The properties of water confined in porous materials are different from those of the bulk due to the confinement effect and the interaction with the pore wall of the material. The thermal behavior, structure, and dynamics of water confined in mesoporous silica (MCM-41) and polymer gel (Sephadex G15) were investigated by differential scanning calorimetry (DSC), X-ray scattering, and neutron scattering, respectively. Water confined in MCM-41 with a pore diameter of 21 Å does not freeze even when it is cooled to 180 K. However, the tetrahedral-like network structure of water (ice-like structure) is developed at a low temperature. Furthermore, confined water strongly interacts with the hydrophilic surface of MCM-41 pore. The dynamics of the unfrozen water shows a crossover from non-Arrhenius type behavior to Arrhenius type one, implying a liquid-liquid phase transition. Sephadex G15 has a wide pore size distribution unlike MCM-41. Hence, there are three states of water in the polymer gel: free water, freezable bound water, and unfrozen water. Water molecules in G15 gels are more strongly bound to the hydroxyl groups of the gel matrix compared with the case of the porous silica.
We have investigated relaxation times and heat capacities of polymer-dimer mixtures of α-methylstyrene by using dielectric relaxation measurements and differential scanning calorimetry. Since both polymer and dimer consists of identical monomers, the local interactions in the system are expected to be uniform. We examined those detailed data to elucidate the polymer concentration dependences of fragilities and cooperativities of molecules at glass transition temperatures. As a result, we found that there is a clear boundary at 20 wt% polymer concentration and that both fragility and cooperativity are large at low polymer concentrations, whereas both fragility and cooperativity decrease rapidly at high polymer concentrations. This suggests that the transition to the ideal glass that exists at the low concentration is lost or weakened at the high concentration side.
In the foam film stabilized by surfactant, a bilayer film of the surfactant is formed at the surfaces. For such a thin liquid film, thermodynamic relational expressions dealing with the thermodynamic quantity changes with the formation of bilayer film can be derived by introducing the divided planes on both surfaces of the thin film to define the interfacial excess quantities. By applying the obtained thermodynamic relations to the temperature dependence of film tension, it is possible to estimate the enthalpy change corresponding to the heat of bilayer film formation. The analysis for the black foam film of the aqueous tetradecyltrimethyammonium bromid and NaBr solution was conducted and then it was demonstrated that the heat of bilayer film formation reflects a minute change of the counter ion condensation in the bilayer of Newton black film.
By monitoring the concentration of NO gas in exhaled breath, the degree of inflammation of the airway due to
asthma or the like can be evaluated. We have been developing an optical sensor to monitor NO gas in exhaled breath using Cobalt(II) tetraphenylporphyrin (CoTPP) as a sensing material. In this article, I introduce our efforts to increase the sensitivity of the sensors and to suppress influence of the atmospheric humidity on their characteristics, which are necessary for manufacturing practical sensors. CoTPP was dispersed in three kinds of hydrophobic polymers: ethyl cellulose (EC), polystyrene (PSt), and polycyclohexyl methacrylate (PCHMA). Due to the high dispersion of CoTPP molecules in the composite film, the sensitivity of the CoTPP/EC sensor was six times that of the film where only CoTPP solution was cast. The calculated NO gas detection limit for the CoTPP/EC sensor was 33 ppb. We also succeeded in suppressing the influence of humidity by making the film hydrophobic.
A comprehensive review of the first principles phonon calculations is given here with special interests on their applications to metals and ceramics science. Thanks to the progress of high-performance computers, first principles phonon calculations are now practical with the accuracy comparable to experiments. They can be made using an ordinary PC-cluster within a reasonable research timeframe. A variety of thermal properties can be estimated from the phonon states. Firstly, we describe the harmonic approximation and derivation of heat capacity at constant volume, Helmholtz energy and entropy. Then, we explain the quasi-harmonic approximation
that treats volume dependence of phonon states. Heat capacity at constant pressure, thermal expansivity and Gibbs energy can be evaluated. Next, we explain a method to compute lattice thermal conductivity by taking account the third order anharmonicity. We show how to trace the collective motion of atoms associated with phase transitions and deformation twins by analyzing imaginary phonon eigenvectors. We also briefly describe challenges of self-consistent phonon calculations to include higher order anharmonicity and electron-phonon interactions. Reliable phonon calculations have become routine because of the development of robust software
and their persistent maintenance. Finally, some open-source codes are exemplified.
Lattice thermal conductivity is a function of the velocity and mean free path of phonons, which can be strongly
correlated to phase transition of solids. Herein we describe our recent progress of studies of the phase 0transition in the molecular crystals by means of thermal conductivity measurements. Thermal conductivity κ and specific heat C were measured by a home-made apparatus, and product of mean free path of phonon l and phonon velocity v was estimated by κ = 1/3Cvl. In most of the case, minima of κ and vl values were found near to the transition temperatures. Below the transition temperature,κ and vl value followed the T−1 functions below the transitions temperature, which meant that the phonon transportation was ballistic. Above transition temperature, temperature coefficient of κ value was positive while vl value was almost constant, as l value was minimized and phonon transportation became diffusive. Such the behavior was observed for 2D organic-inorganic perovskite, the one-dimensional hydrogen bonding ferroelectrics, the onedimensional
semiconductors of TCNQ0.5- salts, and the Fe(III) spin crossover complexes. Our home-made apparatus for
thermal conductivity measurement was also described in detail.