Molecularly engineered copolyimide film for capacitive humidity sensor

We present a capacitive humidity sensor with molecularly engineered polyimide (PI) sensing layer. Molecularly engineered PIs were successfully prepared by synthesizing polyamic acids (PAAs) through blending of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA), and 4,4-(hexafluoroisopropylidene) diphthalic anhydride (6-FDA) as monomer, followed by thermal imidization, respectively. The molecularly engineered PIs exhibited high thermal stability as well as controllable water uptake properties. Capacitive performances of the humidity sensor with PIs were efficiently increased via simple molecular blending.