Anti-Sigmoidal Composition Dependence of Glass Transition Temperature and Excess Heat Capacity across It in a Binary System of Globular Alcohols

Yasuhisa YAMAMURA, Kaoru NOMIYA, Mafumi HISHIDA and  Kazuya SAITO

Differential scanning calorimetry (DSC) revealed an anti-sigmoidal composition dependence of the glass transition temperature in a binary mixture of dicyclohexylmethanol [(C₆H₁₁)₂CHOH, DCHM] and tricyclohexylmethanol [C₆H₁₁)₃COH, TCHM]. The equimolar mixture, of which state was suggested to be robust by the dependence, was subject to adiabatic calorimetry. The glass transition occurred around 257 K while accompanying a significant enthalpy relaxation. The excess heat capacity beyond the weighted average of heat capacities of neat compounds changes its sign from positive to negative upon the glass transition on cooling. The negative excess implies a denser molecular packing than neat glasses. The excess enthalpy is graphically given relative to T = 298.15 K.
(J. Sol. Chem., 53, 144-153 (2024))

X-ray Study of Molecular Association in Alcohols Having Bulky Substituents

Kazuya SAITO, Mafumi HISHIDA, Kent KOIKE, Shigenori NAGATOMO and Yasuhisa YAMAMURA

The formation of globular associate on cooling, which was previously claimed on the basis of small dielectric constant, is supported through measuring X-ray scattering from dicyclohexylmethanol (DCHM). Radial distribution function of the DCHM molecules exhibits strong temperature dependence between 65 deg C and 130 deg C in contrast to a little change in that of tricyclohexylmethanol (TCHM), which is similar to DCHM but essentially non-associating in experimental conditions (95 deg C - 160 deg C).
(Chem. Phys. Lett., 673, 74-77 (2017))

Cyclic Oligomers via Hydrogen Bonds in Organic Liquids

Shigenori NAGATOMO, Yasuhisa YAMAMURA and Kazuya SAITO

Molecular association is ubiquitous in hydrogen-bonding (H-bonding) liquids and is believed to play crucial roles in the determination of their physical properties. Although systems consisting of small and simple molecules are generally preferable for detailed studies from the basic point of view, this is not the case here because such molecules possibly form extending network and/or chains through H-bonds, thus resulting in complexity and difficulty. Based on a thermodynamic discussion, a simple model is proposed of associating liquids in which small cyclic oligomers are preferably formed. Characteristic temperature dependences in thermodynamic, dielectric and spectroscopic (FT-IR and ¹H NMR) properties of liquids of some alcohols with bulky substituents are well described by the model.
(Netsu Sokutei (Calorim. Therm. Anal.), 40, 107-113 (2013), account in Japanese)

Identification of Hydrogen-Bonded Oligomers in Associating Liquid by ¹H NMR: 1-Phenyl-1-cyclohexanol

Shigenori NAGATOMO, Megumi NOBUHIRA, Masato SUMITA,Yasuhisa YAMAMURA and Kazuya SAITO

Non-monotonous temperature dependence, which suggests formation of closed oligomer(s) via hydrogen-bonds, is detected in heat capacity and dielectric constant of the title compound in the liquid state. The ¹H NMR signal of hydroxyl protons showed a temperature-dependent fine structure. Quantum-chemical calculations on oligomers of several types revealed that the fine structure is plausibly interpreted as a temperature-dependent formation/destruction of oligomers. A coherent analysis of calorimetric, FT-IR, dielectric and ¹H NMR results shows that the neat liquid of the title compound consists mostly of closed (square) tetramers via H-bonds at lower temperatures, and oligomers with open (or straight) H-bonding and non H-bonding (monomer) at higher temperature.
(Bull. Chem. Soc. Jpn., 86, 569-576 (2013))

Calorimetric Study of Glass Transition in Molecular Liquids Consisting of Globular Associates: Dicyclorohexylmethanol and Tricyclohexylmethanol

Yasuhisa YAMAMURA, Yu-ta SUZUKI, Masato SUMITA and Kazuya SAITO

Heat capacities of liquids and liquid quenched glasses (LQG) of dicyclorohexylmethanol (DCHM) and tricyclohexylmethanol (TCHM) were measured by adiabatic calorimetry. Upon cooling the liquid compounds, they undergo glass transitions around 250 K and 265 K, respectively. Temperature dependence of the FT-IR spectrum of TCHM liquid showed the gradual formation of dimers in supercooled liquid with decreasing temperature. The magnitude of heat capacity jump at glass transition is discussed through a comparison with other low-molecular mass LQG. Combining the present results with previous heat capacity results on crystalline TCHM, residual entropies of LQG and standard thermodynamic quantities are established for both compounds.
(J. Phys. Chem. B, 116, 3938-3943 (2012))

Neat Liquid Consisting of Hydrogen-Bonded Tetramers: Dicyclohexylmethanol

Nonmonotonous temperature dependence was detected in the heat capacity and dielectric constant of the title compound in the liquid state. A coherent analysis of FT-IR spectra, heat capacity, and dielectric constants shows that the neat liquid at low temperatures consists of closed (square) tetramers via H-bonds.
(J. Phys. Chem. B, 113, 10077-10080 (2009))

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