Phase behavior and mechanism of formation of protofiber morphology of solution spun poly(acrylonitrile) copolymers in DMF‐water system

Abstract

Phase diagrams of a series of copolymers of acrylonitrile (AN) and acrylic acid (AAc) were constructed using linearized cloud point correlation. The miscibility region in the phase diagram was found to increase with the increase in AAc content of the copolymers. For various compositions, v 13 (polymer-water interaction parameter) values were estimated by sorption experiment. As the hydrophilic nature of the polymer increased with the increase in the content of acrylic acid, the v 13 interaction parameter was found to decrease from poly(acrylonitrile) homopolymer to its copolymer with 50 mol % acrylic acid (AA50B). The polymer-solvent interaction parameters (v 23 ) and composition at the critical points for all the polymers were determined by fitting the theoretical bimodal curves to the experimental cloud point curves using Kenji Kamide equations. The polymer composition at the critical point was found to increase by 400% with increasing AAc content. The polymers were solution spun in DMF-water coagulation bath at 30 C and their protofiber structures were investigated under scanning electron microscopy. The observed morphological differences in protofibers were explained on the changes brought about in the phase separation behavior of the polymer-solvent-nonsolvent systems. The copolymers with higher acrylic acid content could be solution spun into void free homogeneous fibers even at conditions that produced voidfilled inhomogeneous fibers in poly(acrylonitrile) and its copolymers with lower AAc content. The experiments demonstrate the important role of thermodynamics in deciding the protofiber morphology during coagulation process.

Preparation and characterization of all para‐position polysulfonamide fiber

“…Furthermore, under such situation, the cross‐sectional shape of the fiber was circular, and no skin‐core morphology is visible. Many studies on the formation of macrovoids, sponge‐like, finger‐like, or macrovoid‐free structure in phase‐inversion processes can be found in the literature 19–22. The result here indicated that the coagulation condition of 60 wt % DMAc/40 wt % water was excellent for the formation of the fiber.…”

Effect of fiber morphology on the capacitance of stretchable supercapacitors based on silver nanowire‐polyurethane hollow fibers

“…It is known 32 that the formation of the pores is governed by the thermodynamics and kinetics of phase F I G U R E 6 FE-SEM micrographs of the cross section of 0.2NW-FR40 fibers spun at an air gap of (A) 10 cm, (B) 2.5 cm; longitudinal section of fiber at an air gap of (C) 10 cm, (D) 2.5 cm; cross section of the fibers showing the presence of compact layer inside the fiber wall when spun at (E) 10 cm, (F) 2.5 cm and (G) Cyclic voltammogram plot of the fabricated supercapacitor device with these two fibers inversion or liquid-liquid demixing. Therefore, it was decided to change the composition of the coagulation bath to further improve the pore size distribution throughout the fiber wall.…”

Highly conducting silver nanowire‐polyacrylonitrile hollow fibres for flexible supercapacitors

“…In case of solution spinning of PAN fibres, it is well reported that the fibre morphology is highly dependent on the coagulation thermodynamics and kinetics, which ultimately determines the flexibility of the obtained fibre. In case of hollow fibres, as the bore fluid governs the coagulation of the fibre's inner surface, the use of AgNWs dispersed in pure water as the bore fluid resulted in formation of highly porous and brittle fibres.…”