Thermal conductivity of molecular crystals of monoatomic alcohols: from methanol to butanol

Experimental data on the thermal conductivity κ(T) of some simple alcohols have been compared, analyzed and generalized. The objects of investigation were methyl, protonated and deuterated ethyl, 1-propyl and 1-butyl alcohols in the thermodynamically equilibrium phase with a complete orientational order. The temperature interval was from 2 K to the melting point under the equilibrium vapor pressure. It is found that in the region above the temperature of the maximum thermal conductivity κ(T) deviates from the 1/Т law. This is because the total thermal conductivity has an extra contribution κII(T) of short-lived phonons in addition to κI(T) contributed by propagating phonons: κ(T) = κI(T) + κII(T). The contribution κI(T) is well described by the Debye–Peierls model allowing for the phonon–phonon processes and scattering of phonons by dislocations. At Т > 40 K the contribution κI(T) obeys the law A/Т and κII(T) is practically temperature-independent. It is shown that the Debye temperature ΘD of alcohol is dependent on the molecular mass as ΘD = 678М⁻⁰.⁴² K and the coefficient А characterizing the intensity of the phonon–phonon scattering increases with the molecular mass of the simple monoatomic alcohol by the law А = 0.85М⁰.⁸ W/m, which suggests a decreasing intensity of the phonon–phonon process

The effect of proton ordering in thermal conductivity of clathrate tetrahydrofuran hydrate

The effect of proton ordering in tetrahydrofuran hydrate has been detected using a technique based on measurement of thermal conductivity. The thermal conductivity of tetrahydrofuran hydrate was measured by the steady-state potentiometric method in an interval of 2–150 K. Two regimes were selected to observe the effect: (i) slow cooling of the hydrate sample and (ii) doping the hydrate with a small quantity of KOH alkali to a concentration of 10⁻⁴. Proton ordering affects the temperature dependence of the thermal conductivity changing its glass-like behavior to crystal-like below 150 K. The phonon maximum that appears in the temperature dependence of the thermal conductivity at T = 17 K is attributed to the cooperative process of local proton ordering stimulated by orientational and ionic defects

Heat transfer in crystalline clathrate hydrates at low temperatures

The experimental results on the thermal conductivity k(T) of crystalline Xe, CH₄, and THF clathrate hydrates have been analyzed. In a wide region of temperatures above 2 K, k(T) exhibits a behavior typical of disordered solids, which depends weakly on their chemical composition, crystalline structure and microstructure. The results are discussed in the context of phenomenological models of phonon scattering by local modes. It has been found that the Xe clathrate has a feature unusual for glasses, namely, k(T) decreases almost two-fold as the temperature increases from 50–100 K. The behavior of k(T) is presumably determined mainly by the strong phonon scattering on water molecules

Heat transfer in solid methyl alcohol

Thermal conductivity coefficient к(T) of two crystalline (orientationally-ordered and orientationally-disordered) phases of pure methanol (at temperatures from 2 K to Tm , Tm is the melting temperature), CH₃OH + 6.6 % H₂O glass from 2 K to Tg , Tg is the glass transition temperature and a supercooled liquid from Tg to 120 K has been measured under equilibrium vapor pressure. The dependence к(T) is described approximately as a sum of two contributions: кI(T) describing heat transport by acoustic phonons and кII(T) —by localized high-frequency excitations. The temperature dependences of the thermal conductivity of primary monoatomic alcohols CH₃OH, C₂H₅OH, and C₃H₇OH in the glass state have been compared. Different mechanisms of phonon scattering in the crystalline phases and glass have been analyzed. The кII(T) has been calculated within the Cahill–Pohl model. There is an anomaly of the thermal conductivity of the glass state near Tg (a smeared minimum in the к(T) — curve)

Anomaly in temperature dependence of thermal transport of two hydrogen-bonded glass-forming liquids

6 págs.; 3 figs.; PACS number s : 66.70. f, 63.50. x, 65.20. w, 65.60. aThe thermal conductivity of two molecular glasses (ethanol and 1-propanol) decrease with increasing temperature up to their glass transitions at Tg 97 and 98 K, respectively. Within their supercooled liquid phases, the conductivity increases with rising temperature up to a maximum which roughly coincides with the liquidus (or melting temperatures Tm 159 K and Tm 149 K, respectively). From there on, the conductivity decreases with increasing temperature, a behavior common to most liquids examined so far, exception made of liquid water. The origin of the rather different dependencies with temperature of thermal transport is understood as a competition between phonon-assisted and diffusive transport effects which are amenable to experiments using high resolution quasielastic neutron scattering and visible and ultraviolet Brillouin light-scattering spectroscopies. © 2007 The American Physical Society.Peer Reviewe

Deuteration effects in the thermal conductivity of molecular glasses

The thermal conductivity κ(T) of pure deuterated ethanol has been measured under its equilibrium vapor pressure in its orientationally-ordered crystal (T = 2 K – Tm), orientational glass and the glass state (T = 2 K – Tg, Tg is the glass transition temperature) solid phases. The temperature dependence of the conductivity is well described by a sum of two contributions: κ(T) = κI(T) + κII(T), where κI(T) account for the heat transport by acoustic phonons and κII(T) for the heat transfer by localized high-frequency excitations respectively. The thermal conductivities of deuterated and hydrogenated ethanols are compared in different phases. The phonon scattering mechanisms in the glasses have been analyzed. In the investigated glasses the effect of complete deuteration shows up as a contribution κII(T)

Experimental evidence of the role of quasilocalized phonons in the thermal conductivity of simple alcohols in orientationally ordered crystalline phases

The thermal conductivity к(T) of crystalline alcohols (methyl, ethyl and 1-propyl) within their thermodynamic equilibrium phases for T ≥ 2 K and under the equilibrium vapor pressures has been measured and analyzed. While such compounds usually exhibit a rich polymorphism including amorphous and partially ordered crystals, the phases here explored correspond to crystals showing complete orientational order. The results show that the temperature dependence of к(T) above its maximum deviates from the expected decrease following a 1/T law with increasing temperature arising from anharmonic interactions involving acoustic excitations. Such a deviation is here attributed to the presence of a component кII(T) corresponding to the shortest-lifetime phonons (Cahill–Pohl model) additional to that кI(T) related to propagating phonons and thus: к(T) = кI(T) + кII(T). Above T = 40 K кI(T) does follow the law 1/T and кII(T) is basically temperature independent. The component кI(T) is well described by the Debye–Peierls model taking into account the phonon–phonon Umklapp processes and phonon scattering by dislocations. In turn, the contribution кII(T) is attributed to the effects of higher lying excitations which get thermally populated above some 40 K. Finally, a systematic trend is found concerning the strength of phonon–phonon scattering which is seen to diminish as the number of carbon atoms in the alcohol molecule increases

Thermal conductivity of solid parahydrogen with methane admixtures

The thermal conductivity of solid parahydrogen crystal with methane admixtures has been measured in the temperature range 1.5 to 8 K. Solid samples were grown from the gas mixture at 13 K. Concentration of CH₄ admixture molecules in the gas varied from 5 to 570 ppm. A very broad maximum of thermal conductivity with absolute value of about 110 W/(m×K) is observed at 2.6 K. The data are interpreted by Callaway model considering phonons resonant scattering on quasi-local vibrations of CH₄ molecules, phonon-grain boundary and phonon-phonon scattering processes. The increase of grain boundary scattering leads to the decrease of the maximum broadening. The analysis shows that the solid mixture of p-H₂ and CH₄ is a heterogeneous solution for CH₄ concentration higher than 0.1 ppm

Effects of internal molecular degrees of freedom on the thermal conductivity of some glasses and disordered crystals

The thermal conductivity κ(T) of the fully ordered stable phase II, the metastable phase III, the orientationally disordered (plastic) phase I, as well as the nonergodic orientational glass (OG) phase, of the glass former cyclohexanol (C 6H 11OH) has been measured under equilibrium vapor pressure within the 2-200 K temperature range. The main emphasis is here focused on the influence of the conformational disorder upon the thermal properties of this material. Comparison of results with those regarding cyanoclyclohexane (C 6H 11CN), a chemically related compound, serves to quantify the role played by the terminal groups -OH and -CN on the phonon scattering processes. The picture that emerges shows that motions of such groups do play a minor role as scattering centers, both within the low-temperature orientationally ordered phases as well as in the OG states. The results are analyzed within the Debye-Peierls relaxation time model for isotropic solids comprising mechanisms for long-wave phonon scattering within the OG and orientational ordered low-temperature phases, as well as others arising from localized short-wavelength vibrational modes as pictured by the Cahill-Pohl model. By means of complementary neutron and Raman scattering we show that in the OG state the energy landscapes for both compounds are very similar. © 2012 American Physical Society.This work was financially supported in part by the Spanish Ministry of Science and Innovation (Grant No. FIS2008-00837) and the Catalan Government (Grant No. 2009SGR-1251)Peer Reviewe

Low-temperature properties of monoalcohol glasses and crystals

We review and jointly discuss both earlier and recent experiments conducted by us on simple aliphatic glass-forming monoalcohols at low temperatures, including specific heat, thermal conductivity, Brillouin scattering and x-ray diffraction experiments. The family of simple monoalcohols constitutes an interesting model system to explore different relevant issues concerning molecular glass-forming liquids, low-temperature universal proper-ties of glasses, and even the glass transition phenomenon itself. More specifically, we discuss the role played by the molecular aspect ratio in vitrification/crystallization kinetics, the reported appearance of particular cases of polymorphism (in ethanol) and polyamorphism (in butanol), and especially the influence of position isomerism and the location of the hydrogen bond on the lattice dynamics and hence on the low-temperature universal prop-erties of glasses