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Recent experiments for various amides and sugars showed a clear correlation of the temperature dependence of the Soret coefficient with the hydrophilicity, quantitatively described by the logarithm of the 1-octanol/water partition coefficient $\log P$. This coefficient is a measure for the hydrophilicity/hydrophobicity balance of a solute and is often used to model the transport of a compound in the environment or to screen for potential pharmaceutical compounds. In order to validate whether this concept works also for other water soluble molecules we investigated systematically the thermophoresis of mono- and poly hydric alcohols. As experimental method we use a holographic grating technique called infrared Thermal Diffusion Forced Rayleigh Scattering (IR-TDFRS). Experiments showed that the temperature dependence of the Soret coefficient of polyhydric alcohols also correlates with $\log P$ and lies on the same master plot as amides and sugars.

We measured the binary diffusion coefficient and the Soret coefficient in the fabrication system of organic photovoltaics (OPVs) by the holographic grating technique we call Soret forced Rayleigh scattering (SFRS). To test the validity of the apparatus we built, we here performed measurements on binary benchmark mixtures: three types of binary solutions (50 wt %) composed of n-dodecane, isobutylbenzene, and 1,2,3,4-tetrahydronaphthalene, at 298.2 K. Our experimental results for the diffusion coefficient and the Soret coefficient agree with the benchmark values within ± 10 %. The uncertainties estimated based on the Guide to the Expression of Uncertainty in Measurement (GUM) for the Soret coefficient on the benchmark mixtures are within 16 % with the coverage factor of k = 2. For OPV systems, our measurements were performed on [60]fullerene or [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) solved in o-dichlorobenzene. We evaluated the Soret coefficient and the diffusion coefficient across a wide concent...

A detailed review of the experimental investigations of the thermodiffusion/thermophoresis process in liquid and gaseous mixtures is presented. Experiments in the laboratories on earth as well as studies in a microgravity environment in space have been described. The former include the non-optical apparatus such as the classical Soret cell , thermodiffusion column , two-chamber thermodiffusion cell and the thermal field-flow fractionation , as well as the optical techniques, viz., classical Soret cell with beam deflection, thermal diffusion forced Rayleigh scattering, thermal lens method and the microfluidic fluorescence method. These methods are discussed along with their advantages and disadvantages. Experiments performed in the microgravity environment are also discussed.

Thermal conductivity enhancement in colloidal silica dispersions (nanofluids) is investigated experimentally using a novel optical technique. The effects of nanoparticle size, concentration, and state of aggregation are examined. New data on well dispersed systems are compared to published data obtained using the more conventional transient hot-wire technique and good agreement was found. Experimental results are also compared with model predictions for relative thermal conductivity based on effective medium theory. For systems composed of larger diameter nanoparticles (~30 nm), good agreement was found between the measured thermal conductivity enhancement and that predicted by the classical Maxwell-Garnett model. For systems composed of smaller nanoparticles (∼10 and 20 nm), thermal conductivity enhancement was reduced by as much as 10%, presumably because interfacial thermal resistance effects become important. Measurements on two systems that were induced to form gels exhibited an increase in thermal conductivity of approximately 5% relative to the well-dispersed systems. The observed increase in thermal conductivity is larger than that predicted by a recently proposed model for aggregated nanofluids.

Anisotropic thermal transport in cross-linked polybutadienes deformed in simple elongation is investigated experimentally. Using a novel optical technique based on forced Rayleigh scattering, two c...

In the present work we studied the thermal diffusion behavior of n-decane in various alkanes by thermogravitational column (TC) technique and the thermal diffusion forced Rayleigh scattering (TDFRS) method. The investigated lighter alkanes compared to n-decane are n-pentane, n-hexane, n-heptane, n-octane, and the heavier ones are n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, and n-eicosane. The binary mixture n-decane/ n-pentane we investigated at several different concentrations; all other mixtures were only investigated at a mass fraction of 50%. Even for the volatile n-pentane/ n-decane mixture the deviations between the thermal diffusion coefficients determined by the different methods agreed within the error bars. Typically the agreement between the two methods was in the order of 5%. In comparison to recently published TC and TDFRS data we found deviations in the order of 30% up to 40%. We analyze and discuss the possible reasons for the discrepancies for the present and the past publications.

Nuclear magnetic resonance studies of translational diffusion in thermotropic liquid crystals

The Soret forced Rayleigh scattering method (S-FRSM) for measurement of mass diffusion coefficient has been developed. In the present paper, the theoretical analysis of the systematic effects of the experimental setup is discussed. It includes the analysis of : (1) effect of dye, (2) effect of sample thickness, (3) effect of Gaussian beam intensity distribution and (4) effect of heating duration time. The analysis of three-dimensional diffusion equation which takes into account the practical experimental conditions has clarified the influence quantity of the inadequate experimental settings. According to the present analysis, it has been found that the difference of diffusion coefficient can be negligible by employing the appropriate setting of experimental parameters. As a result of these considerations, the reliable optimization method of the measuring conditions in S-FRSM can be provided.

In the course of a chemical reaction or structural changes in a material, the thermal diffusivity of the material changes in response to its varying conditions. Real-time information in the form of successive data on the thermal diffusivity during the process is indispensable for an adaptive control system for material production or processing. In the present study, a measurement technique for in-plane thermal diffusivity in micro-scale and at a high repetition rate has been studied. In view of the application of this method for fast processes, the effects of property changes during a single measurement time on the measured value have been quantitatively evaluated. We have developed a measurement system of the in-plane thermal diffusivity by means of the forced Rayleigh scattering method, an optical technique with a measurement time less than 1 ms and at a micro-scale local observation area. In the present system, each thermal diffusivity measurement was conducted every 10 ms; i.e., the repetition rate was up to 100 data per second. The results of preliminary measurements of a polymethylmethacrylate plate with several repetition rates verify the reliability of this technique in tracing high-speed phenomena.

In the first part of the paper, we recall what the Soret effect is, together with its applications in science and industry. We emphasize the need to have a reliable data base for the Soret coefficient. Next we review the different techniques to measure the Soret coefficient (elementary Soret cell, beam deflection technique, thermal diffusion forced Rayleigh scattering technique, convective coupling and, in particular, the onset of convection in horizontal layers and the thermogravitational method). Results are provided for several systems, with both negative and positive Soret coefficients, and comparison between several laboratories are made for the same systems. We end with “benchmark” values of the Soret coefficient for some organic liquid mixtures of interest in the oil industry and to which all future new techniques should refer before gaining confidence. We conclude that correct values of the Soret coefficient can be obtained in earth conditions and we deny the need to go to microgravity. DOI: 10.1115/1.1992517

The self-diffusion and tracer diffusion of asymmetric poly(ethylene-alt-propylene-b-dimethylsiloxane), PEP−PDMS, copolymers were measured using forced Rayleigh scattering. Diffusion measurements we...

In the study of holographic grating relaxation (forced Rayleigh scattering, FRS) in nascent latex films we examined poly(n-butyl methacrylate) films using two complementary diffusing probes: a hyd...

In this study a model that allows the qualitative prediction of polymer thermal diffusion coefficients from polymer-solvent interaction parameters is presented. The Flory-Huggins lattice theory served as a starting point for the thermal diffusion model. From this model it follows that D T is determined by the temperature dependence of the polymer-solvent interaction parameter ( h ), the segmental mobility of the polymer chain, and the polymer concentration. In agreement with literature data, the model predicts that D T is independent of the molecular mass of the polymer, D T increases with temperature, and D T is strongly dependent on the interaction between the polymer and the solvent. Furthermore, it follows from the model that D T should decrease with concentration. A good qualitative agreement with experimental data has been found. In order to study the potentials of the model, the D T values of polystyrene (PS) in several solvents were predicted. The required temperature-dependent polymer-solvent int...

The Soret coefficient S T of ethylene glycol oligomers (EGOs) and crown ethers (CEs) in water were obtained by thermal diffusion forced Rayleigh scattering by changing the temperature, molecular weight, and concentration. The effect of a hydroxyl group on the EGOs and the effect of the cyclic structure of CEs on the thermal diffusion were determined systematically by changing the molecular weights of the EGOs and CEs. For dilute aqueous solutions, EGOs and CEs, except EG, show positive S T values that decrease with increasing temperature, which is similar to the results of previous studies on mixtures of water and organic solvents. The temperature dependence of S T changes its behavior from negative to positive with decreasing number of repeating units of EGOs. This behavior is related to the increase in the number density of the hydroxyl group. The S T values of EG show two different concentration regions, namely, the low concentration (0 2 wt%) and high concentration (2 100 wt%) regions.

We have studied the dynamics of styrene−isoprene (SI) block copolymer micelles in a matrix of linear entangled polyisoprene (PI) chains, using forced Rayleigh scattering (FRS) and dynamic mechanica...

Tracer diffusion of 9,10-phenanthrenequinone (PQ) and its photoproduct in super-cooled phenolphthalein-dimethyl-ether (PDE) was studied by forced Rayleigh scattering. In order to investigate the spatial frequency dependence of the grating dynamics, several spatial harmonics of the grating with non-sinusoidal phase profile produced by non-linear recording were monitored. An optical scheme with a diverging reading beam is proposed for simultaneous reconstruction of the harmonic components.

Forced Rayleigh scattering has been employed to measure tracer and self-diffusion in block copolymer melts, for both entangled and unentangled systems, and in both the ordered and disordered states. It is shown that entanglements are particularly effective in retarding the motion of copolymers parallel to the interface between microdomains. The mechanisms of activated reptation and block retraction are proposed for parallel diffusion. The importance of large amplitude composition fluctuations in the disordered state near the ordering transition is also demonstrated, for both copolymer and homopolymer tracers; the results suggest that copolymer tracers are more affected than homopolymers of comparable molecular weight.

The diffusion of coil-rod-coil triblock copolymers in entangled coil homopolymers is experimentally measured and demonstrated to be significantly slower than rod or coil homopolymers of the same molecular weight. A model coil-rod-coil triblock was prepared by expressing rodlike alanine-rich α-helical polypeptides in E. coli and conjugating coillike poly(ethylene oxide) (PEO) to both ends to form coil-rod-coil triblock copolymers. Tracer diffusion through entangled PEO homopolymer melts was measured using forced Rayleigh scattering at various rod lengths, coil molecular weights, and coil homopolymer concentrations. For rod lengths, L, that are close to the entanglementh length, a, the ratio between triblock diffusivity and coil homopolymer diffusivity decreases monotonically and is only a function of L/a, in quantitative agreement with previous simulation results. For large rod lengths, diffusion follows an arm retraction scaling, which is also consistent with previous theoretical predictions. These experimental results support the key predictions of theory and simulation, suggesting that the mismatch in curvature between rod and coil entanglement tubes leads to the observed diffusional slowing.

The Ludwig-Soret effect for aqueous solutions of α-cyclodextrin (CD), β-CD, γ-CD, and glucose was studied by thermal diffusion forced Rayleigh scattering (TDFRS) in the temperature range of 15-55°C. The Soret coefficient and the thermal diffusion coefficient show the sign inversion behavior from negative to positive with increasing temperature. The values of the temperature dependence of the Soret coefficient for α-CD, β-CD, and γ-CD are identical at all temperatures measured, although the Soret coefficient of glucose is positive at all temperatures. The studies of dye concentration dependence for CDs and glucose show an effect of the inclusion ability of CDs on thermal diffusion behavior.

It is shown that the technique of forced Rayleigh scattering, traditionallyemployed to probe translational diffusion, can be employed to probe rotational diffusion as well. Thus with a single experiment both quantities are measured. The system under investigation is colloid spheres suspended in a glass-forming liquid. Furthermore, it is shown that the Stokes-Einstein and Debye-Stokes-Einstein relations for translational and rotational diffusion, respectively, are valid for spherical colloid particles in a supercooled liquid matrix in the vicinity of the glassy state.

We propose a new method for analysis of nonmonotonic forced Rayleigh scattering (FRS) decay profiles. It is shown that the curvature near the local maximum of a decay–grow–decay profile or a grow–decay profile can be used to determine directly the geometric mean of the unperturbed and photoproduct diffusion coefficients, which will in many cases mitigate the need to apply multiparameter nonlinear fitting routines. FRS tracer‐diffusion measurements of methyl red in poly(vinyl acetate)/toluene solutions at two different probe wavelengths, analyzed using the new method, are in good agreement with results of previous studies. Simulations are used to estimate the systematic error due to the approximation employed, and it is concluded that accuracies of a few percent or better should be routinely achievable in most cases. We have, in addition, investigated the probe‐wavelength dependence of the profile shape for this system.

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.

Forced Rayleigh scattering (FRS) has been used to measure the self-diffusion and tracer diffusion of nearly symmetric, well-entangled, poly(ethylenepropylene)-poly(ethylethylene) (PEP-PEE) block copolymers. The temperature and molecular weight dependence of diffusion in PEP-PEE 1, a completely disordered block copolymer, was studied using three tracers: PEP-PEE 1, PEP-PEE 2, and PEP-PEE 3 (M n = 3.1 5 ×10 4 , 5.0 1 ×10 4 , and 8.1 2 ×10 4 , respectively)