Polymer-ceramic Pressure-sensitive Paint Research Articles

Polymer-ceramic pressure-sensitive paint with high pressure sensitivity and pressure-sensitivity constancy in low-pressure environments

The accurate measurement of tiny pressure variations in low-pressure environments requires pressure-sensitive paint (PSP) with high pressure sensitivity and pressure-sensitivity constancy for aerodynamics testing. In this study, polymer-ceramic pressure-sensitive paints (PC-PSPs) were developed using platinum(II) meso-tetra(pentafluorophenyl) porphyrin (PtTFPP) and palladium(II) meso-tetra(pentafluorophenyl) porphyrin (PdTFPP) as luminophores; titanium dioxide (TiO2) and mesoporous silica (mSiO2) as particles; and poly[1-(trimethylsilyl)-1-propyne] (PTMSP), poly(isobutyl-methacrylate) (PIBM), ethylene-vinyl acetate copolymer (EVA), and polyacrylate (B1000) as polymers. The static characteristics were calibrated and evaluated under low-pressure conditions. The results showed that PC-PSPs using PtTFPP with a short-lifetime and high oxygen-permeable polymer led to high pressure sensitivity. By contrast, if PdTFPP with a long-lifetime was used, the pressure sensitivity was dominated by the luminescence lifetime rather than the oxygen permeability of the polymer. PdTFPP/mSiO2-PTMSP exhibited a remarkable pressure sensitivity of 78.46%/kPa. PC-PSPs employing PIBM, EVA, and B1000, respectively, exhibited excellent pressure sensitivity constancy above 96% after near-vacuum storage for one hour. However, PTMSP-based PC-PSPs exhibited poor pressure-sensitivity constancy owing to the aging of the polymer in vacuum, which can be improved by employing the long-lifetime PdTFPP luminophore and mSiO2 particles. Furthermore, PC-PSPs using mSiO2 particles exhibited lower signal levels, higher pressure sensitivities, lower temperature dependencies and photodegradation than those using TiO2 particles. PdTFPP/mSiO2-PIBM and PdTFPP/mSiO2-B1000 exhibited application potential under low-pressure conditions owing to their favorable static characteristics.

Time-resolved particle image velocimetry and pressure sensitive paint measurements of afterbody flow dynamics

A pair of counter-rotating vortices is produced in the wake of typical cargo aircraft fuselages due to their ramp shape. With a fast polymer-ceramic pressure sensitive paint (PC-PSP), we measure the global pressure fluctuations at very low velocities (15 to 75 m/s) in a surrogate cylinder with a slanted edge model. Through spectral proper orthogonal decomposition, we observe a family of convective pressure waves with peak energy at frequencies matching the vortex wandering frequencies in this flow.

Characterization and Improvement of Heat Resistance of a Polymer-Ceramic Pressure-Sensitive Paint at High Temperatures.

Degradation of fast response pressure-sensitive paints (PSP) above room temperature is a serious problem for PSP measurements in high-temperature environments. A standard polymer-ceramic PSP (PC-PSP) composed of platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorphenyl)-porphyrin (PtTFPP), titania particles and poly(isobutyl methacrylate) (polyIBM) was characterized to elucidate the degradation mechanism. Applying a two-gate lifetime-based method, the PC-PSP has sufficient pressure and temperature sensitivities even at 100 °C, while the luminescence intensity significantly decreases during the test. Subsequent measurements on thermal and photostability as well as luminescence spectra reveal that the main cause of the degradation is the photodegradation of PtTFPP due to direct exposure of the dye molecules to the atmosphere. In order to suppress such degradation, a small amount of urethane resin is added to the dye solution as a simple additional step in the preparation of PC-PSP. The addition of the urethane resin significantly reduces the degradation of the PSP, although its time response is slightly slower than that of the standard PC-PSP.

Back-imaging of polymer-ceramic pressure-sensitive paint

The feasibility of back-imaging polymer-ceramic pressure-sensitive paint (PC-PSP) was investigated, with supersonic flow over a rectangular cavity being the test subject. A PC-PSP formulation in which the luminophore was fully-integrated into the binding layer created a PSP which luminesced from the top and bottom of the layer. This PSP was applied to a clear acrylic plate serving as the cavity ceiling. Two identical high-speed cameras imaged the paint; one viewed the top of the PSP layer (front-imaging) whereas the other viewed the bottom of the layer (back-imaging). The temporal, time-averaged, and spectral response measured by each camera were functionally identical. Specifically, the two data were found to be 90% correlated in time at zero delay. The minor differences can be attributed to random noise and the fact that the cameras viewed through two different materials (one through acrylic and the other through optically-polished glass). These results illustrate that back-imaging is a promising method for overcoming the optical access constraints of conventional PSP imaging techniques.

Effect of Oxygen Mole Fraction on Static Properties of Pressure-Sensitive Paint.

The effects of the oxygen mole fraction on the static properties of pressure-sensitive paint (PSP) were investigated. Sample coupon tests using a calibration chamber were conducted for poly(hexafluoroisopropyl methacrylate)-based PSP (PHFIPM-PSP), polymer/ceramic PSP (PC-PSP), and anodized aluminum PSP (AA-PSP). The oxygen mole fraction was set to 0.1–100%, and the ambient pressure () was set to 0.5–140 kPa. Localized Stern–Volmer coefficient increased and then decreased with increasing oxygen mole fraction. Although depends on both ambient pressure and the oxygen mole fraction, its effect can be characterized as a function of the partial pressure of oxygen. For AA-PSP and PHFIPM-PSP, which are low-pressure- and relatively low-pressure-type PSPs, respectively, peaks at kPa. In contrast, for PC-PSP, which is an atmospheric-pressure-type PSP in the investigated range, does not have a peak. has a peak at a relatively high partial pressure of oxygen due to the oxygen permeability of the polymer used in the binder. The peak of , which is the emission intensity change with respect to normalized pressure fluctuation, appears at a lower partial pressure of oxygen than that of . This is because the intensity of PSP becomes quite low at a high partial pressure of oxygen even if is high. Hence, the optimal oxygen mole fraction depends on the type of PSP and the ambient pressure range of the experiment. This optimal value can be found on the basis of the partial pressure of oxygen.

An optical-chemical sensor using pyrene-sulfonic acid for unsteady surface pressure measurements

Optical measurement techniques are being employed more frequently in unsteady aerodynamic testing. One of these techniques is unsteady pressure-sensitive paint (PSP), used to capture global surface pressure measurements at sampling rates on the order of kilohertz or faster. Polymer ceramic PSP (PC-PSP) is often used for these applications due to its porous structure and increased oxygen diffusivity. A limiting drawback of current luminescent markers used in unsteady PSP is that they have non-negligible temperature dependency, which is a major source of measurement uncertainty. Chemical sensor development is needed to create a sensor with reduced or negligible temperature dependency. This study investigates the development and characterization of a PC-PSP with reduced temperature dependency due to the use of pyrene sulfonic acid as the luminophore, a novel application for this luminescent marker. This study examines the influence of particles and the solvent used to apply the luminescent chemical and particles onto a model in the dipping deposition method on sensor performance. The chemical interaction between these sensor elements, as well as the luminophore and binder material, largely determines the performance of the sensor. Static calibrations were performed from 10 to 120 kPa and 20–80 °C, with a resulting peak pressure sensitivity of 0.4 %/kPa and minimum temperature dependency of 0.3 %/°C using silica gel porous particles. This resulted in an uncertainty in pressure due to change in temperature of 0.75 kPa/°C, an almost 40 % reduction compared to the closest comparison sensor. Dynamic characterization also showed response times on the order of 40-80 μs, which compares well with current PC-PSP sensors.

Temperature Effects on Polymer-Ceramic Pressure-Sensitive Paint as a Luminescent Pressure Sensor

Polymer-ceramic pressure-sensitive paint (PC-PSP) has been used for capturing unsteady pressure over aerodynamic surfaces. Spatial and temporal pressure information is calculated from the luminescent intensity produced by a PC-PSP, which provides a nonintrusive pressure measurement. Despite its benefits, the temperature dependency of PC-PSP makes extraction of quantitative pressure data challenging. The temperature dependency in terms of the static and dynamic characteristics of a ruthenium-based PC-PSP is studied herein. The impact of temperature dependency on PC-PSP characteristics is also discussed in the context of an unsteady pressure measurement.

Pressure distributions on swept/unswept wings using pressure sensitive paint

Pressure sensitive paint (PSP) is an optical-based technique for full-field pressure measurements. A polymer-ceramic PSP, Ru(dpp), with a porous material is used and is applied onto a Mylar tape which affixed to the model surface of NACA 0012 and ONERA M6 wings. The PSP results agree with the data using conventional pressure measurements reasonably well.

Synthesis of an oxygen-permeable block copolymer with catechol groups and its application in polymer-ceramic pressure-sensitive paint

An oxygen-permeable block copolymer, poly (2,2,2-trifluoroethyl-co-isobutyl methacrylate)-b-poly (N-acryloyldopamine) (FEM-b-PDOPA), in which the PDOPA segment acts as an adhesive section to attach TiO2 nanoparticles, was successfully synthesized via RAFT polymerization followed by a post-polymerization modification with dopamine. Conjugates of FEM-b-PDOPA with TiO2 nanoparticles were prepared by mixing them in chloroform and methanol. IR and solid-state CP-MAS 13C NMR spectroscopies clearly indicated the presence of FEM on the TiO2 nanoparticles. Thermogravimetric analysis of the resulting nanoparticles indicated that FEM-b-PDOPA, rather than FEM alone, was tightly bound to the TiO2 nanoparticles, and that the weight fraction was 2.5 wt%. Polymer-ceramic pressure-sensitive paint was prepared by mixing a luminescent dye, FEM, and TiO2 treated with either FEM-b-PDOPA or native TiO2. In comparison with the coating prepared using native TiO2, the pretreatment of TiO2 with FEM-b-PDOPA effectively reduced the photodegradation of the luminescent dye without deterioration in pressure and temperature sensitivity or dynamic response performance.

Construction of bi-layer biluminophore fast-responding pressure sensitive coating for non-contact unsteady aerodynamic testing

Abstract Herein we report on a biluminophore fast-responding pressure sensitive coating with a bi-layer structure prepared by a non-sensitive reference base paint and subsequently a classic polymer-ceramic pressure sensitive paint (PSP). The coating procedure is fully sprayable and allows the separation of the two luminophores in each layer to prevent their interference that may affect the pressure responsibility. The major advance is the use of sol-gel process of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) to make the bottom reference layer which ensures the spreading and affinity of the top PSP, composed of a room-temperature vulcanizing silicone rubber (RTV), so that very thin PSP layer, i.e. less than 5 μm, was achieved. Besides, silane-functionalized carbon dots (CDs) was selected as the reference probe, for it could be well-incorporated with the TEOS/MTES matrix, and gained high loading level and hence strong luminescence of the basecoat to overcome the attenuation effect of the top PSP layer. The resultant biluminophore bi-layer fast-responding PSP (denoted as Fast bi-PSP) showed two completed separated emissions with λmax at 430 and 600 nm for the incorporated CDs and the oxygen sensitive ruthenium complex dye, which enables the utility of intensity ratio from blue and red luminescence for the measurement of surface pressure by following Stern-Volmer relationship. Using a shock tube, the response time of the Fast bi-PSP coating was determined to be 0.4–0.6 ms according to the chemical composition. The ability of the coating for monitoring the dynamic evolution of full-field surface pressure was demonstrated on sample plates at attack angles of 0° and 5°. Our work suggests a facile but efficient way for the future design of self-referenced photoluminescent non-contact surface pressure sensing systems.

Effects of solvents for luminophore on dynamic and static characteristics of sprayable polymer/ceramic pressure-sensitive paint

Polymer/ceramic pressure sensitive paint (PC-PSP) is an optical fast-responding pressure sensor. PC-PSP consists of a polymer and particles as the material for a porous binder layer, and a pressure-sensitive luminophore. The solution of the polymer and particles, and then the solution of the luminophore are separately applied to a model surface. The response time of PSP is mainly determined by the thickness and oxygen diffusivity of the binder layer. However, we found that PC-PSP showed the significantly different response time depending on the solvents for the luminophore despite the same total thickness of the binder layer. Therefore, we investigated the effect of solvents in dissolving luminophore on the PC-PSP characteristics including response time, pressure sensitivity, and luminescence lifetime. PC-PSP’s prepared with solvents for luminophore that poorly dissolve the polymer in the binder layer achieved a faster response time of those prepared with solvents that can dissolve the polymer. Furthermore, it was also found that the solvents caused the change in the response time, luminescence intensity and luminescence lifetime of PC-PSP. We have concluded that the different solubility of the solvents may provide the different state of porous structure and the local distribution of luminophore in the binder layer, and it causes the variation of the dynamic and static characteristics of PC-PSP.

Evaluation of the Characteristics and Coating Film Structure of Polymer/Ceramic Pressure-Sensitive Paint.

Polymer/ceramic pressure-sensitive paint (PC-PSP), which incorporates a high percentage of particles in the binder layer, is proposed in order to improve the characteristics of PSP. The procedure for embedding particles into the binder layer was modified. In the conventional procedure, dye is adsorbed onto a polymer/ceramic coating film (denoted herein as a dye-adsorbed (D-adsorbed) PSP). In the new procedure, the mixture of a dye and particles is adsorbed onto a polymer coating film (denoted herein as the particle/dye-adsorbed (PD-adsorbed) PSP). The effect of particle mass content on PSP characteristics was investigated. In addition, the effect of solvent on PSP characteristics and film structure were evaluated for the PD-adsorbed PSP. As a result, the difference in the PSP characteristics between the two types of PSP was clarified. Although surface roughness and time response increase with increased mass content of particles for both D- and PD-adsorbed PSPs, the critical pigment volume concentration (CPVC) for the PD-adsorbed PSP is smaller than that of the D-adsorbed PSP (88 wt% and 93 wt%, respectively). The PD-adsorbed PSP has a higher frequency response comparing with the D-adsorbed PSP while maintaining the same surface roughness. Observation by scanning electron microscope showed that the CPVC of the PC-PSP is governed primarily by surface structure. The coating film structure can be roughly classified into two states depending on the particle mass content. One is a state in which the coating film consisted of two layers: a lower particle-rich layer and an upper polymer-rich layer. This type of structure was observed in the PD-adsorbed PSP as well as in the D-adsorbed PSP. In the other state, polymer and particles are homogeneously distributed in the film, and pores are formed. This difference in the coating structure results in a change in the time response.

Dynamic and Steady Characteristics of Polymer-Ceramic Pressure-Sensitive Paint with Variation in Layer Thickness.

Polymer-ceramic pressure-sensitive paint (PC-PSP) has been investigated as a surface-pressure sensor for unsteady aerodynamics and short duration measurements. This PSP provides a fast response to a change in pressures with a spray-coating ability. Because it is sprayed onto an aerodynamic surface, the thickness of PC-PSP may play an important role in determining the performance of this sensor. The thickness of other fast PSPs, such as anodized aluminum pressure-sensitive paint, is a major factor in determining its performance. We vary the thickness of PC-PSP from 10 to 240 μm in order to study its effects on PSP measurement characteristics including time response, signal level, pressure sensitivity, and temperature dependency. It is found that the thickness does affect these characteristics. However, a thickness over 80 μm provides uniform performance in these characteristics.

Step Response Characteristics of Polymer/Ceramic Pressure-Sensitive Paint.

Experiments and numerical simulations have been used in this work to understand the step response characteristics of Polymer/Ceramic Pressure-Sensitive Paint (PC-PSP). A recently developed analytical model describing the essential physics in PC-PSP quenching kinetics is used, which includes the effect of both diffusion time scale and luminescent lifetime on the net response of PC-PSP. Step response simulations using this model enables an understanding of the effects of parameters, such as the diffusion coefficient of O2 in the polymer/ceramic coating, attenuation of excitation light, ambient luminescent lifetime, sensitivity, and the magnitude and direction of pressure change on the observed response time scales of PC-PSP. It was found that higher diffusion coefficient and greater light attenuation lead to faster response, whereas longer ambient lifetime and larger sensitivity lead to slower response characteristics. Due to the inherent non-linearity of the Stern-Volmer equation, response functions also change with magnitude and direction of the pressure change. Experimental results from a shock tube are presented where the effects of varying the roughness, pressure jump magnitude and luminophore probe have been studied. Model parameters have been varied to obtain a good fit to experimental results and this optimized model is then used to obtain the response time for a step decrease in pressure, an estimate of which is currently not obtainable from experiments.

Luminophore Application Study of Polymer-Ceramic Pressure-Sensitive Paint

A polymer-ceramic pressure-sensitive paint (PC-PSP) is a fast responding and sprayable PSP which has been applied for capturing global unsteady flows. The luminophore application process is studied to enhance the characterization of the PC-PSP. A dipping deposition method is used to apply a luminophore on a polymer-ceramic coating. The method selects a solvent by its polarity index. The characterization includes the signal level, pressure sensitivity, temperature dependency, and response time. It is found that the luminophore application process affects the steady-state characterizations, such as the signal level, pressure sensitivity, and temperature dependency. A range of change for each characterization, which is based on the minimum quantity, is a factor of 4.7, 9, and 3.8, respectively. A response time on the order of ten microseconds is shown. The application process is not a dominant factor for changing the response time, which is within the uncertainty of the thickness variation. Comparisons of the effects on the luminophore application process and the polymer content are made to discuss the PC-PSP characterization results.

Comparison of Unsteady Pressure-Sensitive Paint Measurement Techniques

The current work focuses on the development and application of fast-responding polymer/ceramic pressure-sensitive paint (PSP) as an advanced surface pressure measurement technique for unsteady flow fields in large-scale wind tunnels. Three different experimental methods for acquiring quality PSP data are discussed: phase-averaging, realtime data acquisition using a high-speed camera, and single-shot lifetime. The three techniques are all demonstrated on a benchmark test case, resolving the unsteady surface pressure distribution on a hemispherical dome tested in the United States Air Force Research Laboratory’s Trisonic Gasdynamics Facility. The hemispherical dome was tested at a freestream Mach number of 0.6 with a total pressure of 1500 psf, where the Reynolds number was 2.4x10. At this flow condition, a predominant shear layer oscillated at 400 Hz over the test model, causing pressure fluctuations on the aft portion of the model. An assessment of the three techniques is presented, with the strengths and disadvantages for each technique evaluated through example.

Characterization and Optimization of Polymer-Ceramic Pressure-Sensitive Paint by Controlling Polymer Content

A pressure-sensitive paint (PSP) with fast response characteristics that can be sprayed on a test article is studied. This PSP consists of a polymer for spraying and a porous particle for providing the fast response. We controlled the polymer content (%) from 10 to 90% to study its effects on PSP characteristics: the signal level, pressure sensitivity, temperature dependency, and time response. The signal level and temperature dependency shows a peak in the polymer content around 50 to 70%. The pressure sensitivity was fairly constant in the range between 0.8 and 0.9 %/kPa. The time response is improved by lowering the polymer content. The variation of the time response is shown to be on the order of milliseconds to ten seconds. A weight coefficient is introduced to optimize the resultant PSPs. By setting the weight coefficient, we can optimize the PSP for sensing purposes.

Application of fast-responding pressure-sensitive paint to a hemispherical dome in unsteady transonic flow

The current work focuses on the development and application of fast-responding polymer/ceramic pressure-sensitive paint (PSP) as an advanced surface pressure measurement technique for unsteady flow fields in large-scale wind tunnels. To demonstrate the unsteady PSP technique, the unsteady surface pressure distribution over a hemispherical dome placed in the United States Air Force Research Laboratory’s Trisonic Gasdynamics Facility (TGF) was studied by phase-locking to the characteristic frequency in the flow caused by an unsteady separated shear layer shed from the dome. The wind tunnel was operated at stagnation pressures of 23.92 and 71.84 kPa, with the test section flow at Mach 0.6. Under the two operating conditions, the predominant shear layer frequency was measured to be 272 and 400 Hz, respectively. The quasi-periodic shear layer frequency enabled a phase-averaged method to be employed for capturing the unsteady shock motion on the hemisphere. Unsteady pressure data resulting from this technique are shown to correlate well with measurements acquired by conventional measurement techniques. Measurement uncertainty in the phase-averaging technique will be discussed. To address measurement uncertainties from temperature sensitivity and model movement, a new implementation of an AC-coupled data representation is offered.