Probing the Viscoelastic Property of Pseudo Free‐Standing Conjugated Polymeric Thin Films

Abstract

The understanding of the structure-mechanical property relationship for semiconducting polymers is essential for the application of flexible organic electronics. Herein pseudo free-standing tensile testing, a technique that measures the mechanical property of thin films floating on the surface of water, is used to obtain the stress-strain behaviors of two semiconducting polymers, poly(3-hexylthiophene) (P3HT) and poly(2,5-bis(2-decyltetradecyl)-3,6-di(thiophen-2-yl)diketopyrrolo[3,4-c]pyrrole-1,4-dione-alt-thienovinylthiophene (DPP-TVT) donor-acceptor (D-A) polymer. To our surprise, DPP-TVT shows similar viscoelastic behavior to P3HT, despite DPP-TVT possessing a larger conjugated backbone and much higher charge carrier mobility. The viscoelastic behavior of these polymers is due to sub room temperature glass transition temperatures (T_g ), as shown by AC chip calorimetry. These results provide a comprehensive understanding of the viscoelastic properties of conjugated D-A polymers by thickness-dependent, strain rate dependent, hysteresis tests, and stress-relaxation tests, highlighting the importance of T_g for designing intrinsically stretchable conjugated polymers.