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• 1.5 times enhanced thermal conductivity of ABS by 0.5% trGO addition. • minimal thermal conductivity linked to phonon scattering/coherence phenomena. • Arrhenius-type function reveals universality in thermal behavior. The thermal conductivity of pure ABS polymer and ABS polymer composite with 0.5 wt% of the thermally reduced graphene oxide (trGO) was measured in a wide temperature range from 2 to 100 K. Adding 0.5 % trGO enhanced the thermal conductivity of ABS polymer by 1.5 times over the entire temperature range. A comparison of the thermal conductivity of ABS and epoxy-resin amorphous polymers and structural glasses shows that it is closely related to the concept of minimal thermal conductivity, which is determined by the intrinsic phonon scattering and the coherence contribution to the thermal conductivity in the material. The temperature dependence of the coherence contribution to the thermal conductivity, related to wave-like tunneling and loss of coherence between different vibrational eigenstates, was approximated by the exponential function of an Arrhenius type with characteristic energy E and a pre-exponential coefficient κ 0. A proportional correlation was found between the low-temperature anomaly of the heat capacity, named the calorimetric Boson peak, and the high-temperature behavior of thermal conductivity of amorphous polymers and structural glasses. Thus, this study provides new physical information about the thermal conductivity in disordered materials and indicates a universality of its temperature dependence. [ABSTRACT FROM AUTHOR]

Thermal conductivity κ of a single crystal triclinic 4-bromobenzophenone polymorph was measured along axis b from 4.5 to 303 K. The κ values versus temperature were represented as a sum of κ 1 , which generally describes the thermal conductivity of ordered crystals, and κ TA responsible for activation processes, which fits nicely experimental data from 120 up. DFT analysis led to the conclusion that the activation agent responsible for the high-temperature behavior is the molecular mode that involves C–Br oscillations. It is for the first time that the exponential thermal conduction was ascribed to a specific intramolecular excitation. [ABSTRACT FROM AUTHOR]

The thermal conductivity of CBr n Cl 4 - n ,(n = 0,1,2) and 2-adamantanone (C 10 H 14 O) crystals which exhibit substitutional disorder has been measured for temperatures between 2 K and 150 K. Such temperatures comprise signatures of dynamical processes involving the site occupancy of the chlorine and bromine atoms for CBr n Cl 4 - n ,(n = 0,1,2) and the oxygen atom for (C 10 H 14 O), as it has been revealed by both, calorimetry and spectroscopic techniques. The data analysis is carried out in terms of several phonon scattering channels contributing to a resistive relaxation rate which can be represented by two contributions due to propagating phonons whose mean-free path exceeds half the phonon wavelength as well as a term attributed to localized short wavelength modes. The implications of the present findings for studies pertaining to glassy dynamics are briefly discussed. [ABSTRACT FROM AUTHOR]

Abstract: The thermal conductivity of solid cyclohexene C6H10 has been measured in two independent experiments in five different stable and metastable phase states: orientational glass (Ig), orientational glass (IIIg) with a partial order, dynamically orientationally disordered state (III) with a partial order, completely orientationally ordered phase (II) and “plastic” phase (I). The measurements were carried out at saturated vapor pressure in the temperature range 2–120K and at isochoric conditions in “plastic” and orientationally ordered phases on samples of different densities. The isochoric thermal conductivity of “plastic” phase increases smoothly with temperature. It can be attributed to weakening of the translational orientational coupling which, in turn, leads to a decrease in phonon scattering on rotational excitations. The thermal conductivity of cyclohexene measured at saturated vapor pressure exhibits a similar behavior in phases Ig, IIIg, and II. At low temperatures (T<8K) the thermal conductivity tends to T 2 dependence, passes through a maximum and decreases further with increasing temperature following the dependence, which is somewhat different from 1/T. It was found that the thermal conductivity can be represented as a sum of two contributions κ(T)=κ 1 (T)+κ 2(T), where κ 1(T) is due to propagating phonons whose mean-free path exceeds half the phonon wavelength, and κ 2(T) is attributed to localized short-wavelength or “diffusive” vibrational modes. [Copyright &y& Elsevier]

Abstract: Thermal conductivity κ(T) data for homologous series of primary mono-hydric alcohols – methanol, ethanol, 1-propanol, 1-butanol – within their molecular glass states are analyzed within the temperature region stretching from 2K up to the glass transition Tg. Below 7K κ(T) increases with the number of carbon atoms in the molecule. Furthermore, its temperature dependence exhibits a behavior akin to that predicted by the phenomenological model of soft potentials (SPM). The data are then rationalized in terms of the SPM parameters such as characteristic energy W and the parameter ¯С which measures the strength of the coupling of acoustic modes with two-level systems. The dependence of such parameters upon the molecular mass of the alcohol seems to agree with the SPM predictions. The parameters ¯С and W were used to calculate the boson peak energies. The values obtained agree well with literature data. [ABSTRACT FROM AUTHOR]

The dynamic interaction of a quantum rotor with its crystalline environment has been studied by measurement of the thermal conductivity of the Kr[sub 1-c](CH[sub 4])[sub c] solid solutions at c=0.05–0.75 in the temperature region 2–40 K. The thermal resistance of the solutions was mainly determined by the resonance scattering of phonons on CH[sub 4] molecules with the nuclear spin I=1 (the nuclear spin of the T species). The influence of the nuclear spin conversion on the temperature dependence of the thermal conductivity κ(T) leads to a well-defined minimum on κ(T). The temperature of the minimum depends on the CH[sub 4] concentration. It was shown that the nonmonotonic increase of the anisotropic molecular field with the CH[sub 4] concentration is caused by a compensation effect due to corrections in the mutual orientations of the neighboring rotors at c κ>0.5. The temperature dependence or Kr[sub 1-c](CH[sub 4])[sub c] is described within the Debye model of thermal conductivity taking into account the lower limit of the phonon mean free path. It is shown that phonon–rotation coupling is responsible for the anomalous temperature dependence of the thermal resistance at varying temperature. It increases strongly when the quantum character of the CH[sub 4] rotation at low temperatures changes to a classical one at high temperatures. A thermal conductivity jump (a sharp increase in κ(T) within a narrow temperature range) was also observed. The temperature position of the jump varies from 9.7 to 8.4 K when the CH[sub 4] concentration changes from 0.25 to 0.45. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Isochoric thermal conductivity of crystalline 1,1-difluoroethane (F-152a freon) is measured on samples of different densities in the dynamically orientationally disordered (DOD) phase. The thermal conductivity increased with temperature, similar to how it occurs in amorphous and glass-like substances above the plateau area. It is found that this behavior can be described by a thermo-activation mechanism with constant activation energy and density-dependent pre-exponential factor. Bridgman coefficient g = − (∂lnκ/∂lnV) T is 6.0 ± 0.5. It is shown that the thermal conductivity of a number of other molecular crystals with the dynamic orientational disorder can be described in a similar way. Possible reasons for the thermal activation behavior of thermal conductivity are discussed. • Isochoric thermal conductivity of crystalline 1,1-difluoroethane in the dynamic orientation disordered phase. • The hopping thermal activation mechanism with constant activation energy and a density dependence of pre-exponential factor. • The thermal conductivity of a number of other molecular disorder crystals can be described in a similar way. [ABSTRACT FROM AUTHOR]

The thermal conductivity of a solid parahydrogen crystal with methane admixtures was measured in the temperature range 1.5 to 8 K. Solid samples were grown from the gas mixtures at 13 K. The concentration of CH[sub 4] admixture molecules in the gas varied from 5 to 570 ppm. A very broad thermal conductivity peak with an absolute value of about 110 W/(m·K) was observed at 2.6 K. The data were interpreted using Callaway’s model with resonance scattering of phonons by quasilocal vibrations of CH[sub 4] molecules and phonon–grain boundary and phonon–phonon scattering. As grain boundary scattering increases, the broadening of the peak decreases. The analysis shows that a solid mixture of p-H[sub 2] and CH[sub 4] is a heterogeneous solution for CH[sub 4] concentration higher than 0.1 ppm. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have concurrently measured the specific heat, the thermal conductivity, and the longitudinal and transverse sound velocities at low temperature of glasses from different isomers of butanol («-butanol, sec-butanol and isobutanol), as well as the low-temperature specific heat for the crystals of «-butanol, isobutanol and ierf-butanol. Whereas the elastic constants both for crystals and glasses are found to be almost independent of the position of the hydrogen bonds, the thermal properties at low temperatures of these glasses at a few kelvin (around the boson peak in the reduced specific heat or around the plateau in the thermal conductivity) are found to vary strongly. Our experiments clearly contradict other works or models claiming a Debye scaling of the boson peak, and hence of the excess low-temperature specific heat of glasses. Data analysis based upon the soft-potential model and its extensions allows us to estimate the Ioffe-Regel limit in these and other alcohol glasses, finding a correlation with the boson-peak position in agreement with that previously reported by other groups [ABSTRACT FROM AUTHOR]

Studies the influence of an orthodeuterium impurity on the thermal conductivity of solid parahydrogen. Thermal conductivity of parahydrogen samples at deuterium concentration; Relative change of the force constants and radial distortion; Deviations from classical scattering of phonons by an isotopic impurity.

The preliminary results of experimental investigations of the thermal conductivity of nanocomposites built of amorphous silica nanoparticles embedded in the structure of crystalline methane are presented. The investigations were carried out on the samples containing the particles of linear dimensions of 5, 10–20 and 42 nm. The measurements were performed with steady-state heat flow method in the temperature interval 2–35 K. A very simple thermal conductivity model shows that the dependence of the thermal conductivity coefficient of the investigated nanocomposites on temperature can be successfully described by taking into account only two mechanisms of the heat carrier dissipation: scattering of phonons by methane crystal grain boundaries and phonon-phonon interaction in U-processes. It was found that the low-temperature phonon mean free path is inversely proportional to the linear dimension of the nanopowder particles embedded in the methane crystal structure. [ABSTRACT FROM AUTHOR]

The low-temperature dependence of thermal conductivity coefficient of dielectric crystals on temperature spreads over a vast region, both in terms of the absolute value of the coefficient as well as its functional dependence on the temperature. However, we were able to notice a group of simple molecular polycrystals which show their thermal conductivity very close to each other. What is more, the similarity of the thermal conductivity of the polycrystals for many reasons resembles known and studied for over 30 years the universality observed for low-temperature thermal conductivity of amorphous solids. Here, utilizing already developed thermal conductivity models, we try to understand what phenomena could result in the similarity of the thermal conductivity of the polycrystals and therefore explain the finding. Provided that some other conditions are met at least each of three different phonon scattering mechanisms could lead to the similarity. [ABSTRACT FROM AUTHOR]

The thermal conductivity of CH[sub 4]-Kr solid solutions is investigated at CH[sub 4] concentrations 0.2-5.0% in the temperature range 1.8-40 K. It is found that the temperature dependence of the thermal conductivity has features typical of resonance phonon scattering. The analysis of the experimental results shows that the main contribution to the impurity-caused scattering of phonons is made by the scattering on rotational excitations of the nuclear spin T-species of CH[sub 4] molecules. The phonon-rotation interaction parameter is estimated. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The thermal conductivity of orthodeuterium crystals containing a neon impurity is investigated in the temperature interval 1.8-17 K. The results of the measurements are described in the framework of the relaxation-time model with allowance for phonon-phonon scattering processes. The intensity of the normal scattering processes for deuterium are determined. The existing theoretical models are used to estimate the intensity of the phonon scattering processes for a number of cryocrystals. The calculated intensity of the normal processes is compared to the experimental result. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]