Electrical and Mechanical Properties of PCDTPT/SEBS Blend Films Driven by SEBS Microphase-Separated Structures and Component Concentrations

Polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) is a commonly used elastomer for blending with conjugated polymers (CPs) to improve their electrical and mechanical performance. However, the effects of the microphase-separated structures of SEBS and the component concentrations on the performance of the CP/SEBS blend films remain unclear. Here, a brittle poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b′]dithiophen-2-yl)-alt-[1,2,5]thia-diazolo[3,4-c]pyridine] (PCDTPT) semiconductor was chosen for blending with SEBS. The equal-concentration and variable-concentration mixing methods were used to finely tune the component concentrations at a fixed weight ratio of PCDTPT/SEBS and to maintain the total concentration variation of the PCDTPT/SEBS blend solution within a narrow range. The PCDTPT/SEBS blend films fabricated by the variable-concentration mixing method exhibit optimized SEBS microphase-separated structures. These structures reduce the surface energy difference between SEBS and PCDTPT, thereby enhancing the long-range molecular order of PCDTPT for efficient charge transport while simultaneously forming interpenetrating networks with reduced phase domain sizes to facilitate effective stress dissipation. As a result, these PCDTPT/SEBS blend films demonstrate greater conductivity (charge carrier mobility) and crack onset strain (COS) than those prepared by using the equal-concentration mixing method. Once the optimal microphase-separated structure is determined, finely tuning the component concentration can further influence the electrical and mechanical performance of the PCDTPT/SEBS blend. This work highlights the critical roles of block copolymer elastomer microphase-separated structures (and their associated surface energies) in optimizing the microstructures and performance of CP/elastomer blend films. Furthermore, this study provides key insights into elastomer modulation strategies, including microphase-separated structure control and component concentration tuning, for developing stretchable semiconducting thin films with both superior mechanical durability and high electrical performance.