Progress on polymer-based materials and composites for humidity sensors applications: Materials aspects to sensor performances

Abstract

Modern life is greatly facilitated by sensor technology, which improves both our comfort and efficiency. In particular, humidity sensors are useful because of the many ways in which they impact our daily life. Humidity sensors can ascertain humidity levels in various sections of an object or in distinct places. The sensing material is a critical component of the device, as it detects humidity. The ability to detect humidity levels in any of the materials varies according to their unique properties. Polymers and polymer-based compounds are widely used as sensing elements in humidity sensors because of their unique properties such as water absorption, flexibility, hygroscopicity and high surface area, which are more favorable for Grotthuss mechanism in humidity sensor operation (H2O + H3O+ = H3O+ + H2O). This comprehensive review presents an in-depth examination of polymer and polymer composite materials employed as sensing elements in humidity detection applications. This review highlights the significance of polymers in the context of blending, cross-linking, co-polymerization, composites, and coatings. This review presents an overview of four main kinds of humidity sensors utilizing polymer-based materials: (i) polymer and polymer blend; (ii) polymer-based composite with inorganic materials; (iii) polymer-based composite with organic materials and metal-organic frameworks (MOF); and (iv) MOF, covalent organic frameworks and metallo-supramolecular polymers as a sensing material. To improve polymers and polymer-based combinations for humidity sensor applications, we have also pointed out possible research directions and obstacles.