Temperature-Compensated Pressure Sensitive Paint (PSP) for use in Nitrogen Environments of Large-Scale Blowdown Hypersonic Facilities

ABSTRACT: We propose to develop a novel form of pressure-sensitive paint (PSP) by exploiting distance-dependent fluorescence resonance energy transfer (FRET) between fluorescent quantum dot (QD) donors and acceptor moieties such as organic dyes, fluorescent QDs, or metallic nanoparticle quenchers) that are attached by flexible linker molecules to measure local pressure fluctuations directly without the presence of oxygen. The linker molecules fix the nominal (baseline pressure) distance between the QD donors and the acceptors so as to control the sensitivity and dynamic range of the proposed FRET-based PSP. Additionally, a recently developed type of bichromatic Mn-doped core/shell QD, whose excitonic and dopant photoluminescence emission peaks increase and decrease, respectively, in proportion to increasing temperature, but are immune to pressure changes, would be used in a temperature-sensitive paint (TSP) to compensate for the influence of dynamic local temperature gradients and fluctuations on the PSP measurements. A novel technique to deposit PSP and TSP in such a way to avoid interaction effects is also proposed. Both the PSP and TSP signals will be measured simultaneously and processed to yield accurate, temperature-compensated dynamic surface pressure measurements in an oxygen-free environment at elevated temperatures. BENEFIT: Since the proposed PSP relies on FRET and not an oxygen-quenching mechanism (such as with traditional PSP materials), it can sense pressure changes directly without the presence of oxygen. By using a second species of Mn-doped quantum dots (QDs) that respond to temperature changes but not pressure changes, dynamic local temperature gradients can be compensated for in the processing of the FRET-based PSP data. Because the proposed FRET-based PSP concept does not rely on diffusion of oxygen, it will have significantly faster response times than conventional PSP. The nominal distance between QD donors and acceptor species can be precisely controlled by using flexible linker strands of specific length whose nominal distance affects the sensitivity and dynamic range of the PSP and so the proposed PSP can be tailored to specific wind tunnel test conditions. Although the proposed technology will find first application in the aerospace industry, the fundamental FRET-based pressure sensing method can be applied to biological investigations as well. For example, sensing the intra-cellular pressures, protein folding strain forces, and even microfluidic flow-induced pressures for lab-on-a-chip applications. As such it will have significant commercialization potential in the life sciences arena.