Investigation of the melting behavior of the reference materials biphenyl and phenyl salicylate by a new type adiabatic scanning calorimeter

doi:10.1016/j.tca.2014.02.023

Thermochimica Acta

Volume 582, 20 April 2014, Pages 68-76

https://doi.org/10.1016/j.tca.2014.02.023 Get rights and content

Highlights

•
Novel type of Peltier-element-based adiabatic scanning calorimeter (pASC).
•
Simultaneous high-resolution enthalpy and heat capacity data.
•
Melting transition of the reference materials biphenyl and phenyl salicylate.
•
Reliable purity analysis procedure.

Abstract

Simultaneously measured high-resolution enthalpy and heat capacity data are obtained by means of a novel type Peltier-element-based adiabatic scanning calorimeter that can also operate as a classical adiabatic heat-step calorimeter. Specific enthalpy and specific heat capacity results with 2% uncertainty and sub-mK temperature resolution are presented for the melting transition of the calorimetric reference materials biphenyl and phenyl salicylate. The simultaneously obtained enthalpy and heat capacity data allow for a simplified and reliable purity analysis.

Graphical abstract

Melting transition of biphenyl by pASC.

Introduction

Many fields of research and applications require detailed information on thermal properties of condensed matter systems. In particular, the temperature dependence of the energy or enthalpy H(T) of a sample of a given substance is important. Although, as we will see further, the direct measurement of H(T) is possible, in many cases one only has direct experimental access to the heat capacity C_p = (∂H/∂T)_p, the slope of the enthalpy curve as a function of temperature. The enthalpy curve itself requires then an additional integration. This approach cannot work properly when there is a discontinuity in the enthalpy curve (latent heat) at a first-order phase transition, where the essential information on the latent heat cannot be obtained from C_p data alone and a direct measurement (in steps or by scanning) of the enthalpy is necessary.

Several types of calorimetric methodologies have been developed in the past with different degrees of uncertainty and resolution depending on the application envisioned. For low-uncertainty data, one usually employs a classical adiabatic (heat-step) calorimeter [1], [2], [3], [4]. After the commercial introduction in the 1960s of differential scanning calorimeters (DSC), the use of these types of instruments has become widespread in thermal analysis [5], [6], [7], [8]. Other heat capacity measuring techniques have been developed, such as ac-calorimetry [9], [10], the 3ω method [11], and photoacoustic and photopyroelectric techniques [12], [13].

Another technique, adiabatic scanning calorimetry (ASC) has only received limited attention so far. It was introduced in the late 1970s by a group at KU Leuven (Belgium) for high-resolution measurements of the heat capacity and enthalpy near phase transitions and critical points in liquid mixtures and liquid crystals [14], [15]. The innovation introduced was to apply under adiabatic conditions a constant, known electrical power to the sample cell instead of imposing a constant rate (as done in DSC-type calorimeters). With the power and temperature evolution known, the heat capacity and enthalpy of the sample can be calculated with high resolution [16]. However, ASCs remained largely research instruments not the least because of complicated sample cell mounting and elaborate construction to impose adiabatic conditions. These problems have been eliminated in a new design of ASCs by incorporating Peltier elements between the sample cell and the adiabatic shield [17], [18]. Measurements, over large temperature ranges on mg-sized samples, are now possible with high resolution in temperature (sub-mk), enthalpy and heat capacity. Accurate data can be obtained by a one-time calibration of the incorporated thermometers and of the background heat capacity of the sample cell and addenda.

In this work, we illustrate the possibilities of the novel Peltier-element-based adiabatic scanning calorimeter (pASC) by a series of measurements on biphenyl and phenyl salicylate (salol) near their melting point. In a first part, the ASC concept and the novel implementation will be discussed. Subsequently, high-resolution enthalpy and heat capacity data will be presented and discussed for both compounds. Attention will also be paid to impurity determination. Biphenyl and phenyl salicylate were chosen because high-purity samples of these compounds are being used as calibration substances for DSC instruments [19]. The DSC technique is a dynamic technique and the quality of DSC measurements is influenced by parameters related to the instrument, the scanning rate, the sample and the operator, and depends critically on the quality of the frequent temperature and caloric calibration of the instrument [19], [20], [21]. For the calibration of a DSC, one is strongly dependent on high-purity reference materials accurately characterized by absolute calorimetric techniques as adiabatic heat-step calorimetry [22], [23], [24], [25].

Section snippets

Methodology of adiabatic scanning calorimetry

Adiabatic scanning calorimetry (ASC) is a calorimetric technique aimed at the simultaneous measurement of the temperature dependence of the enthalpy and the heat capacity of condensed matter materials. The basic concept of ASC resides in applying a constant heating or cooling power to a sample holder containing a sample. This is opposite to what is done in DSC where a constant heating rate is imposed and the changing power needed to maintain the constant rate is measured in a differential

Measurements on biphenyl

In Fig. 3 the time evolution of the direct measurement data for the temperature T(t) (panel a) and the specific enthalpy (per unit mass) h(t) (panel b) are given for a constant power run on a 72.6 mg biphenyl sample in a 120 μl stainless steel medium pressure Mettler-Toledo crucible. In the solid phase, the temperature increases nearly linearly, while during melting the temperature stays constant until all the latent heat is delivered. In the liquid phase, the temperature increase with time

Summary and conclusions

High-resolution specific enthalpy and specific heat capacity results have been obtained for the reference materials biphenyl and phenyl salicylate by means of a novel type of Peltier-element-based adiabatic scanning calorimeter (pASC). The pASC operates by delivering constant power (to sample and sample holder) and measures the changing rate, which is opposite to what is done in differential scanning calorimetry (DSC) where a constant rate is imposed and changing power measured. The pASC

Acknowledgements

This research is supported by FWO research project G.0492.10, FWO research Project G.0360.09 and KU Leuven research project OT/11/064.

References (33)

D.G. Archer et al.
NIST and standards for calorimetry
Thermochim. Acta
(2000)
W. Schnelle et al.
Critical review of small sample calorimetry: improvement by auto-adaptive thermal shield control
Thermochim. Acta
(2002)
C.W. Garland
High-resolution ac calorimetry and critical behavior at phase transitions
Thermochim. Acta
(1985)
E. Gmelin et al.
Temperature, heat and heat flow rate calibration of differential scanning calorimeters
Thermochim. Acta
(2000)
S. Stølen et al.
Critical assessment of the enthalpy of fusion of metals used as enthalpy standards at moderate to high temperatures
Thermochim. Acta
(1999)
R.D. Chirico et al.
The thermodynamic properties of biphenyl
J. Chem. Thermodyn.
(1989)
M. Hanaya et al.
Low-temperature adiabatic calorimetry of salol and benzophenone and microscopic observation of their crystallization: finding of homogeneous-nucleation-based crystallization
J. Chem. Thermodyn.
(2002)
F.D. Rossini
Chemical Thermodynamics
(1950)
R. Jakobi et al.
High-precision adiabatic calorimetry and the specific heat of cyclopentane at low temperature
J. Therm. Anal.
(1993)
E.S. Watson et al.
A differential scanning calorimeter for quantitative differential thermal analysis
Anal. Chem.
(1964)

M.J. O’Neill

The analysis of a temperature-controlled scanning calorimeter

Anal. Chem.

(1964)

E.S. Watson, M.J. O’Neill, Differential microcalorimeter, US Patent 3,263,484...

B. Wunderlich

Thermal Analysis

(1990)

P.F. Sullivan et al.

Steady-state, ac-temperature calorimetry

Phys. Rev.

(1968)

N.O. Birge et al.

Specific-heat spectroscopy of the glass transition

Phys. Rev. Lett.

(1985)

J. Thoen et al.

Photothermal techniques for heat capacities

Cited by (22)

High-resolution and high-accuracy calorimetry of order–disorder and melting transitions in the n-alkanes n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane and n-eicosane
2024, Journal of Chemical Thermodynamics
In this work, a Peltier-element-based adiabatic scanning calorimeter was used to investigate, with high-resolution and accuracy, the temperature dependence of the specific heat capacity and specific enthalpy difference of a series of linear alkanes. More specifically, results are reported for the even n-alkanes; namely n-eicosane, n-octadecane, n-hexadecane and for the odd n-alkanes, namely n-nonadecane, n-heptadecane and n-pentadecane. The measurements cover a temperature range from well in the crystalline solid phase across the solid–solid transitions (when present) in to the liquid phase across the melting transition. Accurate transition temperatures and heat of transitions were derived from the direct experimental data in view of the potential use of n-alkanes as phase change materials.
Phase behavior of medium-length hydrophobically associating PEO-PPO multiblock copolymers in aqueous media
2023, Journal of Colloid and Interface Science
The micellization of block copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) is driven by the dehydration of PPO at elevated temperatures. At low concentrations, a viscous solution of isolated micelles is obtained, whereas at higher concentrations, crowding of micelles results in an elastic gel. Alternating PEO-PPO multiblock copolymers are expected to exhibit different phase behavior, with altered phase boundaries and thermodynamics, as compared to PEO-PPO-PEO triblock copolymers (Pluronics®) with equal hydrophobicity, thereby proving the pivotal role of copolymer architecture and molecular weight.
Multiple characterization techniques were used to map the phase behavior as a function of temperature and concentration of PEO-PPO multiblock copolymers (ExpertGel®) in aqueous solution. These techniques include shear rheology, differential and adiabatic scanning calorimetry, isothermal titration calorimetry and light transmittance. The micellar size and topology were studied by dynamic light scattering.
Multiblocks have lower transition temperatures and higher thermodynamic driving forces for micellization as compared to triblocks due to the presence of more than one PPO block per chain. With increasing concentration, the multiblock copolymers in solution gradually evolve into a viscoelastic network formed by soluble bridges in between micellar nodes, whereas hairy triblock micelles jam into liquid crystalline phases resembling an elastic colloidal crystal.
High resolution study of the n = 7–9 p,p’-n-alkylazobenzenes phase transitions by photopyroelectric and adiabatic scanning calorimetries
2021, Thermochimica Acta
Citation Excerpt :
As discussed in depth in Ref. [37,38], the ASC technique allows the absolute determination of both the specific heat and enthalpy of transition within an accuracy of 2%, provided that uncertainty on the sample mass does not exceed this value. The validity of this assumption has been experimentally confirmed [38] by a statistical analysis of repeated measurements carried out on reference samples (biphenyl and phenyl salicylate), being the results in agreement within 2% with literature values. Unlike ASC, only the specific heat variations with respect to a reference value can be obtained by means of the PPE back configuration.
A study of phase transitions of photochromic p,p’-n-alkylazobenzenes compounds was carried out by means of adiabatic scanning calorimetry (ASC) and photopyroelectric calorimetry (PPE) techniques, yielding accurately the temperature dependence of the enthalpy and of the specific heat capacity across the observed phase transitions, and the corresponding enthalpy of transition values. In addition, polarization microscopy imaging of the sample texture was performed together with the PPE calorimetric evaluations to establish the nature of the involved phases. By performing PPE calorimetric evaluations during UV irradiation of the samples, the influence of the photoinduced trans to cis isomerization of the nAB molecules on the occurrence of the phase transitions was assessed.
Adiabatic scanning calorimetry investigation of the melting and order–disorder phase transitions in the linear alkanes heptadecane and nonadecane and some of their binary mixtures
2021, Journal of Chemical Thermodynamics
Citation Excerpt :
Detailed descriptions of this kind of implementations and results can be found in [25–27] and references therein. However, this approach has in the last decade been superseded by the development of the novel Peltier-element-based adiabatic scanning calorimeter (pASC), providing greater user-friendliness and allowing also much smaller sample quantity [28–31]. In a pASC the uncertainty on the final results, cp(T) and h(T), depends on the uncertainties on the measured quantities T(t), P(t), the sample mass m and the heat capacity of the addenda Cadd.
A novel Peltier-element-based adiabatic scanning calorimeter has been used to investigate the temperature dependence of the specific heat capacity and the specific enthalpy for n-alkanes heptadecane and nonadecane and for a set of their binary mixtures. The measurements have covered a broad temperature range from well into the ordered solid phase to well into the liquid phase. The analysis of the experimental data has allowed us to obtain accurate results for the phase transition temperatures, the transition enthalpies and the specific heat capacity values in the different phases.
High-resolution investigation by Peltier-element-based adiabatic scanning calorimetry of binary liquid crystal mixtures with enhanced nematic ranges
2021, Journal of Molecular Liquids
Citation Excerpt :
Detailed descriptions of this kind of implementations can be found in [40–42] and references therein. However, in the past decade, this approach has been superseded by the development of the novel Peltier-element-based adiabatic scanning calorimeter (pASC), providing greater user-friendliness and requiring essentially smaller amounts of samples [31,43–47]. In Fig. 1 a schematic representation of the central part of the pASC is given.
High-resolution Peltier-element-based adiabatic scanning calorimetry (pASC) has been used to investigate the temperature dependence of the specific heat capacity and specific enthalpy of two mixture systems of the liquid crystal smectic A₁ compound 5-n-nonyl-2-(4′-isothiocyanatophenyl)dioxane-1.3 (9DBT), and one of the smectic A_d compounds 4-n-octyloxy-4′-cyanobiphenyl (8OCB) and 4-nonyloxy-4′cyanobiphenyl (9OCB). For both mixture systems, measurements have been carried out over a large temperature range, from the crystalline solid phase over the smectic and nematic phases into the isotropic liquid phase. Both systems exhibit substantial, mixing-induced, enhanced nematic ranges and large changes in the composition dependence of the transition temperatures between the different phases. In both systems, eutectic melting points have been located and, for the different mixtures, the melting and eutectic transition heats have been obtained. The nematic to isotropic (NI) transitions are weakly first order with latent heat values in the range usually observed for this transition in other liquid crystals. The critical behavior of the specific heat capacity at the NI transition is described by exponent values near the tricritical one of 0.5. Along the smectic A to nematic (AN) transition lines, strong composition dependence was observed for the latent heat, from almost zero to values comparable to those observed at the nematic to isotropic transition. The concentration dependence of these AN latent heats was adequately fitted with a crossover function consistent with a mean-field free-energy expression that has a nonzero cubic term; the latter is induced by the Halperin-Lubensky-Ma coupling between the smectic A order parameter and orientational order director fluctuations. The fitting analysis resulted in the location of a Landau-tricritical point along one branch of the transition line in the system 9DBT-8OCB and one in each branch (for low and high 9OCB mole fractions) of the NA transition line of the 9DBT-9OCB system. The effective critical exponent values for the specific heat capacity of the AN transitions follow the McMillan ratio-dependence observed for other liquid crystal mixtures.
Supercooling of phase change: A new modeling formulation using apparent specific heat capacity
2020, International Journal of Thermal Sciences
Citation Excerpt :
Also, further studies on the DSC sample dynamics [28,29], the identification of particular substances by inversion [30] or the comparison of different equipment have been achieved [31]. The accuracy of the method can be improved using a highly insulated device referred to as adiabatic scanning calorimeter [32]. Some authors [33,34] have focused on supercooling using the T-history methods.
The thermal behavior of Phase Change Materials (PCMs) is a major issue for cooling, heat storage and thermal management of various systems in general. Unfortunately many PCMs present supercooling which is a major drawback regarding the efficiency of cooling systems. Various solutions were proposed to model the thermal kinetics, in particular using the apparent specific heat Cp(T) technique. But among them only few consider the supercooling effect. The present work considers this issue by focusing on the representation of the different steps of the supercooling phenomenon. This leads to different formulations of the apparent capacity Cp (T,f_super). The presented algorithm uses the lumped system analysis approach that is widely spread for first-order and multi-scale resolutions. The apparent capacity laws are explicitly presented for the different melting-crystallization steps. In particular, the punctually negative Cp formulation, a helpful mathematical artifact, permits to reproduce the thermal dynamics during the local crystallization. The formulations and the models are discussed. Eventually, the temperature evolutions of an experimental system are compared to calculated data and the crystallization rate is compared to the literature.

View all citing articles on Scopus

¹: Present address: Institute for Materials Research IMO, Hasselt University, Belgium.

View full text

Investigation of the melting behavior of the reference materials biphenyl and phenyl salicylate by a new type adiabatic scanning calorimeter

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Methodology of adiabatic scanning calorimetry

Measurements on biphenyl

Summary and conclusions

Acknowledgements

Thermochim. Acta

Thermochim. Acta

Thermochim. Acta

Thermochim. Acta

Thermochim. Acta

J. Chem. Thermodyn.

J. Chem. Thermodyn.

Chemical Thermodynamics

High-precision adiabatic calorimetry and the specific heat of cyclopentane at low temperature

J. Therm. Anal.

A differential scanning calorimeter for quantitative differential thermal analysis

Anal. Chem.

The analysis of a temperature-controlled scanning calorimeter

Anal. Chem.

Thermal Analysis

Steady-state, ac-temperature calorimetry

Phys. Rev.

Specific-heat spectroscopy of the glass transition

Phys. Rev. Lett.

Photothermal techniques for heat capacities