Effects of Temperature and Pressure on the Thermal Conductivity of Solid n‐Undecane

We have measured the thermal conductivity, λ, of n-undecane, using the transient hot-wire technique. At low pressures, n-undecane has a plastic crystal phase αH. The increase in λ, going from the liquid to phase αH, was 35%. For a liquid plastic crystal transition, this is a high value. It reflects that orientational disorder is mainly limited to rotation of the rod-shaped molecule around its chain axis. The low temperature phase βO, was shown to exhibit a weak temperature dependence of λ at isochoric conditions. This suggests the presence of structural disorder, probably caused by reorientation of the chain-end methyl groups. The volume dependence of λ in phase βO, g = -(∂ln λ/∂ln V)T, was found to be about 9.5. This result is discussed in terms of the anharmonicity of the weak interchain van der Waal's bonds. Some heat capacity results were also obtained.

[1]  G. A. Slack,et al.  Pressure and temperature effects on the thermal conductivity of CuCl , 1982 .

[2]  W. Wakeham,et al.  The Thermal Conductivity of n-Nonane and n-Undecane at Pressures up to 500 MPa in the Temperature Range 35–90°C , 1982 .

[3]  A. Craievich,et al.  X‐ray study of the ‘‘rotator’’ phase of the odd‐numbered paraffins C17H36, C19H40, and C21H44 , 1981 .

[4]  R. G. Ross,et al.  Thermal Conductivity, Heat Capacity and Phase Diagrams of the Trichloroethanes Under Pressure: I. 1,1,1 – trichloroethane , 1981 .

[5]  A. Jayaraman,et al.  Temperature and pressure dependence of the Raman spectrum of crystalline P 4 S 3 , 1981 .

[6]  R. Landau,et al.  PVT‐Daten von Acetonitril, Undecan und Dodecan bis 3 kbar und −50°C. Druckabhängigkeit der Umwandlungsvolumina, ‐enthalpien und ‐entropien , 1980 .

[7]  G. Strobl,et al.  Phase transitions in crystals of chain molecules. Relation between defect structures and molecular motion in the four modifications of n-C33H68 , 1980 .

[8]  R. G. Ross,et al.  Thermal conductivity and heat capacity of solid phases of benzene under pressure , 1979 .

[9]  P. Andersson.  Thermal conductivity and heat capacity of cyclopentane in the range 100-300 K and up to 2·1 GPa , 1978 .

[10]  P. Andersson.  Thermal conductivity and heat capacity of cyclohexane under pressure , 1977 .

[11]  B. Fanconi,et al.  Low frequency Raman‐active lattice vibrations of n ‐paraffins , 1973 .

[12]  S. Todd,et al.  Low-temperature thermal data for pentane, n-heptadecane, and n-octadecane. Revised thermodynamic functions for the n-alkanes, C5-C18 , 1967 .

[13]  J. Anderson,et al.  Nuclear Spin Relaxation in Solid n-Alkanes , 1965 .

[14]  M. Broadhurst,et al.  An Analysis of the Solid Phase Behavior of the Normal Paraffins , 1962, Journal of Research of the National Bureau of Standards. Section A, Physics and Chemistry.

[15]  J. Hoffman,et al.  Erratum: Hindered Intermolecular Rotation in the Solid State: Thermal and Dielectric Phenomena in Lo , 1952 .