Flexible and Transparent Cellulose-Based Ionic Film as a Humidity Sensor.

Area of Science:

• Materials Science
• Sensing Technology
• Nanotechnology

Background:

• Humidity sensors are crucial for environmental monitoring and wearable devices.
• Existing sensors often lack transparency, flexibility, or fast response times.
• Developing advanced materials for humidity sensing remains an active research area.

Purpose of the Study:

• To fabricate a transparent and flexible cellulose/KOH composite ionic film (CKF) for humidity sensing.
• To evaluate the optical, mechanical, and sensing properties of the CKF material.
• To demonstrate the potential of CKF in wearable electronics and real-time moisture detection applications.

Main Methods:

• Fabrication of CKF via a simple soaking-drying process.
• Characterization of optical transmittance, mechanical flexibility, and electrical properties.
• Testing of humidity sensing performance, including response/recovery times, hysteresis, and selectivity to temperature and pressure.
• Assembly and testing of CKF-based sensors for non-contact fingertip moisture and breathing rate detection, and wearable skin moisture monitoring.

Main Results:

• The CKF exhibited high optical transmittance (87.14% at 550 nm) and good flexibility.
• The sensor demonstrated a wide RH detection range (11.3-97.3%) with a large conductance change (>200 times).
• Fast response (6.0 s) and recovery (10.8 s) times, low hysteresis error (0.57%), and high selectivity to temperature and pressure were achieved.
• Successful demonstrations in non-contact moisture detection, breathing rate monitoring, and wearable skin moisture detection.

Conclusions:

• The fabricated CKF is a promising material for transparent, flexible, and high-performance humidity sensors.
• The CKF-based sensor offers significant advantages in response speed, selectivity, and low hysteresis.
• The material shows great potential for integrated intelligent wearable equipment and real-time human skin moisture monitoring.