NASA EPSCoR: Influence of Gravity on Electrokinetic and Electrochemical Colloidal Self-Assembly for Future Materials

Research in colloids is gaining interest from NASA, NSF, and industry due to potential new materials that could enable advanced solar energy harvesters, mechanically robust materials, inexpensive electronic displays, and analytical instrumentation for both space-related and terrestrial activities. Colloidal suspensions are liquids that contain suspended particles. NASA's Advanced Colloids Experiment (ACE) utilizes the research environment onboard the International Space Station (ISS) to perform unique fundamental physical investigations of colloidal interactions under microgravity. University of Louisville (UL) and Western Kentucky University (WKU) faculty with expertise in colloid synthesis, nanoparticle haloing and electrokinetics will work with ACE researchers from NASA Glenn Research Center on HEOMD, ARMD and STMD priorities. Insights into colloidal physics and, in particular, colloidal self-assembly processes are needed to develop new materials whose properties are dependent on colloidal crystalline structure. Precise control of colloidal assembly will result in the development of materials with enhanced energy, thermal, optical, chemical, and mechanical properties. The proposed research addresses both fundamental and applied investigations. First, we seek to reveal fundamental physics of colloidal nanoparticle haloing. Suspended particles (of negligible charge) that do not aggregate under normal conditions do stabilize with the introduction of charged nanoparticles (~1/100 diameter of larger particles). Nanoparticles form 'halos' around larger colloids which stabilize colloidal crystals. Visualization is needed to resolve conflicting haloing theories. The ISS National Laboratory environment will allow us to "scale up" by substituting nanoparticles with optically observable colloids (~1 um). Microgravity will enable analysis of their interaction with larger particles (~0.1 mm), which would otherwise be skewed by gravity. Images will be acquired with ISS Light Microscopy Module (LMM) and compared to terrestrial experiments. In 2016, a confocal unit (ACE-C) will be available on ISS enabling detailed 3D scans of colloidal suspensions. In parallel, we will investigate reconfigurable colloidal material applications where end-users will be able to 'program' the crystalline structure and mutual crystal spacing by inducing a charge on the colloids with an applied electric field. By combining the physics of nanoparticle haloing and colloid electrokinetics, colloidal crystals can be assembled and disassembled on-the-fly using reversible, tunable physical mechanisms. Such colloidal crystals can be 'programmed' for specific purposes, in particular specialized optical components or energy harvesting crystals tuned to a particular wavelength. Outcomes of the proposed research will: (i) Definitively prove/disprove current nanoparticle haloing theories; (ii) Develop associated colloid-assembly scaling-laws applicable to bulk nanomanufacturing of nanoparticle-stabilized colloidal architectures; (iii) Demonstrate dynamically tunable 3D colloidal crystals and establish governing electrokinetic theory. This work will lead to collaborations with NASA to develop electric-field test cells for future ACE tests on ISS and identify specific colloidal architectures for significant NASA impact. Research infrastructure in Kentucky will benefit from intellectual property stemming from discoveries made on ISS, from a state-of-the-art confocal microscope, and by strengthening a multidisciplinary research team of junior and tenured researchers from comprehensive and research institutions. The new microscope system complements existing infrastructure at UL Micro/Nano Technology Center providing a specialized multidisciplinary research tool for Kentucky researchers. Nearby industrial partners can also benefit from this research aligned with the Kentucky Science & Innovation Strategy.