Effect of small molecule hydrogen-bond crosslinker and solvent power on the electrospinnability of poly(4-vinyl pyridine)

Abstract

The fabrication of electrospun fibers generally requires relatively concentrated solutions to have sufficient chain entanglements acting as physical crosslinks during the electrospinning process. We propose a supramolecular approach to diminish the necessary concentration. To this end, we investigated the use of a small hydrogen-bond effective crosslinker, 4,4′-biphenol (BiOH), on the electrospinning behavior of poly(4-vinyl pyridine) (P4VP) in N,N-dimethylformamide (DMF) and in a mixture of DMF and nitromethane (CH3NO2). Since solution rheology plays a crucial role in the electrospinning process, various solution properties were characterized. Coil dimensions showed expansion with addition of BiOH and contraction with addition of CH3NO2 (a poor solvent). Hydrogen-bond crosslinking in solutions of P4VP/BiOH (equimolar pyridine:hydroxyl) was quantified by attenuated total reflection (ATR) infrared spectroscopy, and was found to increase with increasing P4VP concentration, especially in the mixed solvent. Hydrogen-bond crosslinking and the effect of the poor solvent thus enhance the formation of an effectively crosslinked network. This leads to the earlier onset of the apparent semidilute entangled regime and hence to a lower critical concentration for fiber formation, which decreases by a factor of two. Furthermore, the addition of BiOH leads to the appearance of a clear concentrated regime that enables preparing uniform fibers. Based on this supramolecular strategy for increasing the effective crosslinking network, it is possible to prepare long aligned electrospun fibers without the need for using highly viscous solutions.