Electrostatic Complexation of Conjugated and Bottlebrush Polyelectrolytes Forms Printable, Conductive Inks

Electrostatic complexation of polyelectrolytes is a versatile and powerful method for forming blends of polymers that would phase-separate without the presence of ionic groups. Mixing solutions of oppositely charged polyelectrolytes can lead to liquid-liquid phase separation, providing a polymer-dense phase that allows electrostatic complexes to be readily processed. The design rules for forming electrostatic complexes of functional polyelectrolytes, processable by direct ink writing, were examined using conjugated polyelectrolytes, which provide electrical conductivity, and bottlebrush polyelectrolytes, which provide control of mechanical properties. Water-soluble conjugated polyelectrolytes based on sulfonated poly(3-alkylthiophene) and poly(3,4-ethylenedioxythiophene) were examined. The sulfonated poly(3,4-ethylenedioxythiophene) is electrically self-doped in water, while the sulfonated poly(3-alkylthiophene) remains electrically neutral. The influence of the resulting charge fraction of the ionic groups on electrostatic compatibilization, printability, and the resulting electrical and electromechanical properties of complexes with a model bottlebrush polyelectrolyte were examined. In both cases, the rheological behavior of the complex allowed for direct ink writing into thick, patterned structures. The dried complexes show sufficient electrical conductivity, paired with stretchability and adhesive properties, for applications in organic electronics requiring thick semiconducting materials, such as bioelectronic sensors and conductive adhesives.