Thermodynamic properties of liquid toluene

Abstract

Expansivity and compressibility measurements have been made for toluene in the temperature range 200-450 K up to 4 kbar. The experiments were performed by a modified piezothermal technique bringing out a self-consistent set of data for these quantities. An anomaly is observed in the behavior of the heat capacities at low temperature in the high-density region. This has been interpreted as a progressive conversion from one type of molecular motion to another as volume increases. The qualitative aspects of this phenomenon are discussed.

On the correlation between fragility and stretching in glass-forming liquids

“…If the expansion coefficient is to be smaller than the estimate from this temperature dependence, then it would mean that the temperature dependence of the expansion coefficient should increase as temperature decreases. This is the opposite of what is seen in real liquids, where α P at atmospheric pressure tends to a constant at low temperatures [30]. It is actually most common to assume that the α P of molecular liquids is constant below room temperature (e.g.…”

“…Extrapolating the derivatives rather than the density itself is expected to lead to smaller errors on the latter. In addition, we have checked that this procedure gives physically reasonable pressure and temperature dependences of the expansivity and of the compressibility [30]. Figure 4 shows the density dependence of the alpha-relaxation time along the four different isotherms, the atmospheric-pressure isobar and the 230 MPa isobar.…”

New calibration methodology for calorimetric determination of isobaric thermal expansivity of liquids as a function of temperature and pressure

“…Although the most widely studied second-order derivative is heat capacity, isobaric thermal expansivity a p , has aroused great interest last years [6][7][8][9][10][11][12][13][14][15]. Its knowledge over wide temperature and pressure ranges can help to understand the volumetric behaviour of fluids against temperature, which has been revealed to be much more complex than against pressure [1,8,16].…”

“…It is based on previous works in which calorimetric measurements against pressure and relations between second-order derivatives through Maxwell's relations are used to obtain a p [6][7][8][9][10][11][12][13][14][15], but a new calibration procedure as well as experimental set-up was developed. This new procedure allows obtaining a very precise and fast characterization of a p against temperature and pressure.…”

Effect of pressure on the number of dynamically correlated molecules when approaching the glass transition

“…(No data either are available for the pressure dependence of these jumps.) For other molecular glassforming liquids, one observes that the heat capacity C P of the liquid at T g slightly increases with pressure: a few % for 3-methylpentane and 1-propanol up to 200 MPa [34], a few % for m-fluoroaniline up to 400 MPa [35], and 10 − 12 % for toluene up to 400 MPa [36]. However, the C P of the glass at T g has been found to also increase in 3-methylpentane and 1-propanol where it has been measured [34], so that the heat capacity jump ∆C P,g (P) barely changes with pressure in these systems.…”