Selectable Optical Diagnostics Instrument - Aggregation of Colloidal Solutions (SODI-Colloid) - 01.09.14
Science Objectives for Everyone Selectable Optical Diagnostics Instrument - Aggregation of Colloidal Suspensions (SODI-Colloid) will study the aggregation, or mass, phenomena of colloids in the microgravity environment onboard the International Space Station.
Science Results for Everyone Information Pending
Verhaert Design and Development, Antwerp, , Belgium
Sponsoring Space Agency
European Space Agency (ESA)
ISS Expedition Duration:
March 2010 - March 2011
Previous ISS Missions
21/22 is the first Expedition for the SODI-Colloid investigation.
- 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.
- Unfortunately gravity plays a disturbing role. Sedimentation causes the tips of growing crystals to break, limiting crystal size and greatly modifying their morphology. This deleterious effect is exacerbated when producing binary colloidal crystals using particles of mixed materials, the ones having most promise for applications.
- Selectable Optical Diagnostics Instrument - Advanced Photonic Devices in Microgravity (SODI-Colloid) seeks to study the properties of a peculiar, solvent mediated aggregation of colloidal particles.
The focus of Selectable Optical Diagnostics Instrument - Aggregation of Colloidal Solutions (SODI-Colloid) is on materials that have a special interest in photonics, with emphasis on nano-structured, periodic dielectric materials, known as photonic crystals, which possess appealing properties and make them promising candidates for new types of optical components. Since the key property of photonic crystals lies in the periodic variation of refractive index in two or three dimensions on a length scale that is equivalent to that of visible wavelength, the building block are (often mixtures of) colloidal particles of micrometric dimension. SODI-Colloid will study aggregation phenomena of colloidal systems, trying to tackle the puzzling and still not fully understood mechanisms of this phenomenon, with the benefit of a reduced gravity environment. Within such framework, the experiment here proposed is focused on a peculiar type of aggregation that received quite recently a notable interest in the scientific community. The system is composed of spherical colloidal particles suspended in a solution of two coexisting phases in near critical conditions. The interest of such a configuration lies in the fact that, in the homogeneous phase, the adsorption of one of the two species depends on temperature that is on the distance from the critical point. The exact nature of the interaction is still debated. According to the classical picture, the preferential adsorption of one component on the colloidal particles modifies the interparticle interaction, by weakening the repulsive contribution of surface charges. The resulting stability is strongly perturbed, turning from repulsive to attractive as soon as the distance from the two phase region is approached. The advantage of this system lies in the fact that the interparticle interaction is tuneable by controlling a macroscopic parameter such as the temperature. 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.
The colloidal engineering process will contribute to the creation of new materials and products in space.
SODI-Colloid will improve such colloids as paints, food products, drug delivery systems and ceramics by providing a better understanding of colloidal behavior.
Downlink of data is required to quickly assess the integrity of the liquid sample and to characterize the presence of aggregates in the sample volume. The structure of the aggregates will be measured by Near Field Scattering
Crewmembers will install the SODI ancillary equipment and the Colloid experiment container (equipped with 1 array consisting of 5 cells). After installation, the next steps consist of the optical processing of the experimental cells followed by probing the phase diagram near the critical point and observing the aggregation mechanisms of colloidal particles by way of the Near-Field Scattering optical technique. After processing the Colloid cells, the SODI instrument should be stowed.
Veen SJ, Antoniuk O, Weber B, Potenza M, Potenza M, Mazzoni S, Mazzoni S, Schall P, Wegdam G. Colloidal aggregation in microgravity by critical Casimir forces. Physical Review Letters. 2012 December 14; 109(24): 248302.
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