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Journal of Thermal Analysis and Calorimetry

, Volume 115, Issue 2, pp 1353–1358 | Cite as

Phase- and glass-transition phenomena due to the same configurational order–disorder mechanism in crystalline racemic sec-butylcyclohexane

  • Sergio Luis L. M. Ramos
  • Michihiko Ogino
  • Masaharu Oguni
Article

Abstract

We report molar heat capacities for racemic sec-butylcyclohexane (s-BCH) measured by the adiabatic calorimetric method within the temperature range from 14 to 200 K. In the crystalline state, we identified the presence of a second-order phase transition and a glass transition phenomenon, both originating from the same configurational degree of freedom. The phase and glass transition temperatures T trs and T g were determined to be (136.7 ± 1.0) and (100 ± 1) K, respectively. The entropy of phase transition was estimated to be Δtrs S m = 1.4 J K−1 mol−1 ≈ (1/4) R ln 2. The phase transition was judged to be of an order–disorder type on the basis of the fact that the glass transition occurred in the low-temperature heat-capacity tail. The entropy was interpreted to suggest that four molecules in the crystalline state constitute a unit for producing two distinct configurations in the coexistence of (d)- and (l)-s-BCH.

Keywords

Alkyl cyclohexane Racemic compound Heat capacity Order–disorder phase transition Glass transition 

List of symbols

Variables

M

Molar mass (g mol−1)

R

Gas constant (J K−1 mol−1)

Cp,m

Molar heat capacity (J K−1 mol−1)

T

Temperature (K)

ΔfusCp,m

Fusion contribution to the molar heat capacity (J K−1 mol−1)

ΔfusHm

Molar enthalpy of fusion (J mol−1)

ΔfusSm

Molar entropy of fusion (J K−1 mol−1)

Tfus

Temperature of fusion (K)

f

Liquid fraction

x

Molar fraction of impurity

K

Solubility ratio of the impurities in the solid and liquid phases

ΔexcCp,m

Excess molar heat capacity (J K−1 mol−1)

ΔtrsSm

Molar transition entropy (J K−1 mol−1)

Ttrs

Transition temperature (K)

Tg

Glass transition temperature (K)

τ

Molecular relaxation time (s)

τ0

Pre-exponential time factor in Arrhenius equation (s)

Δεa

Potential energy barrier (J mol−1)

kB

Boltzmann’s constant (J K−1)

W

Number of permissible distinguishable microscopic configurational states

Abbreviations

s-BCH

sec-Butylcyclohexane

n-BCH

n-Butylcyclohexane

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Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2013

Authors and Affiliations

  • Sergio Luis L. M. Ramos
    • 1
  • Michihiko Ogino
    • 1
  • Masaharu Oguni
    • 1
  1. 1.Department of Chemistry, Graduate School of Science and EngineeringTokyo Institute of TechnologyTokyoJapan

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