A Capacitive‐Type Humidity Sensor Using Cross‐Linked Poly(methyl methacrylate) Thin Films

A capacitive‐type humidity sensor was prepared using cross‐linked poly(methyl methacrylate) (PMMA). The electrical capacitance changed linearly with the relative humidity over the range of 10–90% RH and the sensitivity (the ratio of capacitance at 90% RH to that at 10% RH) was about 1.13. The amount of sorbed water on PMMA at 90% RH was 25 mg/g which was one‐third of that on cellulose acetate butyrate. This low hygroscopicity of PMMA was effective in reducing any hysteresis. The decrement of temperature coefficient and high durability for acetone vapor were achieved using the cross‐linked PMMA film with divinyl benzene or ethylene glycol dimethacrylate as the cross‐linking agent.