SODI-Colloid-2 (SODI-Colloid-2) - 09.17.14
ISS Science for Everyone
Science Objectives for Everyone
The Selectable Optical Diagnostics Instrument - Aggregation of Colloidal Suspensions (SODI-Colloid) investigation studies the growth, mixing, and ordering effects during microgravity aggregation from solutions of colloids (i.e., mixtures of particles made of materials and which have the characteristic of remaining evenly distributed within a material medium without settling out). The primary focus is on the use of binary fluid solvent mixture as a growth medium, which may enable the developlent of fine scale tunable crystals resulting in an optically purer product. By examining the three dimensional ordering and crystallization of colloids, this study intends to directly examine the mechanisms that could advance the development of photonic materials, which are useful in developing devices that confine and direct the optical propagation of electromagnetic waves and signals.
Science Results for Everyone
In this microgravity-based investigation of colloids (mixtures of evenly distributed particles), researchers were able to change the strength of particle interactions by using a binary mixture solvent and increasing the temperature. Fractal structures formed through diffusion-limited aggregation even at the lowest strength of attraction, while complexity of patterns decreased with increasing attraction. Ground experiments produced only one type of aggregate with a constant pattern, formed by a reaction-limited process. These results demonstrate that it is possible to fine-tune colloid interaction forces by changing the temperature and to investigate aggregation mechanisms and the resulting structure of colloidal solids.
Sponsoring Space Agency
European Space Agency (ESA)
ISS Expedition Duration
September 2011 - May 2012
Previous ISS Missions
- Selectable Optical Diagnostics Instrument - Advanced Photonic Devices in Microgravity (SODI-Colloid) seeks to study the self assembly properties of a binary solvent (i.e., water and 3-methyl-pyridine (3MP)) mediated aggregation of colloidal particles through optical Near-Field Scattering (NFS) measurements.
- Unfortunately, gravity induces a disturbing role in the self ordering of colloidal materials. Sedimentation causes the tips of growing crystals to break, limiting crystal size and greatly modifying their morphology. This deleterious effect on interpatrticle interaction is exacerbated when producing binary colloidal crystals using particles of mixed materials (i.e., the ones having most promise for future design and production applications).
- One of the most promising applications of colloidal engineering is the fabrication of photonic devices. These devices must possess structures whose scale length is comparable to the wavelength of light, and that are ordered in three dimensions.
The focus of Selectable Optical Diagnostics Instrument - Aggregation of Colloidal Solutions (SODI-Colloid) is to examine materials that are of special interest in the field of photonics, with an emphasis on nano-structured, periodic dielectric materials, known as photonic crystals (i.e., crystals that posses appealing properties and make promising candidates for new types of optical components). The key property of photonic crystals lies in the periodic variation of the structures refractive index in two or three dimensions on a length scale that is equivalent to that of visible wavelength. The building block for these structures is often mixtures of colloidal particles of micrometric dimension. SODI-Colloid studies the aggregation phenomena of colloidal systems with the benefit of a reduced gravity environment, attempting to tackle the puzzling and still not fully understood mechanisms of this phenomenon.
The specific goal of the SODI-Colloid experiment is to observe nucleation and the early stages of aggregation, where the first nuclei with supercritical size are formed, studying the growth rate and size distribution over time.
Within such a framework, the experiment here proposed is focused on a peculiar type of aggregation that has received notable interest within the scientific community. The colloid system is composed of small spherical colloidal particles suspended in a solution of two coexisting phases near a consolution critical point (i.e., thermal boundaries of differing physical phases). The interest of such a configuration lies in the fact that, in the homogeneous phase, attractive forces develop between colloidal particles due to the confinement of density fluctuation as the temperature of the solution approaches the critical point. The advantage of this system lies in the fact that the interparticle interaction is tuneable by controlling macroscopic parameters such as the temperature. That is, the particles form aggregates as the temperature is increase, but revert back to a fully dispersed phase as the temperature is decreased.
Colloidal engineering processes have the potential to contribute to the creation of new materials and products that may enhance electronic communication hardware within various space architectures.
Engineering manipulation and fundamental scientific understanding of colloidal materials potentially improves our ability to produce, store, and manipulate materials which depend on associated physical properties including, paints, food products, drug delivery systems and ceramics.
Downlink of data is required to assess the integrity of the liquid sample and to characterize the presence of aggregates in the sample volume. The structure of the aggregates is measured by Near Field Scattering (NFS).
Crewmembers install the SODI ancillary equipment and the Colloid experiment container (equipped with 1 array consisting of 5 cells) into the MSG. After installation, the ground commands the optical processing of the experimental cells followed by varying cell temperatures which allows for the probing of the phase diagram near the critical point. Observation of the aggregation mechanisms of the colloidal particles uses the optical technique called Near-Field Scattering (NFS). After processing the colloid cells, the SODI instrument is removed from the MGS and stowed.
ESA web story on MSG and SODI COLLOID