In the present study, the simultaneous and accurate determination of liquid viscosity and surface tension of the n-alkanes n-hexane (n-C6H14), n-octane (n-C8H18), n-decane (n-C10H22), and n-hexadecane (n-C16H34) 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-C6H14, 523.15 K for n-C8H18, and 573.15 K for n-C10H22 and n-C16H34. 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-C12H26) and n-octacosane (n-C28H58), 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 additional selected n-alkanes, which were not included in the development procedure, was found.

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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.

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In the present study, the capabilities and limitations of surface light scattering (SLS) experiments in reflection geometry are investigated. Based on the study of the transparent reference fluid toluene at 303.15 K over a wide range of wave vectors between ( 0.3 a n d 6.6 ) × 1 0 5 m − 1 , the performance of two different detection schemes analyzing light scattered from the vapor–liquid interface in a perpendicular and non-perpendicular direction is assessed. Considering various aspects such as the quality of the heterodyne correlation functions, the input information for data evaluation, and the line-broadening effects, both detection schemes show comparable overall efficiency. For wave vectors larger than 4.5 × 1 0 5 m − 1 , where line-broadening effects are suppressed, the results obtained for liquid viscosity and surface tension agree with measurements in transmission geometry, validating the capability of the apparatus. For wave vectors smaller than 1.5 × 1 0 5 m − 1 , the SLS signals are distinctly affected by line-broadening effects, which will result in erroneous values for surface tension and in particular viscosity, even if empirical fitting approaches commonly used in literature are applied. The modeling of the influence of line broadening on the measurements results by a simple Gaussian-weighted sum of individual damped oscillations reveals the increasing complexity of the underlying wave vector distribution toward smaller wave vectors chosen for the scattering geometry.

In this study, the liquid viscosity and interfacial tension of binary and ternary mixtures containing noctacosane (n-C 28 H 58 ) and different byproducts typically found in the Fischer−Tropsch process were investigated. For the binary mixtures having mole fractions of the byproducts between 0.02 and 0.40, the effects of varying branching, alkyl chain length, and degree of oxygenation in selected byproducts on viscosity and interfacial tension were studied. In detail, the isomers n-decane, 2-methylnonane, and 4-methylnonane were used to study differences in branching for alkanes with the same molecular weight. The 1-alcohols ethanol and 1-dodecanol as well as the carboxylic acids formic acid and acetic acid imply variations in the alkyl chain length and degree of oxygenation. In addition, two ternary systems consisting of n-octacosane, n-decane, and ethanol with mole fractions of 0.6 of either n-alkane and 0.2 for each of the other two components were selected. On the basis of the surface light scattering (SLS) method analyzing microscopic surface fluctuations at macroscopic thermodynamic equilibrium, the liquid viscosity and interfacial tension of the studied mixtures could be determined at saturation conditions at temperatures from (373.15 up to 523.15) K with average expanded measurement uncertainties (k = 2) of (2.7 and 2.4)%. Except for systems containing the two branched alkanes showing a distinct decrease in the interfacial tension even at low mole fractions of 0.025, liquid viscosity and interfacial tension at 423 K are not strongly affected with increasing concentration of the byproducts up to 0.10 compared to the values for pure n-octacosane within relative deviations of 10% and 5%. For the studied binary and ternary systems, simple mixing rules for liquid viscosity and interfacial tension based on the corresponding properties of the pure components are discussed.

In the present work, the liquid viscosity and surface tension of tris­(2-ethylhexyl) trimellitate (TOTM) was determined close to 0.1 MPa over a temperature range between 273 and 523 K by surface light scattering (SLS). Such investigations were stimulated by the fact that TOTM is suggested as a potential viscosity standard of moderately high viscosity for temperatures up to 473 K and pressures up to 200 MPa. Based on the SLS experiments at macroscopic thermodynamic equilibrium, a simultaneous determination of liquid viscosity from 273 to 523 K and surface tension from 398 to 523 K with relative expanded uncertainties typically below 0.03 (coverage factor k = 2) was possible. To evaluate the results from SLS and to check possible surface orientation effects found in our previous SLS studies on liquid organic hydrogen carriers, conventional methods in the form of the pendant-drop method and capillary viscometry were used to determine the surface tension and viscosity from 273 to 573 K and from 293 to 353 K, respectively. For evaluating all experimental methods applied, the liquid density was obtained with the help of a vibrating-tube densimeter between 283 and 473 K. From a long-time SLS study at 573 K and subsequent density and nuclear magnetic resonance measurements, a clear sample degradation of TOTM was observed, which may hinder its application as an industrial viscosity standard above 523 K. For both the surface tension and the viscosity which covers a range between about 1500 and 0.9 mPa s at temperatures between 273 and 523 K, agreement between the results from SLS and the conventional methods within combined uncertainties was found, which is also valid by comparison with the literature. In summary, the experimental results from this work could not only contribute to an improved data situation for viscosity and surface tension of TOTM over a broad temperature range but also reveal that TOTM does not show pronounced molecular orientation effects at the vapor–liquid interface which would influence the dynamics of the surface fluctuations probed by SLS.

The surface tension and liquid viscosity of two binary refrigerant mixtures 1,1,1,2-tetrafluoroethane (R32) (1) + 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) (2) and R32 (1) + trans-1,3,3,3-tetrafluoroprop-1-ene (R1234ze) (2) have been measured from 293 K to the critical point by using the surface light scattering (SLS) method. The experimental data were correlated as a function of temperature and mole fraction of the pure components. For the surface tension of R32+R1234yf and R32+R1234ze, the average absolute deviations are 0.053 and 0.029 mN•m −1 , respectively. As for the liquid viscosity, the relative percentage average absolute deviations are 0.86 and 1.01%, respectively.