My Linh Le1,Intanon Lapkriengkri1,Cassidy Tran1,Phong Nguyen1,Rachel Segalman1,Christopher Bates1,Michael Chabinyc1
University of California, Santa Barbara1
My Linh Le1,Intanon Lapkriengkri1,Cassidy Tran1,Phong Nguyen1,Rachel Segalman1,Christopher Bates1,Michael Chabinyc1
University of California, Santa Barbara1
Designing a material that is soft, elastic and conductive for stretchable electronics has remained a major challenge due to the tradeoff between conductivity and mechanical flexibility caused by the high stiffness of conventional conductive materials. In this study, we show that ionic interactions provide an effective pathway to obtain materials with appreciable conductivity and flexibility, while also eliminating many synthetic and processing complications in commonly employed strategies. In particular, a conjugated polyelectrolyte (CPE) was blended with a bottlebrush polymeric ionic liquid (BPIL) whose side chains are oppositely charged. In this design, the CPE provides electrical conductivity, while the BPIL offers a super-soft elastomer matrix for mechanical flexibility. Due to the strong electrostatic attraction between the oppositely charged pendant side chains of the CPE and the BPIL, phase separation was effectively suppressed and the polymers formed a homogeneous blend. The resulting material has a Young’s modulus of 100 kPa, lying well within the range of soft tissues moduli (25 kPa to 140MPa), and is highly stretchable with a tensile strain to break of 400% and an ultimate tensile strength of 800 kPa. Once electronically doped with a strong acid, this polymer blend has an electronic conductivity that was ~ 0.1 S/cm, a comparable value to that of as-cast commercial PEDOT:PSS. Lastly, the ionic interactions physically crosslinked the polymers, forming a network that strained elastically up to 40% strain without any added crosslinkers.