Advanced Colloids Experiment-Heated-1 (ACE-H-1) - 12.13.17

Overview | Description | Applications | Operations | Results | Publications | Imagery

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The Advanced Colloids Experiment-Heated-1 (ACE-H-1) experiment examines densely packed microscopic spheres, or colloidal mixtures, to study their transition from ordered crystals into disordered glass. The particles are fluorescent and change size in different temperatures, so scientists are able to see how they move and change forms as they are heated and cooled. Studying particle interactions without the influence of gravity improves   the ability of scientists to understand how increasing disorder in a crystal material affects its freezing, melting, aging and structural integrity.
Science Results for Everyone
Information Pending

The following content was provided by Arjun Yodh, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details

OpNom: ACE

Principal Investigator(s)
Arjun Yodh, Ph.D., University of Pennsylvania, Philadelphia, PA, United States

Co-Investigator(s)/Collaborator(s)
Mathew Lohr, University of Pennsylvania, Philadelphia, PA, United States
Matthew Gratale, Ph.D., University of Pennsylvania, Philadelphia, PA, United States

Developer(s)
Information Pending

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)

Research Benefits
Information Pending

ISS Expedition Duration
March 2014 - September 2014; March 2015 - September 2015

Expeditions Assigned
39/40,43/44

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • The microscopic process of the transition from a crystal to a glass has been referred to as one of the deep mysteries of our time.  A better understanding of this phenomenon will lead to better control and improved mechanical properties of glass forming materials.
     
  • The crystal-to-glass transition is induced over a series of samples by including and increasing the fraction of small, randomly distributed dopant particle inclusions in a dense packing on uniformly sized colloidal microspheres.  The colloidal systems, in particular, are well suited for the investigation of the microscopic structural and dynamic mechanisms that underlie this crossover.  These particles have diameters which are sensitive to temperature This property allows the use of heating and cooling to change the sample phase from crystal/glass, to fluid, and back. The particles are also fluorescent so that their position and motion can be tracked from microscope videos taken throughout the experiment.
     
  • These experiments provide insight into how increasing disorder in an initially crystalline material can affect melting, freezing, aging and other structural and dynamic properties.

Description

The nature of solidification and dynamic arrest of microscopically disordered materials is an important topic of study in materials science and condensed matter physics.  The conventional model of the fluid-to-solid transition is marked by a discontinuous increase in structural order at the atomic scale.  In the solid phase, such systems exhibit obvious crystalline order.  However, there also exists a class of materials where the system forms a phase with solid-like macroscopic properties but no apparent atomic structural order.  We will refer to these disordered solid packings as "disordered solids", or "glasses."  Gaining new understanding about how these disordered materials solidify is an important goal in condensed matter physics and materials science that could lead to engineering of new materials with tunable strength, fragility, and malleability.

By introducing disorder into a system, glasses can be formed from components which would otherwise form a crystalline solid.  This route to glass formation can be achieved by adding anisotropic interactions between constituent particles; by rapidly quenching as system from the fluid phase; or, by adding multiple species of particles together with opposing ordered ground states.  We model this last route to glass formation via a bidisperse mixture of colloidal spheres with slightly different radii.  Each particle species would, on its own, form a colloidal crystal at high packing fraction; mixed together at a number ratio of 1:1, they form a disordered colloidal glass.  At intermediate number ratios, one expects a series of states transitioning from a largely uniform crystal with defects, to a sample with polycrystalline domains, to a packing with zero structural order.  Our goal is in this work is to study the nature of this colloidal crystal-to-glass crossover with respect to the amount of disorder introduced to the system in the form of differently sized “dopant” particles.  Ideally, we plan to examine these colloidal packings using microscopy techniques that track the particle positions in three dimensions.  However, the underlying physics of colloidal suspensions are complicated on Earth by gravitational effects, (e.g., sedimentation).  Performing these experiments in zero gravity allows us to examine a more “pure” version of the crystal-to-glass crossover in a colloidal system.

Our first experiments, of this nature, to be performed on ACE-H-1, will be comprised of a series of dense, bidisperse colloidal packings with equilvalent room-temperature packing fractions, but varying ratios of comparatively large and small particles. (Note, the particles that will be used in the present experiments are similar, but not exactly the same as the particles needed for the fully optimized three-dimensional tracking studies.)  These colloidal suspensions will consist of poly-N-isopropylacrylamide (pNIPA) microgel spheres of room temperature diameter ~ 1.5 μm and 2.1 μm dispersed in water.  The diameter of these particles is temperature-sensitive: upon heating from room temperature to 32 °C, their diameter decreases significantly (10-20%), returning to their previous size upon cooling back to room temperature.  The volume fraction of these samples at room temperature will be above both the colloidal-fluid melting volume fraction (ф =0.545) and the colloidal glass transition (ф =0.58).  Upon a temperature increase to 32 C, the particle radii (and thus volume fraction) will decrease to a low enough value to be well within the colloidal fluid phase (ф < 0.494).  Each sample well will contain a different ratio of small (~1.5um) to large (~2.1um) particles, r, varying from r=0 to r=1.  Particles are labeled with covalently bondend fluorescent carboxytetramethylrhodamine (TAMRA) molecules to allow fluorescent imaging on the LMM.  If possible, particles will include a small (300nm) fluorescent polymer core of PMMA in lieu of TAMRA labeling, in order to increase visibility of individual particles in dense packings under fluorescence microscopy.  In this case, small particles may be labeled with a different fluorophore than large particles, requiring near simultaneous observation of two different fluorescent wavelengths to distinguish between particle species (i.e., serial with two different filter cubes).

We intend to record and track the microscopic structure and dynamics of these packings over time in order to characterize the ordering behavior of these suspensions after a rapid quench to high volume fractions.  Initially, a layer of particles at least several microns into the bulk of a single three dimensional sample will be imaged in an epi-fluorescent mode of the LMM using a 63x oil-immersion objective.  (If particle centers are not easily distinguishable / resolvable, then a 100x oil-immersion objective should be used).  Once the microscope is properly focused, the sample will be heated to 32 °C, decreasing the volume fraction of the packing so it enters a fluid state.  Once the sample has been given ample time to equilibrate (10 minutes), the heating element will be turned off, allowing the sample to return to room temperature (and thus to a volume fraction above the crystal melting / glass transition).  Short videos of the particles will then be recorded periodically (ideally, at 1 fps for at least 60 seconds at a time, every 20 minutes) for a period of 2-3 days, or until all obvious signs of structural rearrangements / aging have ceased.  If time allows, the aged sample will then be heated to 32 °C a second time, while video is recorded at 1fps from the beginning of heating until obvious total melting of the packing. This procedure will be repeated for each sample with different composition of large and small colloidal particles.

After video acquisition, structure and dynamics will be analyzed.  Assuming clear enough resolution of individual particles, positions and dynamics will be determined using particle-tracking algorithms.  If this level of resolution is not possible, Fourier analysis of the images should still provide insight into the level of crystalline order in the samples, though this analysis will be more qualitative.  Analyzing the microscopic structural order in well-aged samples will provide insight into the nature of the crystal-to-glass transition as a function of particle size composition.  Additionally, changes in the dynamics / structure of each individual sample over time will elucidate the nature of aging, rearrangement events, and nucleation and growth in packings with varying order / crystallinity.  Lastly, video of the sample re-heated after several days of aging at high volume fraction will provide insight into the changes in melting behavior with across the order/disorder crossover.

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Applications

Space Applications
Previous studies of colloidal mixtures show that even a small gravitational influence dramatically affects the way crystals form. By performing experiments on dense particle mixtures in microgravity, scientists can better understand the physical processes of nucleation (particles clumping together), aging and melting. These findings could be used to design new colloidal mixtures in microgravity, including metamaterials and advanced photonics. Additionally, the experiments will pave the way for future colloid research in space.

Earth Applications
Understanding how ordered crystals become disordered, glassy materials will help materials scientists alter the way microscopic particles interact. This could enable new ways to change the large-scale behavior of glasses. The experiments provide insight into the fundamental processes of particle clumping, melting and other physical behaviors.

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Operations

Operational Requirements and Protocols

• One experiment (one 5 well strip) per week. Duration of experiment for 5 wells lasts approximately 1 ½ days. There are 3 strips in a sample cell module. Repeat until all 30 wells (2 sample modules) have been tested (15 good wells required to meet success criteria, 30 wells desired - time allowing).
• Skip wells when air bubbles are too big.
• Use rest of week to analyze data, re-write scripts, and adjust parameters.
• Number of 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 oil, although ACE-M-1 seems to indicate that doing 5 wells on a strip at once will not be a problem (may require initially dispensing two drops of oil on strip); air objective has no such constraints.


Experiment Steps:
1. Inspect Samples
2. Ground to choose first Sample to test; feedback to crew.
3. Mix first sample cell using drill BCAT magnet for 30 seconds.
4. Apply oil in Auxiliary Fluids Container (AFC) and install assembly.
5. Define XYZ offsets (assembly alignment per ACE-1 method).
6. Adjust camera parameters using 2.5x objective and B/S cube.
7. Survey well at 2.5x; determine primary (and secondary?) test locations (select locations away from stir bar or bubble).
8. Adjust and record best camera parameters using 63x oil objective and Texas Red filter – (or optimal filter for TAMRA fluorescence.  If multiple fluorophores are used to distinguish large and small particles, adjust and record parameters for a second filter – FITC filter).  It may be better to do all 5 wells on a strip with one filter cube before switching to the other filter cube.
9. Survey and record best Z-depth at each primary test location.
10.  Heat sample to 32 C until particles have obviously entered mobile, fluid state.  Keep at temperature for 10 minutes.
11.  Turn off heat, returning sample to room temperature.
12. Experiment on one well using 63x oil objective; each image set at 1 fps, no binning, 8 bpp (highest supported), full frame images.  Store 60 to 500 images (the more the better – based on what hardware will allow) using Texas Red filter (if second fluorophore used for second particle species, store same number of images using second filter – FITC filter).  Tests may show that it is more efficient to do this after imaging all five wells with the first filter (e.g., Texas Red).
13. Repeat step 12 for other 4 wells on strip.  If two filters used, image 5 wells on strip (using parameters in step 12) using first filter.  Then, repeat imaging for all 5 wells using second filter.
14. Repeat at 60-minute intervals (20-minute intervals would be even better, if hardware storage and throughput allows this).
15. Complete upon dynamics evaluation by PI (estimate 1 to 1 1/2-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, if hardware allows).
16. Upon evaluation of PI that the sample has ceased aging/rearrangements (or set expiration time, probably after waiting for a week, rack does not need to be powered during this waiting period provided it will stay below 28C in temperature, which it should), heat once more to 32C (sample crystal structure melts at 28C to 32C), recording as many images as possible at 1 fps commencing at start of heating.  Melt by raising temperature 1 degree C until temperature stabilizes taking images for each sample strip of 5 wells (as noted in steps 12 and 13), raise temperature another 1 degree C … from 28C to 32C, repeat until images have been taken at 32C.
 

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Decadal Survey Recommendations

CategoryReference
Applied Physical Science in Space AP5
Fundamental Physical Sciences in Space FP1

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Results/More Information

Information Pending

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Related Websites
ACE
LMM Brochure

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Imagery

image

European Space Agency astronaut Paolo Nespoli operating the Light Microscopy Module microscope aboard the International Space Station on a previous mission. (Credit: NASA)


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The Light Microscopy Module (LMM) features a modified Leica RXA research imaging light microscope with powerful laser-diagnostic hardware and interfaces. The LMM is being used in the Advanced Colloids Experiment (ACE-H-1) investigation. (Credit: NASA)


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