Soft Matter Dynamics - FOAM-C
  1. 2019 • ISS Increments 61-62
  2. 2020 • ISS Increment 63
  3. 2020 • ISS Increment 64
Physical Sciences:
  • Foams
FSL (Fluid Science Laboratory)
D. Langevin (1), E. Rio (1), A. Salonen (1), D. Weaire (2), S. Hutzler (2), N. Vandewalle (3), H. Caps (3), S. Cohen-Addad (4), R. Höhler (4), D. Durian (5), K. Okumura (6), A. Sonin (7), A. Cagna (8), J.F. Argillier (9)
Université Paris Sud
Trinity College
School of Physics
Université de Liège
Institut de Physique
Université Pierre & Marie Curie (Paris 6)
Institut des NanoSciences de Paris
University of Pennsylvania
Department of Physics & Astronomy
Ochanomizu University
Faculty of Science
Department of Physics
Moscow Polytechnic University
IFP Institut Français du Petrole
The SOFT MATTER DYNAMICS instrument has multiple motivations covering the studies of foams, emulsions and granular matter.

Foams are dispersions of gas into liquid or solid matrices. They are typically made in conditions where the matrix is liquid (in solid foams, the matrix is solidified afterwards). 

The behaviour of foams in micro-gravity and on Earth are very different, because the process of drainage is absent in micro-gravity conditions. By drainage, we are referring to the irreversible flow of liquid through the foam (leading to the accumulation of liquid at the foam bottom, and to a global liquid content decrease within the foam); in this case the bubbles deform to polyhedra throughout the upper portion of the foam, creating the so-called "dry foam". When the liquid films between the bubbles are very thin, they eventually break, and the foam collapses. This happens when suitable stabilizing agents are absent (well-chosen surfactants or solid particles for aqueous foams).

Micro-gravity offers the opportunity to investigate the so-called "wet" foams, which cannot be stabilized on Earth because of drainage (drainage gets faster as the foams gets wetter). Theoretical approaches of drainage rely on assumptions, which are only valid for dry foams. New behaviours or regimes are expected to appear for wet foams, masked by convective instabilities on Earth. Elastic and viscous properties of wet foams are also expected to be strongly modified by the presence of solid particles. The Physics of wet foams is therefore poorly known, and is one major goal of this project.

The FOAM project aims at the study of aqueous and non-aqueous foams in the micro-gravity environment on-board the International Space Station (ISS). The FOAM project is divided in two experiments: 
  • FOAM coarsening - FOAM-C and 
  • FOAM stability.
The FOAM-C experiment studies the stability of foams away from the influence of Earth’s gravity. The scientists are interested in the behaviour of the foams at different liquid fraction and in particular around the point of un-jamming (transition from a solid-like to liquid-like structure), which can be studied only in microgravity.

The objective of FOAM coarsening is the study of the quiescent coarsening of foams as a function of the liquid fraction. Gas diffuses between bubbles, from smaller bubbles to larger bubbles, until the smaller bubbles disappear, changing the structure and the properties of the foam.

The project focuses on very wet foams which cannot be studied on ground, due to drainage effect. Multiple light scattering measurements will provide measurements of the bubble structure and dynamics of the material during coarsening. The rational for the systematic measurement vs. foam age is not just to observe and quantify coarsening, but perhaps, to obtain a reproducible self-similar distribution of bubble size. The stability of foams will also be studied in parabolic flight campaigns, giving precursor or complementary results. The rheology of wet foams is intended to be studied in a future project, using the results and technological developments for “FOAM coarsening” and “FOAM stability” investigations.

Justification for the need of space experiment
Gravity plays an important role in the formation of foam and its subsequent evolution. Its primary effect is to cause excess liquid to drain rapidly away. When the foam is stable enough, it becomes dry and the gravitational force is balanced by a vertical pressure gradient in the liquid (and hence a vertical profile of liquid fraction).

The same difficulty occurs with rheology, in which case a very interesting transition occurs at a critical fraction of liquid where the foam changes from solid-like (finite shear modulus) to liquid-like (disconnected bubbles). This is the “jamming transition” also encountered in other assemblies of randomly packed objects, such as emulsions, sand, clays, etc. In the case of foams, the 20%-35% range, which extends to the wet foam limit at which individual bubbles separate, remains inaccessible on earth. This restricts ground experiments to stable dry foams, and indeed the idealized theoretical models are largely confined to the dry foam limit. The present trend of the subject is therefore towards wet foams as well as dynamic effects.

A micro- or zero-gravity study of wet foam hydrodynamics enables one to overcome the limits imposed by various instabilities experienced under normal gravity. This broader experimental characterization and corresponding insight will provide a scientifically valid alternative for the necessarily conservative empiricism currently employed to estimate the operational window and design for foam handling in industrial processes (such as gas/liquid contacting, flotation and pumping).

The role of gravity on quiescent wet foams can be captured in 2 key questions:
  1. Is the growth law for average bubble size R~√ time, such that R dR/dt is a constant? If so, what is the liquid-fraction dependence of this rate?
  2. How do the rate and the nature of the bubble rearrangement dynamics change as the liquid fraction is increased to the point of un-jamming (transition solid-like to liquid-like)? 
Both questions require prolonged microgravity to capture the dramatic changes expected for the very wet foams. Answers to both represent baseline knowledge of structure/dynamics upon which flow and rheology shall be interpreted.

Previous flight experiments (precursors)
Related studies about foams (not exhaustive):
29 April 2001: Maxus 4 rocket campaign (M. Adler and B. Kronberg)

April 2003: 34th ESA parabolic flight campaign, (A. Saint-Jalmes/EADS)

October 2003: 35th ESA parabolic flight campaign, (A. Saint-Jalmes/EADS)

June 2004: 37th ESA parabolic flight campaign, (S. Marze, A. Saint-Jalmes)

November 2004: Maxus 6 rocket campaign, (S. Marze, A. Saint-Jalmes, O. Pitois, M. Adler, D.Langevin, SSC and EADS)

March 2005: 41st CNES parabolic flight campaign, (S. Marze, H. Ritacco, A. Saint-Jalmes + 6 students from “Ecole Polytechnique”)

December 2007: 47th ESA parabolic flight campaign, (H. Caps + 4 students, G. Delon, A. Saint-Jalmes + 1 student, S. Vincent-Bonnieu)

December 2009 and January 2012: FOAM-Stability on board ISS

May 2012: 56th ESA Parabolic Flight Campaign (H. Caps, L. Saulnier, C. Gehin-Delval, Astrium)

APPLICATIONS of the research
This experiment might provide useful insights for the manufacture, use and ageing behaviour of foams, which are utilised in a wide range of areas, including in cosmetics and personal-hygiene products, in the food industry, in cleaning products, sealing products and for firefighting.
FOAM-C, was developed and manufactured by Airbus for the European Space Agency (ESA). 
It was launched on 5 December 2019 with SpX-19 cargo vessel.
The research was installed into the Fluid Science Laboratory (FSL) and activated on 06 March 2020 by astronaut Jessica Meir, who has been on the ISS since September 2019.

Experiment cells
The FOAM-C experimental set-up comprises five segments with a total of 20 small test cells containing a variety of liquid mixtures. The Fluid Science Laboratory on the ISS Columbus module will automatically shake and analyse these mixtures using complex laser optics, highly sensitive photodiodes and high-resolution cameras that can take up to 10,000 images per second.

Each test cell weighs only 20 grams and contains less than 2 cm³ of the liquid mixture, while each segment comprises four test cells and weighs a total of 320 grams.

- Overview video,
- Multiple light scattering spectroscopies (SVS - Speckle Variance Spectroscopy and/or DWS - Diffusing-Wave Spectroscopy)

Example of Protocols
- First, the foam is made at the time T0. Then the foam is left to age while optical diagnostics measure its dynamics during aging (up to 24 hours foam age). These cycles can be repeated several times. Another cell with a different composition (liquid fraction, concentration) is then subject of a new series of experiments.
- Granular matter samples of defined volume concentration shall be agitated until a steady state is reached.
Consequently, optical diagnostics measure the grains dynamics in the steady state and after turning the agitation off.

Experiment protocol
For each foam sample, there are different sets of measurements that are to be repeated in sequence, for the total run duration. 

The maximum experiment duration shall be assumed with 24h per experiment run for each sample.
At the beginning of a science campaign on orbit replaceable units shall be exchanged (if necessary) and the EC is installed in FSL by the Crew. Each run starts with the foaming process. Data acquisition (t=0) shall start just at the end of the foaming process. After a run, either the same sample can be processed again, or another sample can be processed. 

After a run, data post processing and downlink of results can occur. The results can influence the experiment procedure of subsequent runs, and the possibility to change experiment parameters through telecommand shall be provided. At the end of a science campaign selected scientific data is downlinked and then the EC is uninstalled by the Crew.

Runs repetition
Each sample shall be tested 3 times (one just needs to “re-foam” the sample after its first period of coarsening). 

Experiment Duration and amount of data
The measurements (alternatively SVS, DWS, DTS, Camera) shall be performed during the whole run duration.
In the following the measurement time is a requirement. On the opposite, the resulting amount of data is based on the required scientific measurements and the specific data production of the instrument, it is an indication but not a requirement.

SVS measurements
In total SVS should be used for 50% of the run time. For a 10 KHz acquisition SVS generates image data at a rate of 10 Mb/s.
If analysed on-board this results in a rate of 40 kb/s per tau-value of SVS measurements. One hour of run time (equivalent of 30 minutes of SVS measurements) therefore requires either 18 Gb storage for images or 70 Mb per tau-value to store the SVS measurements. The SVS measurements for 5 per-run tau-values shall be downlinked.
That means, for a 12 h run at least 4,200 Mb of SVS measurements shall be stored. At least 10 acquisitions of at least 100 s duration each, i.e., 40 Mb shall be downlinked per run.
Estimates for image storage assume a 1,024 pixel 8-bit line camera and no compression.

DWS and DTS measurements
In a 12 h run the total amount of data generated by each of these measurements is less than 1Mb.

Camera measurements
The duration of the acquisitions in video and still mode are defined in the general optical diagnostics requirements.
The Video mode generates for a video at 8 images/s for 10 s duration and 1 video per h:
9600 Mb for 24 h run.
4800 Mb (120 minimum) for 12 h run.
Two sequences of 10 sec, in total 800 Mb, shall be downlinked.
The Still mode generates for a sequence of 3 images per hour:
180 Mb (36 images) for 12 h run.
360 Mb (72 images) for 24 h run.
Further reduction possible with reduced field of view or resolution.

DWS DWS - Backscattering 
Purpose: To characterise the nature and average rate of bubble rearrangement dynamics and particle dynamics through measurement of the time-averaged intensity autocorrelation function <I(0)I(t)>/<I2> vs. t for backscattered light.

DWS/DTS - Transmission
Purpose: As for DWS in backscattering, the purpose is to characterize the nature and average rate of bubble rearrangement dynamics and particle dynamics by measurement of the time-averaged intensity autocorrelation function <I(0)I(t)>/<I2>.
Use of transmission will (1) test whether or not bulk behaviour is identical to the near-surface behaviour probed by DWS backscattering and by SVS, and (2) will also give complementary information on the transport mean-free path l* via measurement of the average intensity <I>. The latter is referred to as DTS. (For foams, the mean free path in turn yields the average bubble size with much better significance than surface observations). As a rule of thumb, the diffuse light transmission coefficient scales as l* divided by the sample thickness and for the wettest foams l* is comparable to the bubble size. In granulars the fast rearrangement and the small length scales probed with DWS as compared to the particle sizes makes very precise measurements at short delay times τ necessary. Significant improvement of measurement precision at very short delay times can be achieved by cross-correlating the transmitted light signal (optimal configuration)

Purpose: This technique is a multi-speckle time-resolved version of DWS. It is to be used to characterise the duration of rearrangement events, and the speed of bubble/droplet/grain motion during an event, via measurement of the temporal correlation g2(τ,t) of the speckle pattern for a specified time lag τ vs time t. Specifically, g2 is the correlation function of pairs of images of a CCD camera. The size of events may also be deduced by variation of illumination/detection spot.
Only in the backscattering geometry, TRC experiments can be used to resolve individual rearrangement events. In a TRC transmission experiment, the signals due to many individual events are superposed and therefore hard to analyse. The Science team recommends testing the instrument with foams in order to check the system.

Foam Samples compositions
Compositions of the samples listed by priority order:
Composition 1: TTAB 5g/l + water / 14 samples
Composition 2: TTAB 5g/l +dodecanol + water / 6 samples
Composition 3: TTAB 5g/l +dodecanol+glycerol+ water / 6 samples
Composition 4: Pluronic + water / 5 samples
Composition 5: C12G2 5g/l + water / 2 samples
Composition 6: TTAB 5g/l+ glass beads + water / 6 samples
Composition 7: SDS 4g/l + PNIPAM microgels / 1 sample
Composition 8: Rapeseed Oil + Water + SDS 4g/l / 1 sample
Composition 9: Dodecane + Water + SDS 4g/ 2 samples
Composition 7: SLES+CPAB+myristic acid / 8 samples
Composition 8: proteins + water / 9 samples
Composition 9: TTAB 0.1g/l + water / 6 samples
Composition 10: Rapeseed Oil + Water + SDS 4g/l / 7 samples
Composition 11: Dodecane + Water + SDS 4g/ 7 samples
Composition 12: Silicon Oil + Water + C10E4 80g/l / 3 samples
Important: the cells might need a coating for the samples containing oils (as for the FOAM-S cells)
The first two compositions are required as “minimal” (20 samples total)
The first nine compositions are “optimum” (40 samples total)

Minimum number of samples: 20 samples
Optimal: 40 samples
Nice to have: 80 samples.
Y. Houltz, C. Lockowandt, P. Andersson, O. Janson, D. Langevin, A. Saint-Jalmes, S. Marze, M. Adler, O. Pitois, B. Kronberg, M. Andersson, (2005), "The Physics of foams: the module FOAM 2 and its flight on Maxus 6", Proceedings of the 17th ESA Symposium on European Rocket Sandefjord, Norway, ESA, SP-590, pp. 565-572.
A. Saint-Jalmes, S. Marze, D. Langevin, S. Cox, D. Weaire, (2005), "Aqueous foam experiments in the MAXUS 6 sounding rocket: towards the development of an ISS module", Proceedings of the 17th European ESA conference on rockets, SP-590, pp. 573-578.
A. Saint-Jalmes, S.J. Cox, S. Marze, M. Safouane, D. Langevin, D. Weaire, (2006), "Experiments and simulations of liquid imbibition in aqueous foams under microgravity", Microgravity Science and Technology, 18, 3-4, DOI: 10.1007/BF02870391, pp. 108-111.
A. Saint-Jalmes, M. Safouane, S. Marze, D. Langevin, (2006), "Foam experiments in parabolic flights: development of an ISS facility and capillary drainage experiments", Microgravity Science and Technology, 18, 1, DOI: 10.1007/BF02908416, pp. 22-30.
A. Saint-Jalmes, S. Marze, H. Ritacco, D. Langevin, S. Bail, J. Dubail, G. Roux, L. Guingot, L. Tosini, P. Sung, (2007), "Diffusive liquid transport in porous and elastic materials: the case of foams in microgravity", Physical Review Letters, 98, pp. 058303.
J. Banhart, F. García-Moreno, S. Hutzler, D. Langevin, L. Liggieri, R. Miller, A. Saint-Jalmes, D. Weaire, (2008), "Foams and emulsions in space", Europhysics News, 39, 4, DOI: 10.1051/epn:2008402, pp. 26-28.
N. Vandewalle, H. Caps, D. Delon, A. Saint-Jalmes, E. Rio, L. Saulnier, M. Adler, A.L. Biance, O. Pitois, S. Cohen-Addad, R. Hohler, D. Weaire, S. Hutzler, D. Langevin, (2011), "Foam Stability in Microgravity", Journal of Physics: Conference Series, 327, pp. 012024.
R. Carpy, G. Picker, B. Amann, H. Ranebo, S. Vincent-Bonnieu, O. Minster, J. Winter, J. Dettmann, L. Castiglione, R. Höhler, D. Langevin, (2011), "Foam generation and sample composition optimization for the FOAM-C experiment of the ISS", Journal of Physics: Conference Series, 327, pp. 012025.
M. LeMerrer, S. Cohen-Addad, R. Höhler, (2013), "Duration of bubble rearrangements in a coarsening foam probed by time-resolved diffusing-wave spectroscopy: Impact of interfacial rigidity", Physical Review E, 88, pp. 022303.
click on items to display

Figure 1: Schematic experimental set-up.

Figure 2: Foam C instrument.

Figure 3: Foam C scientific objectives.

Figure 4: Schematic of the DWS experimental set-up.

Figure 5: Schematic of the SVS experimental set-up.

Figure 6: Experiment hardware before upload to the ISS. Credit: Airbus2020-ArnePiontek

Figure 7: The Sample Cell Unit S/N 6 of the Foam Coarsening experiment used for commissioning on the International Space Station. It contains three sample cells filled with liquid. By shaking the pistons inside the cell (the white and black items at the bottom of the cells are the most visible parts of the pistons), foam is generated. The white cell (in third position) contains a humidity sensor. Credit: NASA

Figure 8: The Sample Cell Unit S/N 6 of the Foam Coarsening experiment used for commissioning on the International Space Station. Credit: NASA

Figure 9: NASA astronaut Jessica Meir installed the FOAM-C experiment in the Fluid Science Laboratory on 6 March after removing the Multiscale boiling experiment Rubi. The experiment is controlled and data collected by the Belgian User Operations Centre who processed this image on 9 March. It is one of the first images of foam formed inside the Fluid Science Laboratory in Europe’s space laboratory Columbus and serves the team in the Belgian User Operations Centre in Brussels, Belgium, to keep track of the experiment and set it up. The actual Foam-Coarsening experiment will be activated before the end of March but this image shows that the liquids held in cells are already bubbling as planned.
© 2024 European Space Agency