Amplitudes of power laws which describe the viscosity of binary liquid mixtures in the close neighbourhood of a critical solution temperature were determined along the coexistence curve and along the critical isochore for a number of different systems. Dynamic renormalisation group theory predicts that the ratio of amplitudes along these two paths should be a universal constant, with a value of 0.950, for every binary system close to a critical point. If the amplitudes are determined by fitting the experimental viscosity data to a power law in which the critical exponent is treated as a disposable variable, the resulting ratios vary from about 0.94 to 0.97. If corrections for shear gradient dependence of the viscosity close to a critical point are made and the critical exponent is fixed at the value xi. = 0.040 predicted by dynamic renormalisation group theory, then all the systems considered show amplitude ratios which converge to 0.950 f 0.001, in excellent agreement with theory. A similar analysis of results for the thermal conductivity anomaly detected in the system perfluoromethylcyclohexane + methylcyclohexane shows that, to within experimental error, the predicted amplitude ratio of 0.473 for thermal conductivity is compatible with the experimental data. Amplitude ratios for these transport properties appear indeed to be universal constants, as dynamic renormalisation group theory predicts. Chenziluminescence / Fluidity / Fluorescence / Radiation Chemistry 1 VesiclesThe fluidity changes of the Didodecyldimethylammonium Bromide (DDAB) vesicular bilayer, mimetic agent of biological membranes, following y-irradiation were investigated under conditions where mainly OH radicals existed. The chemiluminescence (CL) quantum yields of Lucigenin light reaction were found to be strongly depended upon the irradiation dose above 0.65 kGy. Quenching of N-Methylacridone fluorescence, the primary emitter of the light reaction, after irradiation was not observed. Thus, the increase in fluidity of the vesicular bilayer structure seems to be the principal cause of the CL decrease.Ber. Runsenges. Phys. Chem. 94, 428-430 (1990) -VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1990 0005 -9021/90/0303 -0428 $ 02.50/0
Thermal conductivities of all six binary mixtures of the gases hydrogen, deuterium, oxygen and nitrous oxide have been measured at 50 and 100°C. In all cases the observed thermal conductivities fall below molar average values, though for mixtures of oxygen with nitrous oxide deviations froin linearity are small.For each system the results have been fitted to an equation of the Wassiljewa form and values of Aij which give the best agreement with experiment have been found. A9 derived from the empirical equation of Lindsay and Bromley lead to thermal conductivities for the mixtures which range from a good agreement with experiment for mixtures of oxygen+nitrous oxide and deuterium+nitrous oxide (mean absolute deviation < 0-5 %) to a poor agreement for the remaining four mixtures (mean absolute deviation between 1.2 and 3-9 %). The Lindsay and Bromley approximation predicts values of Aij which are qualitatively similar to the " best experimental " AG except for mixtures of hydrogen with deuterium.In addition, the predictions of the Hirschfelder and Eucken approximation to rigorous theory have been compared with the experimental results. For mixtures of oxygen+nitrous oxide and hydrogen+deuterium these predictions give good agreement with experiment (mean absolute deviations < 0.9 %), but underestimate the experimental observations in the remaining systems by between 1.1 and 3.7 %.
Shear viscosities η are reported for pure liquid methylcyclohexane (MCH) from 298.610 K to 333.694 K, for perfluoromethylcyclohexane (PFMCH) from 319.196 K to 333.114 K and for a MCH + PFMCH mixture of overall PFMCH near-critical mole fraction, x c ) 0.3640, from (T UCS /K -7) in the region of biphase liquid coexistence to (T UCS /K + 20) in the uniphase region, where T UCS ) 320.13 K is the air-saturated upper liquidliquid critical solution temperature. The measurements were made using a capillary rheometer that permits the measurement of the viscosity of thermally equilibrated coexisting-liquid phases. The results confirm that the near-critical viscosity exhibits a weak enhancement that strictly speaking becomes a divergence when account is taken of the finite shear gradients in the capillary during measurements. The viscosity of the uniphase mixture of critical composition is well-described after shear gradient correction by a multiplicative combination of an Arrhenius background and a critical power expression with an index close to the now-accepted universal value y ) 0.0435. The chief objective of the work, in addition to contributing to knowledge of this aspect of near-critical rheology, is the development for the biphase of a simple expression for the temperature dependence of the viscosities of the coexisting phases, η + and η -, that combines (a) an expression for the viscosity diameter <η> ) 1/2(η + + η -) similar to that for the viscosity of the critical mixture in the uniphase region, with a similar best critical index y′ between 0.041 and 0.0435, and (b) an expression for ∆η ) (η + -η -) that behaves like an order parameter, with an index very close to the normal value ) 0.325 and as many Wegner correction terms as the data require. The best two-phase fit emerges from a freely fitted exponent y′ ≈ 0.037 with one Wegner-extended scaling term, but we believe that were shear gradient correction to be applied, the best y′ would be the consensus value y′ ) 0.0435. The magnitude of y′ notwithstanding, we believe that our primary objective has been satisfied, namely, the formulation of an expression that affords a good description of the shear and background viscosities of nearcritical mixtures in the one-and two-liquid phases in relation to our estimates of the nano-or molecular-viscosity derived from measurements of fluorescence polarization decay rates.
The thermal conductivities of seven sets of binary gaseous mixtures containing one polar constituent (sulphur dioxide or ammonia) have been measured at 50 and 100°C. The mixtures investigated were: S 0 2 + A r , S02+N20, SOzfCO2, S02+CH4, and NH3+Ar, NH3+N20, NH3+CH4. The apparatus was of the two-wire type used previously. The precision of the measurements is about 1 %. The thermal conductivities of mixtures containing ammonia show positive departures from the molar average; when SO2 is the polar constituent the thermal conductivities of the mixture either show negative departures from the molar average (+CH4 and +Ar) or else vary almost linearly with coinposition ( +NzO and + CO,). The results are analyzed in terms of the Hirschfelder-Eucken approximation to rigorous theory which underestimates the experimental observations by 3.5 % on average. Modifications to the Hirschfelder-Eucken theory based on a re-apportionment of the contributions to translational and internal energy transport are also examined, and are shown to improve agreement with experiment. Calculations for systems containing argon show some slight anomalies, which are discussed. A simple modification which uses a theoretical value for f& rather than for ftrans, decreases the average discrepancy between the observed and calculated thermal conductivities to 0.5 %, which is within the experimental uncertainty of the measured values.
Results of measurements of the temperature dependence of the thermal conductivity of the binary system perfluoromethylcyclohexane + methylcyclohexane are reported. These were obtained using a modified hot‐wire transient technique which allowed measurements to be made using very small temperature rises (<100 mK), with a precision of better than ± 0.5%. The results show a small but unmistakable anomalous rise in thermal conductivity on very close approach to the critical point. Analysis shows that this rise is compatible with a value for the critical exponent χλ = 0.572, in agreement with the theoretical predictions of dynamic renormalisation group theory. The anomaly is very small‐some five hundred times smaller in magnitude than the corresponding anomaly in thermal conductivity for a one component fluid near its gas‐liquid critical point.
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