Rubber elasticity in the introductory thermodynamics course

An experimental set-up is described in which the temperature of a piece of rubber is measured with thin wire thermocouples. It measures and records the temperature change of the rubber as it heats and cools in response to elongation and contraction. This mechano-caloric effect arising from the entropy elasticity of rubber represents a reversible thermal process in clear distinction from most of other heat effects encountered in our daily experience where the irreversibility is inevitably involved. The demonstration experiment has been proved useful in elementary thermodynamic courses for introducing the entropy concept. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal risk evaluation of organic peroxide by automatic pressure tracking adiabatic calorimeter

An automatic pressure tracking adiabatic calorimeter (APTAC) has been developed to obtain the thermokinetic and vapor pressure data during runaway reactions. The heat onset temperature is important data for estimating the thermal hazardous materials. DTBP(di-tert-butyl peroxide)/toluene was chosen for evaluating the measurement values and the thermokinetic parameters. The relationships between the sample mass and the heat onset temperature in the addition to the maximum temperature were investigated to explain the heat of reaction measured by the APTAC. The apparatus properties and the reliability of the data obtained by the APTAC were examined on the basis of the experimental data.     

Measurement of sorption and diffusion in nonporous membranes by transient permeation experiments

The knowledge of sorption and diffusion of liquids or vapors and their mixtures in nonporous membranes facilitates systematic membrane selection and process design. A novel experimental technique for the measurement of sorption and diffusion in nonporous membranes is described. An experimental apparatus has been designed for carrying out the transient permeation experiments. A general time-lag analysis procedure has also been developed in order to obtain the sorption and diffusion parameters from the transient permeation data. The effects of concentration dependent diffusivities, polymer swelling and a thermodynamic correction factor have been included in the analysis. Transient permeation experiments have been carried out to determine the sorption and diffusion of acetone in polydimethylsiloxane (PDMS). The results obtained are in good agreement with data from the literature, indicating that the proposed technique is suitable for the measurement of sorption and diffusion in nonporous membranes.     

An alternative approach to rubber elasticity theory based on a lattice model

An alternative rubber elasticity theory for bulk elastomers has been developed. It is based on the model of a cubic lattice which is filled completely with long flexible chains. The dependence of the configurational entropy on the orientation factor of Hermans has been derived for a uniaxial homogeneous orientation of the system. With the assumption of a constant stress-optical coefficient, the dependence of the true stress Γ on the deformation λ = L/L₀, with L the length of the sample, can be described approximately as τ ∝︁ in λ both for uniaxial extension and compression, which agrees quite well with experimental results on bulk elastomers.     

Solubility of CF4 in lower alcohols

This work is inserted in a research program that consists mainly in the experimental and theoretical study of the effect of association/solvation between solute and solvent molecules in the solubility of gases in liquids. The solubilities of tetrafluoromethane in lower alcohols (methanol, ethanol, 1-propanol, 1-butanol) have been determined in the temperature range of 288–308 K, at atmospheric pressure, using an automated apparatus recently assembled in our laboratory. An accuracy of 0.6% and a precision of the same order of magnitude was achieved. The solubility is the lowest in methanol which is the highest associated alcohol and increases with the C-content of the alcohol. The molar Gibbs energy, enthalpy and entropy of solution were calculated from the experimental results (at 1 atm partial pressure of the gas and 298 K). A semiempirical correlation between the solubility of CF₄ in alcohols at 298 K and the Gutmann acceptor number (AN) of the solvents has been developed.     

Burnett—isochoric P—V—T measurements of a nominal 20 mol% hydrogen—80 mol% methane mixture at elevated temperatures and pressures

A new apparatus is described which has been developed to measure P—V—T relations for hydrogen—hdyrocarbon systems at elevated temperatures and pressures. The principal components are three heavy-walled spherical pressure cells with the same outer/internal diameter ratio, a fully submerged differential pressure cell, and measuring equipment including calibrated piston guages and a platinum resistance thermometer. This apparatus was used to measure densities of a 20.05±0.05 mol% hydrogen?79.95±0.05 mol% methane mixture from 273.15 to 600 K and pressures to 72 MPa. Two Burnett isotherms at 273.15 K established fluid densities without direct measurement of either mass or volume. Eight isochores, ranging in density from 1.62 to 14.91 mol dm^?3, were anchored to the Burnett isotherms at 273.15 K where their densities were firmly established. An analytic equation for the thermodynamic surface has been fitted to the resulting P—V—T data, giving a 0.01% root mean square deviation of calculated compressibility factors from experimental results.     

A simplified calorimeter for the precise determination of purity

A calorimetric apparatus has been constructed for the determination of the mole fraction of impurity in a highly purified sample of a chemical compound by measurement of the temperature of solid-liquid equilibrium as a function of the fraction of the sample melted. An experimental value of the heat of fusion of the compound is also obtained, thus yielding the cryoscopic constant A. The apparatus, though relatively simple to Operate, has given results of good precision. The method has been tested over a wide temperature range using methylcyclopentane, n-heptane, n-decane, cyclohexylcyclohexane, and n-hexadecane, which have freezing points ranging from —142°C to +18°C.     

Constitutive characterization of rubber blends by means of capillary-viscometry

A new procedure for the material characterization of rubber blends is proposed. It is based on a generalized Newton-Raphson procedure. Such a model has to consider the effect of wall slippage on the viscous properties as well as the non-linear coupling of the viscosity and shear strain rate, which is typical for rubber blends and polymers, respectively. The main goal of this method is the reduction of the experimental effort for determination of the viscosity function. Application of the new method is shown for four rubber materials.An experimental investigation of the viscous properties of rubber blends by means of capillary-viscometry serves as the basis of the work. Because of the pseudo-plastic material behavior of the proposed material, characterization is represented by a coupled system of non-linear equations. Describing their solution requires a numerical integration algorithm.Verification of the developed method for parameter identification was done by comparison of the obtained viscosity curves and the respective velocity profiles in capillary dies with the one obtained by the commonly used material characterization based on correction methods.     

An electron diffraction apparatus for small particle beams

An electron diffraction apparatus is described which has been developed for use with small particle beams. The apparatus features a pulsed 100 kV electron beam and on-line parallel measurement of the diffraction pattern using linear charge coupled devices. Preliminary results on a molecular beam of small silver particles are presented.     

Determination of bound rubber composition of filled SBR/BR blend compounds by analysis of the unbound rubber composition and bound rubber content

Analytical method for determination of the bound rubber composition of a filled SBR/BR blend compound was developed using measurement of the bound rubber content and microstructural analysis of the unbound rubber composition. Various filled SBR/BR blend compounds with different blend ratios were prepared using SBRs with different microstructures. This method included measurement of the bound rubber content, extraction of the unbound rubber, microstructural analysis of the unbound rubber composition, and process for determination of the bound rubber composition. Composition of the unbound rubber was analyzed using liquid proton nuclear magnetic resonance spectroscopy (H-NMR) and transmission Fourier transform infrared spectroscopy (FTIR). It was found that the analytical results using H-NMR had less experimental errors than those using transmission-FTIR. The raw SBR/BR blends were also analyzed in order to evaluate level of the experimental errors. Average SBR/BR ratios of the unbound rubbers were obtained using the 1,2- and 1,4-unit contents determined by the H-NMR analysis. The bound rubber compositions were obtained using the bound rubber contents and the average unbound rubber compositions. It was found that most of the bound rubbers had higher SBR ratios than the formulation value.     

Study of a core-shell type impact modifier by inverse gas chromatography

Inverse gas chromatography (IGC) has been used to study the Lewis acid-base properties of a technologically and commercially important core-shell type elastomer (MBS rubber). The parameters determined were the dispersive component of the surface tension, the surface free energy, the enthalpy and the entropy of adsorption of polar and apolar probes, the surface Lewis acidity constant (Ka), and the surface Lewis basicity constant (Kb). The results show that the MBS rubber is amphoteric but strongly Lewis basic. It is weakly Lewis acidic. The results are in accord with the analysis of the molecular structure of PMMA, the shell component of this impact modifier (IM). The interactivity of this elastomer with the remaining materials in multicomponent polymeric systems is expected to be strongly influenced by the particular surface energetic properties of the MBS rubber. The results presented would contribute to the interpretation, forecast and optimization of the adhesion properties and phase preferences shown by this impact modifier when incorporated in such complex polymeric systems as polymer blends and composites.     

Local orthotropic shrinkage determination in injected moulded polymer plates

An apparatus to precisely measure local orthotropic shrinkage in polymer plates has been designed. The principle of local shrinkage determination is based on the comparison of the distance between two small engravings on the plate mould and the distance between the reproduced engravings on the polymer plate. Under a microscope, the distances are measured in two directions on micrometric translation stages. The performance of the entire device, which includes on-line experimental data acquisition, is discussed; the precision of shrinkage measurement remains below 4%. Shrinkage prediction models, which are based on statistical analysis and built with the first experimental results, have proved reliable and have been integrated as an experimental database in a general deformation prediction process of polymer parts.     

A New Approach to the Estimation of a Stationary State in Flow-Injection Analysis

An approach to calculating the rate of entropy production in a system was developed to characterize the stationary state in flow-injection systems on the basis of principles of nonequilibrium thermodynamics, and its relationship to the parameters of the measured peak was found. Thus, it became possible to make quantitative relative estimations in real systems. By the example of a classical flow-injection spectrophotometric determination of uranium with Arsenazo III, it was shown that the rate of entropy production can be estimated from experimental data. It was found that the peak-averaged rate of entropy production decreases with concentration. It was found that, at the moment of the measurement of the peak maximum, this value is actually minimum and nonzero, and the nonlinear dependence corresponds to the best calibration function because of the effect of nonequilibrium factors.     

Light induced atomic desorption from dry-film coatings

We report the first experimental evidence of nonthermal light induced atomic desorption (LIAD) from octadecyltrichlorosilane dry film. The experiment has been made with Rb confined in a coated cell kept at room temperature. A detailed study of the main features of LIAD effect has been made by varying intensity and wavelength of desorbing light. A discussion about the differences and similarities with other organic films that were studied first is reported. This result is important as it expands the list of materials showing such an effect and increases the possibilities to get suitable light controlled atomic sources for spectroscopy and applications. In particular, we plan to exploit this feature in a Fr magneto-optical trap apparatus.     

超临界萃取装置的研制及其应用

超临界流体萃取是近的上来兴起的一种新的分离技术，报道了将超临界萃取原理与回流技术相结合研制的二氧化碳回流中低压超临界流体萃取设备，解决了关键实验手段，通过应用证明设备可靠，费用低廉，有实用价值。     

An investigation of dynamic mechanical, thermal, and electrical properties of housing materials for outdoor polymeric insulators

The present paper reports the results about a study of mechanical, thermal, dynamic mechanical and electrical properties of housing (weather shed) materials for outdoor polymeric insulators. Silicone rubber, ethylene-propylene-diene monomer (EPDM) and alloys of silicon-EPDM are known polymers for use as housing in high voltage insulators. The result of dynamical mechanical measurement shows that the storage modulus of blends enhances with increase EPDM in formulation. It can be seen from the result of TGA measurement that initial thermal degradation of silicone rubber improves by the effect of EPDM in blends. The blends of silicone-EPDM show good breakdown voltage strength compared to silicone rubber. Surface and volume resistance of silicone rubber improve by EPDM content. The mechanical properties of EPDM such as strength, modulus and elongation at break improve by silicone.     

Vapor–liquid equilibria for pentafluoroethane + propane and difluoromethane + propane systems over a temperature range from 253.15 to 323.15 K

This paper provides vapor–liquid equilibrium (VLE) data obtained for two binary systems of pentafluoroethane (R125)+propane (R290) and difluoromethane (R32)+R290 over a temperature range from 253.15 to 323.15 K. The measurement of VLE was performed at isothermal conditions in a vapor recirculation apparatus. Both systems form azeotropes in the temperature range of this study. The experimental results were well correlated with the Peng–Robinson equation of state (PR EoS) using one parameter van der Waals one fluid model. The binary interaction parameters were optimized using the experimental data of bubble point pressure. A comparison with published experimental VLE data has been carried out by means of the PR equation of state.     

Application of the zone-melting technique to metal chelate systems-VI A new apparatus for zone-melting chromatography

An improved apparatus has been constructed for zone-melting chromatography. An essential feature of the apparatus is that the length of the molten zone can be kept constant during a zone-melting operation, by employing heating and cooling compartments which are separated from each other by double partition plates. Each compartment is heated or cooled with jets of hot or cold air. The apparatus is suitable for organic materials melting in the range between 40 degrees and 180 degrees . The distribution of metal ion along the column after zone melting of copper acetylacetonate in 2-methoxynaphthalene was a smooth curve. The plot of the position of maximum concentration, x(max), against the number of zone passes, n, gave a relationship in accordance with theoretical prediction.     

Effects of Epoxidation Content of ENR on Morphology and Mechanical Properties of Natural Rubber Blended PVC

This research work has concerned a study on toughness of PVC/natural rubber (NR) blends compatibilized with epoxidized natural rubber (ENR). The aim of this work was to investigate the effect of degree of epoxidation on morphology and mechanical properties of the blends. Epoxidized natural rubber with a variety of epoxidation contents were prepared by reacting the NR latex with formic acid and hydrogen peroxide at various chemical contents. Chemical structure and epoxidation content of epoxidized natural rubber were evaluated by FTIR and ¹H-NMR techniques. After that, three grades of ENR with epoxidation contents of 15, 25 and 42 % (by mole) were further used for blending with PVC and NR in an internal mixer at 60 rpm and at 170 °C. From tensile and impact tests, it was found that tensile elongation and impact strength of the materials remarkably increased with degree of epoxidation. On the other hand, tensile strength and modulus of the materials rarely changed with the epoxidation content. An increase in toughness of the blends with epoxidation content was related to a better molecular interaction between PVC and ENR as suggested by torque-time curves of the materials.