Advanced Colloids Experiment-Heated-2 (ACE-H-2) - 01.13.16
The ACE-H2 experiment involves the design and assembly of complex three-dimensional structures resulting from the interaction of different sized particles suspended within a fluid medium. These so-called “self-assembled colloidal structures”, are vital to the design of advanced materials. In the microgravity environment, insight will be provided into the relationship between particle interactions and their shape, surface charge, and concentration. Their resulting structure and stability is a fundamental issue in condensed matter science. The use of the Light Microscope Module (LMM) on the international space station will enable insight into finer control of the self-assembly (as well as directed-assembly) of such colloidal-based structures. Science Results for Everyone
Information Pending Experiment Details
Stuart K. Williams, Ph.D., The University of Arizona, Tucson, AZ, United States
Suzanne Smith, PhD, University of Kentucky, Lexington, KY, United States
Gerold Willing, PhD, University of Louisvi, Louisville, KY, United States
Hemali Rathnayake, PhD, Western Kentucky University, Bowling Green, KY, United States
NASA Glenn Research Center, Cleveland, OH, United States
ZIN Technologies Incorporated, Cleveland, OH, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
Earth Benefits, Space Exploration
ISS Expedition Duration 1
September 2015 - September 2016
Previous ISS Missions
- Why is the research needed?
New functional materials can, in principle, be created using microscopic particles (called colloids) that self-assemble into a desired structure by means of a recognition and binding scheme. The ACE-H2 experiments will utilize optical microscopy for time- and space-resolved imaging of spherical colloids of various sizes and concentrations. Colloidal assembly and the structure’s stability can be controlled by mediating the particles’ electrostatic charge and surface chemistry. The introduction of smaller particles allows the tuning of the interactions between the larger colloids, and in this way control the structure of the colloidal dispersion. The particle surface interactions are reversible and sensitive to temperature.
- What will be accomplished?
In ACE-H2, fundamental insight will be gained into the interaction of smaller nanoparticles with larger colloids, i.e. the “nanoparticle haloing” (NPH) phenomenon, as a function of particle concentration. Crystallization behavior of the larger colloids will also be observed whose structure is a function of the size and concentration of nanoparticles. In the microgravity, we hope to observe unobstructed NPH interactions which would otherwise be significantly hindered by gravity on earth due to sedimentation issues (high density contrast between particles and fluid).
- What will be the impact of the research?
Ultimately, the ability to design colloidal particles with a variety of well-controlled three-dimensional bonding symmetries opens a wide spectrum of new structures for colloidal self-assembly, beyond particle assemblies whose structures are defined primarily by repulsive interactions and shape. Such materials might include photonic crystals with programmed distributions of defects. Optical technology utilizing such materials may offer intriguing solutions to unavoidable heat generation and bandwidth limitations facing the computer industry.
Nanoparticle Haloing (NPH) is a colloidal stabilization technique that has been discovered relatively recently. In NPH, highly charged nanoparticles are used to stabilize much larger (by 2 orders of magnitude or more), non-charged particles. To accomplish this stabilization, the volume fraction of nanoparticles within the suspension need only be on the order of 10 -5 up to 10 -4 to stabilize at 1 to 2 vol% suspension of the larger particles.
When these suspensions were allowed to settle under gravity, those that were stabilized (while in suspension) formed highly ordered, 3-dimensional colloidal crystal structures. Further experiments using confocal microscopy revealed that the crystals were composed entirely of the larger particle with the nanoparticles remaining in suspension. Based on these measurements, it was concluded that the nanoparticles were not creating a charge layer by adsorbing onto the surface of the larger particle. Instead, it was thought that the nanoparticles created a charge layer by forming cage, or Halo, around the larger particles.
Another hypothesis regarding the NPH stabilization mechanism focuses entirely on nanoparticle adsorption to the surface of the larger particle. Based on the measurement of the interaction forces between two larger colloidal surfaces in a nanoparticle suspension, it was found that the force curves obtained could be fitted using a model based on nanoparticle adsorption. In this case, the van der Waals interaction between the larger colloidal surfaces was shielded by the adsorbed nanoparticle layer. This layer also supplied an electrostatic charge barrier to add an additional repulsive force within the system.
Using Atomic Force Microscopy, our group recently measured the interaction forces between two colloidal surfaces in a suspension of highly charged nanoparticles. We varied the nanoparticle volume fraction by 5 orders of magnitude (from 10 -6 up to 10 -2 ). Our results indicate that the two hypotheses are not mutually exclusive, but actually exist at different ends of the nanoparticle concentration spectrum. At low nanoparticle volume fractions, NPH tends to be the dominant stabilization mechanism. Nanoparticle adsorption tends to dominate at higher nanoparticle volume fractions.
The proposed experiment will (i) investigate the nature of three-dimensional colloidal structures formed by NPH under microgravity and (ii) assess the structure’s stability under induced thermal “shocks” using Brownian motion analysis.
NPH stabilizes larger colloids to form crystalline structures. Unfortunately, previous work investigating these structures are heavily influenced by gravity as a typical particle under investigation (ex: 1 m m silica) will sediment relatively quickly on earth. This experiment will utilize the microgravity environment to discover how 3D NPH crystalline structures are formed and investigate this characteristic as a function of suspended nanoparticle concentration.
The sample will contain two particles. The smaller nanoparticles will be non-fluorescent 8 nm zirconia (ZrO 2 ) particles. The larger particles will be 600 nm particles (not tagged). Nanoparticle (8 nm) visualization is not required; however, aggregations formed by the larger colloids (600 nm) will need to be identified.
This experiment will use the existing 15 well chamber for ACE-H. The larger particle (600 nm) volume concentration for the all 15 samples will be constant at 1.0%. Three (3) different small particle (20 nm) volume concentrations will be prepared (0.01%, 0.055%, and 0.1%). These samples will be duplicated for a total of five (5) 0.01% samples, five (5) 0.055% samples, and five (5) 0.1% samples. The solution for the suspensions will be 0.35M nitric acid.
General Experimental Trials:
Aggregate identification and visualization : Experiments will focus initially on determining how the three-dimensional NPH structures form in their environment. First, a specific sample well will be scanned at 20X magnification to identify NPH clusters. The PIs will identify, within each sample well, a region/aggregation of interest to be imaged at larger magnification (40X). Digital images will be analyzed and processed offline. Measurements will be able to clearly assess how NPH forms 3D colloidal crystals, as replicated experiments on earth would be severely hindered on earth, providing an “incomplete picture” of 3D NPH. It is expected that structure formation is a function of nanoparticle concentration.
Thermal shock : We will use the inherent capabilities of the platform to induce a heat shock to the system, i.e. uniformly and rapidly heating the sample from ambient to 43 o C at the maximum rate for the ACE-H platform. During thermal ramp, a region of interest (and/or identified NPH crystal or interest) will be imaged. The relative position of the colloids will be tracked and the integrity of the crystalline structure will be assessed during the thermal shock, providing stability dynamics associated with NPH. This should allow us to visualize, for the first time, the three-dimensional dynamics of Halo disruption and reformation.
[ Note : ‘Thermal shock’ experiments will only be performed on those sample cells that created NPH-induced colloidal aggregates. It is not expected that all 15 samples will be a part of this experiment series.]^ back to top
We will need a micro-gravity environment to gain fundamental insight into nanoparticle haloing. We will be able to ‘scale-up’ traditional nanoparticle haloing experiments to properly visualize particles thereby making fundamental discoveries related to this phenomenon. Further, we will be able to observe three-dimensional aggregations formed by NPH, which have not been accomplished previously. Discoveries herein will lay the foundation for applying this technique to synthesize the next generation of colloidal-based materials, including enhancing optically-based energy platforms and sensors.
This work will pursue the fundamental studies of order and particle interactions in nanoparticle haloing and subsequent colloidal structure stability and crystallinity. Understanding this is needed for technologies that will underlie complex processes like self-assembly and motility. With understanding comes specificity, control, and reversibility in interactions for materials with submicron-features.
The experiment will be conducted over 12 weeks, including several offline periods for data analysis. Experiments are separated into three four-week experiments. The first four-week period will perform “Aggregate identification and visualization” experiments. The second four-week period will perform the “Thermal shock” experiments. The third four-week period will be a repeat of the “Thermal shock” experiments.
General experiment steps:
- Mix all samples in sample module to be viewed using BCAT drill magnet for 1 minute each (15 minutes). After a brief break (5 minutes) 9 cells (chosen by the PIs) will be mixed for an additional minute each.
- Load samples - inspect all samples.
- Ground to choose first sample to test; feedback to crew.
- Define XYZ offsets (assembly alignment per established ACE method).
- Adjust camera parameters using 2.5x objective and B/S cube.
- Survey chamber(s) at 2.5x. Determine bubble locations and location of stir bar.
- Switch to 10x objective.
- Adjust and record best camera parameters using an appropriate Z-depth.
- Aggregate identification and visualization: Methodically scan all samples with a 10X objective. This includes proper x- and y-scans to capture images of the complete chamber. Acquire each image at full frame resolution. It is assumed that a complete sample scan as outlined here will take approximately 20 minutes (i.e. 15 samples will take 5 hours). Each week three samples will be selected for a comprehensive 20X scan. The PIs will select a region within this scan for additional image acquisition at 40X magnification; a z-scan routine will accompany the 40X image acquisition. Two movies (Week 2, Day 1; Week 4, Day 1) will be acquired on selected samples at 20X, one image per minute, for an hour each.
- Thermal shock: Mix all samples as outlined in (3). Follow the “Aggregate identification and visualization” instructions to acquire images of all sample wells at ambient temperature at 10X magnification. Next, a specific sample will be chosen by the PI for a comprehensive sample scan at 20X while at ambient temperature. The platform is then to ramp at its maximum rate to 43oC. During this ramp, a two-hour movie at 40X magnification is acquired with one image being acquired every minute. If the stage temperature is interrupted, allow the sample to reach 43oC and continue image acquisition. At the end of the two hour period a comprehensive sample scan at 20X will be conducted (while at elevated temperature). At the end of this scan the temperature can be deactivated and returned to ambient conditions. This process is repeated for additional samples during the experiment set.
Decadal Survey Recommendations
Information Pending^ back to top
Information Pending^ back to top
2011 ACE Science Concept Review (SCR) presentations
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-2) investigation. (Credit: NASA)
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