Experimental Investigation of Leaf Wetness Sensing Properties of MoS2 Nanoflowers-Based Flexible Leaf Wetness Sensor

Abstract

To abate crop loss, it is important to explore the plant disease management systems, where leaf wetness sensors (LWS) are widely used. The leaf wetness duration (LWD) extracted from the LWS is related to plant diseases. In this work, we have fabricated the LWS on the polyamide flexible substrate where Molybdenum disulfide (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) is used as the sensing film to explore the leaf wetness sensing mechanism. Further, we have passivated the MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with the help of acrylic protective lacquer (APL) conformal coating (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> + APL), which reduce the interaction of the water molecules with the sensor. Lab measurements indicated that fabricated LWS on the flexible substrate with MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> + APL as the sensing film offers a response of about ≈ 40 000% and ≈ 250%, respectively, at 500 Hz excitation frequency when the entire sensing area is filled with the water molecule. The response time of the MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and APL-coated flexible sensor is about 180 s. Fabricated LWS sensors offer hysteresis of about ± 4% in wetness. Further, we have identified that oxidation of the sulphur in the MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> plays an important role in the leaf wetness sensing mechanism. Furthermore, we understood that MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> when passivated with APL coating, the oxidation effect is reduced and the sensor response is negligible.