Improving Charge Carrier Mobility of Polymer Blend Field Effect Transistors with Majority Insulating Polymer Phase

The key approach to achieve high performance field effect transistor fabricated from semiconducting/insulating polymer blends with majority insulating polymer phase is the formation of connected fibrous structures of semiconducting polymer and good interfacial interaction of semiconducting polymer with the dielectric layer. Herein, tetrahydrofuran (THF) as a marginal solvent was used as an additive in marginal/good solvent mixtures to control the crystallite structure, phase segregation, and hole transport properties of poly­(3-hexylthiophene)/poly­(styrene) (P3HT/PS; weight ratio: 1/4) blends, with the advantage that marginal/good solvent mixture gives P3HT sufficient time for phase segregation and relatively better solvent quality to aggregate to more stable structures compared to other reported strategies as bad/good solvent mixtures or directly marginal solvents. Incorporation of THF reduces the P3HT solubility, forming connected fibrous structures as observed in both neat P3HT and blend films; it appears these structures are responsible for improved charge transport. Furthermore, enhanced molecular ordering, π–π stacking and conjugation length are observed with increasing THF amount. THF promotes the edge-on orientation and more stable crystal structures in P3HT, while the lattice spacing remains the same. Finally, the added THF increases hole mobility for P3HT/PS blend FETs, reaching a maximum value of 4 0.0 × 10^–3 cm²/(V s) with 20 vol % THF and being comparative to neat P3HT; however, THF has an insignificant influence on the hole mobility for neat P3HT FETs. Morphological characterization supports the idea that differential solubility creates both enhanced chain ordering and vertical phase segregation that both improve FET performance. These results are promising for the development of environmentally stable and lower cost polymer electronics

Melt Processing Pretreatment Effects on Enzymatic Depolymerization of Poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) is a common thermoplastic material, used in a wide variety of applications (i.e., bottles, fabrics, packaging, electronics, and automotive components). Increasing demand for PET has precipitated a need for improved recycling technology, especially for single-use PET waste. Recently, enzymatic depolymerization has shown promise as an environmentally responsible alternative for PET chemical recycling that yields economically useful products (e.g., terephthalic acid, adipic acid, and ethylene glycol). However, the depolymerization system still suffers from low rates on crystalline PET substrates, and effects of realistic waste streams are not known. In our work, PET waste is pretreated using an ultra-high-speed twin-screw extruder system. PET substrates were modified by various processing pretreatments to allow enzymes better access to depolymerize substrate materials. The effect of varying throughput and mechanical shear on structural properties of the PET waste was analyzed using molecular weight and thermal characterizations. These pretreated samples exhibit modifications in molecular weight, glass transition temperature, crystallinity, and specific surface area. The unpurified leaf-branch compost cutinase enzyme produced from the fed-batch fermentation of Escherichia coli BL21(DE3) was used in enzymatic depolymerization, where a faster reaction was observed as crystallinity was decreased and the specific surface area was increased. The rate of terephthalic acid production was also significantly higher for samples processed at lower mechanical shear with higher throughputs. This work demonstrates the potential for tailoring pretreatments in pursuit of faster and more energy efficient PET recycling using enzymes, with facile adaptation to the industrial scale for the circular economy