Organic mixed ionic-electronic conductors are (semi)conducting polymers capable to transport both ions and electronic charges. Compared with inorganic mixed conductors, conducting polymers have gained popularity in applications where flexibility and operation under wet conditions are necessary. These applications include actuators, wearable sensors, and organic electrochemical transistors for bioelectronics. Amongst organic mixed conductors the polyelectrolyte complex poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is by far the most commonly used, yet modifying its properties or function remains challenging. Current approaches to increase the electronic performance to PEDOT:PSS relies on additive blending (e.g., ethylene glycol to increase electronic conductivity). This approach, however, makes it difficult to control structure-property relationships, particularly if additional functionality is needed for a specific application. To address this issue, our group develops diblock polyelectrolyte complexes comprised of PSS blocks tethered to neutral polymer blocks to control the self-assembly and function of PEDOT-based mixed ionic-electronic conductors: block polyelectrolyte complexes. In this presentation, I will focus on our progress toward thermo-responsive mixed ionic-electronic conductors. We synthesized PSS block copolymers with poly(N-isopropylacrylamide) (PSS-<i>b</i>-PNIPAm) by RAFT polymerization. Oxidatively polymerizing PEDOT in this matrix affords PEDOT:PSS-<i>b</i>-PNIPAm as a dark blue homogeneous dispersion in water. Upon heating above the LCST of PNIPAm we observed either the formation of aggregated particles or gelation, depending on the relative ratio of PSS to PNIPAm, and full reversion to a homogeneous solution upon cooling. These observations represent the first example of a stimuli-responsive and conductive polyelectrolyte complex. We believe that these materials could have a major impact on understanding mixed ionic-electronic transport and find applications in injectable conductive hydrogels, soft actuators for robotics, and theranostic devices.

Tuning the performance and functionality of mixed ionic-electronic conductors with block polyelectrolyte complexes

ACS Spring 2022

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