On the Rational Design of Mesoporous Silica Humidity Sensors

Abstract

Abstract Mesoporous silica is commonly used as matrix for humidity sensors which operate on the principle of relative humidity (RH)‐dependent water uptake and read‐out by resistance (R) monitoring. Although numerous studies have been dedicated to improving sensitivity with conductive additives, the role of the pore architecture on the sensing behavior has not been systematically investigated so far. Herein, the effects of pore size and porosity on resistive sensing performance in the 0.5–85% RH range are showcased. Across various sensors, a clear correlation is identified between mesopore size and linear RH sensing range. Sensors with larger pores (≈15 nm) exhibit linear response in the 65 to 85% RH range with larger slope (ΔlogR/ΔRH) than sensors with smaller pores (<8 nm). Additionally, increasing porosity while retaining pore size, yields better overall sensor performance across the 15–85% RH range. In particular, a combination of pore size around 15 nm and porosity of 70% showcased a large resistance versus RH response (R0/R ≈ 10000) in the measured range, with quick response and recovery times of 3 and 9 seconds, respectively. These findings may serve as guidelines for developing broad spectrum high performance mesoporous sensors and for sensors specifically engineered to operate in specific RH ranges.

Keywords

• block copolymers
• co‐assembly
• ellipsometric porosimetry
• humidity sensors
• mesoporous thin films
• surfactants