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)

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

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)

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

Disorder effects on heat transport properties of orientationally disordered crystals

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Analysis of large scale linear programming problems with embedded network structures Detection and solution algorithms

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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 (C6H11OH) 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 (C6H11CN), 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