Ultrasonic studies of rotational isomerism in 2,3-dimethyl-butane and 2,2,4-trimethylpentane at elevated pressures

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The phase behaviour and dielectric relaxation of cyclooctanol has been studied in the temperature range 240 — 300 K and up to pressures of 300 MPa. Two recently found pressure‐induced solid phases have been confirmed and designated as orientationally disordered ones. The complex dielectric permittivity for the orientationally disordered phases is determined as a function of pressure and temperature for frequencies between 1 kHz and 13 MHz. The loss curves are described with modified Debye theories and the Jonscher equation. The results are compared with previous findings on smaller cyclic alcohol

Section: Relaxation Timementioning

confidence: 99%

Dielectric Behaviour at High Pressure of Cyclo‐Octanol

Poser

Würflinger

1988

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“…tic crystals [4] and seems to be typical for intermolecular reorientations. On the other hand in ultrasonic studies of internal rotations of flexible molecules the opposite pressure dependence is observed [20].…”

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confidence: 99%

Thermal Conductivity of Benzene and Cyclohexane under High Pressures

Tanaka

Hase

Kubota

et al. 1988

The thermal conductivity of benzene and cyclohexane has been measured by a transient hot‐wire method in the temperatue range from 283–373 K under pressures up to 250 MPa or freezing pressures with an estimated uncertainty of ±1.0%. The thermal conductivity of each substance decreases almost linearly with rising temperature at a constant pressure, and increases with increasing pressure at a constant temperature. The absolute value of the temperature coefficient of the thermal conductivity, (∂λ/∂T)P decreases with increasing pressure. The pressure coefficient (∂λ/∂P)T increases with rising temperature. The thermal conductivity obtained are correlated with temperature and pressure by a similar expression to the Tait equation. The dense hard‐sphere model presented by Menashe et al. also provides good representation of the present experimental results.

“…The high pressure apparatus used for the P,V,T [4-61 and ultrasonic [7,8] measurements have been described previously. The high pressure dilatomer [S] was originally designed to determine P, V, T data for plastic crystals, but can also be applied for liquids.…”

Section: Methodsmentioning

confidence: 99%

“…Atmospheric pressure velocities reported by Young and Petrauskas [lS] agree well with the presented data which are compiled in Table 2. It is interesting to mention that the velocities of sound for 2-methylbutane are significantly smaller than for 2.3-dimethylbutane [8,9] . I I I I I I I I I I I I I t v/rns-'…”

Section: Ultrasound Velocitiesmentioning

confidence: 99%

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Ultrasonic Studies of Rotational Isomerism and P,V,T Data of 2‐Methylbutane at Elevated Pressures

Walter

Bardelmeier

Würflinger

1992

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Ultrasonic velocity and attenuation have been measured in 2‐methylbutane from 203 to 253 K and pressures up to 100 MPa. P,V,T data are determined in the temperature range from 210 to 290 K up to pressure of 300 MPa. Both activation and equilibrium parameters are derived from the temperature and pressure dependences of the relaxation frequency and the maximum of absorption. P,V,T data enable us to treat the rotational isomerism under isochoric conditions. Activation volumes of the order 4–8 cm3 mol−1 are observed, increasing with increasing temperature. The isochoric activation energy is of the order of 15–18 kJ mol−1, decreasing with increasing density. This finding is in reasonable accordance with the negative volume change associated with the rotational isomerism.