W. Köhler

Thermal nonequilibrium phenomena in fluid mixtures

Concepts, Theory, and Computer Simulations.- Computer Simulations of Thermal Diffusion in Binary Fluid Mixtures.- Thermodiffusion in the Critical Region.- On the Theory of the Soret Effect in Colloids.- Principle of Entropy Maximization for Nonequilibrium Steady States.- A Comprehensive Theory of the Soret Effect in a Multicomponent Mixture.- Thermodiffusion and Nonlinear Heat Equation.- Nonequilibrium Concentration Fluctuations in Binary Liquid Systems Induced by the Soret Effect.- Thermodiffusion in Ionic Solids -Model Experiments and Theory.- Hip, Hip, Soret!.- Experimental Techniques and Special Systems.- Measurement of Transport Coefficients by an Optical Grating Technique.- A Survey of the Thomaes Flow Cell Method for the Soret Coefficient.- Validity Limits of the FJO Thermogravitational Column Theory.- Determination of Thermodiffusion Parameters from Thermal Field-Flow Fractionation Retention Data.- Thermodiffusion of Polymer Solutions in Convectionless Cells.- Convection and Porous Media.- Soret Effect and Free Convection: A Way to Measure Soret Coefficients.- Convective Patterns in Binary Fluid Mixtures with Positive Separation Ratios.- Convective Instability of Magnetized Ferrofluids: Influence of Magnetophoresis and Soret Effect.- On the Soret-Driven Thermosolutal Convection in a Vibrational Field of Arbitrary Frequency.- Thermodiffusion in Porous Media and Its Consequences.- Soret Effect and Mixed Convection in Porous Media.- Soret Effect in Multicomponent Flow Through Porous Media: Local Study and Upscaling Process.

Benchmark values for the Soret, thermal diffusion and diffusion coefficients of three binary organic liquid mixtures

With the aim of providing reliable benchmark values, we have measured the Soret, diffusion and thermal diffusion coefficients of the three binary mixtures of dodecane, isobutylbenzene and 1,2,3,4 tetrahydronaphthalene for a concentration of 50 wt% at a temperature of 25C. The experimental techniques applied by the five participating laboratories are transient holographic gratings, annular and parallelepipedic thermogravitational columns, and vertical parallelepipedic columns with velocity amplitude determination by laser doppler velocimetry. The systems have also been studied in a annular thermogravitational column filled with a porous medium in the gap. There is a good agreement between the different experiments with deviations of the order of a few per cent in most cases (8.5% at most). The numerical values are tabulated in the paper.

Second harmonic generation and thermally stimulated current measurements: A study of some novel polymers for nonlinear optics

The relaxation of electric field‐induced polar orientation in novel side and main chain polymers was measured by simultaneous second harmonic generation and thermally stimulated discharge current techniques. Using this combination of experiments, individual microscopic relaxation mechanisms could be discriminated and identified. The relaxation of a polymer bearing polar chromophores on a side chain polymer was found to occur through local reorientation. For polymers containing the polar chromophore within the main chain, both a local rotation of the chromophores and the reorientation of the end‐to‐end vectors of the chains could be detected. Physical aging near the Tg of the polymers greatly increased the stability of the poling‐induced orientation below Tg. Nonlinear dependencies on the poling field were observed for low fields and are discussed in terms of screening due to space charges. Kirkwood–Frohlich correlation factors were found to be very close to unity.

Thermodiffusion in polymer solutions as observed by forced Rayleigh scattering

Thermodiffusion, the cross coupling between temperature and concentration, is studied in dilute polymer solutions by forced Rayleigh light scattering. First a spatial temperature grating is created within the solution by absorption of an optical interference grating and subsequently a concentration grating builds up. The time‐dependent diffraction efficiency of both gratings is described by a phenomenological model from which the thermal diffusivity, the ordinary diffusion coefficient, and the thermodiffusion coefficient are obtained without the need for absolute intensity measurements or calibration with a known standard. No labeling of the polymer chains with photochromic dyes is required. Experimental details and potential pitfalls are discussed. Measurements are carried out on polystyrene in ethyl acetate and the obtained values compare well with data taken from the literature.

Measurement of the Soret, diffusion, and thermal diffusion coefficients of three binary organic benchmark mixtures and of ethanol–water mixtures using a beam deflection technique

We have measured the Soret (S T ), diffusion (D), and thermal diffusion (D T ) coefficients of three binary mixtures of dodecane (DD), isobutylbenzene (IB) and 1,2,3,4-tetrahydronaphthalene (TH) for a concentration of 50 wt% at a temperature of 25°C by means of an optical beam deflection cell. This relevant experimental technique was still missing from a recent benchmark campaign for the measurement of the Soret effect. The measured coefficients agree to within a few percent (10% for S T , D of TH/IB) with the proposed benchmark values. A detailed analysis of the measurement process of the beam deflection cell, which allows for an elegant extension to include temperature gradients within the windows, is given, and improved benchmark values are suggested. In addition, ethanol–water mixtures have been investigated very carefully over a broad concentration and temperature range. Comparison with data of Kolodner and Wiegand gives a generally good agreement with some systematic deviations. Contrary to theoretical predictions, we have not been able to identify a second sign change of S T at high ethanol concentrations.

Precise determination of the Soret, thermal diffusion and mass diffusion coefficients of binary mixtures of dodecane, isobutylbenzene and 1,2,3,4-tetrahydronaphthalene by a holographic grating technique

Within the framework of an international benchmark test, the Soret coefficient S T , thermal diffusion coefficient D T and mutual mass diffusion coefficient D of the three binary mixtures of dodecane, isobutylbenzene and 1,2,3,4-tetrahydronaphthalene with a concentration of 50 wt% of each component at a temperature of 25C have been measured with a holographic grating technique. For the analysis of the experimental data a new numerical correction algorithm based on linear response theory has been employed. The corrections applied are on the order of 1% for S T and 5% for D . The coefficients S T , D and D T are determined with relative errors of a few per cent.

Soret and mass diffusion coefficients of toluene/n‐hexane mixtures

Soret coefficients and mass diffusion coefficients of mixtures of toluene and n‐hexane have been measured by thermal diffusion forced Rayleigh scattering (TDFRS) and are compared with literature data. For the mass diffusion coefficients a good agreement between different experimental techniques is found. For the Soret coefficients contradictory results are obtained from thermogravitational column measurements, small angle Rayleigh scattering, and TDFRS. Arguments supporting the TDFRS data are presented.

Measurement of diffusion and thermal diffusion in ternary fluid mixtures using a two-color optical beam deflection technique

We have developed a highly sensitive two-color beam deflection setup to measure diffusion and thermal diffusion in ternary fluid mixtures following a suggestion of Haugen and Firoozabadi [J. Phys. Chem. B 110, 17678 (2006)]. Simultaneous detection of two laser beams with different wavelengths makes it possible to determine the time dependent concentration profiles of all three components. By comparing the measured beam deflection signals to a numerical solution of the coupled heat and mass transport equations, the diffusion matrix, the thermal diffusion, and the Soret coefficients are obtained by a numerical model combined with a nonlinear least-squares fitting routine. The results can be improved by additional thermal diffusion forced Rayleigh scattering experiments, which yield a contrast-weighted average thermal diffusion coefficient. The three Soret coefficients can be obtained independently from the stationary beam deflection amplitudes. Measurements have been performed on the symmetric (equal weight fractions) ternary mixtures dodecane/isobutylbenzene/1,2,3,4-tetrahydronaphthalene and 1-methylnaphthalene/octane/decane. There is only partial agreement between our results and literature data.

Poly[2]catenanes and Cyclic Oligo[2]catenanes Containing Alternating Topological and Covalent Bonds: Synthesis and Characterization

Large bifunctionalized catenate and catenand, composed of macrocycles containing 45 atoms, have been synthesized and copolymerized with a terephthalic acid derivative to afford a cyclic oligo[2]catenand and a linear poly[2]catenate. Poly[2]catenand was obtained by demetalation of poly[2]-catenate. The molecular weight distribution of these polymers, which are composed of alternating topological and covalent bonds, has been characterized by gel permeation chromatography (GPC) with universal calibration, viscometry, and MALDI-TOF mass spectrometry. We were able to synthesize a poly[2]catenate and a poly[2]catenand with a degree of polymerization (DP) equal to 8-9. In addition, an upper value of the Kuhn segment length of poly[2]catenand has been determined and is discussed in the light of its structure.

A comprehensive study of diffusion, thermodiffusion, and Soret coefficients of water-isopropanol mixtures

We report on the measurement of diffusion (D), thermodiffusion (D(T)), and Soret (S(T)) coefficients in water-isopropanol mixtures by three different instrumental techniques: thermogravitational column in combination with sliding symmetric tubes, optical beam deflection, and optical digital interferometry. All the coefficients have been measured over the full concentration range. Results from different instruments are in excellent agreement over a broad overlapping composition (water mass fraction) range 0.2 < c < 0.7, providing new reliable benchmark data. Comparison with microgravity measurements (SODI/IVIDIL (Selected Optical Diagnostic Instrument/Influence of VIbration on DIffusion in Liquids)) onboard the International Space Station and with literature data (where available) generally gives a good agreement. Contrary to theoretical predictions and previous experimental expectations we have not observed a second sign change of S(T) at low water concentrations.