Self-assembled copolymeric nanoparticles as chemically interactive materials for humidity sensors.

Chemical interactive materials (CIM), based on poly(methylmethacrylate-co-bis(benzocyclobutene)) P(MMA-co-BCB) and poly(styrene-co-bis(benzocyclobutene)) P(S-co-BCB) nanoparticles, have been prepared through modified emulsion technique. Experimental conditions, in particular the co-monomer ratio and reaction time, have been tuned to modulate nanoparticles' dimension and optimize their monodispersity. Resistive relative humidity (RH) sensors based on self-assembled copolymeric nanoparticles, cast deposited onto metal interdigitated electrodes (Al, Au, Cr), have been fabricated. The electrical response and the devices' stability have been studied in the range 10-90% RH. Applying 1 V to interdigitated electrodes, a variation of four orders of magnitude, from 10(-12) to 10(-8) A, has been observed and a response time of 130 s has been calculated. Response reproducibility and stability have been tested in subsequent cycles of measurements (working times as long as two days and after six months), confirming the stable performance of the CIMs. Copolymeric nanoparticle assembly has also been studied by quartz microbalance (QMB) devices, where phase shift occurred, by varying RH in the range 10-90%. The CIM coated device shows a sensitivity of about 30 Hz/% (at 10-70% RH), that rapidly increases up to about 2000 Hz/% at 90% RH. The results give evidence for versatile applications of P(MMA-co-BCB) and P(S-co-BCB) nanoparticles for sensing applications.