Colorimetric and Resistive Polymer Electrolyte Thin Films for Real-time Humidity Sensors

Abstract

We have developed fast responsive, colorimetric and resistive-type polymeric humidity sensors from a series of self-assembled poly(styrenesulfonate-methylbutylene) (PSS-b-PMB) block copolymers with tailored hygroscopic properties. In dry state, the PSS-b-PMB films exhibit hexagonal cylindrical morphology where hydrophobic PMB cylinders are dispersed within a PSS matrix. Under levels of humidity, the PSS-b-PMB thin films self-displayed discernible reflective color changes, covering almost entire visible light regions from violet (RH = 20%) to red (RH = 95%). The sensors also revealed a few orders of magnitude changes in impedance with exposure to humid air by taking advantages of strong polymer electrolytes characteristics. Remarkably, the time to complete the changes in the signals was only a few seconds, as rationalized by good connectivity of the PSS domains and short water diffusion pathways in nanometer scales. Repeated hydration/dehydration tests demonstrated reliable sensor properties, which is in sharp contrast to the poor stability of PSS homopolymer sensors lacking organization.

Humidity Sensors Principle, Mechanism, and Fabrication Technologies: A Comprehensive Review

“…The design configuration of most resistive sensors is based on interdigitated (interdigital) electrodes [97] in which the humidity sensitive films are deposited in between them such that they touch the E1 and E2 electrodes. The platform substrate can be coated either with electrolytic conductive polymers such as salts and acids [98,99] or doped ceramic sensing films [100,101]. In some cases, the film-based sensors are formed by applying both printing techniques e.g., screen or inkjet printing, and coating techniques, e.g., chemical vapour deposition (CVD) methods such as spin coating and dip coating, or vacuum physical vapour deposition (PVD) techniques such as thermal evaporation and cold sputtering [102].…”

Inkjet‐Printable Amphiphilic Polydiacetylene Precursor for Hydrochromic Imaging on Paper

“…[3][4][5][6] Hydrochromic substances bearing amino-coupled fl uorophores also have been employed to determine the presence of water in organic solvents. [ 13,14 ] Sensors of this type emit only weak fl uorescence owing to the occurrence of facile quenching caused by photoinduced electron transfer (PET) from the amine moiety to the fl uorophore.…”

Characterization and Biomimcry of Avian Nanostructured Tissues

“…(nm) water!uptake! (%) For our SMNP films, only 13 % water adsorption in mass can lead to 77 nm color shifts, therefore S is 5.9 nm / 1%, which is much larger than that those reported for polymer electrolyte films (2.2 nm /1%, 195 nm shift in max peak is achieved with 90% water uptake)._ENREF_14 17 With lower water uptake, the SMNP is more likely to avoid structural deterioration after multiple wetting and drying cycles. Relative to 1D multilayer structures, SMNP film doesn't require several types of coating procedures and more importantly, the SMNP film has some porosity between closed packed particles, making it adsorb/desorb water vapor more rapidly than solid films.…”