The effect of critical micelle concentration on the amphiphilic species response using P3HT-based organic electrochemical transistors

Abstract

Here, we present a proof-of-concept approach to study the effect of critical micelle concentration on alkyl sulfonate amphiphilic species response using organic electrochemical transistors (OECT) working in the accumulation mode. First of all, the drastic enhancement of the OECT response allows us to estimate the critical micelle concentration of alkyl sulfonate amphiphilic species yielding quite similar values compared to bulk solution conductivity experiments reported in the literature. Above the critical micelle concentration (i.e. 100 mM), the best responsive OECT devices yielded ON/OFF ratios of 30–60, maximum normalized transconductance of and threshold voltage of −V_th = 0.39–0.55 V at V_g = −1.0 V. Our impedance spectroscopy studies performed at ON and OFF modes suggested that, in the presence of a sufficiently strong negative gate voltage (V_g = −1.0 V), not only the sodium counterions are ejected from the interface, but also the amphiphilic molecules from the monolayer probably reverse their orientation and get injected into the P3HT region. In this scenario, the sulfonate groups of the amphiphilic species synchronously induce doping of P3HT thus leading to a drastic enhancement of the channel current above the critical micelle concentration. Our results indicate that OECT devices represent a promising platform to estimate the critical micelle concentration of amphiphilic species but also to study the formation of amphiphilic monolayers of more complex systems of biological interest.