Dielectric and Calorimetric Study of Orientationally Disordered Phases in Two Unusual Two-Component Systems

Abstract

In the present communication, investigations of two interesting (two-component) solid solutions are reported where one is a hydrogen (H-)-bonded pair and the other is a non-H-bonded pair. The former is the two-component system cyclooctanol (COOL) + cycloheptanol (CHOL), which forms a simple cubic phase [Rute, M. A.; Salud, J.; Negrier, P.; López, D. O.; Tamarit, J. Ll.; Puertas, R.; Barrio, M.; Mondieig, D. J. Phys. Chem. B 2003, 107, 5914]. This solid phase has been investigated at low temperatures and for several concentrations by means of low-frequency dielectric spectroscopy and differential scanning calorimetry (DSC). Depending upon the concentration, this phase reveals a glass transition in the temperature range of 138-172 K and a pronounced relaxation process identifiable with the so-called alpha process characteristic of a single-component orientationally disordered crystal. The dielectric spectra are found to follow the Havriliak-Negami (HN) equation. The analysis of the various parameters obtained show an isomorphic relationship between the simple cubic phases of both pure components through a continuous change of parameters. In addition, a sub-T(g) process, which is Arrhenius, is found. The kinetic freezing of the various dielectric processes has been critically examined in relation to the T(g) found in the DSC experiments. The non-H-bonded pair that has been studied is cis-1,2-dimethylcyclohexane (DMCH) and cyclohexylchloride (CHC). The liquid mixture of DMCH and CHC upon lowering the temperature forms a solid solution on the DMCH-rich side, which is an orientationally disordered crystal. This phase demonstrates a pronounced alpha process in the dielectric measurements that follows the HN equation. The results are discussed in the context of the solid-liquid phase diagram of this binary system. The observed deviations from Arrhenius and Debye behaviors in the solid solutions studied in this paper are shown to follow the "strong-fragility" pattern of Angell.

Study of supercooled orientationally disordered binary solid solutions II: cyclohexyl derivatives, neopentanol and neopentylglycol

“…which are also of interest to physicists working on glass transition phenomena. As shown in some of our recent publications, 37,38 the above said solid-solid transition can be supressed by addition of a second component which forms a solid solution with the first component. Although, the theoretical reasons responsible for the supression of this crystallization to rigid-crystalline phase are not yet understood; it never the less, led to a detailed study of the supercooled phases of the mixtures of these substances.…”

“…5. The a-process follows the critical power law [34][35][36][37][38][39] given by the equation below,…”

“…The nature of the b-process in frozen OD phase (or glassy crystals) is the subject of exclusive discussion in some papers. [36][37][38][39][40][41][42][43][44][45][46] Arguments are made in favour of both intermolecular (or the so called Johari-Goldstein (JG-) relaxation) 6,36 and intramolecular origin. [40][41][42] Here b JG relaxation is due to the small angle reorientational motion of the entire molecule in the cage formed by the surrounding molecules, and all the molecules contribute to the b JG process.…”

Solid phases in cycloheptanol: Dynamic disorder and glass transitions

“…6(A) shows at 148 K, the loss spectrum of the supercooled phase I (empty circles) together with the loss spectrum of phase III/ IV (full circles) at the same temperature. It seems to be obvious that the loss spectra of phase I present two additional relaxations besides the well-developed a-relaxation, denoted as b and c. Very recently, Singh et al [35] have published that only one additional relaxation, identified as c-relaxation, is present in phase I. The secondary b and c-relaxations of phase I are observed to persist in phase III/IV whereas the a-process is wholly suppressed, contrarily to what is reported in the work of Tyagi et al [20], in which phase III/IV displays a well-developped a-relaxation.…”

Secondary relaxations of orientationally disordered mixed crystals at temperatures lower than the glass transition temperature

“…Several authors of the present work have recently undertaken a study of the dynamics of the OD mixed crystals formed between cC7‐ol and cC8‐ol 11. The motivation of such study was the findings previously found by the Murthy's group for some compositions of the cC7‐ol + cC8‐ol two‐component system, (cC7‐ol) 1− x (cC8‐ol) x 24. They found, in addition to the α ‐relaxation process, only one secondary relaxation ascribed to the conformations of the –OH group ( γ ‐relaxation), but no evidence of the β ‐relaxation.…”