Engineering Soft, Elastic, and Conductive Polymers for Stretchable Electronics Using Ionic Compatibilization

Designing materials that are soft, elastic, and conductive-a complement of properties that are useful in a number of applications such as bio-interfacing-remains a major challenge due to the high stiffness of conventional conductive materials. For all-polymer systems, this problem is compounded by the general immiscibility of elastomeric and conducting polymers, resulting in inhomogeneous mixing and poor properties. Here, electrostatic interactions are shown to be an effective strategy to compatibilize distinct polymer chemistries and backbone architectures, resulting in homogeneous and multifunctional polymer complexes that are soft, elastic, and highly conductive. An anionic conjugated polyelectrolyte (CPE) based on polythiophene was blended with a cationic bottlebrush polyelectrolyte (BPE). The CPE provided electrical conductivity, while the BPE helped to control the mechanical properties. Strong electrostatic attractions between oppositely charged side chains of the CPE and BPE suppressed phase separation and the polymers formed a nearly homogeneous charged complex despite marked differences in their chemistry and architecture. Upon drying of the solvent, the ionic groups act as dynamic crosslinks and the resulting material behaved as a viscoelastic and reprocessable solid. Once doped with a strong acid, this composite had an electrical conductivity of up to 0.3 S/cm while maintaining a low tensile modulus (0.2 MPa). These findings highlight the potential of designing advanced materials with processing and performance advantages through the use of electrostatic interactions to compatibilize polymers.