In recent years, and due to its applicability in different sectors, the study and interest of mass transport properties based on concentration (molecular diffusion) and temperature gradients (thermodiffusion) has grown considerably [1]. In 1999, the first joint investigations dealt with the analysis of binary subsystems considering different ground conditions techniques. In 2003, the first collaborative results were published and today this database is used for the validation of new experimental techniques [2]. Nevertheless, most of the systems present in natural processes comprise more than two components and therefore, the interest of the scientific community focused on the study of multicomponent systems, for which a ternary mixture is the simplest representation. At the start, the determined transport coefficients were not in good agreement by considering the different experimental techniques. The complexity of the analysis of ternary mixtures increases and any convective flow generated by the effect of the gravity force can disturb the experiments. In this context, the Diffusion and thermodiffusion Coefficients in ternary MIXtures (DCMIX) project was founded to generate a reference database of different binary and ternary systems by studying them both in terrestrial and microgravity conditions [3]. Throughout the four missions of the DCMIX project, a total of five ternary systems were examined. In this context, one of the mixtures of interest during the fourth campaign (DCMIX4) was a polymeric system and its transport coefficients have not yet been published. Thus, the motivation of this work was to analyse the thermodiffusion experiments conducted under microgravity conditions with the focus on the polymer solution of DCMIX4. The investigated mixtures were the binary reference subsystem polystyrene toluene at a mass fraction of 2% (polystyrene) and the ternary mixture composed of polystyrene, toluene and cyclohexane at a mass fraction of 2% (polystyrene) and equimass fraction of the remaining solvents. The experiments were carried out via the selectable optical instrument technique. Additionally, four different working temperatures were considered starting from 20ºC up to 35ºC (increment of 5ºC). Regarding the followed methodology and obtained preliminary results, first, the quality of the captured interference patterns, the contrast, saturation, as well as the phase-shifting technique were evaluated. Additionally, the temperature recorded during the thermodiffusion experiments was examined to assess the potential presence of thermal instabilities. It was concluded that experiments were carried out successfully and data processing is currently underway to determine the mass transport coefficients of the binary and ternary polymeric mixtures.

Convective instabilities on Earth hinder the study of the phenomenon of thermodiffusion in multicomponent liquid mixtures. Orbital laboratories, on the contrary, provide an ideal environment for the measurements, due to the absence of the destabilizing buoyancy driven convection. Several years ago, the DCMIX project was promoted, sponsored by the European Space Agency. The project, completed in four campaigns, aimed to establish a reliable set of guaranteed convection free reference data for the validation and calibration of present and future ground-based measurements and prediction models [1].
Experiments on the ternary system C60 (0.0007 gg-1) | THN (0.6000 gg-1) | Tol (0.3993 gg-1) flown during the DCMIX4 microgravity campaign are presented [2]. The fullerene-based ternary mixture has been investigated by means of the Selectable Optical Diagnostics Instrument at four mean temperatures of 20 ºC, 25 ºC, 30 ºC and 35 ºC. As Soret experiments were developed in microgravity, the mixture was tested in three terrestrial laboratories. The Optical Beam Defection (Universität Bayreuth) and the Optical Digital Interferometry (Université libre de Bruxelles) were used for direct determination of the Soret coefficient of each component, while thermodiffusion coefficients of each constituent were measured by the Thermogravitational Column Technique (Mondragon Unibertsitatea).
Reasonable agreement was obtained between convective and non-convective techniques on the ground, together with those analysed under microgravity conditions in the ISS, where thermal dependency of both Soret and thermodiffusion coefficients is observed. All experiments revealed that the mixture behaves as a quasi-binary system, where the Soret and thermodiffusion coefficients of the solute are small and the ones corresponding to the solvents are consistent with the associated binary subsystem THN (0.60 gg-1) | Tol (0.40 gg-1) [3]. Thus, experiments performed in SODI allowed validating the experiments on nanofluids in earth laboratories.

In ternary mixtures, three species interact through cross-diffusion, where each species is transported not only by its own concentration gradient but also by the gradient of the other two species. The focus of our research is on the toluene-methanol-cyclohexane ternary mixture, studied both on-board the ISS (DCMIX2 mixture) and in ground laboratories. The integral studies reveal that depending on composition, the cross-diffusion coefficients can be as large as the main ones. This mixture also exhibits the Soret effect and the studies showed that the Soret coefficients of the denser components are negative in a wide range of compositions that result in the hydrodynamic instability in non-isothermal gravity field. Our attention lies on the state point, which is located on the boarder of stability and its surroundings. Such point is characterized by nearly zero the net separation ratio, while individual separation ratios are typical.

We explore the behaviour of the system under three different conditions. The systems with thermal gradient when the Soret effect comes into play: a thermogravitational column (TGC) and a Soret cell. In isothermal conditions, we observe the diffusion of two layers of mixture with slightly varying compositions. In each of these cases, the emerging instability exhibits intriguingly distinct behaviour.

In TGC small variations of cross-diffusion lead to emergence distinctive patterns, ranging from oscillatory to monotonically standing Turing-like patterns [1, 2]. In contrast, the Soret cell shows the prevailing effect of the small net separation ratio over cross-diffusion. The behaviour of the system depends on initial conditions or external perturbations, revealing meta–stable behaviour. In the case of minor perturbations, the mixture remains motionless, facilitating the measurement of transport coefficients, while strong perturbations lead to the development of convective flow [3]. Under isothermal conditions, the composition-dependent cross-diffusion may induce the simultaneous development of double diffusion [4] (DD) and diffusive-layer convection (DLC) on two different sides of an initial contact line

References:
[1] B. Seta, A. Errarte, I. I. Ryzhkov, M. M. Bou-Ali, V. Shevtsova, Phys. Fluids 35 (2) (2023) 021702.
[2] B. Seta, A. Errarte, A. Mialdun, I. I. Ryzhkov, M. M. Bou-Ali, , V. Shevtsova, Phys. Chem. Chem. Phys. 25 (2023) 15715–15728.
[3] S. Prokopev, T. Lyubimova, A. Mialdun, V. Shevtsova,Phys. Chem. Chem.Phys. 23 (2021) 8466–8477.
[4] B. Šeta, A. Errarte, D. Dubert, Jo. Gavaldà, M. M. Bou-Ali, X. Ruiz, Acta Astronautica, 160, 2019, 442-450

Introduction:

On Earth, electric circuits dissipate heat through convection flows driven by gravity, facilitating the transfer of energy from electronic devices to the surrounding environment. However, in microgravity, the absence of buoyancy disrupts this cooling mechanism, and heat accumulates around its sources. Recent works showed that acoustic streaming generated by ultrasound enhances heat transfer in gases in normal gravity [1,2]. In microgravity this effect has only been studied with liquids up until now [3]. We present an experimental study where ultrasound is used to enhance heat transfer in air in microgravity.

Method:

An experimental setup was designed and built to test the physical phenomenon in the ZARM drop tower. The setup consists of a test cell and systems for acoustic actuation and data acquisition. The test cell contains a heating element. Ultrasound is generated by means of a piezoelectric transducer attached to the cell. Temperature is measured at different positions near the heating element. Video images are acquired for Schlieren processing. The experiment run in five catapult launches at the tower, with 9.4 s of microgravity in each launch.

Results:

Figure 1 shows the temperature at a position near the heating element during the microgravity time of a drop. Red dots and line correspond to the case when no acoustic actuation is applied, while blue dots and line correspond to an acoustic actuation with a frequency of 43.7 kHz. Temperature increased approximately 2°C in the considered position when the acoustic actuation was applied, which shows the acoustic effects on heat transfer.

Figure 2 shows Schlieren-processed images of the air density in the test cell. Bottom row shows the evolution in time when no acoustic actuation is applied, while middle and top row show the time evolution when an acoustic actuation of 43.7 kHz and 60.2 kHz is applied, respectively. The strongest effects on the air density variation (i.e. on heat transfer) take place at the resonance frequency of the piezoelectric transducer (43.7 kHz).

This study highlights the feasibility of using ultrasound to enhance heat transfer in gases in microgravity. This result lays the foundation for potential new cooling technologies for electronic devices in satellites and manned spacecraft.

The exploration of space is constrained by the capabilities of our heavy lift-off vehicles. To extend the boundaries of our exploration, the establishment of an in-orbit propellant depot is crucial. This is the main motivation behind our project, ZBOT-FT, whose primary objective is to investigate the complexities associated with the removal, filling, and transfer of liquids in a microgravity environment. A preliminary focus in this current piece of work is to achieve gas-free liquid removal under different initial conditions in microgravity. The Screen Channel Liquid Acquisition Device (SC-LAD) is identified in the literature as one of the most promising liquid acquisition devices for these propellant depot operations, effectively separating phases and ensuring the delivery of gas-free liquid.

In the presented work, we have focused on the process of liquid removal and the phase separation capability of a specially designed SC-LAD, aiming to provide gas-free liquid from an experimental tank in microgravity. Our experiments were conducted in the ZARM drop tower under different initial conditions. The test liquid was HFE-7500, and the working conditions were assumed to be isothermal. The observations from the drop tower experiments were analyzed and compared with analytical solutions, showing close agreement [1]. Additionally, various other phenomena, such as the reorientation of the free surface under microgravity, capillary rise of liquids between parallel plates, flow through screen pressure loss due to the applied removal flow rate, and bubble point breakthrough of the screen, were captured through a high-speed camera, presenting intriguing insights

These findings not only demonstrate the viability of SC-LAD for gas-free liquid removal in space but also contribute valuable insights into the complex fluid behaviour under reduced gravity conditions, propelling forward the capabilities for extended space exploration.

In 1991, famous French scientist Pierre-Gilles de Genes was awarded Nobel prize for his impactful research in soft matter, more specifically polymers. He is defined as the founding father of soft matter. In his Nobel lecture [1] he described soft matter aka complex fluids as materials with two primary features – (a) complexity and (b) flexibility. The sub-categories of soft matter (e.g.- granular materials, polymers, foams, colloids etc.) are defined on the basis of Pierre-Gilles de Gennes’ definition. At NASA GRC, we are pushing the boundaries for fundamental study of soft matter on Lunar Surface. With regard to Lunar surface science, we are focusing on developing capabilities pertaining to granular materials and bio-soft/active matter to facilitate future efforts in ISRU and bio-ISRU capabilities. In order to achieve fundamental goals of soft matter research within the limitations of Lunar environment, the scientific capabilities need to be small, flexible, modular, off the shelf and the focus needs to be more on developing an interdisciplinary capability that leverages the recent growth in AI/ML a‎nd‎ Computer Vision to augment our understanding of fundamental science. This strategy would allow us to reduce our resource requirement during launch, installation, and occupied real estate footprint on Lunar surface
In this talk, we will go over 3 different capabilities that we have developed in house and in close collaboration – (a) Differential Dynamic Microscopy (DDM), (b) Portable In-situ Chemical Spectroscopy (PICS) and (c) Computer Vision Enabled Observation. At very high level, Differential Dynamic Microscopy (DDM) allows us to study the structure-property-process relation (microrheology) of bio-soft/active matter using optical microscope and improved image analysis capabilities. PICS uses AI/ML-based advanced signal deconvolution and analysis technique that can work with existing portable spectroscopy tools to perform materials analysis (e.g.- granular materials and bio-soft/active matter) inspection on the go. Finally, computer vision enabled analysis allows us to use simple camera images for 3D reconstruction of experimental process and tracking of objects of interest in an experiment.
We expect that this detailed process will allow us reach a thorough understanding of soft matter in Lunar environment. The capabilities developed by us will help to validate and establish fundamental understanding in Lunar environment. This will, in turn, allow us to guide future space exploration missions and expand the knowledge base of the scientific and engineering communities.

Introduction

Some smectic liquid crystals are known for a unique feature: the can form thin, freely suspended films with extraordinarily large aspect ratios, widths may reach several centimeters at uniform thicknesses of only few nanometers. In the smectic A phase, for example, they show liquid-like behavior without long range positional order of the mesogenic molecules in the film plane. These films can be considered as excellent models for two-dimensional (2D) fluids. Rheology in 2D is often more complicated than in 3D, the Stokes paradox is an eminent example for that. We study the coalescence of inclusions in this quasi-2D liquid environment, and the aging dynamics of emulsions formed by islands (circular plateaus of larger film thickness) in the surrounding homogeneous films.

Methods

Spherical smectic films (bubbles) with 15 mm diameter were prepared in microgravity on the ISS. The dynamics of inclusions in these films was recorded by optical imaging, including high-speed videos.

Results

Merging of droplets of molten film material was recorded and analyzed. Droplet coalescence shows a crucial dependence on details of the droplet structures [1,2]. In biphasic droplets, the merging process is retarded by roughly three orders of magnitude. A thin nematic membrane forms between the isotropic droplet cores.
Arrays of islands were prepared as 2D emulsion to analyze their aging [3]. The patterns coarsen primarily by merging events, yet contributions of Ostwald ripening can clearly be found. The peculiarity is that the continuous and the dispersed phases consist of the same mesogenic material.

Conclusion

Our experiments with droplets in free-standing films provided new insights into the merging of flat len¬ses in a 2D plane. In contrast to grease drops on water, the influence of a subphase is negligible. The studies of quasi-2D emulsions provided qualitative and quantitative data on aging processes in such a geometry. Long-term experiments are needed to establish the exponents for the growth dynamics.