Thermal expansion of polymers subjected to low-amplitude temperature cycling

The temperature dependence of the thermal expansion of polymers subjected to small harmonic temperature oscillations about certain base temperatures near the glass transition range is considered. The conformational component of the expansion as a function of temperature is calculated in terms of the conformational transition kinetics. The temperature dependences of the expansion and the expansion vs. oscillation phase shift are analyzed with allowance for the vibrationally anharmonic component. The thermal expansion of polyvinylacetate at base temperatures of 295–320 K, oscillation frequencies of 0.3 and 0.1 Hz, and an oscillation amplitude of 0.8 K are studied experimentally. The measured and calculated data for the expansion and expansion vs. temperature phase shift are shown to be in good agreement.     

Mechanisms of elementary events in the kinetics of electrical breakdown of polymer and ceramic dielectrics

The kinetics of electrical breakdown of thin (15–70 μm) layers of polymers and ceramics in a constant-sign field at 77–480 K has been investigated. The temperature dependences of the longevity (breakdown waiting time) of both dielectrics have been found to be similar to each other. At elevated temperatures, the longevity of the dielectrics varies exponentially with increasing temperature, and at reduced temperatures, it is temperature-independent (there is an athermal plateau). The mechanisms of elementary events controlling the process of preparation of the dielectrics for breakdown at elevated and reduced temperatures are the thermal-fluctuation over-barrier electron transition from trap to trap and the tunneling (under-barrier) transition, respectively. The hopping electron transport in the field direction gives rise to critical space charges causing breakdown of the dielectrics. The transition barrier heights (trap depths) have been determined. The low-temperature longevities of the polymer and the ceramic have been found to be similar, whereas the transition barrier for the ceramic is much higher than that for the polymer and the applied field in the former case is significantly (by a factor of tens) lower than that in the latter case. Electron traps in the polymer are adequately described by the Coulomb center model, whereas this is not the case for the ceramic.     

Features of the kinetics of electrical damage of polymers

The kinetics of electrical damage (breakdown) of polymer films 20–50 μm thick in a constant-sign field of 0.5–0.6 GV/m at 77–300 K has been studied. At elevated temperatures (250–300 K), the exponential temperature dependence of the durability and the above-barrier thermal-fluctuation mechanism of electron emission from traps, i.e., space charge accumulation leading to breakdown, take place. At low temperatures (77–200 K), there are separate local decreases in the durability (minima) at the athermal durability level. The identity of the temperatures of durability minima and measured thermoluminescence maxima of polymers was found. A conclusion is made about the mechanism of thermally stimulated tunneling (subbarrier emission) of electrons from traps.     

Solubility isotherm for the Na<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-H<Subscript>2</Subscript>O system

Solubility in the Na₂MoO₄-Na₂SO₄-H₂O system was studied using isothermal saturation at 5–100°C. The boundaries of crystallization fields were determined for sodium sulfate and sodium molybdate. Solid solutions were not observed within the range of the temperatures studied. The density, refractive index, and dynamic viscosity of the saturated solutions of the system were determined, and these data were used to calculate the molar volume, kinematic viscosity, and apparent molar volume of the sum of salts in these solutions. All property isotherms of solutions are in a strict correlation with the solubility in the system; this correlation is represented as an isobaric-isothermal diagram.     

Possible manifestations of the quantum effect (Tunneling) in elementary events in the fracture kinetics of polymers

An elementary event in the kinetics of fracture of polymers, i.e., breaking of a stressed skeletal bond in a chain molecule, has been simulated by the decay of a loaded quantum anharmonic oscillator. The probability and the average time of expectation of the escape of a particle from the potential well in the Morse potential under the action of a tensile force have been calculated over a wide range of temperatures. It has been demonstrated that the escape of the particle occurs predominantly through the tunneling mechanism at low and medium temperatures and through a combination of the tunneling (under-barrier) and over-barrier (thermal-fluctuation) mechanisms with comparable contributions at high temperatures. The calculations have revealed that the participation of the tunneling mechanism in the kinetics of fracture of polymers manifests itself in a low-temperature athermal plateau in the temperature dependence of the breaking strength. A comparison between the calculated and experimental temperature dependences of the breaking strength for the oriented polymer polycaproamide has shown that the calculated and experimental results are in qualitative and quantitative agreement, which allows the conclusion that the tunneling mechanism can contribute to the fracture of polymers.     

A possible effect of quantum characteristics of vibrational dynamics on the conformational dynamics in polymers

Dielectric losses in poly(vinyl acetate) and poly(ethyleneterephthalate) polar polymers are measured in wide ranges of frequencies and temperatures. The temperature dependences of the frequency of activation transitions of two types, small-scale and conformational, are derived. For conformational transitions, it is revealed that the temperature dependence of their frequency exhibits nonlinear behavior (in Arrhenius coordinates); it determines the temperature dependence of barriers to transitions and the defreezing temperature of conformational dynamics (∼300 K for poly(vinyl acetate) and ∼370 K for poly(ethyleneterephthalate)). This temperature is found to be close to the temperatures of the quantum defreezing of the molecular dynamics of poly(vinyl acetate) and poly(ethyleneterephthalate) (∼300 and 400 K) according to IR spectroscopy data. It is assumed that a decrease in the barrier to the conformational transitions that provide defreezing of the conformational dynamics is caused by a decrease that occurs in the rigidity of polymer molecules owing to quantum defreezing of the vibrational molecular dynamics of the polymers.     

Tensor field tomography of residual stresses

An approximate method is proposed for determining residual stresses in elonagted transparent articles featuring weak variation of the stress field along the axis. The proposed method is a generalization of the well-known method of determining internal stresses in optic fibers based on the integrated photoelasticity measurements. Complete determination of the stress tensor components is performed within the framework of the concept of temperature-dependent residual stresses.     

Calculation of multipole components in the macroscopic theory of the polarization of dielectrics

Expressions are derived for the calculation of multipole corrections to the magnitude of the electric field produced by a polarized dielectric. The quadrupole correction to the Lorentz field is calculated.Translated from Izvestiya VUZ. Fizika, No. 6, pp. 36–38, June, 1973.     

Solubility and physicochemical properties of lithium molybdate-<Emphasis Type="Italic">n</Emphasis>-butanol-water solutions at 25°C

Solubilities in the Li₂MoO₄-n-C₄H₉OH-H₂O system at 25°C have been studied. New chemical compounds are not formed in the system. The miscibility of the solvents noticeably decreases with increasing Li₂MoO₄ concentration. The C₄H₉OH solubility decreases from 7.45 wt % in neat water to 0.01 wt % in a saturated (44.40 wt %) aqueous solution of Li₂MoO₄. The H₂O solubility in n-C₄H₉OH decreases from 20.48 to 5.50 wt % in the presence of trace amounts of Li₂MoO₄. In the invariant state, saturated liquid phases (\(L_{E_1 } \) and \(L_{E_2 } \)), which are in equilibrium with solid Li₂MoO₄, have the following compositions (wt%): for \(L_{E_1 } \), 43.94% Li₂MoO₄, 0.01% C₄H₉OH, and 56.05% H₂O; and for \(L_{E_2 } \), 0.0011% Li₂MoO₄, 94.50% C₄H₉OH, and 5.50% H₂O. The density, refractive index, dynamic viscosity, and electrical conductivity of the saturated solutions of the system have been determined. The isotherms have been calculated for the specific and molar volumes, kinematic viscosity, and equivalent and reduced electrical conductivity of the solutions.