Facile fabrication of flexible PDDA@PANI/PVDF humidity sensor and applications for non-contact monitoring

Flexible humidity sensors play a crucial role in the real-time monitoring of human physiological activities by being integrated with smart terminals, compact medical devices and flexible electronic skins. In this work, a facile fabrication method of a flexible humidity sensor based on a composite material of poly(diallyldimethylammonium chloride) (PDDA) and polyaniline (PANI) using in-situ polymerization and dip-coating techniques was proposed on a microporous poly(vinylidene fluoride) (PVDF) filter membrane substrate. The resulting PDDA@PANI/PVDF-3.50 % sensor demonstrates remarkable sensitivity with a response of up to 5249 % across a humidity range of 11–97 % relative humidity (RH), minimal hysteresis (∼1.2 %), rapid response and recovery times (11 s and 28 s), stable performance under mechanical deformation, and excellent long-term durability. Additionally, the sensor can readily identify three breathing states and detect finger movements as short as 1 mm. The excellent performance is attributed to the hydrophilic modification and synergistic effect of PDDA on PANI chain, and the rich microporous structure of PVDF membrane. This work offers a novel strategy for developing advanced flexible sensors with significant potential in wearable electronic devices for healthcare and human-computer interaction.