Diffusivities of Ternary Mixtures of n-Alkanes with Dissolved Gases by Dynamic Light Scattering

Abstract

Theoretical approaches suggest that dynamic light scattering (DLS) signals from low-molecular-weight ternary mixtures are governed by fluctuations in temperature as well as two individual contributions from fluctuations in concentration that are related to the eigenvalues of the Fick diffusion matrix. Until now, this could not be proven experimentally in a conclusive way. In the present study, a detailed analysis of DLS signals in ternary mixtures consisting of n-dodecane (n-CH) and n-octacosane (n-CH) with dissolved hydrogen (H), carbon monoxide (CO), or water (HO) as well as of n-CH or n-CH with dissolved H and CO is given for temperatures up to 523 K and pressures up to 4.1 MPa. Thermal diffusivities of pure n-CH and n-CH as well as thermal and mutual diffusivities of their binary mixtures being the basis for the ternary mixtures with dissolved gas were studied for comparison purposes. For the investigated ternary mixtures, three individual signals could be distinguished in the time-resolved analysis of scattered light intensity by using photon correlation spectroscopy (PCS). For the first time, it could be evidenced that these signals are clearly associated with hydrodynamic modes. In most cases, the fastest mode observable for ternary mixtures is associated with the thermal diffusivity. The two further modes obviously related to the molecular mass transport are observable on different time scales and comparable to the modes associated with the concentration fluctuations in the respective binary mixtures. Comparison of the experimental data with results from molecular dynamics simulations revealed very good agreement.

Characterization of Water Solubility in n-Octacosane Using Raman Spectroscopy

“…The Raman setup used here represents an extension of the optical arrangement previously developed for the measurement of diffusivities of gases and water dissolved in heavy n -alkanes by means of dynamic light scattering (DLS). , A drawing of the extension of our DLS setup for Raman spectroscopy is represented in Figure A. Raman spectroscopy was conducted using a QE65Pro spectrometer (from Ocean Optics), a frequency-doubled Nd:YVO 4 laser source (λ 0 = 532 nm, from Coherent) operated at 1.75 W, and a collection of optical components including lenses (L), mirrors (M) and a long pass filter (LF).…”

Mutual and Thermal Diffusivities in Polystyrene Melts with Dissolved Nitrogen by Dynamic Light Scattering

“…In this case, the DLS theory becomes more complex, as discussed, e.g., for ternary polymer solutions of PS and poly­(methyl methacrylate) in dioxane in the literature . In the case of a ternary mixture, DLS gives access to the thermal diffusivity and the Eigenvalues of the Fickian diffusion matrix . However, due to large differences in the diffusivities for mixtures of liquids and for mixtures consisting of a liquid with a dissolved gas, the present mixtures can be assumed to be pseudo-binary mixtures.…”

One-pot neutron imaging of surface phenomena, swelling and diffusion during methane absorption in ethanol and n-decane under high pressure

“…The method, which is based on the neutron imaging of a cell containing a deuterated liquid upon its pressurization with a gas containing protium in its molecule, proved the ability to provide information on the methane diffusion into liquid, its swelling and capillarity from the single experiment in one pot. Hence, our new method enabled to collectively observe quantities, which could otherwise be studied only using multiple single-purpose methods, such as those for the visualization and measurement of diffusion in liquids [ 10 , 11 , 18 , 21 , 22 , 32 , 33 , 35 – 39 , 41 ], measurement of capillarity [ 16 – 18 , 24 – 31 ] and liquid density [ 7 , 8 , 23 ]. Our method provided values of methane diffusivity and partial molar volume, liquid density of the solution, surface tension and its pressure derivative and contact angle at titanium under harsh conditions, while the observed quantities showed good agreement with the literature data where literature data or methods for their prediction are available [ 6 – 8 , 10 , 11 , 13 , 14 , 16 , 25 , 26 , 53 , 54 , 74 , 81 ].…”

“…Recently, several advanced methods allowing for the observation of mass transport in bulk bodies have been reported. These methods involve the detection based on i ) Raman spectroscopy, which was used to characterize diffusion in liquids and liquids at pressures near atmospheric [ 32 , 33 ] and the distribution of methane in methane hydrate at pressures up to 140 bar [ 34 ], ii ) dynamic light scattering, which was used for the studies of diffusion of gases in liquids at pressures up to 34 bar [ 35 ], iii ) Nuclear Magnetic Resonance (NMR), which was used for the studies on diffusion in liquids at pressures close to atmospheric [ 36 – 38 ], propane diffusion in liquids at pressures up to 10 bar [ 39 ] or methane distribution in methane hydrate at pressures up to 250 bar [ 40 ], iv ) X-ray tomography, which was used for the studies on diffusion in liquids at pressures near atmospheric [ 38 , 41 ] and methane hydrate formation at pressures up to 62 bar [ 42 ], and, most recently, v ) neutron imaging, which was used for the observation of ammonium absorption in solids at pressures near atmospheric [ 43 ].…”