Tunable Solubility Parameter of Poly(3-hexyl thiophene) with Hydrophobic Side-Chains to Achieve Rubbery Conjugated Films

Abstract

A highly pi-conjugated nanofibrillar network of poly(3-hexyl thiophene) (P3HT) embedded in polydimethylsiloxane (PDMS) elastomer films on SiO2 dielectrics was facilely developed via solution-blending of an ultrasound-assisted dilute P3HT solution with a PDMS precursor followed by spin-casting and curing. In contrast, simple blending without ultrasonication against the dilute P3HT solution yielded large agglomerates in cast films owing to a great difference in solubility parameter (delta) values (P3HT = 9.5 cal(1/2) cm(-3/2), PDMS = 7.3 cal(1/2) cm(-3/2)). In the ultrasound-assisted 0.1 vol % P3HT solutions, the pi-conjugated polymer could develop crystalline nanofibrils surrounded by nonpolar hexyl side chains with the same delta value as that of PDMS, yielding homogeneously dispersed 10 wt % loaded P3HT/PDMS blend films. Spun-cast P3HT/PDMS blend films could yield high electrical properties in organic field-effect transistor, including mobilities of up to 0.045 cm2 V-1 s(-1) and on/off current ratios of >5 x 10(5), as well as excellent environmental stability owing to the outer PDMS layer.