Hydrophobic monolayer coating on anodized aluminum pressure-sensitive paint

Hydrophobic mono-coated anodized aluminum paint (AA-PSP) is developed to reduce water adsorption from a test gas. AA-PSP is a fast responding global pressure sensor, consisting of a pressure sensitive probe (luminophore) on a porous supporting matrix of anodized aluminum. Water adsorption on this sensor is one of the major factors of the measurement uncertainty. Hydrophobic monocoating of alkanoic acids is applied on AA-PSP by using self-assembled monolayer technique. Alkanoic acids are selected by their carbon chain lengths as six (hexanoic acid), 12 (dodecanoic acid), and 14 (myristic acid). Hydrophobic mono-coated AA-PSPs greatly reduce the luminescence change by water adsorption from a test gas by maximum 54%. Steady-state characteristics of pressure sensitivity and temperature dependency are improved by applying dodecanoic acid and myristic acid on AA-PSP as hydrophobic substrates. AA-PSP with dodecanoic acid improves the pressure sensitivity by 26% from AAPSP without hydrophobic monocoating. There is an order of magnitude improvement in temperature dependency by applying myristic acid compared with that of non-hydrophobic mono-coated AA-PSP. Even though the steady-state characteristics are improved, response time increases because of a reduction in pore size by hydrophobic monocoating. The slowest response time of 150 μs obtained from AA-PSP with myristic acid is a factor of three greater than that of AA-PSP without hydrophobic monocoating. Results tell that a longer hydrophobic substrate gives better hydrophobic and steady-state characteristics but reduces the time response.