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Dielectric dispersion measurements were made on aqueous solutions of a triple-helical polysaccharide schizophyllan over a wide concentration range 10−50 wt % at −45 to +30 °C. In the solution state, three different water structures with the different relaxation times τ were found, namely, bound water (τl), structured water (τs), and loosely structured water (τls) in addition to free water (τP). Structured water is less mobile and loosely structured water is nearly as mobile as free water, but bound water with τl is much less mobile, thus τl ≫ τs ≫ τls ≳τP. The order−disorder transition accompanies the conversion between structured water and loosely structured water. However, the species with τs remains even in the disordered state and constitutes part of bound water in the entire temperature range. In the frozen state, in addition to bulk water formed by partial melting, two mobile species existed, which were assigned to liquidlike bound water and found to be a continuation of bound water in the solution state. These relaxation time data are discussed in connection with the entropy levels of the four structures deduced from heat capacity data (cf. Yoshiba, K.; et al. Biomacromolecules 2003, 4, 1348−1356).

Heat capacity measurements were made on aqueous solutions of a triple-helical polysaccharide schizophyllan by precision adiabatic calorimetry over a wide range of concentrations 30.45−90.93 wt % at temperatures between 5 and 315 K. The heat capacity curves obtained were divided into four groups depending on the weight fraction of schizophyllan w regions I−IV. In region I, triple-helices with the sheath of bound water, structured water, and loosely structured water forming layers around the helix core are embedded in free water. In region II, there is no free water, and loosely structured water decreases until it vanishes, but structured water stays constant with increasing w. In region III, bound water remains unaffected, but structured water decreases with increasing w by overlapping each other. Finally, in region IV, only schizophyllan and bound water exist, the latter decreasing upon increasing w. The maximum thickness of each layer is 0.183 nm for bound water, 0.134 nm for structured water, and 0.236 nm for loosely structured water, and these layers of water are at the enthalpy levels of 53%, 93.7%, and nearly 100%, respectively, between ice (0%) and free water (100%).

Heat capacities of the organic free radical magnet 2-tert-butylaminoxylbenzimidazole (BABI) have been measured in the 0.2−300 K range by adiabatic calorimetry for investigation of its magnetic properties from a thermodynamic viewpoint. An antiferromagnetic phase transition was observed at TN = 1.7 K. A heat capacity hump arising from short-range spin ordering characteristic of low-dimensional magnets was found around 2 K. The magnetic enthalpy and entropy were determined to be 17.4 J mol^-1 and 5.34 J K^-1 mol^-1, respectively. The magnitude of the magnetic entropy is in good agreement with the theoretical value for the magnetic ordering of spin quantum number S = ¹/2 systems, R ln 2 = 5.76 J K^-1 mol^-1, where R is the gas constant. The heat capacity hump above TN is well reproduced by the S = ¹/2 two-dimensional antiferromagnetic bilayer Heisenberg model with the intralayer interaction J1/kB = −1.2 K and the interlayer interaction J2/kB = −1.9 K, where kB is the Boltzmann constant. The bilayer model gives a close fit to both the present calorimetric and previously reported magnetic data with very similar intra- and interlayer exchange interaction parameters. Lower dimensionality models (such as dimeric interaction) for the magnetic and heat capacity behavior are not consistent with experimental results.

Heat capacities of the organic free radical ferromagnet 4-benzylideneamino-2,2,6,6-tetramethylpiperidin-1-oxyl (BATMP) crystal were measured in the temperature range between 0.1 and 300 K by adiabatic calorimetry. A ferromagnetic phase transition was found at TC = 0.19 K, and a broad heat-capacity anomaly was found arising from the short-range ordering above TC characteristic of low-dimensional magnetic spin systems. The enthalpy and entropy gains due to both the magnetic phase transition and the heat-capacity anomaly were evaluated to be ΔH = 3.86 J mol^-1 and ΔS = 5.64 J K^-1 mol^-1, respectively. The value of the experimental magnetic entropy agrees well with the theoretical value R ln 2 (5.76 J K^-1 mol^-1) expected for a spin quantum number S = ¹/2 spin system (R is the gas constant). The magnetic heat capacity hump due to the short-range order was well accounted for in terms of an S = ¹/2 one-dimensional ferromagnetic Heisenberg model with the intrachain exchange interaction J/kB = 0.95 K (kB is Boltzmann's constant). This fact suggests that BATMP crystal is a one-dimensional ferromagnet above TC. The spin wave analysis of the magnetic heat capacities below TC revealed that BATMP crystal is in a three-dimensional ferromagnetic state below TC and the averaged interchain exchange interaction is J‘/kB = 0.026 K.

Heat capacity of the halogen-bridged mixed-valence complex Pt2(dta)4I (dta = CH3CS2^-) has been measured in the temperature region between 6 and 386 K. The complex exhibited a phase transition of order−disorder type at Ttrs = 373.4 K, from being arranged in an ordered helical form of four dta ligand planes around the central Pt−Pt axis to dynamically jumping between two orientations. Neither latent heat nor distinct thermal hysteresis was observed for the phase transition, suggesting that the phase transition is of higher-order rather than of first-order. The transition enthalpy and entropy were determined to be ΔtrsH = 1.91 ± 0.02 kJ mol^-1 and ΔtrsS = 5.25 ± 0.07 J K^-1 mol^-1, respectively. The transition entropy close to R ln 2 (= 5.76 J K^-1 mol^-1), where R is the gas constant, implies that the twisting motion of the four dta ligands takes place in a synchronized way. No thermal anomaly was detected around 300 and 90 K, where a Mott transition from the one-dimensional metallic phase to the semiconducting phase and a spin-Peierls-like transition have been expected. The reason for the absence of these transitions in calorimetry is discussed briefly.

The heat capacities of the binary system consisting of a nonionic surfactant, hexaoxyethylene n-dodecyl ether (C12E6), and water were precisely measured as a function of temperature by adiabatic calorimetry over the temperature and the concentration ranges where lyotropic liquid crystals are formed. The enthalpy and entropy of transitions were determined for all transitions observed. The enthalpy and entropy of transition between liquid crystalline phases suggest that the liquid crystalline phases in this system are mainly constructed by C12E6 molecules with a fixed amount of water. The excess heat capacities, as estimated by measuring the heat capacity of neat C12E6, are positive over the entire temperature and concentration ranges. The excess heat capacities also support the suggestion given above concerning the role of C12E6 molecules on the structure building.