Molecular orientation and solvent affinity in electrospun fibers of miscible blends

The detailed structural characterization of electrospun fibers is crucial for understanding their processing-structure-properties relationships and optimizing their preparation. While many advanced applications of electrospun fibers incorporate multiple components, our current knowledge is predominantly based on one-component fibers, raising questions about its applicability to more complex materials. In this work, we investigate electrospun fibers composed of miscible blends of polystyrene (PS) with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) to identify the key factors that impact their structure. Confocal Raman microscopy is employed to quantify the molecular orientation of PS and PPO at the single fiber level. The results reveal that PPO is much more oriented than PS at all compositions, with a widening gap as the PPO content increases. This unexpected behavior for a miscible blend coincides with a broadening of the glass transition, attributed to increased composition fluctuations at higher PPO content. The results suggest that a difference in solvent affinity between the two polymers, where PPO is less solvated than PS, reduces the relaxation of PPO and promotes that of PS, especially at high PPO content. This work demonstrates that electrospun fibers of miscible blends do not behave as a mere average of the properties of their constituents. Instead, the relative polymer-solvent affinity emerges as a central factor shaping their molecular organization. • Molecular orientation in electrospun PS:PPO fibers deviates from expectations. • PPO orientation is high and rises with PPO content; PS orientation is negligible. • The orientation gap correlates with composition fluctuations in the miscible blend. • PPO's lower solvent affinity hinders relaxation and increases its orientation. • Relative polymer-solvent affinity is key to shaping the structure in binary fibers.