Effects of different ionic liquids on the electrospinning of a polyacrylonitrile polymer solution

Abstract

Additives have been proven to be useful in improving electrospinnability and controlling fiber morphology through the modification of solution properties, including the conductivity, viscosity, and surface tension. In this study, the effects of adding small amounts of four different types of ionic liquids [i.e., 1‐butyl‐3‐methylimidazolium chloride (C₄MIMCl), 1‐dodecyl‐3‐methylimidazolium chloride (C₁₂MIMCl), 1‐ethyl‐3‐methylimidazolium bromide (C₂MIMBr), and 1‐ethyl‐3‐methylimidazolium phosphate (C₂MIM)₃PO₄] on the solution properties, electrospinning process, and characteristics of polyacrylonitrile (PAN) were investigated. The results show that the solution conductivities significantly increased with the addition of different ionic liquids with concentrations varying from 0.1 to 1.0 wt %, and the tendency depended on the structures of the ionic liquids. (C₂MIM)₃PO₄ showed the highest conductivity value; this was followed by C₂MIMBr, C₄MIMCl, and C₁₂MIMCl. The ionic liquids formed visible crystals; this made the fiber surfaces rough, and some fiber segments underwent partial aggregation. A regular varying tendency between the minimum mean diameter of the PAN/ionic liquid fibers and the structure of the ionic liquid was found. The PAN/N,N‐dimethylformamide (DMF)/(C₂MIM)₃PO₄ solution showed the highest conductivity among the four systems with different ionic liquids added, and the thinnest minimum diameter of the PAN/(C₂MIM)₃PO₄ fibers appeared with a relatively low ionic liquid concentration of 0.25 wt %, whereas the PAN/DMF/C₁₂MIMCl solution had the lowest conductivity, and the minimum mean diameter of PAN/C₁₂MIMCl fibers appeared at a relatively high ionic liquid concentration of 0.8 wt %. Although the conductivity of the PAN/DMF/C₂MIMBr solution was higher than that of the PAN/DMF/C₄MIMCl solution, the minimum mean diameters of the PAN/C₂MIMBr and PAN/C₄MIMCl fibers appeared at the same ionic liquid concentration of 0.5 wt % because of the similar ionic activities of C₂MIMBr and C₄MIMCl. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2359–2368, 2013