Search

During the processes of hydrogenation or dehydrogenation of liquid organic hydrogen carriers (LOHCs), knowledge of the current degree of hydrogenation (DoH) is often essential. The present study shows that depolarized Raman spectroscopy allows the accurate determination of the DoH of the model LOHC system diphenylmethane (H0-DPM)/dicyclohexylmethane (H12-DPM) at temperatures up to 573 K. Using two independent experimental setups and binary mixtures of H0- and H12-DPM, a temperature-independent calibration factor could be obtained by analyzing Raman bands characteristic for the aromatic and aliphatic carbon rings. The successful transfer of the calibration to technical mixtures is validated by DoH measurements of samples from deliberately stopped hydrogenation reactions containing also the intermediate cyclohexylphenylmethane (H6-DPM) and of pure H6-DPM. Here, the average absolute deviation of the DoHs obtained by depolarized Raman spectroscopy from those measured analytically is 0.018, which demonstrates the applicability of the method at arbitrary and process-relevant temperatures.

In the present study, the mutual diffusivity D11 in binary mixtures of water with technical polydisperse poly(ethylene) glycol (PEG) blends with molar masses of (1000, 4000, or 6000) g⋅mol−1 as well as with a purified monodisperse PEG homolog with a polymerization number of 21 and a molar mass of 943 g⋅mol−1 was investigated by heterodyne dynamic light scattering (DLS) as a function of temperature and/or PEG concentration. The measured D11 for technical PEG 1000 and pure PEG 943 match within the experimental uncertainties and agree well with the available literature data. D11 decreases with increasing molar mass of the PEGs at constant temperature and weight fraction. For the technical PEG 4000, it could be shown that D11 increases with increasing temperature and exhibits a non-linear concentration dependence. This study demonstrates that heterodyne DLS can be applied for the reliable determination of D11 of aqueous solutions of PEGs over a broad range of PEG weight fractions from 0.01 up to the solubility limit with an average expanded uncertainty (k = 2) of 5.5%. Moreover, the results show that monodisperse PEGs are suitable model systems for studying the diffusion behavior of bimodal and also multimodal particulate systems.

This work contributes to the characterization of three binary liquid hydrocarbon-based mixtures via the determination of density, viscosity, and interfacial tension over the entire concentration ra...

This work is a continuation of previous studies focusing on the influence of intermolecular interactions on the diffusive mass transport in mixtures consisting of liquids with dissolved gases by de...

In this study, the thermal conductivity of diphenylmethane, benzyltoluene, and dibenzyltoluene and their fully hydrogenated counterparts relevant in the context of the liquid organic hydrogen carri...

Ionic liquids (ILs) are interesting working fluids in many areas of chemical and energy engineering such as gas separation, catalysis, or energy storage. For the optimum design of related processes...

In the present study, the influence of the molecular characteristics of the solvent and solute on the dynamic viscosity and interfacial tension of binary mixtures consisting of a liquid with a dissolved gas is investigated using surface light scattering (SLS) and equilibrium molecular dynamics (EMD) simulations. In detail, binary mixtures consisting of linear, branched, cyclic, or oxygenated hydrocarbons and the solutes hydrogen, helium, methane, water, carbon monoxide, or carbon dioxide are studied in the temperature range between (298 and 573) K and for solute mole fractions up to 0.2. With SLS, the liquid dynamic viscosity and interfacial tension of the binary mixtures could be accessed in macroscopic thermodynamic equilibrium with average expanded uncertainties (coverage factor k = 2) of (2.4 and 2.3)%, respectively. While EMD simulations were able to predict the influence of the dissolved gases on the interfacial tension of the binary mixtures, the simulations fail to represent the influence of the dissolved gas on the viscosity. Due to the systematic variation of the solvent and solute molecules, the influence of the molecular characteristics, e.g., in the form of size, shape, or polarity, on the thermophysical properties of the mixtures is discussed. Dissolving carbon dioxide, e.g., leads to a reduction of both properties by up to 60% compared to the properties of the pure solvent. Dissolved helium, on the other hand, has only a small influence on the properties of the pure solvent. The influence of dissolved water was found to be negligible in mixtures with an alkane but strongly increases both properties when dissolved in an alcohol, which may be explained by the formation of hydrogen bonds.

For the efficient design of hydrogenation and dehydrogenation processes, a comprehensivedatabase for the viscosity, surface tension, and density of mixtures of thediphenylmethane-based liquid organic hydrogen carrier system and the pure intermediatecyclohexylphenylmethane measured by complementary optical and conventionalmethods and calculated by molecular dynamics simulations at process-relevant temperaturesup to 623 K is presented. The simulations employ self-developed force fieldsincluding a new one for cyclohexylphenylmethane and reveal surface enrichment andorientation effects influencing the surface tension. Relatively simple correlation and predictionapproaches yield accurate representations as function of temperature and degreeof hydrogenation (DoH) of the mixtures with average absolute relative deviations (AARD) of0.07% for the density and 2.9% for the surface tension. Application of the extended hardspheretheory considering the presented accurate density data allows capturing thehighly nonlinear DoH-dependent behavior of the dynamic viscosity with an AARD of 2.9%.© 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

In hydrogenation and dehydrogenation processes of liquid organic hydrogen carriers (LOHCs), molecular hydrogen (H2) is present, but its influence on the thermophysical properties of the LOHC compounds is still hardly known. This study provides experimental results from surface light scattering and predictions from molecular dynamics simulations on the influence of dissolved H2 on the liquid viscosity, interfacial tension, and liquid density of the LOHC system based on diphenylmethane at varying degree of hydrogenation, process-relevant temperatures up to 573 K, and pressures up to 7 MPa. First-time measurements of the viscosity of bicyclic hydrocarbon compounds in the presence of dissolved H2 at saturation conditions reveal a negligible effect of pressure. The interfacial tension decreases independently of the LOHC composition by about 6% at 7 MPa. The simulations can adequately represent the effect of H2 on the interfacial tension and evidence a weak enrichment of H2 at the interface.

The present work contributes to the development of the shadowgraph method for its routine application for an accurate determination of the Fick diffusion coefficient D11 of binary fluid mixtures. In this context, measurement and data evaluation strategies for thermodiffusion experiments where confinement and advection are potentially present are elaborated by studying two binary liquid mixtures with positive and negative Soret coefficients, i.e., 1,2,3,4-tetrahydronaphthalene/ n-dodecane and acetone/cyclohexane. For obtaining accurate D11 data, the dynamics of non-equilibrium fluctuations in concentration is analyzed considering recent theory by data evaluation procedures that are demonstrated to be suitable for different experimental configurations.

This work contributes to an improved understanding of the fluid-phase behavior and diffusion processes in mixtures of 1-hexanol and carbon dioxide (CO2) at temperatures around the upper critical end point (UCEP) of the system. Raman spectroscopy and dynamic light scattering were used to determine the composition at saturation conditions as well as Fick and thermal diffusivities. An acceleration of the Fick diffusive process up to CO2 mole fractions of about 0.2 was found, followed by a strong slowing-down approaching vapor-liquid-liquid equilibrium or critical conditions. The acceleration of the Fick diffusive process vanished at temperatures much higher than the UCEP. Experimental Fick diffusivity data were compared with predictions from equilibrium molecular dynamics simulations and excess Gibbs energy calculations using interaction parameters from the literature. Both theoretical methods were not able to predict that the thermodynamic factor is equal to zero at the spinodal composition, stressing the need for new methodologies under such conditions. Thus, new sets of temperature-dependent interaction parameters were developed for the nonrandom two-liquid model, which improve the prediction of the Fick diffusion coefficient considerably. The link between the Fick diffusion coefficient and the nonrandomness of the liquid phases is also discussed.

The diffusive behavior of nanoparticles inside porous materials is attracting a lot of interest in the context of understanding, modeling, and optimization of many technical processes. A very powerful technique for characterizing the diffusive behavior of particles in free media is dynamic light scattering (DLS). The applicability of the method in porous media is considered, however, to be rather difficult due to the presence of multiple sources of scattering. In contrast to most of the previous approaches, the DLS method was applied without ensuring matching refractive indices of solvent and porous matrix in the present study. To test the capabilities of the method, the diffusion of spherical gold nanoparticles within the interconnected, periodic nanopores of inverse opals was analyzed. Despite the complexity of this system, which involves many interfaces and different refractive indices, a clear signal related to the motion of particles inside the porous media was obtained. As expected, the diffusive process inside the porous sample slowed down compared to the particle diffusion in free media. The obtained effective diffusion coefficients were found to be wave vector-dependent. They increased linearly with increasing spatial extension of the probed particle concentration fluctuations. On average, the slowing-down factor measured in this work agrees within combined uncertainties with literature data.

In the present study, the wettability of ground AISI 321 steel and PTFE surfaces with a polyalkylene glycol-based lubricant in air and 1,1,1,2-tetrafluoroethane (R-134a) atmospheres is characterized. For this, spreading velocities are determined from videos recorded during the continuous dosing of lubricant on the solid surfaces. The results are compared with interfacial tension data for the lubricant measured by the pendant-drop method in air and R-134a atmospheres. Significantly higher wettability was found in the presence of refrigerant atmosphere, on the steel surface and along its grinding grooves, whereas no consistent temperature-dependent trends could be identified. The interfacial tension of the lubricant decreases with increasing temperature at ambient air atmosphere as well as with increasing R-134a pressure at a fixed temperature. The temperature-dependent behavior of the interfacial tension for a given refrigerant pressure is affected by the temperature itself and by the resulting solubility of the refrigerant in the lubricant.

The influence of the strength of intermolecular interactions on mass diffusive processes remains poorly understood for mixtures of associative liquids with dissolved gases. For contributing to a fundamental understanding of the interplay between liquid structures and mass diffusivities in such systems, dynamic light scattering, Raman spectroscopy, and molecular dynamics simulations were used in this work. As model systems, binary mixtures consisting of the gases hydrogen, helium, nitrogen, carbon monoxide, or carbon dioxide dissolved in ethanol, 1-hexanol, or 1-decanol were selected. Experiments and simulations were performed at macroscopic thermodynamic equilibrium close to infinite dilution of solute for temperatures between 303 and 423 K. The Fick diffusion coefficients and self-diffusivities of the gas solutes increase with increasing temperature, decreasing alkyl chain length of the 1-alcohols, and decreasing molar mass of the solutes except for helium and hydrogen showing the opposite behavior. The analysis of the liquid structure of the mixtures showed that the fraction of hydrogen-bonded alcohol molecules decreases with increasing alkyl chain length and temperature. From the obtained structure-property relationships, a new correlation was developed to predict mass diffusivities in binary mixtures consisting of n-alkanes or 1-alcohols with dissolved gases close to infinite dilution within 10% on average.

In the present contribution, diffusivities of binary mixtures of propane (C3H8), carbon dioxide (CO2), and methane (CH4) were investigated between T = (293 and 353) K, p = (0.5 and 12) MPa, and mol...

Hypothesis The application of dynamic light scattering (DLS) is well-established for measuring diffusion coefficients related to either molecular or translational micelle diffusion. The simultaneous determination of both transport properties should be feasible, but has not been reported in the literature yet. Experiments Different diffusion modes present in a microemulsion and selected subsystems consisting of a polyol mixture, a binary surfactant mixture, and carbon dioxide (CO2) were investigated systematically by DLS at temperatures of (314, 333, and 353) K and corresponding pressures of (10, 13, and 16) MPa. Findings Diffusion coefficients related to molecular and translational micelle diffusion could be measured simultaneously and increase with increasing temperature. From the translational diffusion coefficients, an increase in the hydrodynamic diameter of the micelles from their non-swollen to the CO2-swollen state being in agreement with literature data for the same and similar microemulsions was found. The effective diffusion coefficients related to the faster molecular diffusion process only observable in the presence of CO2 are not affected significantly by the surfactant. The time-dependent parts of the recorded intensity correlation functions related to molecular diffusion processes are heterodyne because the scattered light modulated by molecular concentration fluctuations is superimposed with light scattered by the micelles.

In modelling heating and evaporation of fuel droplets, intra-droplet heat and mass transfer has to be considered. This is only possible with the help of reliable data for thermal and mutual diffusivity. At present, research activities in connection with the modelling of the evaporation of fuel droplets are based on theoretical diffusivity data. For their check and validation, there is, however, a lack of reliable experimental data. In this study, a dynamic light scattering apparatus which was especially developed for the simultaneous determination of both thermal and mutual diffusivity for fuel-related mixtures is presented. In the apparatus, fuel-related mixtures can be investigated under defined conditions in the compressed liquid phase close to saturation conditions in macroscopic thermodynamic equilibrium. Model binary mixtures composed of five different substances representative for fuel-related compounds were investigated at temperatures up to 523 K and close to their bubble point line. In detail, the mixtures investigated in the present study include 9 of the 10 possible binary combinations of isopentane, isooctane, toluene, n-decane, and ethanol. The results document that even under extreme conditions, thermal and mutual diffusivities are accessible with average expanded uncertainties (k = 2) of 8% and 6%. For all systems, concentrations, and temperatures, the thermal diffusivity changes only slightly. In contrast, the mutual diffusivity varies by more than two orders of magnitude from about 10−10 to 10−8 m2·s−1. For mixtures of isooctane and toluene, the concentration dependency of the mutual diffusivity reveals a nonideal behavior which becomes more pronounced with increasing temperature. For all binary mixtures, the temperature dependency of the mutual diffusivity can be correlated well with the vapor pressure of the individual components. The presence of the biofuel ethanol strongly slows down the molecular diffusion process at low temperatures.

In the present study, the simultaneous and accurate determination of liquid viscosity and surface tension of the n-alkanes n-hexane (n-C(6)H(14)), n-octane (n-C(8)H(18)), n-decane (n-C(10)H(22)), and n-hexadecane (n-C(16)H(34)) by surface light scattering (SLS) in thermodynamic equilibrium is demonstrated. Measurements have been performed over a wide temperature range from 283.15 K up to 473.15 K for n-C(6)H(14), 523.15 K for n-C(8)H(18), and 573.15 K for n-C(10)H(22) as well as n-C(16)H(34). The liquid dynamic viscosity and surface tension data with average total measurement uncertainties (k = 2) of (2.0 and 1.7) % agree with the available literature and contribute to a new database at high temperatures. Over the entire temperature range, a Vogel-type equation for the dynamic viscosity and a modified van der Waals equation for the surface tension represent the measured data for the four n-alkanes within experimental uncertainties. By also considering our former SLS data for n-dodecane (n-C(12)H(26)) and n-octacosane (n-C(28)H(58)), empirical models for the liquid viscosity and surface tension of n-alkanes were developed as a function of temperature and carbon number covering values between 6 and 28. Agreement between these models and reference correlations for further selected n-alkanes which were not included in the development procedure was found.

In the present study, physico-chemical properties of the liquid organic hydrogen carrier (LOHC) system diphenylmethane/dicyclohexylmethane in the presence of dissolved hydrogen are presented for temperatures up to 523 K and pressures up to 10 MPa. Solubility of hydrogen, interfacial tension, and liquid density were measured by the isochoric saturation method, the pendant-drop method, and vibrating-tube method, respectively, which are realized in two experimental setups. The solubility of hydrogen increases with increasing temperature and pressure. For the fully hydrogenated dicyclohexylmethane, it is about 50% higher than for the non-hydrogenated diphenylmethane and similar to that of a mixture from a deliberately stopped hydrogenation process containing also partially hydrogenated cyclohexylphenylmethane. While the interfacial tension decreases slightly with increasing hydrogen pressure at constant temperature, the density remains approximately constant. The latter properties obtained for different mixtures with similar degree of hydrogenation show that the influence of the presence of cyclohexylphenylmethane is small.

In this study, the liquid viscosity and interfacial tension of binary and ternary mixtures containing n-octacosane (n-C28H58) and different byproducts typically found in the Fischer–Tropsch process...

In the present study, the effective thermal conductivity of nanoparticle dispersions, so-called nanofluids, is investigated experimentally and theoretically. For probing the influence of the nanoparticles on the effective thermal conductivity of dispersions with water as liquid continuous phase, nearly spherical and monodisperse titanium dioxide (TiO2), silicon dioxide (SiO2), and polystyrene (PS) nanoparticles with strongly varying thermal conductivities were used as model systems. For the measurement of the effective thermal conductivity of the nanofluids with particle volume fractions up to 0.31, a steady-state guarded parallel-plate instrument was applied successfully at temperatures between (298 and 323) K. For the same systems, dynamic light scattering (DLS) was used to analyze the collective translational diffusion, which provided information on the dispersion stability and the distribution of the particle size as essential factors for the effective thermal conductivity. The measurement results for the effective thermal conductivity show no temperature dependency and only a moderate change as a function of particle volume fraction, which is positive or negative for particles with larger or smaller thermal conductivities than the base fluid. Based on these findings, our theoretical model for the effective thermal conductivity originally developed for nanofluids containing fully dispersed particles of large thermal conductivities was revisited and also applied for a reliable prediction in the case of particles of relatively low thermal conductivities.

This work contributes to the characterization of long linear and branched alkanes and alcohols via the determination of their thermophysical properties up to temperatures of 573.15 K. For this, experimental techniques including surface light scattering (SLS) and molecular dynamics (MD) simulations were used under equilibrium conditions to analyze the influences of chain length, branching, and hydroxylation on liquid density, liquid viscosity, and surface tension. For probing these effects, 12 pure model systems given by the linear alkanes n-dodecane, n-hexadecane, n-octacosane, n-triacontane, and n-tetracontane, the linear alcohols 1-dodecanol, 1-hexadecanol, and 1,12-dodecanediol, the branched alkanes 2,2,4,4,6,8,8-heptamethylnonane (HMN) and 2,6,10,15,19,23-hexamethyltetracosane (squalane), and the branched alcohols 2-butyl-1-octanol and 2-hexyl-1-decanol were investigated at or close to saturation conditions at temperatures between 298.15 and 573.15 K. Based on the experimental results for the liquid densities, liquid viscosities, and surface tensions with average expanded uncertainties (k = 2) of 0.061, 2.1, and 2.6%, respectively, the performance of the three commonly employed force fields (FFs) TraPPE, MARTINI, and L-OPLS was assessed in MD simulations. To improve the simulation results for the best-performing all-atom L-OPLS FF at larger temperatures, a modified version was suggested. This incorporates a temperature dependence for the energy parameters of the Lennard-Jones potential obtained by calibrating only against the experimental liquid density data of n-dodecane. By transferring this approach to all other systems studied, the modified L-OPLS FF shows now a distinctly better representation of the equilibrium and transport properties of the long alkanes and alcohols, especially at high temperatures.

The liquid viscosity, surface tension, and liquid density of the two branched alkanes 2-methylnonane and 4-methylnonane were studied for temperatures between 283.15 and 448.15 K. The surface tension and liquid dynamic viscosity were obtained from surface light scattering (SLS) measurements close to saturation conditions with average relative expanded uncertainties (k = 2) of 1.5 and 0.9 %. Two vibrating-tube densimeters were used for the measurement of the liquid density at atmospheric pressure with relative expanded uncertainties (k = 2) between 0.01 and 0.5 %. The measured data could be correlated mostly within their expanded uncertainties by appropriate equations. Comparison with the few available literature data shows good agreement.

This study contributes to a fundamental understanding of how the liquid structure in a model system consisting of weakly associative n-hexane (n-C6H14) and carbon dioxide (CO2) influences the Fickian diffusion process. For this, the benefits of light scattering experiments and molecular dynamics (MD) simulations at macroscopic thermodynamic equilibrium were combined synergistically. Our reference Fickian diffusivities measured by dynamic light scattering (DLS) revealed an unusual trend with increasing CO2 mole fractions up to about 70 mol %, which agrees with our simulation results. The molecular impacts on the Fickian diffusion were analyzed by MD simulations, where kinetic contributions related to the Maxwell–Stefan (MS) diffusivity and structural contributions quantified by the thermodynamic factor were studied separately. Both the MS diffusivity and the thermodynamic factor indicate the deceleration of Fickian diffusion compared to an ideal mixture behavior. Computed radial distribution functions as w...

Chronic injury of limb nerves leading to neuropathic pain affects deep somatic nerves. Here the functional properties of injured afferent fibers in the lateral gastrocnemius-soleus nerve were investigated 20 and 80 days after suturing the central stump of this muscle nerve to the distal stump of the sural nerve in anesthetized rats. Neurophysiological recordings were made from afferent axons identified in either the sciatic nerve (87 A-, 63 C-fibers) or the dorsal root L4/L5 (52 A-, 26 C-fibers) by electrical stimulation of the injured nerve. About 70% of the functionally identified A-fibers had regenerated into skin by 80 days after nerve suture; the remaining A-fibers could be activated only from the injured nerve. In contrast, 93% of the functionally identified C-fibers could only be activated from the injured sural nerve after 80 days. Nearly half of the injured A- (45%) and C-fibers (44%) exhibited ongoing and/or mechanically or thermally evoked activity. Because ~50% of the A- and C-fibers are somatomotor or sympathetic postganglionic axons, respectively, probably all injured muscle afferent A- and C-fibers developed ectopic activity. Ongoing activity was present in 17% of the A- and 46% of the C-fibers. Mechanosensitivity was present in most injured A- (99%) and C-fibers (85%), whereas thermosensitivity was more common in C-fibers (cold 46%, heat 47%) than in A-fibers (cold 18%, heat 12%). Practically all thermosensitive A-fibers and C-fibers were also mechanosensitive. Thus, unlike cutaneous axons, almost all A- and C-fibers afferents in injured muscle nerves demonstrate ectopic activity, even chronically after nerve injury. NEW & NOTEWORTHY After chronic injury of a muscle nerve, allowing the nerve fibers to regenerate to the target tissue, 1) most afferent A-fibers are mechanosensitive and regenerate to the target tissue; 2) ectopic ongoing activity, cold sensitivity, and heat sensitivity significantly decrease with time after injury in A-afferents; 3) most afferent C-fibers do not regenerate to the target tissue; and 4) injured C-afferents maintain the patterns of ectopic discharge properties they already show soon after nerve injury.

For the first time, we demonstrate that it is possible to simultaneously analyze microscopic fluctuations at the surface and in the bulk of a binary liquid mixture by dynamic light scattering in macroscopic thermodynamic equilibrium. For a model system containing n-octacosane and ethanol, three individual signals distinguishable in the time-resolved analysis of the scattered light intensity appear on different time scales. One oscillatory signal from surface fluctuations at the vapor-liquid interface in the short-time range and two exponential Rayleigh signals from fluctuations in temperature and concentration in the bulk of fluid in the long-time range could be associated with hydrodynamic modes. This microscopic information allows for a simultaneous determination of the macroscopic properties interfacial tension, kinematic viscosity, thermal diffusivity, and mutual diffusivity within a single experimental run. The presented approach represents a worthwhile strategy, for example, in the context of sensor development for an effective multiproperty determination of fluid systems.

The binary diffusion coefficients of mixtures consisting of glycerol and water with glycerol mole fractions of 0.299, 0.500, and 0.699 were investigated by dynamic light scattering (DLS) in macroscopic thermodynamic equilibrium over the temperature range 323–448 K. Furthermore, a beam displacement method implemented in the same experimental setup was used to determine the refractive indices of the mixtures required for the evaluation of the DLS measurements. The reported results represent the first temperature-dependent data set for the binary diffusion coefficient of glycerol–water mixtures, where increasing diffusion coefficients were found for increasing temperature and decreasing glycerol concentration. The latter finding is consistent with literature data that are restricted to specific temperatures. The present results are in good agreement with the absolute values and concentration-dependent trends of the binary diffusion coefficients for glycerol–water mixtures available in the literature.

The present contribution provides experimental data for the liquid viscosity and surface tension of n-alkane based model systems at temperatures up to 573 K. The fundamental advantage of the used surface light scattering (SLS) method lies in its application in thermodynamic equilibrium without calibration in a contactless way. The investigated systems comprise the pure fluids n-dodecane (n-C12H26) and n-octacosane (n-C28H58), their binary mixture at a n-C12H26 mole fraction of about 0.3, and the commercially available hydrocarbon wax SX-70 representing a multicomponent mixture of n-alkanes with a broad chain length distribution. For the first time, it could be demonstrated that the SLS method can simultaneously access the liquid viscosity and surface tension of such medium- to long-chained n-alkane systems close to saturation conditions over a broad temperature range from 323 to 573 K. Typical measurement uncertainties of 2% based on a coverage factor k = 2, i.e., a level of confidence of more than 95%, w...

13 pags., 7 figs., 2 tabs., Thermophysical properties of low-viscosity ionic liquids (ILs) based on the tetracyanoborate ([B(CN)]) anion carrying a homologous series of 1-alkyl-3-methylimidazolium ([AMIM]) cations [EMIM] (ethyl), [BMIM] (butyl), [HMIM] (hexyl), [OMIM] (octyl), and [DMIM] (decyl) were investigated by experimental methods and molecular dynamics (MD) simulations at atmospheric pressure and various temperatures. Spectroscopic methods based on nuclear magnetic resonance and surface light scattering were applied to measure the ion self-diffusion coefficients and dynamic viscosity, respectively. In terms of MD simulations, a nonpolarizable molecular model for [EMIM][B(CN)] developed by optimization to experimental data was transferred to the other homologous ILs. For the appropriate description of the inter- and intramolecular interactions, precise and approximate force fields (FFs) were tested regarding their transferability within the homologous IL series, aiming at reducing the computational effort in molecular simulations. It is shown that at comparable simulated and experimental densities, the calculated and measured data for viscosity and self-diffusion coefficients of the ILs agree well mostly within combined uncertainties, but deviate stronger for longer-chained ILs using an overly coarse FF model. For the [B(CN)]-based ILs studied, a comparison with literature data, the influence of varying alkyl chain length in the cation on their structural and thermophysical properties, and a correlation between self-diffusivity and viscosity are discussed., This work was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) by funding the Erlangen Graduate School in Advanced Optical Technologies (SAOT) within the German Excellence Initiative. In addition, financial support from the seventh European Commission Framework Program for Research and Technological Development for the project “Novel Ionic Liquid and Supported Ionic Liquid Solvents for Reversible Capture of CO2” (IOLICAP project no. 283077) is gratefully acknowledged. J. Ramos acknowledges financial support through the Ramón y Cajal program (MINECO, Spain, Contract RYC-2011-09585).

This work contributes to the characterization of the liquid organic hydrogen carrier (LOHC) system diphenylmethane/dicyclohexylmethane by the experimental determination and molecular simulation of the thermophysical properties of the dehydrogenated and fully hydrogenated compounds in a process-relevant temperature range of up to 623 K. Liquid density, liquid viscosity, surface tension and liquid self-diffusion coefficient data measured by vibrating-tube densimeters, surface light scattering, rotational viscometry and NMR spectroscopy are correlated and compared with available literature data which are mostly restricted to temperatures below 473 K. Furthermore, it is demonstrated that an L-OPLS force field (FF) modified in the present study outperforms commonly used FFs from literature in predicting the thermophysical properties of both substances by equilibrium molecular dynamics simulations.

Mixtures of fluorinated and non-fluorinated ionic liquids (ILs) show a distinct structural organization in the bulk and at the surface. To understand how such microscopic effects influence the macroscopic bulk and surface properties of IL mixtures, knowledge of corresponding thermophysical properties including viscosity and surface tension is required yet lacking. With the intention of investigating surface enrichment effects of the fluorinated IL [PFBMIm][PF6] (3-methyl-1-(3,3,4,4,4-pentafluorobutyl)imidazolium hexafluorophosphate) in mixtures with the structurally similar, non-fluorinated IL [C4C1Im][PF6] (1-butyl-3-methylimidazolium hexafluorophosphate) observed with angle-resolved X-ray photoelectron spectroscopy (ARXPS), the pendant drop method and surface light scattering (SLS) were applied in the present study to determine surface tension and dynamic viscosity between (293 and 368) K. By adding small amounts of [PFBMIm][PF6] up to 9 mol %, a distinct increase in the viscosity and decrease in the surface tension of the mixtures relative to the properties of pure [C4C1Im][PF6] was found. This behavior reflects the nanosegregated structure in the bulk and at the surface of the binary IL mixtures. Using the results about the pronounced surface enrichment of the fluorinated chain of [PFBMIm][PF6] quantified by ARXPS, a linear mixing rule for the surface tension of the IL mixtures based on the surface tensions of the pure ILs and the surface concentration of their most surface-active groups is suggested.

Polarized dynamic light scattering (DLS) gives access to orientation-averaged translational and rotational diffusion coefficients of anisotropic particles dispersed in fluids in a single experiment. As the combination of both diffusivities contains information on the morphology of the particles, their simultaneous and accurate measurement for the same sample and thermodynamic state is beneficial for particle characterization. For nontransparent model suspensions of gold nanorods in water and water-glycerol mixtures, a scattering geometry in reflection direction was realized, which minimizes multiple scattering and allows using low laser powers to avoid laser heating. Furthermore, a heterodyne detection scheme was guaranteed by superimposing much stronger reference light to the scattered light. This ensures an unambiguous data evaluation and reduces the uncertainties for the rotational and the translational diffusivity, where the latter is accessible with smaller uncertainty. For the water-based suspensions, both diffusivities agree well with the stick hydrodynamic theory for rods and show an Andrade-type behavior in the studied temperature range from 271 to 323 K. The measured results for both diffusivities, particularly for the rotational diffusivity, indicate a breakdown of the stick boundary conditions for dynamic viscosities larger than 4 mPa·s.