Flexible and Transparent Polymer-Based Optical Humidity Sensor

Abstract

Thin spin-coated polymer films of amphiphilic copolymer obtained by partial acetalization of poly (vinyl alcohol) are used as humidity-sensitive media. They are deposited on polymer substrate (PET) in order to obtain a flexible humidity sensor. Pre-metallization of substrate is implemented for increasing the optical contrast of the sensor, thus improving the sensitivity. The morphology of the sensors is studied by surface profiling, while the transparency of the sensor is controlled by transmittance measurements. The sensing behavior is evaluated through monitoring of transmittance values at different levels of relative humidity gradually changing in the range 5–95% and the influence of up to 1000 bending deformations is estimated by determining the hysteresis and sensitivity of the flexible sensor after each set of deformations. The successful development of a flexible sensor for optical monitoring of humidity in a wide humidity range is demonstrated and discussed.

Advances in Humidity Nanosensors and Their Application: Review

“…In recent years, flexible and wearable sensing devices have been of great interest due to their unique characteristics such as portability, endurance, light weight and the combination with the IoT environment-monitoring concept [ 82 , 83 ]. Another superior characteristic of polymer-based humidity sensors is compatibility with other sensing materials.…”

“…Another superior characteristic of polymer-based humidity sensors is compatibility with other sensing materials. By integrating a sensing material onto a polymer substrate such as cellulose [ 84 , 85 , 86 , 87 , 88 , 89 , 90 ] or PET [ 82 , 91 ] using the PVD, CVD or solution methods, it is able to enable the high-strength materials to achieve flexible characteristics. Table 2 lists several different sensing materials with polymer-based substrates [ 82 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 ].…”

“…By integrating a sensing material onto a polymer substrate such as cellulose [ 84 , 85 , 86 , 87 , 88 , 89 , 90 ] or PET [ 82 , 91 ] using the PVD, CVD or solution methods, it is able to enable the high-strength materials to achieve flexible characteristics. Table 2 lists several different sensing materials with polymer-based substrates [ 82 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 ]. The semiconductor, graphene oxide and ceramic materials were integrated on PET, cellulose, cellulose nanofibers (CNF), cellulose nanocrystals (CNC), or carboxymethyl cellulose (CMC) for flexible and portable devices.…”

Review of Optical Humidity Sensors

“…The dynamic range is 40%RH–80%RH. Katerina Lazarova et al [ 195 ] reported the use of amphiphilic poly(vinyl alcohol-co-vinyl acetal) copolymer, where a gold or palladium layer is deposited onto a flexible substrate such as polyethylene terephthalate, followed by spin coating polymer overlayer. The functional composite coating swells in response to increasing RH and changes the transmittance of light.…”

Highly Sensitive and Ultra-Responsive Humidity Sensors Based on Graphene Oxide Active Layers and High Surface Area Laser-Induced Graphene Electrodes

“…Up to now, many different transduction methods have been explored, including capacitance [ 5 ], resistance [ 6 ], optical fibers [ 7 ], field effect transistors [ 8 ], and quartz crystal microbalance [ 9 ]. Many materials have been explored as humidity sensing layers to develop devices displaying high sensitivity, a good linear range, a fast response, and fast recovery times, such as carbon nanotubes [ 10 ], metal oxides [ 11 ], polymers [ 12 ], and graphene-like materials [ 13 ]. Among graphene-like materials, graphene oxide (GO) has been one of the most investigated materials.…”