Ideality of pressure-sensitive paint. III. Effect of the base-coat permeability on the luminescence behavior of the sensing layer

The response time and temperature dependence of a pressure-sensitive paint (PSP) based on platinum tetra(pentafluorophenyl)porphine (PtTFPP) in the fl uoroacrylic polymer FIB significantly increases for bilayer paint systems t hat include a base coat made of different polymers with solid TiO2 added as scattering agent, compared to the single-layer sensor paint. The temperatu re dependencies at vacuum are the same in the various bilayer coatings (pai nt/base coat) as compared to monolayer paint, roughly -0.53%/degrees C. Wit h FIB base coat the percent of TiO2 is adjusted to reduce photodegradation, in which case only a slight increase in response time (0.6 --> 0.8 s) is c aused by the base coat and there is almost no change in temperature depende nce at 1 atm. However, in the cases of the less permeable polymers, poly(me thylmethacrylate) (PMMA) and poly(vinyl acetate) (PVA), there is increased response time of the bilayer coating (rising, respectively, to 15 and 7 s) and significantly greater temperature dependence at 1 atm. The highly imper meable polyacrylonitrile (PAN) as base coat shows little effect on response time but a somewhat higher temperature dependence at 1 atm compared to vac uum. For the highly permeable polydimethylsiloxane (PDMS), adjustment of th e TiO2 concentration is needed to prevent an increase in temperature depend ence but both PDMS base coats tested have response times < 2 s and low-temp erature dependence. (C) 2000 John Wiley & Sons, Inc.