition, pure organic crystals are usually bonded by weak van der Waals forces, often resulting in poor mechanical properties. Indeed, organic impurities are frequently incorporated into these systems during crystallization resulting in poor crystallinity, spurious absorptions, and low damage thresholds. This is particularly true in the case of polymeric NLO materials, where impurities result from the polymerization steps and/or starting materials.
Investigations of a New Reversible Strain Induced Chromic Transition in Polydiacetylene Elastomers
Authors: Nallicheri R. A. , Rubner M. F.
Published: March 2011

In-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

For 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.
Theoretical Studies of the Nonlinear Optical Properties of L-Arginine Phosphate
Authors: Langhoff C. A.
Published: March 2011

This paper will present quantum calculations on the L-arginine part of the nonlinear crystal L-arginine phosphate. The emphasis here will be on understanding the NLO properties in terms of the excited states of the system and accompanying charge movements in these excited states. Both the carboxylate and the guanidyl ends of the molecule contribute to the values of β. The guanidyl seems to be the bigger contributor, but the contribution varies with the particular tensor component. The properties of the crystal will not be discussed here.
Mechanical Property-Microstructural Relationships in Abalone Shell
Authors: Sarikaya M. , Gunnison K. E. , Yasrebi M. , Aksay I. A.
Published: March 2011

The microstructure and mechanical properties of abalone shell were studied. It was found that fracture strength, αf, is 180 MPa, and fracture toughness, KIC, is 7 ± 3 MPa-m1/2; these values are comparable with or better than most “high technology” ceramic materials. The microarchitecture of the nacre section of the red abalone shell is similar to a “brick and mortar” structure, where CaCO3is the brick and organic matter is the mortar, constituting 95% and 5% of the microstructure by volume, respectively. This impressive combination of af and KIcvalues is attributed to the laminated structure of the shell with hard and thick (0.25±0.5 μm) CaCO3and superplastic and thin (20–30 nm) organic components. Although there are several toughening mechanisms operating in the shell, fractographic studies identified sliding of CaCO3layers and bridging by the organic layers to be the most effective ones. These phases also have a strong interface. The results of our experiments are discussed in the context of using abalone shell as a model for the design of synthetic laminates such as cermet (ceramic-metal) and cerpoly (ceramic-polymer) composites.
Ontogenetic and Phylogenetic Variation of Form and Function of the Ocular Lens
Authors: Sivak J. G.
Published: March 2011

The 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

Bacterial 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

This 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.
Modification of Proteases for Peptide Synthesis
Authors: Bibbs Jeffrey A. , Zhong Ziyang , Wong Chi-Huey
Published: March 2011

Polypeptides with well defined structures have the potential for the development for novel materials [1]. Synthesis of polypeptides suffer from racemization and protection-deprotection problems and has been dependent on the anhydride method using phosgene. There is definitely a need for a milder, stereoselective, and racemization-free procedure and it appears that enzyme-catalyzed synthesis can provide most of these features. Although proteases have been used in peptide synthesis with the above mentioned advantages, these enzymes have their own inherent catalytic properties which are disadvantageous, that is, they tend to cdeave peptide bonds. Two strategies presented here have been developed to overcome these problems.
Characterization and Structure of Mussel Adhesive Proteins
Authors: Laursen Richard A. , Ou Jung-Jung , Shen Xiao-Tong , Connors Michael J.
Published: March 2011

Many 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

The 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

Genetic 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

Sol-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

This 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

The 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

Magnetic 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

Characterisations 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

Poly (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.
Synthesis of Segmented Anisotropic-Isotropic Poly(Aryl Ester)Poly(Arylene Ether) Copolymers
Authors: McGratn J. E. , Cooper K. L. , Waehamad W. , Huang H. , Wilkes G. L.
Published: March 2011

Carboxyl functional poly(arylene ether) oligomers of controlled number average molecular weight were synthesized via nucleophilic aromatic substitution step polymerization using p-hydroxy benzoic acid as the molecular weight and end group controlling reagents. The subsequent functionalized polyarylene ethers were copolymerized with acetoxy benzoic acid or acetoxyphenoxy benzoic acid via melt acidolysis procedures. Successful copolymers were generated using chlorobenzene as a solvent for the first s age of the reaction followed by melt reaction at temperatures as high as 325°C. Resulting copolymer composition and segment size were investigated. It was possible to prepare improved solvent resistant copolymers through incorporation of the liquid crystal polyester (LCP) segment. Extraction tests using boiling chloroform showed that a high percentage of segmented copolymer were generated. Swelling characteristics were also noted and were observed to decrease as a function of the LCP concentration utilized. Multiple transitions were observed in differential scanning calorimetry consistent with Tg's, Tm's and possibly with liquid crystal transitions. Optical microscopy showed an ordered microstructure developed which is consistent with the presence of liquid crystalline phases. The materials were successfully compression molded to afford tough coherent films at all compositions, implying the likelihood of improved compressive strength relative to the LCP homo- or copolyesters.
Nature of the Chemical Bonds in Polymer-Salt Complexes: Raman and IR Studies
Authors: Nazri Gholamabbas , MacArthur Donald M.
Published: March 2011

Polymer electrolytes are attracting interest because of potential use in ‘solid state’ batteries and electrochromic windows. In this work the nature of the chemical bonds and ion association in polymer-salt complexes were studied. The fundamental vibrational frequencies of LiClO4− were calculated using valence force constants which are obtained from the ClO4− anion. The calculated frequencies and the band assignments agree quite well with the observed frequencies. Raman and IR spectroscopy were used to investigate the interaction of Li+ and ClO4− with the PEO chains. Lithium ion interacted with the negatively charged oxygen of PEO and C104 interacted electro- statically with the positively charged hydrogens. The strong electrostatic interactions induced changes in the intensity of the Raman bands and IR absorption bands of the polymer. The Raman and IR spectra of the polymer-salt complexes clearly show the existence of ‘free’ ions, ionpairs and salt clusters at various concentrations of the lithium salt. The maximum concentration of “free” ions deduced from the spectroscopy is in excellent agreement with the salt concentration required to obtain maximum ionic conductivity.
Estimation of Longevity of Portland Cement Grout Using Chemical Modeling Techniques
Authors: Alcorn S. R. , Coons W. E. , Gardiner M.A.
Published: March 2011

Portland cement has been identified as a likely candidate seal material by programs investigating the deep burial of nuclear waste as a disposal mechanism. The longevity of performance of cement grout is currently being investigated, along with bentonite, under the auspices of the Stripa Project. Coordinated laboratory, field, and modeling studies are underway to produce fundamental data, practical experience, and estimates of long-range performance, respectively. Long-term performance of cement grout is of particular concern. Since most of the solid phases of which grout is comprised are metastable, it is likely that grout performance will decrease with time. The question is whether performance will still be acceptable after this decrease. This issue is being addressed with the coupled use of geochemical and permeability modeling. For a simplified cement system, two mechanisms for chemical degradation have been considered: phase change and dissolution. For dissolution, both equilibrium (slow flow) and open (fast flow) systems have been analyzed as bounding scenarios. Granitic terrain groundwaters ranging from fresh to saline have been used in the analyses. To assess the consequences in terms of flow, an empirical relation between cement permeability and porosity has been developed. Performance changes with time have been predicted by making conservative estimates of local hydraulic head conditions for successive periods of repository history. For the granitic rock environments considered, preliminary results indicate that cement grout performance may be acceptable for tens of thousands to millions of years, providing its initial hydraulic conductivity is on the order of 10−12 m/s. Other conditions favoring long-term performance include minimizing the ettringite content of the grout, and emplacement at a site where the groundwater has an elevated TDS, and where the local hydraulic gradient is flat or repository resaturation times are short.
Dissolution Kinetics of a Simple Analogue Nuclear Waste Glass as a Function of Ph, Time and Temperature
Authors: Knauss Kevin G. , Bourcier William L. , McKeegan Kevin D. , Merzbacher Celia I. , Nguyen Son N. , Ryerson Frederick J. , Smith David K. , Weed Homer C. , Newton Leon
Published: March 2011

We have measured the dissolution rate of a simple five-component borosilicate glass (Na2O, CaO, Al2O3, B2O3, SiO2) using a flow-through system. The experiments were designed to measure the dissolution rate constant over the interval pH 1 through pH 13 at 3 temperatures (25°, 50° and 70°C). Dilute buffers were used to maintain a constant pH. Analyses of solutions and solid surfaces provided information that is used to develop a kinetic model for glass dissolution.

Under all conditions we eventually observed linear dissolution kinetics. In strongly acidic solutions (pH 1 to pH 3) all components but Si were released in their stoichiometric proportions and a thick, Si-rich gel was formed. In mildly acidic to neutral solutions the gel was thinner and was both Si- and Al-rich, while the other components were released to solution in stoichiometric proportions. In mildly to strongly alkaline solutions all components were released to solution in stoichiometric proportions. By varying the flow rate at each pH we demonstrated a lack of transport control of the dissolution rate.

The dissolution rates were found to be lowest at near-neutral pH and to increase at both low and high pH. A rate equation based on transition-state theory (TST) was used to calculate dissolution rate constants and reaction order with respect to pH over two pH intervals at each temperature. At 250C between pH 1 and pH 7 based on the Si release rate the log rate constant for glass dissolution (g glass/m20d) was −0.77 and the order with respect to pH was −0.48. Between pH 7 and pH 13 the log rate constant for glass dissolution was −8.1 and the order with respect to pH was +0.51. The measured simple glass dissolution rate constants compare very well with constants estimated by fitting the same TST equation to experimental results obtained for SRL-165 glass and to dissolution rate estimates made for synthetic basaltic glasses.
Immobilization in Cement of Ion Exchange Resins
Authors: Bescop P. Le , Bouniol P. , Jorda M.
Published: March 2011

Recent studies were carried out in France to improve ion exchange resin solidification in cement-based matrices. Work is conducted on different types of waste - cationic, anionic and mixed-bed resins - under regenerated and loaded states. The main objective is to increase the waste incorporation rate up to roughly 50% (in volume). Hydraulic cement formulas are developed taking into account waste chemistry, in particular the presence of ions which inhibit setting.
Chemistry of Glass Corrosion in High Saline Brines
Authors: Grambow B. , Müller R.
Published: March 2011

Experimental data were obtained for conventional pH values corrected for liquid junction, amorphous silica solubility and glass corrosion in concentrated salt brines. The data were interpreted with a geochemical model. The brine chemistry was described with the Pitzer formalism [1] using a data base which allows calculation of brine compositions in equilibrium with salt minerals at temperatures up to 200°C.

In MgCl2 dominated brines Mg silicates form and due to the consumption of Mg the pH decreases with proceeding reaction. A constant pH (about 4) and composition of alteration products is achieved, when the alkali release from the glass balances the Mg consumption. The low pH results in high release of rare earth elements REE and U from the glass. In the NaCl dominated brine MgCl2 becomes exhausted by Mg silicate formation. As long as there is still Mg left in solution the pH decreases. After exhaustion of Mg the pH rises with the alkali release from the glass and analcime is formed.
Comparison of the Layer Structure of Vapor Phase and Leached SRL Glass by Use of AEN
Authors: Biwer Bruce M. , Bates John K. , Abrajano Teofilo A. , Bradley John P.
Published: March 2011

Test samples of 131 type glass that have been reacted for extended time periods in water vapor atmospheres of different relative humidities and in static leaching solution have been examined to characterize the reaction products. Analytical electron microscopy (AEM) was used to characterize the leached samples, and a complicated layer structure was revealed, consisting of phases that precipitate from solution and also form within the residual glass layer. The precipitated phases include birnessite, saponite, and an iron species, while the intralayer phases include the U-TI containing phase brannerite distributed within a matrix consisting of bands of an Fe rich montmorillonite clay. Comparison is made between samples leached at 40°C for 4 years with those leached at 90°C for 3-1/2 years. The samples reacted in water vapor were examined with scanning electron microscopy and show increasing reaction as both the relative humidity and time of reaction increases. These samples also contain a layered structure with reaction products on the glass surface.
Hydrothermal Leaching of R7-T7 Borosilicate Glass
Authors: Caurel J. , Vemaz E. , Beaufort D.
Published: March 2011

The results of hydrothermal leach tests are intended to be used to predict long-term low-temperature glass dissolution. It is often assumed that data can be extrapolated to other conditions using an Arrhenius-type equation. Hydrothermal leaching mechanisms and their temperature dependence in R7T7 glass were investigated in static experiments lasting from 7 days to 1 year at 150°C and 250°C. Leachates, surface layers and crystalline products were analyzed by ICP, TEM, SEM, EMP, XRD and cathodoluminescence. Unexpectedly, no actual saturation conditions in solutions were reached after one year leaching at 150°C nor at 250°C. The effect of precipitation of alteration products (a silica-enriched amorphous layer and aluminosilicates [smectite at 150°C, smectite and zeolites at 250°C]) is discussed. However, the formation of large cracks in the bulk glass results in a higher glass reacting surface and a higher dissolution rate at 250°C. Arrhenius calculations cannot be used to extrapolate our hydrothermal data to lower-temperatures.