Is it possible to dynamically control the spectral radiative properties of nanoparticles dispersed in a fluid? That is the fundamental question at the heart of this research proposal. Nanoparticles are known to offer a variety of benefits for thermal transport, and of particular relevance here the vast changes to the radiative properties that can be achieved through the dispersion of nanoparticles. With the advent of nanoparticles it is possible to control the radiative properties of dispersions as opposed to just passively observing such properties. In particular, a dispersion of core-shell multifunctional nanoparticles will be created that are capable of dynamically changing their volume and thus their spectral radiative properties. Preliminary experiments have shown that these multifunctional nanoparticles are capable of being synthesized to achieve temperature sensitive volumetric changes. To date most of these particles have been synthesized with polymer shells and inorganic cores while this proposal plans to reverse this with polymer cores and inorganic and metallic shells to achieve large radiative property shifts in the visible-infrared wavelengths. This proposal addresses this question through a comprehensive set of experiments and analyses. The experiments will largely focus on measuring the spectral radiative properties of different dispersions at different temperatures and thus different volumes using spectrophotometric techniques. These measurements will then be correlated with modeling results to improve fundamental understanding of the dynamic control of radiative transport as a function of the core material, shell material, size and volumetric shift achievable. Intellectual Merit. This research comprises an intriguing nanoscale thermal transport problem. The potentially transformative nature of the proposed project is the exciting capability to dynamically (and reversibly) change the radiative properties of a dispersion of nanoparticles. Fundamental questions will be addressed such as: can a single dispersion of core-shell multifunctional nanoparticles be controlled so that it can serve as either an absorber, or as an emitter of energy? Can this control be achieved in a passive manner? Can this be done using cost effective, environmentally benign materials? By coupling radiative property control with the dynamic capabilities offered by multifunctional nanoparticles innovative passive control methods will be investigated addressing further questions such as: Can volumetric changes be effected with changes in temperature? Are volumetric changes possible with other passive methods such as the chemical environment of the dispersion? How many times can the dispersion go through the reversible volume change process? What are the fundamental structure-property relationships in these core-shell materials that give rise to changes in absorbance and how can this relationship be tuned? Broader Impacts. The broader impacts of this project come in three different areas. The first is the technological opportunities that may be enabled by developing dynamically controllable radiative properties within the proposed nanoparticle dispersions. One potential system that may result from such a system is a dual-use solar thermal collector and night-sky radiator. The use of nanoparticles acting as direct absorption receivers has been shown to offer improved efficiencies over conventional surface-based receivers. Another intriguing option is the ability to create a thermo-optical switch. Such a switch would allow for creating a liquid filter that at times is transparent while at other times could be opaque. The second impact lies in the direction of undergraduate research and education. As part of this project the results of the research will be integrated into the undergraduate curriculum through the design of one full-scale experimental demonstration and one bench-top laboratory demonstration on the radiative properties of dispersions. Lastly, the participation of underrepresented groups, through research and classroom opportunities, which make up 29% of LMUs undergraduate population will be actively encouraged and promoted.
Is it possible to dynamically control the the optical properties of a fluid? That was the fundamental question of the research performed within this award. The vision was to generate a new class of nanoparticles with unique capabilities, specifically a nanoparticle capable of dynamically changing size with temperature. With drastic size induced changes it will be possible to drastically (and reversibly) change the optical properties of a fluid where such particles are dispersed. Such control would be useful in a potential system such as a dual-use solar thermal collector and night-sky radiator. The use of nanoparticles acting as direct absorption receivers has been shown to offer improved efficiencies over conventional surface-based receivers. Another intriguing option is the ability to create a thermo-optical switch. Such a switch would allow for creating a liquid filter that at times is transparent while at other times could be opaque. Initial investigations were both experimental and analytical. The first thrust was in the development of synthesis techniques for the desired particles. As a result we have developed what is believed to be the first metallic shell polymer core thermal-responsive nanoparticles. To date most temperature sensitive multifunctional particles have been synthesized with polymer shells and inorganic cores while we have reversed this with polymer cores and inorganic and metallic shells. The second thrust focused on characterizing the temperature dependent optical properties of more traditional nanoparticle suspensions. This thrust was both analytical and experimental and led to further understanding of the impact of a variety of mechanisms leading to the temperature induced modification of the optical properties of fluids. These results confirmed the limited ability of simple suspensions for drastic optical property modification. Impact to the broader field will be achieved in future work and through the dissemination of the results highlighted above, particularly the novel thermal-responsive particle. The project also impacted multiple undergraduate students (including one from an underrepresented group) at the primary institution who were supported under the award. Two of these students have continued on to pursue graduate education and one accepted a position in industry.
