Fabrication of carbon black–polymer composite sensors using a position-selective and thickness-controlled electrospray method

A shadow-masked electrospray method was used to fabricate a high performance carbon black–poly(vinyl pyrrolidone) (CB–PVP) composite sensor on a position-selected area of a sensor substrate. This new approach, when compared to the common drop-casting method, was shown to be much advantageous for the preparation of an active layer with optimum average thickness and porous microstructure, which is important to obtain high sensitivity and fast detection times. The thickness obtained was proportional to the electrospray scan number, and the field-assisted generation of small droplets led to the formation of rough, porous microstructures. The CB content-dependent variation in sensor resistance exhibited percolation behavior with an abrupt decrease in the specific middle region with increasing CB content. The most sensitive methanol detection was observed for sensors with slightly larger CB content rather than that of the most rapidly varying midpoint in a percolation curve, which was probably due to increased susceptibility to noise resulting from high porosity. Polymer concentration was also observed to have a significant effect on sensing properties owing to a change in film morphology: the optimum concentration was approximately 0.25%, at which the conditions were suitable for the formation of a porous, sensitive sensor with a reasonable deposition speed.