(668b) Poly (ethylene oxide) (PEO) Nanofiber Design Space Using Spinneret-Based Tunable Engineered Parameters (STEP) Technique

Poly(ethylene oxide) (PEO) nano fibers as 1D building blocks in polymeric composites have potential applications in tissue engineering, pharmaceuticals and structural components. Furthermore, addition of PEO improves the spinnability of otherwise difficult to spin bio-polymeric systems like chitosan and silk. However, a comprehensive design strategy to increase the spinnability of polymer systems using PEO as an additive is currently missing due to incomplete knowledge on spinnability of stand-alone PEO system.  Currently state-of-the-art fiber manufacturing platforms of electrospinning, template synthesis, and phase separation are capable of depositing fibers of different polymers. However, depositing smooth, uniform diameter fibers of sizeable length in aligned configurations has been challenging using aforementioned techniques  In this respect, we have recently reported the pseudo-dry spinning based STEP technique, which deposits aligned polymeric fibers with control on fiber dimensions (diameter: sub 100nm-micron, length: mm-cm) in single and multiple layers at tunable porosity. Using the STEP technique, this study explores the design space of PEO fibers for achieving control on fiber diameter by varying the molecular weight, solution concentration and solvent (i.e. ethanol) concentration in water. We also demonstrate fabrication and tensile strength characterization of PEO fibers’ bundles composed of approximately fifty thousand of PEO individual nanofibers, which can then be used as 1D structural component in a hierarchical composite design. PEO of M_w 100K (g. mol^-1), 400K (g. mol^-1), and 900K (g. mol^-1) (Scientific Polymer Products, USA), were dissolved without further purification in deionized water/ethyl alcohol (Decon labs, Inc, USA) in varying concentrations. PEO was dissolved in ethanol solution (wt.-% of 20-80%) at wt.-% concentrations ranging from 3-12% and used to explore the diameter design space. Bundles were made by using PEO (M_w 400 000) dissolved in 70% ethanol solvent with 6 %( w/w) PEO concentration. Bare fibers’ bundles were braided at different twist turns (3, 6, 9, and 12) using an in-house custom braiding device. The effect of strain rate on tensile behavior and fracture mechanisms is observed at varying rates of 1mm/s, 2.5 mm/s, and 5 mm/s. The tensile strength increases gradually with increasing twist angle and peaks at 6 twists compared with parallel fibers bundles, and decreases with further increase in twist angle.  Strain rate variation effects (1-5 mm/s) on tensile properties for 6 twists of 6% PEO (M_w 400K (g. mol^-1)) fibers’ bundles resulted in a 33.8% increase of tensile loads and 30.8% decrease of ultimate strain. It is envisioned that the fiber design space of PEO presented in this study will help in integration of PEO in polymeric systems with defined properties, thus, leading to improved spinnability and increased applications.