Application of polymethyl[4-(2,3-difluoro-4-hydroxyphenoxy)butyl] siloxane in surface acoustic wave gas sensors for dimethyl methylphosphonate detection

Abstract

The application of polymethyl[4-(2,3-difluoro-4-hydroxyphenoxy)butyl] siloxane (PMFOS) as a sensor coating in a surface acoustic wave (SAW) gas sensor is presented. PMFOS is a linear polysiloxane functionalized with pendant 4-(2,3-difluoro-4-hydroxyphenoxy)butyl groups, in order to enhance its ability to interact via acidic hydrogen bond formation. The PMFOS sensor was fabricated by deposition of a PMFOS layer onto a 195 MHz SAW resonator by vacuum evaporation. The response of the PMFOS sensor to dimethyl methylphosphonate (DMMP) and triethyl phosphate (TEP), commonly-used nerve CWAs simulants, was investigated, and directly compared with another sensor containing hydrogen bonding acidic polysiloxane-polymethyl [3-(1,1,1,3,3,3-hexafluoropropan-2-ol)propyl]siloxane (PLF). This comparative study shows that both sensors demonstrate similar selectivity toward basic vapor, as well as similar sensitivity and limit of detection for DMMP. However, the investigation of the influence of humidity on DMMP sensing revealed the superior humidity resistance of the PMFOS sensor. This is a significant advantage, as the loss of sensitivity in humid air toward nerve CWAs is one of the biggest drawbacks of commercial gas analyzers based on SAW devices.