Advanced Colloids Experiment-Microscopy-1 (ACE-M-1) - 03.04.14
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Advanced Colloids Experiment-Microscopy-1 (ACE-M-1) studies the behavior of microscopic particles in gels and creams. Many consumer products are colloidal mixtures with stabilizers added to make them last longer. But eventually, particles still clump together and sink to the bottom in a process known as coarsening which can spoil a product. The International Space Station is an ideal location to study the physics of coarsening which could lead to manufacturing longer lasting products.
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Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
September 2012 - March 2014
Previous ISS Missions
Recent work (Lynch, Weitz) demonstrates that polydispersity, or inconsistent sizes of particles in the polymer, makes a huge difference in the time scale of collapse of weak gels. In many cases the time scale is in orders of magnitude. Polydisperse (real-world) systems are complicated and not well understood. There are at present no basic measurements/theories that allow us to understand the role of polydispersity in these processes.
To control these systems, an understanding of the evolution (coarsening) of microstructure is required. On earth this process occurs on a timescale of minutes due to gravitational sedimentation; while on the International Space Station (ISS) the timescale will be several days to a week in duration. Microgravity is required to detach phase separation from coarsening. This is crucial for the practical application of these concepts to product design, as products are inherently polydispersed--the basic need.
Colloidal stability is critical to soft matter systems, as it relates to products. These products are often structured by attractive forces between constituent particles (solids, vesicles, drops)--in the form of weak, flowable colloidal gels. These structures change in time, by processes know as coarsening--meaning the particles move under thermal motion to compact. This compaction continually changes this structure. When the structures created in the products can longer support the gravitational stresses (e.g. buoyancy) on the structures, they collapse. The collapse is often abrupt and without warning (delayed collapse). This is the essence of product instability.
In the scientific community, there is a large disconnect between microscopic structure and dynamics of these mixtures to the macroscopic changes in the structure which lead to collapse. Understanding this relationship may enable us to anticipate instability in products.
There are a number of factors that influence these coarsening rates. Some are reasonably understood of monodispersed systems--e.g. the magnitude/shape of the inter-particle forces and colloid concentration. These variables are often built into the design of the experiment by, for example, changing the polymer concentration (via depletion force) and amount of colloidal. In many cases, the systems are ‘frozen’ or arrested during preparation and thermodynamic driving forces conspire to alter the systems to some low energy minimum--see e.g. Russell and Gast (1982).
We are starting to take the next step, which directly applies more to product stability. In particular, we are beginning address questions on the effect of polydispersity on these system. Recent work (Lynch, Weitz) demonstrates that polydispersity in the polymer makes a huge difference in the time scale of collapse of weak gels- orders of magnitude. There are no basic measurements/theories that allow us to understand the role of polydispersity in these processes. This is crucial for the practical application of these concepts to product design, as products are inherently polydispersed--the basic need.
It is expected that polydispersity in the colloid (our ACE experiments) will demonstrate similar differences, and a product design vector we want to exploit--it also pushes the frontiers of physics. Our inability to generate quality data in this regards stems from the fact that in recent Earth-based experiments, the time scale of sedimentation (or creaming) is far faster than the dynamics of the movement of the colloids. As a consequence, all the motions are biased appreciably by hydrodynamics. This does not allow us to effectively deal with the fundamentals of coarsen--microgravity is a key here.
On Earth, colloidal research is greatly affected by the force of gravity which tends to mask results. Studying colloids in the microgravity environment of the International Space Station (ISS) can give much better data and enhance our understanding of liquid mixture coarsening. This puts the unique research capabilities of the ISS to good use which could improve manufacturing processes for making new and longer-lasting products for space and Earth use.
Understanding the behavior of mixtures and coarsening can help materials scientists to make colloidal mixtures with longer shelf lives. This has great potentials in creating a wide range of products from food, medicine, cosmetics, gels, and cleaning solutions which do not expire quickly.
One experiment per week; duration of 3-4 days. Repeat until all ten wells tested.
Switch Sample Modules if air bubbles too big.
Skip ops second week to analyze data, re-write scripts, adjust parameters.
# wells per experiment limited by:
1. Data bottlenecks on IPSU and IOP
2. XY position repeatability (need to return to the same particle set or don’t move during experiment => one well position. This takes too long, so find a solution. Images can be registered in post-processing via port or stir bar location, or pattern of particles stuck to bottom of cover slip.
3. Oil availability – too much repeat movement from well to well may lose immersion, so limits test points; air objective has no such constraints.
- Inspect Samples
- Ground to choose first Sample to test; feedback to crew.
- Mix using drill BCAT magnet for 30 seconds.
- Apply oil in AFC and install assembly.
- Define XYZ offsets (assembly alignment per ACE-1 method).
- Adjust camera parameters using 2.5x objective and B/S cube (Filter #6).
- Survey well at 2.5x; determine primary (and secondary?) test locations (select locations away from stir bar or bubble).
- Adjust and record best camera parameters using 63x oil objective and FITC filter (Filter #3).
- Adjust and record best camera parameters using 63x oil objective and Texas Red filter (Filter #4).
- Survey and record best z depth at each primary test location.
- Experiment on one well using 63x oil objective; each images set at 1 fps, no binning, 8 bpp (highest supported), full frame images. Store 500 images using FITC filter, Store 500 images using Texas Red filter
- Repeat at 20-minute intervals
- Complete upon dynamics evaluation by PI (estimate 3-day duration) Imaging goal is to resolve particle centroid positions with less than 20% error. Shutter lamp between image sets to prevent sample bleaching. Repeat of cycles is desired every 60 minutes, but desired as often as every 20 minutes.
Current ACE website
2011 ACE Science Concept Review (SCR) presentations (describe some exiting peer-reviewed science approved for the ACE flight experiments)
LMM brochure (describes capabilities of remotely controlled microscope on ISS)