A differential scanning calorimeter equipped with a shearing system (shear rate of  < 400 s-1) was developed to elucidate the thermodynamic properties of liquid crystalline phase transitions under shear flow. An analytical method was proposed to accurately estimate the heat flow caused by shear friction to evaluate the transition entropies. The phase transitions of 4'-n-octyl-4-cyano-biphenyl (8CB) under shear flow were investigated using the developed calorimeter. Although several shear-induced transitions for 8CB have been reported in the past using viscosity and small-angle X-ray scattering (SAXS) measurements, only the nematic-isotropic (N-I) and smectic-A-nematic (SA-N) transitions were detected as heat flow peaks. The N-I transition temperature was almost independent of the shear rate. The SA-N transition temperature was also independent of the shear rate, but the transition peak was broadened by applying shear flow. For both transitions, the transition entropies were independent of the shear rate. These results suggest that the thermodynamic properties were not considerably changed by shearing because the molecular alignments in the domains were not substantially changed, whereas shearing changed the LC domain directions, which can be detected by viscosity and SAXS measurements.

Phase stabilisation elongates spin–lattice relaxation times.

Laser-ablated polyyne molecules, H(C≡C)nH, were separated by size in solutions and co-condensed with excess hexane molecules at a cryogenic temperature of 20 K in a vacuum system. The solid matrix samples containing C8H2, C10H2, and C12H2 molecules were irradiated with UV laser pulses and the phosphorescence 0–0 band was observed at 532, 605, and 659 nm, respectively. Vibrational progression was observed for the symmetric stretching mode of the carbon chain in the ground state with increments of ~2190 cm−1 for C8H2, ~2120 cm−1 for C10H2, and ~2090 cm−1 for C12H2. Temporal decay analysis of the phosphorescence intensity revealed the lifetimes of the triplet state as ~30 ms for C8H2, ~8 ms for C10H2, and ~4 ms for C12H2. The phosphorescence excitation spectrum reproduces UV absorption spectra in the hexane solution and in the gas phase at ambient temperature, although the excitation energy was redshifted. The symmetry-forbidden vibronic transitions were observed for C10H2 by lower excitation energies of 25,500–31,000 cm−1 (320–390 nm). Detailed phosphorescence excitation patterns are discussed along the interaction of the polyyne molecule and solvent molecules of hexane.

The thermodynamic properties of the cationic surfactant cetyltrimethylammonium bromide (CTAB)/water system were investigated using differential scanning calorimetry (235–395 K) and adiabatic calorimetry (78–320 K), and the stable phase diagram was established, in which the locations of phase boundaries were precisely determined. The micellar phase and the lyotropic liquid crystalline (LC) phases were found to transform into a metastable gel phase via rapid cooling, and a metastable phase diagram was also constructed. The hexagonal LC phase was found to consist of two types of phases with different thermodynamic characteristics. The transitions from the separated two-phase “CTAB crystal + solution” to the micellar and LC phases were also investigated, and it was found that the transition occurs in a two-step manner, wherein the transitions at lower temperatures depended on the thermal history. The enthalpy of fusion of the ice that coexisted with the CTAB crystal did not provide any evidence for the CTAB crystal being hydrated by non-freezing water.

© 2020 Elsevier B.V. Cyanopolyyne molecules, HC9N and HC11N, were isolated in solutions and UV, IR, and resonance Raman spectra were measured for the study of their electronic and vibrational properties. Strong signals were observed both in the IR and resonance Raman spectra for the stretching vibrational mode of the sp-hybridized linear carbon chain in the electronic ground state, i.e., σ4 at 2141 cm−1 for HC9N and σ6 at 2105 cm−1 for HC11N. Trapped in cryogenic solid acetonitrile matrix hosts at 20 K, transitions in phosphorescence, a˜3Σ+ → X˜1Σ+, were observed for HC9N at 582.3 nm (0–0) and longer wavelengths and for HC11N at 643.7 nm (0–0) and longer wavelengths. Electronic transitions in the UV, 1Σ+ ← X˜1Σ+, were elucidated by phosphorescence excitation mapping to observe asymmetric patterns with sharp emission-absorption features explainable by Shpolsky effects. For HC9N, three distinct trapping sites were discernible in solid acetonitrile, while the phosphorescence spectra were blurred in solid n-hexane. The observed phosphorescence lifetime of HC9N was longer than that of HC11N, comparable to the trend reported for the series of cyanopolyyne molecules in solid krypton matrix hosts.

Two crystal polymorphs of Ni(cyclam)I-2 (cyclam = 1,4,8,11-tetraazacyclotetradecane) were synthesized, and their magnetic properties were investigated. Temperature-dependent X-ray structural analysis and magnetic measurements revealed gradual spin transition in molecular-crystal polymorph trans-[Ni(cyclam)I-2] (1a), whereas the zigzag-chain polymorph catena-[Ni(cyclam)(mu-I)]I (1b) did not show an obvious spin transition. The entropy difference between high- and low-spin states of la estimated by assuming the spin-equilibrium model is much smaller than those in typical iron(II)-based spin-crossover (SCO) complexes, suggesting that the normal mode softening is less remarkable in la. In this system, it is clearly evidenced that the interaction mode responsible to the spin equilibrium in octahedral nickel(II) complexes is highly anistropic, i.e., z-elongation and x,y-shortening of the coordination octahedron.

Calorimetric and terahertz-far-infrared (THz-FIR) spectroscopic and infrared (IR) spectroscopic measurements were conducted for [Li+@C-60](PF6-) at temperatures between 1.8 and 395 K. [Li+@C-60](PF6-) underwent a structural phase transition at around 360 K accompanied by the orientational order-disorder transition of Li+@C-60 and PF6-. The transition occurred in a step-wise manner. The total transition entropy (Delta S-trs) of 40.1 +/- 0.4 J K-1 mol(-1) was smaller than that of the orientational order-disorder transition in a pristine C-60 crystal (Delta S-trs = 45.4 +/- 0.5 J K-1 mol(-1)). Thus, the orientational disorder of Li+@C-60 in the high-temperature phase of [Li+@C-60](PF6-) was much less excited than that of the pristine C-60 owing to the Coulombic interactions, which stabilized the ionic crystal lattice of [Li+@C-60](PF6-). At T < 100 K, upon cooling, Li+ ions were trapped in two pockets on the inner surface of C-60, and no phase transition was observed. Finally, the Li+ ions achieved a complete order at 24 K through antiferroelectric transition. The Delta S-trs value of 4.6 +/- 0.4 J K-1 mol(-1) was slightly smaller than R ln 2 = 5.76 J K-1 mol(-1) expected for the two-site order-disorder transition. The extent of the Li+ motion in the C-60 cage was related to the selection rule in the THz-FIR and IR spectroscopy of the C-60 internal vibrations, because a C-60 cage should be polarized by the Li+ ion. It is shown that the local symmetry of the caged molecule can be modified by the rotational or hopping motion of the encaged ions.

© 2019 American Chemical Society. The heat capacity of H 2 O encapsulated in fullerene C 60 is determined for the first time at temperatures between 0.6 and 200 K. The water molecule in H 2 O@C 60 undergoes quantum rotation at low temperature, and the ortho-H 2 O and para-H 2 O isomers are identified by labeling the rotational energy levels with the nuclear spin states. A rounded heat capacity maximum is observed at ∼2 K after rapid cooling due to splitting of the rotational J KaKc = 1 01 ground state of ortho-H 2 O. This anomalous feature decreases in magnitude over time, reflecting the conversion of ortho-H 2 O to para-H 2 O. Time-dependent heat capacity measurements at constant temperature reveal three nuclear spin conversion processes: a thermally activated transition with E a 3.2 meV and two temperature-independent tunneling processes with time constants of δ 1 1.5 h and δ 2 11 h.

Heat capacity measurements were made down to 0.35 K for the isotopic modifications of methanol, CH3-nDnOH, and methyl iodide, CH3-nDnI, (n = 0, 1, 2, 3) to determine the orientation of the partially deuterated methyl group in the solid phase. The mono-deuterated modifications favor the symmetric conformation, whereas the di-deuterated ones favor the asymmetric conformation. Infrared spectroscopy demonstrates that some vibrational modes change in intensity depending on temperature, which supports the energy scheme obtained by calorimetry. Zero-point kinetic energies were obtained by single molecule density functional theory calculations. Although the favorable conformations of CH2DOH and CHD2OH were confirmed, the energy difference between symmetric and asymmetric conformations was twice as large as that determined experimentally, which indicates that intermolecular forces significantly decrease the energy difference. For CHD2OH, the conversion between the two asymmetric conformations becomes very slow at low temperature and results in a residual entropy of R ln 2. Published by AIP Publishing.

As terahertz (THz) frequencies correspond to those of the intermolecular vibrational modes in a polymer, intense THz wave irradiation affects the macromolecular polymorph, which determines the polymer properties and functions. THz photon energy is quite low compared to the covalent bond energy; therefore, conformational changes can be induced "softly," without damaging the chemical structures. Here, we irradiate a poly(3-hydroxybutylate) (PHB) / chloroform solution during solvent casting crystallization using a THz wave generated by a free electron laser (FEL). Morphological observation shows the formation of micrometer-sized crystals in response to the THz wave irradiation. Further, a 10-20% increase in crystallinity is observed through analysis of the infrared (IR) absorption spectra. The peak power density of the irradiating THz wave is 40 MW/cm(2), which is significantly lower than the typical laser intensities used for material manipulation. We demonstrate for the first time that the THz wave effectively induces the intermolecular rearrangement of polymer macromolecules.

Structural changes induced by water desorption from D-penicillaminato (D-pen) (Cu8Cu6II)-Cu-I clusters aggregated into three polymorphic crystal structures ((1) 1D helical, (2) 2D hexagonal sheet, and (3) discrete cubic) were investigated by terahertz (THz) absorption spectroscopy and X-ray diffractometry (XRD), which provided information on the skeletal and crystal structures of the clusters, respectively. The water molecules incorporated into the crystals were removed by evacuation and heating to 100 degrees C. In the case of crystal 1, the helical structure collapsed upon water evacuation, whereas the skeletal structure of the D-pen (Cu8Cu6II)-Cu-I clusters did not change. However, the skeletal structures were distorted by the heating process. For crystals 2 and 3, water evacuation did not affect either the skeletal or the sheet and cubic crystal structures of the clusters, which, however, collapsed upon heating. The mechanisms driving these structural changes were discussed in relation to the type and amount of water molecules removed in each process.

Li+ ions encapsulated in fullerene C-60 cages (Li+@C-60) are expected to be suitable as molecular switches that respond to local electric fields. In this study, the rotational dynamics of Li+ ions in C-60 cages at low temperatures are experimentally revealed for the first time using terahertz absorption spectroscopy. In crystalline [Li+@C-60](PF6-), the Li+ ion rotates in the carbon cage even at 150 K. The rotational mode gradually changes into a librational mode below 120 K, which is associated with the localization of Li+ ions due to the electrostatic interactions with its screening image charge on the C-60 cage as well as with the neighboring Li+@C-60 and PF6- ions. A simple rotational/librational energy scheme for the Li+ ions successfully explains the spectroscopic results, and the potential of Li+@C-60 as a molecular switch is discussed based on the energy scheme.

The alpha and gamma crystals of polyamide-6 were examined by terahertz absorption spectroscopy from -90 to 230 degrees C. For the alpha crystals, the absorption band at 6.5 THz, assigned as a lattice vibration perpendicular to the molecular chain, decreased in intensity with increasing temperature, ending near the Brill transition temperature (T-Brill approximate to 160 degrees C). The band at 8.7 THz, assigned as the skeletal vibration along the molecular chain, shifted to higher frequency with increasing temperature. The rate of shift changed at the glass transition temperature (T-g approximate to 50 degrees C), indicating coupling of the molecular vibration in the crystal with freezing/relaxing phenomena in the surrounding amorphous phase. A significant annealing effect was observed. On heating polyamide-6 films that had been annealed at a temperature (T-ann) >= 80 degrees C, an increase in spectral intensity above 9 THz occurred at similar to T-ann, due to the melting of semi-crystals formed by recrystallization during annealing. (C) 2015 Elsevier Ltd. All rights reserved.

The phase behaviors and kinetics of the polymorphic transitions of cyclohexanol, C6H11OH, were investigated by terahertz absorption spectroscopy over the temperature range of 150-330 K. A new phase was found, labeled phase I', which is more stable than the previously observed phase I but less stable than phase III'. The kinetics of the irreversible transitions from phase I to I', phase I to III', and phase III' to III were analyzed using Avrami's theory. The transition geometries of the first two transitions were found to be one-dimensional, while the latter was two-dimensional. The transitions from phase I to III and phase III to II were revealed to occur through two-step processes. The mechanism of these irreversible transitions is discussed in relation to the formation and dissociation of hydrogen bonds between the hydroxyl groups as well as the steric restriction effects of the cyclohexyl ring.

Terahertz (THz) absorption spectra of organogels consisting of (1R,2R)-1,2-bis(dodecanoylamino) cyclohexane/2-nitrophenyl octyl ether (RR-BDC/NPOE) and RR-BDC/n-dodecane were measured by Fourier-transform far-infrared (FT-FIR) spectroscopy. The vibrational peaks of the gels were observed at the same frequencies as those of the pure gelator, suggesting that the intermolecular structure around the N-H center dot center dot center dot O=C hydrogen bond is maintained in the gel phase. Temperature-dependent spectroscopy showed a drastic spectral change at the sol-gel transition temperature, in which the vibrational peak at 3.5 THz disappears and a new peak appears at 2.9 THz. The change in THz vibrational frequency is indicative of the structural collapse of the hydrogen-bonded fibrous architecture in the sol phase. (C) 2014 Elsevier B.V. All rights reserved.

With the aim of opening a route toward new applications of terahertz (THz) spectroscopy to studies of polymer science, the conformations and structural transitions of polycaprolactam (nylon-6) were investigated by THz spectroscopy in the alpha, gamma, pseudo-hexagonal, and amorphous phases. A Brill transition from the alpha form to the pseudo-hexagonal form was detected at 160 degrees C from a temperature variation of the peak intensity at 6.6 THz in the second-derivative spectrum of nylon-6. In the amorphous phase, a glass transition was observed at 60 degrees C, and a new anomaly was found at 110 degrees C. (C) 2013 Elsevier B. V. All rights reserved.

Heat capacity measurements were conducted between temperatures of 5 K and 360 K by adiabatic calorimetry for the liquid crystalline material 4-cyano-3-fluorophenyl 4-butylbenzoate to investigate the phase behavior and determine the thermodynamic functions. Five phases are identified: the metastable nematic phase, its glass phase (T-g = 210 K), stable crystal I (T-fus = 288.43 K), a new metastable crystal (crystal II), and the isotropic liquid. The enthalpy of fusion of crystal I is 22.22 kJ . mol(-1), and the entropy is 76.91 J . K-1 . mol(-1). Polarizing microscopy observations were also conducted between T = 100 K and 300 K to confirm the phase behavior. The melting point of crystal II (T-fus = 286 K) and the clearing temperature of the nematic phase (T-c = 279.4 K) were obtained using a microscope. On the other hand, the enthalpy of the clearing transition (526 J . mol(-1)) and the entropy (1.88 J . K-1 . mol(-1)) were obtained from the thermodynamic functions. The Debye temperature of crystal II (55.3 K) is significantly lower than that of crystal I (60.7 K), indicating that the phonon density of states is considerably different between the two crystals. The existence of low-energy excitations in the nematic glass and a low-energy shift of the intramolecular modes in crystal II are also identified. (C) 2012 Elsevier Ltd. All rights reserved.

The studies performed for right-handed (S)-4-(2-methylbutyl)-4'-cyanobiphenyl glass former using calorimetry (down to 0.35 K) and spectroscopy methods are reviewed. The substance reveals isotropic and cholesteric liquid phases, glass of cholesteric phase and two crystalline polymorphs, one of which transforms to glass. Two anomalies in heat capacity below 5K and their relation to ordering of the molecules in three solid phases are discussed.

Quasi-elastic neutron scattering measurements were performed for five cyanobiphenyl compounds with different terminal chains (5CB, 5*CB, 80CB, 8*OCB and 6O2OCB) in their liquid and liquid-crystalline phases to investigate the molecular dynamics. The spectra were successfully decomposed into two components, indicating that two types of molecular motions are involved. For the broad (or fast) component, the temperature dependence as well as the momentum transfer dependence did not differ very much among those compounds. For the narrow (or slow) component, on the other hand, the compounds with a branched alkyl-chain (5*CB and 8*OCB) gave significantly smaller diffusion constants than the others. A molecular dynamics simulation for 5*CB and 5CB suggests that the reorientational motion of the whole molecule around the long molecular axis is responsible for the broad component, whereas a diffusive motion of the terminal chain is responsible for the narrow one. (C) 2010 Elsevier B.V. All rights reserved.

Extracting accurate heat capacities by conventional relaxation calorimetry at first-order or very sharp second-order phase transitions is extremely difficult. The so-called "scanning method" provides a key to overcome this challenge. Here, we introduce new corrections in the data analysis of this method. Critical examinations of the improvements are made experimentally by investigating the well-studied first-order ferroelectric phase transitions of KH2PO4 and BaTiO3 using a commercial relaxation calorimeter Physical Property Measurement System (PPMS) supplied by Quantum Design. The results for KH2PO4 are shown to be excellent; a very sharp peak in heat capacity is obtained and the absolute values are shown to agree well with the previous results obtained by adiabatic calorimetry on much larger samples. The critical behavior of the heat capacity in the vicinity of the transition temperature, as well as the thermodynamic quantities such as the transition enthalpy and entropy, also agrees very well with the previous results. For BaTiO3, clear hysteretic behavior of the transition is observed for heating and cooling curves. (C) 2010 Elsevier Ltd. All rights reserved.

The heat capacity of two glass formers 5*CB and 8*OCB, each of which has two crystalline polymorphs (phases I and II) as well as a glass phase, was determined between 0.35 K and 20 K. The T-linear term of the heat capacity becomes significant below 1 K for both glasses. The glassy crystalline phase II of 5*CB also shows such contribution, which is consistent with the existence of a residual entropy. Unexpectedly, however, the 'stable' phase II of 8*OCB shows the similar contribution, indicating that this phase is disordered, whereas the glassy crystalline phase I shows no such contribution. (c) 2008 Elsevier B.V. All rights reserved.

As a part of a project of clarifying the physical properties and dynamics of cyanobiphenyls with chiral molecules, thermodynamic properties of (S)-4-(2-methylbutyl)-4'-cyanobiphenyl (5*CB) were investigated by adiabatic calorimetry between T = (5 and 350) K. The complicated phase behaviour was solved and the thermodynamic functions were determined. A new glass transition was identified in the phase II (metastable crystal) at T = 105 K. No inversion of the stability between two crystalline phases was found, being contrary to the expectations from the previous neutron scattering studies. (C) 2008 Elsevier Ltd. All rights reserved.

In this research, terahertz (THz) vibrational circular dichroism (VCD) and very low frequency Raman optical activity (ROA) were developed for studying chiral vibrations of higher order conformation of macromolecules. Low-frequency ROA spectra of chiral molecules such as 2-phenyl-propion acid and poly-alanine were measured and compared with the result of quantum calculation, which reveals that the chiral vibration of whole molecular motion appears in the low frequency region. Also, aiming to control the chirality of macromolecules, high-power THz wave was irradiated for polymer solution. The conformational change of polymer sample was observed after irradiating high-power THz wave generated by THz free electron laser.