Solute Diffusion in Nonionic Liquids—Effects of Gravity

Abstract

We have been engaged in examining the influence of gravity on the results of experiments to measure the variation of solute diffusion coefficients (D) with temperature (T) in fused metals and semimetals since our first STS flights in 1992. These early experiments, conducted with the in situ g-jitter of the shuttle, showed the near-parabolic variation of D with T reported by others. However, with the aid of the Canadian Space Agency's microgravity isolation mount (MIM) to isolate the diffusion facility from the existing g-jitter of the Russian space station MIR, we showed that in all the alloy systems and over the temperature range studied, D increased linearly with T. If the isolating system was deactivated, then the more familiar parabolic relationship appeared. We have always assumed that the values of D measured using the MIM would be closer to the intrinsic values for the alloy system considered; to test this contention, we have been involved in two modeling activities. The first has been to estimate the effects of g-jitter-level disturbances on solute distributions in long capillary diffusion couples. The second has been to conduct various molecular dynamics modeling studies of solute diffusion. This paper presents results of these studies.

A molecular dynamics simulation of the diffusion of the solute (Au) and the self-diffusion of the solvent (Cu) in a very dilute liquid Cu–Au solution

“…The very small parabolic deviation would not be observed within the narrow temperature range normally available to obtain experimental data [8]. (2) This work gives further support to the conclusions from the QUELD II/MIM/MIR mission [1] that, for the dilute alloy systems and temperature range used, the solute diffusion coefficient increases linearly with temperature if measured in a low earth-orbiting laboratory in the absence of significant solute transport induced by the ambient gjitter.…”

“…It has been noted [1,2] that, in order to achieve optimum control of crystal growth and casting processes involving multi-component alloys on earth, it is necessary to develop numerical control models. The usefulness of these will depend on the quality/accuracy of the diffusion data incorporated; unfortunately, current data, where available, are often widely inaccurate.…”

“…Summaries of the most often quoted theoretical predictions of this dependence are available [1][2][3]: each prediction arises from a particular description of the liquid state and the associated diffusion mechanism. Those most commonly quoted are: D proportional to: exp(− 1 T ); T ; √ T ; T 2 ; T (1.7→2.3) .…”

Comprehensive Multi-omics Analysis Reveals Mitochondrial Stress as a Central Biological Hub for Spaceflight Impact

“…Another study reported decreased mitochondrial activity in the roots of space-flown soybean seedlings (Klimchuk, 2007). Low doses of radiation trigger severe mitochondrial damage (Shimura et al, 2016), and the lower diffusion rates of solutes in microgravity (Smith et al, 2009) reduce the hydrogen gradient at the mitochondrial intermembrane space, reducing electron transport chain and ATP synthesis (Nelson, 2013). Our findings report transcriptomic, epigenetic, proteomic, and metabolomic patterns (Figures 2 and 3) consistent with mitochondrial stress in different cells and multiple organs, including muscle tissues (Jha et al, 2017;Topf et al, 2019).…”

Influence of Gravity on Atomic Mobility in a Liquid

“…parabolic flights, changes in the residual acceleration ("g-jitter") can lead to additional mass transport in liquid samples Mathiak et al (2005). Specially designed isolators which decouple the experimental setup from the structure of the platform reduce this influence Smith et al (2009). Marangoni convection caused by differences in surface tension due to bubbles or free both on earth and in microgravity Ruiz et al (2015), Pallarés (2011), Roşu-Pflumm et al (2009), Kargl et al (2013).…”