High styrene–rubber ionomers,an alternative to thermoplastic elastomers

High styrene rubber ionomers were prepared by sulfonating styrene–butadiene rubber of high styrene content (high styrene rubber) in 1,2‐dichloroethane using acetyl sulfate reagent, followed by neutralization of the precursor acids using methanolic zinc acetate. The ionomers were characterized using X‐ray fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), dynamic mechanical analysis (DMA), and also by the evaluation of mechanical properties. The FTIR studies of the ionomer reveal that the sulfonate groups are attached to the benzene ring. The NMR spectra give credence to this observation. Results of DMA show an ionic transition (T_i) in addition to glass–rubber transition (T_g). Incorporation of ionic groups results in improved mechanical properties as well as retention of properties after three cycles of processing. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2294–2300, 2002     

Phylloquinone (vitamin K1) and dihydrophylloquinone content of fats and oils

Assessment of vitamin K (VK) dietary intakes has been limited by the incompleteness of VK food composition data for the U.S. food supply, particularly for VK-rich oils. The phylloquinone (VK-1) and 2′,3′-dihydrophylloquinone (dK) concentrations of margarines and spreads (n=43), butter (n=4), shortening (n=4), vegetable oils (n=6), and salad dressings (n=24) were determined by RP-HPLC with fluorescence detection. Each sample represented a composite of units or packages obtained from 12 or 24 outlets, which were geographically representative of the U.S. food supply. Butter, which is derived from animal fat sources, had less VK-1 compared to vegetable oil sources. The VK-1 and dK of the margarines and spreads increased with fat content and the degree of hydrogenation, respectively. In some margarines or spreads and in all shortenings, the dK concentrations were higher than the corresponding VK-1 concentrations. As the fat content of salad dressings increased, the VK-1 concentrations also increased. Fat-free foods had <1 μg/100 g of either form of the vitamin. No dK was detected in the salad dressings or oils tested. Some margarines, spreads, and salad dressings may be significant sources of vitamin K in the U.S. food supply.     

Synthesis of N,N-diethyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}amine via in situ diazotisation and coupling in supercritical carbon dioxide

The synthesis of azo dyes via a conventional aqueous-based diazotisation and coupling reaction requires the use of relatively high concentrations of mineral acids, which leads to high electrolyte concentrations in wastewater. Reported in this paper is an environmentally benign one-pot method for the synthesis of a nonionic azo dye, N,N -diethyl- N -{4-[( E )-(4-nitrophenyl)diazenyl]phenyl}amine, in supercritical carbon dioxide without using a mineral acid. The product yield increased significantly with temperature, with 91% theoretical yield afforded at 80 °C. The pressure of the system had little influence on product yield.     

Rheological properties of bitumen in water emulsions with added solids

Experimental work was carried out to investigate the rheological properties of bitumen in water emulsions containing solids of different shape and size. The bitumen volumetric concentration was varied up to 60%, solids free basis, and the solids volume fraction (total volume basis) was varied up to 0.2. Irregular-shaped silica sand (average diameter: 9 and 33 μm) and smooth spherical glass beads (average diameter: 27 and 44 μm) were used as the added solids. In the low shear stress range, shear thinning behavior was observed for bitumen in water emulsions. At high shear stress, the viscosity of the emulsions became fairly independent of the shear stress. The addition of solids to the bitumen emulsions increased the mixture viscosity. The addition of irregular-shaped silica sand gave a higher viscosity than a similar addition of the spherical glass beads. The viscosity of the emulsion/solids mixtures was influenced by the solids size as well; the smaller size particles gave a higher viscosity. The addition of solids to the bitumen emulsions also induced shear thickening (dilatancy) behavior at high solids volume fraction. The degree of the shear thickening increased with the oil concentration.     

Enzyme‐catalyzed hydrolysis of poly(ethylene terephthalate) cyclic trimer

Oligoesters present in poly(ethylene terephthalate) fibers are commonly extracted from the fiber during processing, such as aqueous‐based dyeing. Aqueous, insoluble oligoesters, particularly cyclic trimers that precipitate on processing machinery and on the fiber surface are difficult to remove under benign conditions. Reported is a new method for the efficient removal of cyclic trimer by enzyme‐catalyzed hydrolysis. Almost complete hydrolysis of trimer was accomplished at pH 8 and 60°C. Effects of time, agitation, surfactant, and enzyme and trimer concentrations on the efficiency of hydrolysis are reported. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2545–2552, 2003     

Effect of Mechanical Constraint on Domain Reorientation in Predominantly {111}‐Textured Lead Zirconate Titanate Films

Ferroelectric/ferroelastic domain reorientation was measured in 2.0 μm thick tetragonal {111}‐textured PbZr_0.30Ti_0.70O₃ thin films using synchrotron X‐ray diffraction (XRD). Lattice strain from the peak shift in the 111 Bragg reflection and domain reorientation were quantified as a function of applied electric field amplitude. Domain reorientation was quantified through the intensity exchange between the 112 and 211 Bragg reflections. Results from three different film types are reported: dense films that are clamped to the substrate (as‐processed), dense films that are partially released from the substrate, and films with 3% volume porosity. The highest amount of domain reorientation is observed in grains that are misoriented with respect to the {111} preferred (domain engineered) orientation. Relative to the clamped films, films that were released from the substrate or had porosity exhibited neither significant enhancement in domain reorientation nor in 111 lattice strain. In contrast, similar experiments on {100}‐textured and randomly oriented films showed significant enhancement in domain reorientation in released and porous films. Therefore, {111}‐textured films are less susceptible to changes in properties due to mechanical constraints because there is overall less domain reorientation in {111} films than in {100} films.     

Scaling Effects in Perovskite Ferroelectrics: Fundamental Limits and Process‐Structure‐Property Relations

Ferroelectric materials are well‐suited for a variety of applications because they can offer a combination of high performance and scaled integration. Examples of note include piezoelectrics to transform between electrical and mechanical energies, capacitors used to store charge, electro‐optic devices, and nonvolatile memory storage. Accordingly, they are widely used as sensors, actuators, energy storage, and memory components, ultrasonic devices, and in consumer electronics products. Because these functional properties arise from a noncentrosymmetric crystal structure with spontaneous strain and a permanent electric dipole, the properties depend upon physical and electrical boundary conditions, and consequently, physical dimension. The change in properties with decreasing physical dimension is commonly referred to as a size effect. In thin films, size effects are widely observed, whereas in bulk ceramics, changes in properties from the values of large‐grained specimens is most notable in samples with grain sizes below several micrometers. It is important to note that ferroelectricity typically persists to length scales of about 10 nm, but below this point is often absent. Despite the stability of ferroelectricity for dimensions greater than ~10 nm, the dielectric and piezoelectric coefficients of scaled ferroelectrics are suppressed relative to their bulk counterparts, in some cases by changes up to 80%. The loss of extrinsic contributions (domain and phase boundary motion) to the electromechanical response accounts for much of this suppression. In this article, the current understanding of the underlying mechanisms for this behavior in perovskite ferroelectrics is reviewed. We focus on the intrinsic limits of ferroelectric response, the roles of electrical and mechanical boundary conditions, grain size and thickness effects, and extraneous effects related to processing. In many cases, multiple mechanisms combine to produce the observed scaling effects.     

Current Understanding of Structure–Processing–Property Relationships in BaTiO3–Bi(M)O3 Dielectrics

As part of a continued push for high permittivity dielectrics suitable for use at elevated operating temperatures and/or large electric fields, modifications of BaTiO₃ with Bi(M)O₃, where M represents a net‐trivalent B‐site occupied by one or more species, have received a great deal of recent attention. Materials in this composition family exhibit weakly coupled relaxor behavior that is not only remarkably stable at high temperatures and under large electric fields, but is also quite similar across various identities of M. Moderate levels of Bi content (as much as 50 mol%) appear to be crucial to the stability of the dielectric response. In addition, the presence of significant Bi reduces the processing temperatures required for densification and increases the required oxygen content in processing atmospheres relative to traditional X7R‐type BaTiO₃‐based dielectrics. Although detailed understanding of the structure–processing–property relationships in this class of materials is still in its infancy, this article reviews the current state of understanding of the mechanisms underlying the high and stable values of both relative permittivity and resistivity that are characteristic of BaTiO₃‐Bi(M)O₃ dielectrics as well as the processing challenges and opportunities associated with these materials.     

Probing the Ion Binding Site in a DNA Holliday Junction Using F?rster Resonance Energy Transfer (FRET)

Holliday Junctions are critical DNA intermediates central to double strand break repair and homologous recombination. The junctions can adopt two general forms: open and stacked-X, which are induced by protein or ion binding. In this work, fluorescence spectroscopy, metal ion luminescence and thermodynamic measurements are used to elucidate the ion binding site and the mechanism of junction conformational change. Förster resonance energy transfer measurements of end-labeled junctions monitored junction conformation and ion binding affinity, and reported higher affinities for multi-valent ions. Thermodynamic measurements provided evidence for two classes of binding sites. The higher affinity ion-binding interaction is an enthalpy driven process with an apparent stoichiometry of 2.1 ± 0.2. As revealed by Eu³⁺ luminescence, this binding class is homogeneous, and results in slight dehydration of the ion with one direct coordination site to the junction. Luminescence resonance energy transfer experiments confirmed the presence of two ions and indicated they are 6–7 Å apart. These findings are in good agreement with previous molecular dynamics simulations, which identified two symmetrical regions of high ion density in the center of stacked junctions. These results support a model in which site-specific binding of two ions in close proximity is required for folding of DNA Holliday junctions into the stacked-X conformation.     

Recycling of EPDM waste. II. Replacement of virgin rubber by ground EPDM vulcanizate in EPDM/PP thermoplastic elastomeric composition

Virgin ethylene propylene diene monomer (EPDM) rubber in a thermoplastic elastomeric blend of polypropylene (PP) and EPDM rubber was substituted by ground EPDM vulcanizate of known composition, after which the mechanical properties of the raw EPDM/waste EPDM/PP blends were determined. The ratio of the rubber content in the waste EPDM (r‐W‐EPDM) to the raw EPDM (R‐EPDM) in the blends was varied from 0 : 100 to 45 : 55. Attempts to replace higher amounts (>45%) of R‐EPDM by W‐EPDM failed because of processing difficulty. Although a drop in mechanical properties of the blends was observed at lower loadings of W‐EPDM, the properties showed improvement at intermediate W‐EPDM loadings. The R‐EPDM/W–EPDM/PP blends were found to be reprocessable. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3304–3312, 2001