Adsorption equilibria of argon, nitrogen, and methane on the 13X
molecular sieve and the AS activated
carbon were measured at five temperatures over a wide pressure range
from 0.1 to 20 MPa using a
microbalance. From experimental adsorption isotherms, which are
excess functions, the absolute isotherms
were calculated using equations of state for a real gas phase.
Grand canonical Monte Carlo simulations
and density functional theory calculations were carried out in order to
explain specific features of the
resulting isotherms. Different thermodynamic functions evaluated
from the excess and absolute adsorption
isotherms were analyzed over a wide pressure range at the average
temperature of the range studied.
This paper deals with theoretical investigation of interfacial properties between two coexisting liquid or fluid phases in thermodynamical equilibrium. The Cahn-Hilliard gradient theory was combined with an activity coefficient model (Koningsveld-Kleintjens model) or with an equation of state (Sanchez-Lacombe lattice fluid model). Using an activity coefficient model, only one variable (concentration) changed passing the interface. The interfacial tension between demixed liquids was calculated for two systems (water + ethylene glycol isobutyl ether (EIB) and water + diethylene glycol diethyl ether (DDE)). Adjusting one parameter, the theory yields satisfactory estimates of interfacial tensions as a function of temperature. Applying an equation of state, two variables (density and concentration) change in the interface. In this case the theory gives the density profiles of both components. The calculated density profiles demonstrate the ability of the concept to predict preferential adsorption phenomena in binary systems. The theoretical approach was applied to three systems (aniline + cyclohexane, acetone + carbon disulfide, and stearic acid + propane). If the systems show a closed miscibility gap, the interfacial tension passes a maximum. A comparison of theoretical and experimental interfacial tensions of the system aniline + cyclohexane indicates that the theoretical concept is able to describe the experiment if two parameters were fitted.
Rate constants k iso of the thermal cis-trans isomerization of four 4,4'-nitro-aminoazobenzenes with different amino groups have been determined in homogeneous aprotic solvents and polyglykol oligomers, primarily by means of conventional flash photolysis. The rate constants have been correlated with polarity (according to max from UV/Vis absorption spectra of the trans isomers) and bulk viscosity of the solvents. Qualitative conclusions about the influence of varying concentrations of water with respect to polarity and hydrogen bonding on k iso -and max -values in acetone/water mixtures were derived. Based on these results the data from microheterogeneous solutions have been interpreted.In microheterogeneous water/surfactant solutions k iso -values of selected azo dyes were strongly dependent on the concentrations of SDS, Triton ᭨ X-100, C 12 EO 8 in water, and varied with the composition of bicontinuous microemulsions of Igepal ᭨ CA-520/ heptane/water. The large spread of isomerization rate constants is in part due to varying microviscosity.Replacement of H 2 O by D 2 O in aqueous surfactant solutions produced surprisingly large kinetic solvent isotope effects.
We have studied the thermotropic and lyotropic phase behaviour of di †erent monoalkyl glycosides using polarizing microscopy, di †erential scanning calorimetry and rheology. The dependence of the liquid crystal transition temperature and mesophase formation on the chain length of the hydrophobic tail has been studied. The melting transition for each of the dry alkyl-glycosides corresponds to one or two solidÈsolid transitions, a solidÈliquid crystalline transition and a liquid crystallineÈliquid isotropic transition. The lyotropic behaviour follows the classical pattern established for the surfactants. In the system (X \ 8, 10)Èwater, the C X G 1 mesophases observed with increasing the concentration are a hexagonal phase, a cubic phase and a lamellar phase. Caused by the strong kinetic hindrance, the cubic and hexagonal phases for the system C 10 G 1 (n-decylare only visible by polarization microscopy experiments. Rheological oscillation b-D-glucopyranoside)Èwater experiments permit detection of phase transition. In the low-frequency range the rheological data are consistent with the simple Maxwell model.
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