Effects of Solvents on the Preparation of PLLA/PEDOT:PSS Conductive Polymer Alloy Films

Polymer alloys, formed by blending biodegradable and conductive polymers, offer properties challenging to achieve with a single material, thus garnering significant attention. Among these, Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS), a biocompatible conductive polymer composed of PEDOT doped with PSS, has been extensively researched due to its electrochemical, thermal, and oxidative stability, paving the way for practical applications. In this study, we delve into the preparation process of polymer alloy films comprising PEDOT:PSS and poly(L-lactic acid) (PLLA), a biodegradable polymer. We explore the compatibility of immiscible polymer blends by mixing a PLLA solution in either 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) or dimethyl sulfoxide (DMSO) with a PEDOT:PSS aqueous dispersion. Using a solvent mixture of HFIP and water resulted in separate phase domains of PLLA and PEDOT:PSS, failing to form a cohesive film. However, employing a DMSO and water solvent mixture yielded films with uniformly dispersed PLLA and PEDOT:PSS phases at a microscopic level. We conducted numerical thermodynamic simulations based on Hansen Solubility Parameters (HSP) to elucidate the experimental results and examine the impact of solubility changes during solvent evaporation on polymer precipitation. Our findings demonstrate the feasibility of fabricating alloy films with uniformly dispersed constituent polymer phases by selecting solvents with comparable solubilities for both polymers.