C. Talón

Thermodynamic and structural properties of the two isomers of solid propanol

Abstract We have measured the specific heat, Cp, of the two chemical isomers of propanol, both at low temperatures (1.5–30 K) and around the glass-transition region (≈100 K ) . Although the two substances present only the stereoisomeric difference, their glass-transition temperatures differ ( T g ≃98 K for 1-propanol and T g ≃115 K for 2-propanol), though with comparable changes in specific heat. At temperatures below 10 K, both isomers in the glassy state have the typical maximum in Cp/T3. Nevertheless, the magnitude of the low-temperature specific heat is much larger in 2-propanol than in 1-propanol, a difference which is also found in the Debye contributions in the corresponding crystalline states. To investigate the structural differences between the two isomers of propanol, and their possible influence on the thermodynamic properties, X-ray scattering experiments have been performed on samples of the glassy and crystalline states. In the glassy state, both isomers present the expected amorphous pattern, with characteristic distances of 0.40±0.06 and 0.42±0.07 nm for 1- and 2-propanol, respectively. Preliminary structural analysis of the crystalline states would assign a triclinic structure for 1-propanol and a monoclinic structure for 2-propanol.

Low-temperature specific heat and thermal conductivity of glycerol

We have measured the thermal conductivity of glassy glycerol between 1.5 and 100 K, as well as the specific heat of both glassy and crystalline phases of glycerol between 0.5 and 25 K. We discuss both low-temperature properties of this typical molecular glass in terms of the soft-potential model. Our finding of an excellent agreement between its predictions and experimental data for these two independent measurements constitutes a robust proof of the capabilities of the soft-potential model to account for the low-temperature properties of glasses in a wide temperature range.

Low-temperature thermal properties of molecular glasses and crystals

Abstract We have developed two instrumental arrangements for the measurement of low-temperature specific heat and thermal conductivity of molecular glasses and crystals, which are liquid at ambient temperature. We present measurements carried out with ethanol (CH3CH2OH). Ethanol is an organic low-molecular-weight substance, which exhibits polymorphism. There are three different phases at low temperature: a stable monoclinic crystal, a conventional structural glass, and an orientational glass produced by supercooling a plastic crystalline state. Fully-deuterated ethanol (CD3CD2OD) has also been studied. The specific heat C p(T) and the thermal conductivity κ(T) of several crystalline and glassy states of ethanol have been measured in the temperature range from around 2 K up to 30 K. All structural and orientational glassy states show the so-called “anomalous” thermal properties of common inorganic glasses.

Low-temperature specific heat of molecular glasses and crystals

Abstract We have measured the low-temperature specific heat C p of several glass-forming alcohols. Special attention has been paid to ethanol, either hydrogenated or deuterated, in its different solid phases (fully ordered crystal, disordered crystal or orientational glass, and true structural glass). New measurements have been carried out on 1- and 2-propanol (for crystal and glass states) and on the glass phase of glycerol. The comparison of the isotopic effects in ethanol, as well as that with two isomers of propanol, provide a unique benchmark to study the relative importance of different kinds of disorder. In this work, the whole set of maxima in C p / T 3 is discussed in the framework of the scaling procedure of Liu and Lohneysen [Europhys. Lett. 33 (1996) 617].

Low‐Temperature Specific Heat and Brillouin Scattering Measurements on Hydrogen‐Bonded Glasses

We review specific‐heat and Brillouin‐scattering experiments, that have been conducted as a function of temperature on different hydrogen‐bonded glasses. Specifically, we have measured the low‐temperature specific heat for a set of glassy alcohols: normal and fully‐deuterated ethanol, 1‐ and 2‐ propanol, and glycerol. In addition, we are currently performing Brillouin‐scattering experiments on the same glasses in order to obtain their sound velocities and hence their Debye coefficients. First acoustic measurements conducted on 1‐ and 2‐ propanol are presented.