Humidity Sensitive Materials And Sensor Based On Polyelectrolyte

Three kinds of humidity sensitive materials, namely, silicon-containing polyelectrolytes, hyperbranched polycarboxylates and their composites with nano-sized ZnO, and hyperbranched quartemary ammonium salts were prepared and characterized by ¹H-NMR, TGA, SEM, TEM, FT-IR. They were used to construct resistive type and surface acoustic wave (SAW) type humidity sensors by different film-forming methods including electrospinning, dip-coating, electrospraying. Their humidity sensitive properties have been investigated. Moreover, the electrical response to water content in organic solvent of the silicon-containing polyelectrolytes was explored.Resistive-type humidity sensors based on nanofibers of a composite of silicon-containing polyelectrolyte were obtained by electrospinning. Their humidity sensitive properties such as sensitivity, sensing linearity and hysteresis were measured. It was found that the polymer composite nanofibers showed impedance change from 10⁴ to 10⁷Ωwith the increment of relative humidity (RH) from 22 to 97% at room temperature, exhibiting high sensitivity and good linearity ( R² = 0.979 ) on a semi-logarithmic scale. In addition, they exhibited fast and highly reversible response as characterized by small hysteresis (1.6%RH) and short response time (7 s and 19 s for adsorption and desorption, respectively).SAW type humidity sensors were obtained by electrospraying the silicon-containing polyelectrolyte onto the surface of a single-port surface acoustic wave sensor with a resonance frequency of 433 MHz. The effects of concentration of the electrospray solution and electrospray time have been discussed. Preliminary experimental results showed that the humidity sensor had wide detection range from 10% to 97% RH, high sensitivity of 400Hz/%RH, rapid response time (less than 10s) and excellent durability under high humidity.Thin film resistive-type humidity sensors based on hyperbranched polycarboxylates (HBPC) with different alkali metal cations (Li⁺, Na⁺, K⁺) and their composites with ZnO nanorods and ZnO colloids were fabricated by the method of dip-coating. The morphologies of films of HBPC and the composite were investigated by AFM, which revealed uniform distribution of nano-sized ZnO in HBPC. It was found that the type of cations greatly affected the humidity sensing behaviors of HBPC. Moreover, the nanocomposites of HBPC and ZnO exhibited smaller hysteresis and faster response as compared to HBPC alone.Thin film resistive-type humidity sensors based on hyperbranched quaternary ammonium salts materials were constructed by the method of dip-coating. It was revealed that the sensor exhibited excellent humidity sensitive properties: wide humidity detection range (5-96%RH), small hysteresis (1.1%RH), fast response (absorption time:8 s, desorption time:9 s) and good sensing sensitivity . In comparison, the typical humidity sensitive materials of linear quaternary ammonium salts (PDMAEM-BB ) exhibited narrower humidity detection range (20-96%RH), while the salt doped polymer ( PEO/LIClO₄) showed large hysteresis (5.3%RH) and slow response (absorption time: 39s, desorption time: 118s)The electrical response of silicon-containing polyelectrolyte to water content in different organic solvents was explored, including sensitivity, detection limit, hysteresis, dynamic sensing behaviors and durability.