Shozaburo Saito

A new model for the thermally induced volume phase transition of gels

A theoretical model that considers hydrophobic interaction is proposed for the thermally induced discontinuous shrinkage of hydrogels. In this model, the free energy of a hydrogel is divided into four parts: the elastic free energy of networks formulated according to the theory which takes the limit of elongation into account, the free energy arising from osmotic pressure of dissociated counterions in the gel, the free energy of interactions except for the hydrophobic interaction represented by a virial‐type volume interaction equation, and the free energy of the hydrophobic interaction. By the former three terms, the thermally induced swelling of gels and the effects of aspect ratio of segment are expressed. The incorporation of the fourth hydrophobic interaction term makes it possible to explain the thermally induced shrinkage of gels, and suggests the possibility of an explanation of ‘‘convexo’’‐type volume phase transition by means of the hydrophobic interaction.

High pressure liquidliquid equilibria for the system of water, ethanol and 1,1-difluoroethane at 323.2 K

Abstract A new static apparatus was designed and constructed for the measurement of high pressure liquidliquid equilibria up to 450 K and 20 MPa. Binary phase equilibria for the water + 1,1-difluoroethane system at 323.2 K and ternary liquidliquid equilibria for the water + ethanol + 1,1-difluoroethane system at 323.2 K were measured. The liquefied gas 1,1-difluoroethane was found to be an excellent solvent for the extraction of ethanol from low ethanol concentration aqueous solutions. 1,1-Difluoroethane could achieve more than double the ethanol distribution coefficients obtained with carbon dioxide at much lower pressures. The liquidliquid equilibrium data were correlated by the UNIQUAC and NRTL equations. The UNIQUAC and NRTL equations gave comparable correlation of the experimental data, however, the UNIQUAC equation yielded slightly better results.

Volume phase transition of N-alkylacrylamide gels

Experimental and theoretical studies performed on thermoshrinking N-alkylacrylamide gels are described. Equilibrium swelling ratios are presented for the gels in the presence of no additives, a surfactant (SDS), inorganic salts, polar organic components and tetraalkylammonium bromides. The gel studies are carefully matched to polymer cloud point studies and it is shown that the hydrophobicity of the monomer unit of the polymer greatly controls the phase behavior. A new model which can describe not only thermoswelling but also thermoshrinking types of volume phase transitions is presented. Dynamical studies performed with light scattering during spinodal decomposition provide new information on diffusion coefficients and mass transfer in the gels. Our studies provide new data on the use of a gel in membrane applications. We report permeation characteristics of a composite membrane of thermosensitive gel and porous glass. These include volume flux and rejection properties. It is pointed out that the change in the permeation characteristics results from that in micropore structures of the gel.

Swelling behaviours of N-alkylacrylamide gels in water: effects of copolymerization and crosslinking density

N-isopropylacrylamide (NIPA)/N-n-propylacrylamide (NNPA) copolymer gels of various molar ratios were prepared by radical polymerization and the relationship between the swelling behaviour of the gels and the copolymerization ratio was studied experimentally. The effect of a crosslinking point on the swelling behaviour of the NIPA gels was investigated by preparing the gels with various crosslinking densities. The results of our experiments revealed that the transition temperatures of the NIPA/NNPA copolymer gels were changed in proportion to the monomer ratio used in copolymerization and that the crosslinking density strongly affected the swelling ratios but not the transition temperatures of the gels.

Vaporliquid equilibria for CO2/hydrocarbon mixtures at elevated temperatures and pressures

Vaporliquid equilibrium data were obtained for CO2/benzene/tetralin and CO2/n-decane/tetralin systems in the temperature range from 340 to 520 K at several pressures up to 15 MPa using a flow type apparatus and the binary CO2/benzene system at 343 – 414 K and 2.3 – 15.4 MPa. An attempt was made to predict the vaporliquid equilibria for the above ternary mixtures using new extended mixing rules and a corresponding states principle. Calculation results have shown that the experimental tie lines can be well predicted with the present method although the conjugate lines are not satisfactory.

Molecular dynamics simulation of infinitely dilute solutions of benzene in supercritical CO2

Abstract Molecular dynamics simulations of infinitely dilute solutions of benzene in supercritical CO 2 have been performed using site-site potential models for both molecules. The simulations were made for systems of 256 molecules (1 solute, 255 solvent) in the NVT ensemble, at slightly supercritical temperatures with respect to the solvent, and over a reduced density range of 0.5 ϱ r Angular distribution functions revealed that CO 2 molecules tend to be oriented parallel to the benzene plane. Sector-dependent radial distribution functions indicated that solvation is preferentially polar. Solvation dynamics, and the density dependence of benzenes rotational and translational diffusion coefficients were inverstigated.

Density dependence of the molar absorption coefficient—Application of the beer-lambert law to supercritical C02—Naphthalene mixture☆

Abstract Infrared absorption spectra of naphthalene in supercritical carbon dioxide (C0 2 ) solutions of various concentrations were measured at 318.15 K at various pressures. The molar absorption coefficient of naphthalene in supercritical CO 2 was found to be dependent on the density of C0 2 . As the density of CO 2 increased, a red shift of peak wavenumber of the C-C vibration (quadrant stretching) were observed. This suggests that the molecular vibration of naphthalene in supercritical C0 2 was affected by the fluid density.

Measurement of vapor-liquid equilibria at elevated temperatures and pressures using a flow type apparatus

Abstract Vapor-liquid equilibrium data were obtained for CO 2 -n-heptane, CO 2 -n-decane, CO 2 -trans-decalin, CO 2 -tetralin, CO 2 -quinoline, benzene-tetralin and benzene-quinoline systems in the temperature range from 340 to 710 K at several pressures up to 25 MPa. A flow-type apparatus was developed and used for vapor-liquid equilibrium measurements in order to reduce the residence time of heat sensitive substances at high temperatures. The operation of the present apparatus was easy and improved by employing an overflow type self-control system equipped with a back pressure regulator. The reliability of this experimental apparatus and procedure was proven since the vapor-liquid equilibrium data for the CO 2 -n-heptane system were in good agreement with literature data and the vapor and liquid phase compositions were independent of the sample flow rate within the range of flow rate employed. Measured data were correlated using equations of state and mixing rules based on the corresponding state principle.

Molecular dynamics study on solvent clustering in supercritical fluid solutions based on particle radial kinetic energy

Abstract The objective of this work was to study the dynamic structures of solute-solvent clusters in supercritical fluids with molecular dynamics (MD) simulation. A new definition for cluster formation, based on the relative radial kinetic energy, is proposed. The method defines a cluster member as a solvent molecule which has a relative solute-solvent radial kinetic energy less than or equal to their pair potential energy. MD Simulations of Lennard-Jones (LJ) mixtures are shown for CO2 + pyrene and CO2 + model substances using one solute molecule and 863 solvent (CO2) molecules at T ∗ =1.40 , ϱ ∗ =0.35 via a Nose-Hoover thermostat. The average number of member CO2 molecules in a sphere with diameter of 13.5σCO2 surrounding the pyrene solute was found to be 58. By tagging cluster and non-cluster members, we observed that approximately half of the particles in the first cluster shell exchanged in about 4 ps. Our simulations show that the number of remaining initial cluster members decay very rapidly in the beginning and approach a constant exponential decay after around 1 ps in all systems. The behavior of the time dependent radial distribution function of the remaining initial members indicated that only those members which were initially located in the solvation shell remained as members after about 1 ps. We considered the number of cluster members on the constant decay curve as the number of solvation members. By using the exponential decay rate, the cluster half-life and the solvation number of the CO2 + pyrene system was found to be around 1 ps and 16 solvent molecules, respectively. Other LJ mixtures were also studied and it was found that the LJ energy parameter strongly influences the decay rate while the LJ size parameter directly affects the solvation number. Molecular weight only had a small effect on solvation number.

Sol—gel transition of alginate solution by additions of various divalent cations: critical behavior of relative viscosity

Abstract The critical behavior of viscosity near the gelation point was experimentally investigated for alginate solutions by additions of four different divalent cations. The critical exponent for viscosity was found to lie in the range 0.88–1.14 and is in good agreement with the predictions of percolation theory. The results are also comparable with those of several experiment systems reported in the literature.