Coatings and Nano-Materials

Fluorescent Pressure and Temperature Sensitive Coatings - SensorkoteTM

In the Past:

Traditionally, “Pressure Sensitive Paint” (aka PSP) was a luminescent coating that was applied to models used in test facilities, such as wind tunnels or tow tanks, to acquire global surface pressure data for vehicle design or performance.  Until recently PSP formulations have exploited the photochemical process of dynamic quenching by oxygen to achieve a response to variations in pressure in air.  The first figure below illustrates the use of these PSP formulations on scale models of a supersonic airplane in two different test facilities.  PSP is one of four key components included in advanced optical measurement systems commonly called “PSP Systems.”  The other three components are an illumination or excitation source, a detector such as a scientific grade CCD camera and image processing/data reduction software.  Each of these components is marketable itself, as is the complete system and services related to specifying, implementing and using such systems. 

There is a relatively strong global market for PSP and related components.  Large companies and governmental agencies such as the U.S. Air Force and NASA maintain an interest in PSP technology.  NASA Langley Research Center has developed a number of PSP formulations, some of which included a temperature probe.  Even though there is not as much “new product development” for commercial aircraft as there was in the 1980’s and 1990’s, the market for traditional PSP stays relatively strong because of the significant cost savings PSP offers users.  For example, one model at NASA Langley Research Center had over 12,000 square centimeters of surface area costing roughly of $23,100.00 for the PSP to cover it.  However, using pressure taps and transducers for the same model for one week of testing, (including model fabrication and instrumentation) would have cost in excess of $1M.  The cost savings using PSP are substantial. 


Research started at LeaTech, LLC in the early 2000's in several areas related to Pressure Sensitive and Temperature Sensitive Paints (TSP) is beginning to pay off.  For example, the non-oxygen PSP formulations that operate as true pressure sensors – not an oxygen sensor.  The new “PSP’s” would be used initially in environments where the traditional PSP formulations would not work, e.g. marine and nitrogen test environments.  But, these new coatings can also be used as a “plug ‘n play” component in existing PSP systems.  

LeaTech’s new pressure sensitive coatings operate by exploiting the photochemical energy transfer that occurs from the formation of an excited state complex (exciplex) or through fluorescence resonance energy transfer (FRET).  The resulting coatings emit multiple wavelengths of light as shown in the second figure below.  The shift in emission intensity between wavelengths is also shown in that figure.  Because these energy transfers are distance dependent, as pressure is exerted on the coating and the distance between participating compounds decreases the level of energy transfer increases creating an apparent shift in light emission, e.g. from blue to green for an anthracene/aniline combination.  Conversely as pressure is reduced the light emitted appears to return from green to blue.  This reversible process is repeatable.  The optical properties of these new PSP’s can be selected, e.g. the perylene/aniline exciplex forming combination and the fluorescein/rhodamine FRET combination emit light at yellow and orange-red wavelengths.  Most importantly, the material properties of these coatings can be “tuned,” e.g. through cross-linking, to desired pressure sensitivities and operating ranges.    

LeaTech began developing these pressure sensitive coatings under contract to the Office of Naval Research (ONR) for use in marine environments.  That work continued beyond the ONR contract and today is funded, in part, by NASA’s Hypersonics Project.  LeaTech’s new pressure sensitive coatings are really, novel nano-materials designed at the molecular level to have a specific macroscopic response (a change in fluorescent emission intensity) to changes in pressure.  Because these coatings are true pressure sensors their use can be expanded to include a wide range of applications from the existing markets in aerospace and marine applications to flow and process control, sports equipment, biotech/biomedical applications and more.  The accuracy and precision of the desired pressure measurements dictate the sophistication of the required, related equipment.  In addition, LeaTech is working on technologies that incorporate these coatings into electronics or micro-electro-mechanical systems (MEMS) for applications as gas “sniffers”, e.g. to detect hydrogen leaks in hydrogen fueled vehicles or at hydrogen refueling stations, and optical pressure transducers. 

Temperature Sensitive Coatings:

LeaTech has also developed a TSP formulation that will operate over higher thermal operating ranges than existing TSP’s. LeaTech’s TSP formulation has been used by the U.S. Air Force in hypersonics testing at AEDC White Oak’s Hypervelocity Wind Tunnel 9 for over five years now.  The third figure below illustrates the use of TSP to evaluate differences between shock / boundary layer interaction for turbulent and laminar boundary layers at Mach 14. Similar to LeaTech’s PSP formulation, our TSP exhibits a change in fluorescent emission intensity with changes in temperature.  These changes can be used to illustrate temperatures from cold (blue) to hot (red) by application of an artificial color map.  Data from TSP is currently being used to calculate heat transfer on vehicles such as NASA’s Space Shuttle.  As with the new PSP’s, there are a number of potential new markets for these TSP’s.  For example, TSP could be incorporated as an “optical thermometer” by coating various electronics that could not otherwise be instrumented.  This would allow development of a control system for turning on and off a variety of cooling devices.