Hydrophobic nanocellulose/graphene aerogels via synergistic structural regulation and surface functionalization for high-performance piezoresistive sensing.

Cellulose-based aerogels have been widely employed in flexible sensing applications. However, their inherent hydrophilicity and poor compressive toughness severely limit long-term stability in humid environments. To address this, a composite aerogel piezoresistive sensor with high elasticity, sensitivity, and moisture resistance was developed. Specifically, TEMPO-oxidized cellulose nanofibers (TOCN) served as the structural scaffold, and electrochemically exfoliated graphene (EG) was introduced as the conductive filler. An anisotropic layered porous architecture was constructed via bidirectional freezing and subsequently modified with methyltrimethoxysilane (MTMS) through chemical vapor deposition (CVD). The lamellar network provided a robust mechanical foundation, while MTMS treatment increased the water contact angle from 40° to over 135°, effectively blocking moisture intrusion. At an EG loading of 3 wt%, a high sensitivity of 4.26 kPa-1 was achieved, with response and recovery times of 50 ms and 70 ms, respectively. After 50 compression cycles at 50% strain, compressive strength retention exceeded 80%, and recovery rate surpassed 95%. No significant signal degradation was observed after 10,000 cycles at 860 Pa. Notably, stable signal output was maintained over a relative humidity (RH) range of 33%-85%, avoiding signal drift caused by moisture absorption in traditional cellulose-based sensors. Reliable performance was demonstrated in high-humidity environments, providing a viable strategy for high-performance flexible piezoresistive sensors with promising potential for electronic skin applications.