Investigation of Viscoelastic Properties of Amorphous Selenium near Glass Transition Using Depth‐Sensing Indentation

Abstract

New procedures involving depth‐sensing indentation are used to measure the submicron scale elastic modulus, hardness, viscosity, and activation energy and volume for creep of amorphous selenium below glass transition. The accurate measurement of Young's modulus in a highly viscoelastic situation using depth‐sensing indentation remains a challenge, and a creep correction procedure is employed here to measure the modulus. The measured Young's modulus exhibits a strong decreasing trend from ～10 GPa to 4.4 GPa as temperature increases from ～302 K to 309 K, in reasonably good agreement with bulk behavior. Two new procedures are also proposed here to measure the viscosity. The measured shear viscosity decreases from ～1×10¹² Pa‐s to ～2×10¹⁰ Pa‐s when the temperature increases over the same range, and the variation with temperature is found to obey an Arrehnius rate equation. The activation energy for the viscous creep process is found to be ～463 kJ/mol. Both the viscosity and the activation energy are lower than the bulk values, and this is thought to be due to the much higher stress levels of over 200 MPa involved in the nanoindentation experiments here. The apparent activation volume exhibits a rising trend from 1.04×10^?31 to 2.35×10^?30 m³ over the same temperature range.     

The effect of strain rate on craze yielding,shear yielding,and brittle fracture of polymers at 77°K

The tensile strength of poly(methyl methacrylate) (PMMA), polycarbonate (PC), polychlorotrifluoroethylene, and polysulfone was measured in liquid nitrogen over the strain rate range of 2 × 10^?4 to 660 min^?1. These polymers deformed by crazing which was induced by the liquid nitrogen. The stress versus log strain rate curve was sigmoidal in that its slope increased and then decreased with strain rate. Above a critical strain rate of about 200 min^?1, which varied somewhat with the polymer, crazing was not observed with the optical microscope; the behavior became brittle, and the tensile strength became constant. The nonlinear behavior of stress versus log strain rate at low strain rates was associated with a decrease in activation volume with increasing strain rate whereas the nonlinear behavior at high strain rates was associated with an increase in density and decrease in length of the crazes with strain rate. The strain rate effect was the basis for calculating the diffusion coefficient of nitrogen into the polymers at 77°K. The shear deformation mode of PC was measured under compression and under tension. The compressive strength versus log strain rate was linear throughout the entire range giving a compression shear activation volume of 360 ų. The shear tensile strength of PC varied only slightly with strain rate when compared to the compressive strength. The brittle fracture stress of PMMA, in the absence of crazing, in compression and in tension, did not vary with strain rate.     

Sorption of organic vapors into drawn and undrawn polyethylene

Drawing of linear polyethylene at 60°C. to an extension ratio of ten drastically reduces the sorption and diffusion of n-pentane, benzene, methylene chloride, and tetrachloroethylene. Methylene chloride was chosen for more detailed study. The sorption is of the normal Fickean type. It is also fully reversible in the temperature range between 25 and 45°C. if the sorbed amount is kept to below 0.5%. At higher concentrations the sample relaxes so that sorption irreversibly increases. The reversible sorption per gram of amorphous component is about 1/6 of that in undrawn polyethylene. The diffusion constant has a larger temperature and concentration dependence than in the undrawn material. At zero concentration the activation energy for diffusion is 34.4 kcal./mole and the diffusion constant at 25°C. is 8 × 10^?11 cm.²/sec. as compared with 14.4 kcal./mole and 1.5 × 10^?8 cm.²/sec. in undrawn PE. Cold drawing reduces the sorption sites without changing their energy content, but drastically cuts down diffusion and increases the activation energy. A smaller part of the increase of the latter is a consequence of the lower enthalpy of the amorphous material and a larger part is probably due to the increased distance between sorption sites.     

A determination of the NaAr ground state potential from differential cross section measurements

The differential cross sections for the interaction of Na with Ar has been measured in an atomic beam experiment at thermal collision energies. The data yield 0.85 × 10^?14 erg for the well depth and 5.05 × 10^?8 cm for the equilibrium distance. The result is compared with experimental and calculated results given previously.     

Direct determination of pesticides in vegetable samples using gold nanoelectrode ensembles

Gold nanowires were produced by electrodeposition in polycarbonate membrane, with an average diameter of 200 nm and a height of about 2 μm. The nanowire array prepared by the proposed method can be considered as nanoelectrode ensembles (NEEs). An amperometric pesticides sensor based on gold NEEs has been developed and used for determination of phoxim and dimethoate in vegetable samples. The electrochemical performance of the gold NEEs has also been studied by the amperometric method. The electrode provided a linear response over a concentration range of 5.9 × 10^?5 to 1.2 × 10^?2 M for phoxim with a detection limit of 4.8 × 10^?6 M and 6.3 × 10^?5 to 1.1 × 10^?2 M for dimethoate. This sensor displayed high sensitivity and selectivity, long-term stability and wide linear range. In addition, the ellipsis of enzyme and the reactivation of enzyme make the operation simple. This sensor has been used to determine pesticides in a real vegetable sample.     

Intrinsic viscosity and axial extension ratio of random-coiling macromolecules in a hydrodynamic shear field

The shear dependence of the intrinsic viscosity and the conformation of high molecular weight polyisobutylene in dilute solutions of decahydronaphthalene under shear were determined simultaneously. Experimental variables investigated were the shear rate (0 to 2 × 10³ sec^?1), the molecular weight (1.0 × 10⁷ to 1.7 × 10⁷) and the polymer concentration (1.8 × 10^?4 to 8.4 × 10^?4 g/cc). Correlations allowing concentration and shear rate normalization for any one sample are described. Conformational extention ratios along the orientation direction of the deformed molecule to 1.42 and intrinsic viscosity ratios (sheared to zero shear) to 0.5 were observed.     

The molecular Zeeman effect in HCP,HCN, and HCCBr and a comparison with similar molecules

The molecular Zeeman effect has been observed in the J = 0 → 1 ΔM = 0, and ± 1 transitions in H¹²CP, D¹²CP, H¹²C¹⁵N, H¹²C¹²C⁷⁹Br, and H¹²C¹²C⁸¹ Br giving the molecular g-values, magnetic susceptibility anisotropies, and corresponding molecular quadrupole moments. The results are g_⊥(HCP) = ?0.0430 ± 0.0010, g_⊥(DCP) = ?0.0353 ± 0.0010, x_⊥ - x_| = (8.4 ± 0.9) × 10^?6 erg/G² mole and Q_|(HCP) = (4.4 ± 1.2) × 10^?26 esu; g_⊥(HC¹⁵N) = ?0.0904 ± 0.0003, x_⊥ - x_| = (7.2 ± 0.4) × 10^?6 erg/G² mole, and Q_|(HC¹⁵N) = (3.1 ± 0.6) × 10^?26 esu; g_⊥(HCC⁷⁹Br) = ?0.00395 ± 0.00032, g_⊥(HCC⁸¹Br) = ?0.00388 ± 0.00014, x_⊥ - x_| = (9.5 ± 0.9) × 10^?6 erg/G² mole, and Q_| = (8.5 ± 1.1) × 10^?26 esu. The results in HCN agree very well with an earlier prediction of the magnetic properties. The new results presented here are compared to other members in the acetylene and cyanide series of molecules and we conclude that the sign of the g-value in acetylene should be positive.The deuterium nuclear quadrupole coupling constant was also determined in DCP to be x_D = 233 ± 40 kHz.     

Kinetics of styrylquinolinc formation

A comprehensive kinetic investigation of reactions occurring in the formation of styryl-quinolines has been conducted. Specific rate data such as rate equations, rate constants, and thermodynamic activation values have been determined and utilized in a study of which factors are of greatest importance in the reactions forming 2-styrylquinolines. A mechanism has been proposed for the condensation reaction which agrees with rate relationships found. Gas-liquid partition chromatography was used to follow the kinetics of the condensation reactions. A rate constant of 5.41 × 10^?2M^?1min^?1 was found for the reaction of benzaldehyde with 2-methyl-quinoline using zinc chloride as a catalyst at 104.0°. Rate constants of 1.28 × 10^?2 MT^?1 min^?1 and 1.05 × 10^?2 M^?1 min^?1 were found for the reactions of p-methylbenzaldehyde and p-methoxybenzaldehyde with quinaldine to form 2-(p-methylstyryl)quinoline and 2-(p-methoxystyryl)-quinoline, respectively at 92.4°. A linear relationship was found using the Hammett equation. An Arrhenius plot was constructed from rate constants determined at five different temperatures for the reaction of benzaldehyde and quinaldine to form 2-styrylquinoline, using zinc chloride as a catalyst. The energy of activation, E_a, was found to be 22.2 kcal/mole for this reaction. The enthalpy of activation, ΔH?, free energy of activation, ΔF?, and entropy of activation, ΔS?, were found to be 21.4 kcal/mole, 27.7 kcal/mole and -16.7 eu/mole, respectively, at 104.0°. The mechanism proposed in the formation of 2-styrylquinoline involves the fast formation of a carbanion-zinc chloride complex, which then attacks, in the rate determining step, the aldehyde utilized in the reaction. The lack of reaction of certain methylquinolines is attributed to the inadequacy of the carbanion formed and not to the difficulty involved in the initial formation of the carbanion.     

A relative rate study of the reaction of bromine atoms with a variety of organic compounds at 295 K

The relative rate technique has been used to determine rate constants for the reaction of bromine atoms with a variety of organic compounds. Decay rates of the organic species were measured relative to i-butane or acetaldehyde or both. Using rate constants of 1.74 × 10^?15 and 3.5 × 10^?12 cm³ molecule^?1 s^?1 for the reaction of Br with i?butane and acetaldehyde respectively, the following rate constants were derived, in units of cm³ molecule^?1 s^?1: 2, 3?dimethylbutane, (6.40 ± 0.77) × 10^?15; cyclopentane, (1.16 ± 0.18) × 10^?15, ethene, (≤2.3 × 10^?13); propene, (3.85 ± 0.41) × 10^?12; trans-2-butene, (9.50 ± 0.76) × 10^?12, acetylene, (5.15 ± 0.19) × 10^?15; and propionaldehyde, (9.73 ± 0.91) × 10^?12. Quoted errors represent 2σ and do not include possible systematic errors due to errors in the reference rate constants. Experiments were performed at 295 ± 2 K and atmospheric pressure of synthetic air or nitrogen. The results are discussed with respect to the mechanisms of these reactions and their utility in serving as a laboratory source of alkyl and alkyl peroxy radicals.     

Dynamooptical and electrooptical properties of poly(methylphenylsiloxane) in solution and bulk

The dynamooptical, electrooptical, and hydrodynamic properties of a low-molecular-mass poly(methylphenylsiloxane) containing 33% phenyl radicals (with respect to the total amount of side groups) in dilute solutions and in bulk are studied. The size of macromolecules, as well as the molecular mass of the polymer, its shear optical coefficients Δn/Δτ = (0.29 ± 0.3) × 10^?10 (in decalin) and (0.43 ± 0.03) × 10^?10 cm s²/g (in bulk), and the specific Kerr constants K = (2.30 ± 0.02) × 10^?12 (in benzene), (2.23 ± 0.02) × 10^?12 (in decalin), and (2.24 ± 0.09) × 10^?12 cm⁵/[g (300 V)²] (in bulk), are estimated and compared with the corresponding characteristics of poly(dimethylsiloxane). The effect of solvents on the intramolecular mobility, optical anisotropy, and dipole structure of polymer macromolecules is considered.     

Organo-sulfonic acid catalyzed degradation kinetics and thermodynamic studies of nylon-6 by hydrothermal method

Nylon-6 as an engineering polymer and its starting monomer are both costly. Chemical reutilization offers some economic and environmental benefits. Depolymerization of nylon-6 was carried out by the conventional technique of hydrothermal method using various organo-sulfonic acids such as Methane sulfonic acid (MSA), para-toluene sulfonic acid (p-TSA), benzene sulfonic acid (BSA), and tetra-butyl ammonium bromide (TBAB) as a phase transfer catalyst. Various parameters such as temperature, time, normality of acids, and phase transfer catalyst concentration were varied to optimize its parameters, and characterization techniques such as amine value titrations and Fourier transform infrared spectroscopy were used for quantitative measurements. Solid-state ¹³C NMR was done for structure confirmation. A chemical kinetics interpretation shows degradation mechanism follows first-order kinetics under various catalysts. MSA has the highest reaction rate of 8.49 × 10^?2 h^?1 at 90°C; it decreases to 7.72 × 10^?2 h^?1 at 100°C. At the same time, aromatic Sulfonic acids such as p-TSA and BSA have a higher reaction rate of 8.995 × 10^?2 h^?1 and 5.582 × 10^?2 h^?1, respectively. The activation energy was lowered as the acidity of organo-sulfonic acids increased as benzene sulfonic acid has the lowest E_a. Followed by p-TSA, and MSA has the highest E_a. Free energy shows a similar kind of value. A simple theoretical model was used to calculate the activation energy. Thermodynamic parameters such as heat of enthalpy and entropy of reaction were evaluated using the Eryig–Polanyi equation. The combined catalytic effect of organo-sulfonic acids and phase-transfer catalyst provides a better environment-friendly method for depolymerizing nylon-6.     

Molecular weight distributions in radiation-induced polymerization. III. γ-Ray-induced polymerization of styrene at low temperatures

The kinetics of the γ-radiation-induced polymerization of styrene was studied at radiation intensities of 8 × 10⁴, 2.4 × 10⁵, 3.1 × 10⁵, and 8.3 × 10⁵ rad/hr over a temperature range of ?10°C to 30°C. The water content of the irradiated samples varied from 1.0 × 10^?3 to 7.5 × 10^?3 mole/l. The power dependence of the rate of polymerization on the dose rate at ?10°C varied from 0.53 to 0.71 as the water content of the sample varied from 7.5 × 10^?3 to 1.0 × 10^?3 mole/l. A value of 3.1 kcal/mole was determined for the overall activation energy. Molecular weight distribution studies by gel-permeation chromatography indicated the presence of two distinct peaks. The contribution of each peak was dependent on specific experimental parameters. Kinetic data and molecular weight distribution data indicate the coexistence of two propagating species. Analysis of the data strongly suggests that a free-radical mechanism and a cationic mechanism are involved.     

Surface and bulk conduction and thermodynamic properties of ionic salt CsH<Subscript>5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Transport properties of ionic salt CsH₅(PO₄)₂ are studied by the impedance method. The salt’s bulk conductivity ranges from 10^?8 to 10^?4 S cm^?1 in the temperature interval 90 to 145°C. The apparent activation energy is high (1.6–2.0 eV). The conductivity is slightly anisotropic: it is maximum in the [001] direction and minimum in the [100] direction (～5.6 and 1 times × 10^?6 S cm^?1, respectively, at 130°C). The conductivity of polycrystalline samples is higher by 1–2 orders of magnitude, and the activation energy drops to 1.05 eV due to the formation of a pseudoliquid layer with a high proton mobility at the intercrystallite boundary. The salt’s thermodynamic properties are examined by differential scanning calorimetry and thermogravimetry. No phase transitions are discovered in the salt up to the melting point (151.6°C), with the melting enthalpy equal to ～34 kJ mol^?1. The crystallization occurs at lower temperatures (107°C) and the crystallization enthalpy (?18 kJ mol^?1) is lower than the melting enthalpy. The melting is accompanied by slow decomposition of the salt. Factors affecting the proton transport in the salt are analyzed.     

Microstrain investigation of polyethylene

The small-strain mechanical behavior of crystalline polyethylene has been studied by using a microstrain technique with strain resolution on the order of 10^?6. The strain rate was varied from 10^?6 to 10^?4 sec.^?1, and a temperature range of 17–28°C. was investigated. A strong dependence on strain rate and temperature has been observed for the following parameters which characterize the mechanical response of polyethylene in the microstrain region: the initial modulus of the stress–strain curve, the deviation in strain from ideal linear elastic behavior at a given stress amplitude, and the energy dissipated in a deformation cycle. The Young's moduli that were observed by means of tensile tests in the microstrain region were only about 20% lower than the values reported in other investigations at kilocycle and megacycle frequencies. The experimental method made it possible to isolate a deformation process which was attributed to a crystallographic shear mechanism corresponding to a yield point of 27 psi. This shear mechanism is discussed in terms of the various shear processes, such as slip, twinning, and the orthorhombic–monoclinic phase change.     

Pattern Recognition of Sweeteners in Biological Fluids,Beverages, and Ketchup using Stochastic Sensors

Three stochastic sensors based on nanodiamond (nDP) paste modified with α, β, and γ‐cyclodextrin were designed and characterized for pattern recognition of aspartame, acesulfame K and sodium cyclamate in beverages, ketchup, and biological fluids. The linear concentration ranges obtained for acesulfame K (between 1.00×10^?10 mol L^?1and 1.00×10^?3 mol L^?1), for aspartame (between 1.00×10^?12 mol L^?1 and 1.00×10^?3 mol L^?1) and for sodium cyclamate (between 4.97×10^?12 mol L^?1 and 4.97×10^?3 mol L^?1) allow their assay in biological fluids, beverages and ketchup. The lowest limits of quantification were obtained using the stochastic sensor based on γ‐CD/nDP: for acesulfame K 1.00×10^?10 mol L^?1, for aspartame 1.00×10^?12 mol L^?1 and for sodium cyclamate 4.97×10^?12 mol L^?1. All three stochastic sensors revealed very high values of sensitivities. The proposed method was reliable for qualitative and quantitative assay of aspartame, acesulfame K and sodium cyclamate in beverages, ketchup, and in biological fluids such as urine.     

Proton NMR studies of lanthanum nickel hydride: Structure and diffusion

The proton magnetic resonance spectrum of lanthanum nickel hydride LaNi_5.3H₆ was measured over the temperature range 118°K < T < 300°K. The second moment of the absorption at 118°K is M₂ = 13.4 ± 0.3 G². Several possible arrangements of the hydrogen atoms are discussed. Narrowing of the line above 140°K is analyzed in terms of proton diffusion and gives an activation enthalpy E = 21 ± 1 kJ mol^?1, NMR correlation time pre-exponential 0.2 ps < τ_c⁰ < 1.6 ps and a self diffusion coefficient at 300°K of 2 × 10^?12 m² s^?1 < D < 2 × 10^?11 m² s^?1.     

Preparation and Study of Thermal Decomposition Mechanism of Zn(Thr)(AcO)_2·2H_2O

Introduction -Amino acids as additive have a wide application in medicines, foodstuff and cosmetics.1-3 The synthetic methods of amino acid have been reviewed.4,5 The solu-bility property of Zn(AcO)2-Thr-H2O (Thr=Threonine) system at 298.15 K has been investigated by the semimicro-phase equilibrium method, in which the phase region of the complex did not exist.6 The prepara-tion of Zn(Thr)SO4H2O was reported in Ref. 7∶3 times volume of acetone relative to that of water was added into t…     

Ene reaction between 4-phenyl-1,2,4-triazoline-3,5-dione and hex-1-ene. The enthalpies,entropies, and volumes of activation and reaction in solution

The rates of an ene reaction between 4-phenyl-1,2,4-triazoline-3,5-dione and hex-1-ene were studied in a temperature range of 15–40 °C and in a pressure range of 1–2013 bar. The enthalpy of reaction in 1,2-dichloroethane (?158.2±1.0 kJ mol^?1), the enthalpy (51.3±0.5 kJ mol^?1), entropy (122±2 J mol^?1 K^?1), and volume of activation (?31.0±1.0 cm3 mol^?1), and the volume of this reaction (?26.6±0.3 cm³ mol^?1) were determined. The high exothermic effect of the reaction suggests its irreversibility.     

New solid polymer electrolytes based on polyester diacrylate for lithium power sources

New solid polymer electrolytes are developed for a lithium power source used at the temperatures up to 100°C. Polyester diacrylate (PEDA) based on oligohydroxyethylacrylate and its block copolymers with polyethylene glycol were offered for polymer matrix formation. The salt used was LiClO₄. The ionic conductivity of electrolytes was measured in the range of 20 to 100°C using the electrochemical impedance method. It is shown that the maximum conductivity in the whole temperature range is characteristic of the electrolyte based on the PEDA copolymer and polyethylene glycol condensation product (2.8 × 10^?6 S cm^?1 at 20°C, 1.8 × 10^?4 S cm^?1 at 95°C).     

Rate Constants and Activation Energies for Gas‐Phase Reactions of Three Cyclic Volatile Methyl Siloxanes with the Hydroxyl Radical

Reaction with hydroxyl radicals (OH) is the major pathway for removal of cyclic volatile methyl siloxanes (cVMS) from air. We present new measurements of second‐order rate constants for reactions of the cVMS octamethylcyclotetrasiloxane (D₄), decamethylcyclopentasiloxane (D₅), and dodecamethylcyclohexasiloxane (D₆) with OH determined at temperatures between 313 and 353 K. Our measurements were made using the method of relative rates with cyclohexane as a reference substance and were conducted in a 140‐mL gas‐phase reaction chamber with online mass spectrometry analysis. When extrapolated to 298 K, our measured reaction rate constants of D₄ and D₅ with the OH radical are 1.9 × 10^?12 (95% confidence interval (CI): (1.7–2.2) × 10^?12) and 2.6 × 10^?12 (CI: (2.3–2.9) × 10^?12) cm³ molecule^?1 s^?1, respectively, which are 1.9× and 1.7× faster than previous measurements. Our measured rate constant for D₆ is 2.8 × 10^?12 (CI: (2.5–3.2) × 10^?12) cm³ molecule^?1 s^?1 and to our knowledge there are no comparable laboratory measurements in the literature. Reaction rates for D₅ were 33% higher than for D₄ (CI: 30–37%), whereas the rates for D₆ were only 8% higher than for D₅ (CI: 5–10%). The activation energies of the reactions of D₄, D₅, and D₆ with OH were not statistically different and had a value of 4300 ± 2800 J/mol.