A Novel Technique for Fiber Formation: Mechanotropic Spinning—Principle and Realization

Abstract

We present basic experimental data and the theoretical background of a novel technique for fiber spinning from polymer solutions. The principal feature of the advanced process is realization of phase separation with detachment of a solvent, accompanied by the orientation of macromolecules, under the action of high extension rates. This is similar in some respects to dry spinning, though the driving force is not diffusion with subsequent evaporation of a solvent but redistribution of polymer-solvent interactions in favor of polymer-polymer and solvent-solvent ones governed by mechanical stresses. A promise of this approach has been demonstrated by experiments performed with polyacrylonitrile solutions in different solvents and solutions of the rigid-chain aromatic polyamide. We examined mechanotropic fiber spinning in model experiments with stretching jets from a drop of polymer solution in different conditions, and then demonstrated the possibility of realizing this process in the stable long-term continuous mode. During extension, phase separation happens throughout the whole section of a jet, as was confirmed by visual observation. Then a solvent diffuses on a jet surface, forming a liquid shell on the oriented fiber. Instability of this cover due to surface tension leads either to formation of separate solvent drops “seating” on the fiber or to the flow of a solvent down to the Taylor cone. The separate liquid droplets can be easily taken off a fiber. The physics underlying this process is related to the analysis of the influence of macromolecule coil-to-stretched chain transition on the intermolecular interaction.

Orientation and Aggregation of Polymer Chains in the Straight Electrospinning Jet

“…This behavior is consistent with the behavior of the filaments of polymer solutions under extension [ 25 ]. It has been found that threads formed by solutions of flexible-chain polymers can show exponential thinning, which is further replaced by the emergence of blistering structures and, as a result, a fiber is formed [ 26 , 27 , 28 , 29 ]. Exponential thinning is associated with the unfolding of polymer chains along the stretching axis [ 30 ] and the blistering mechanism can be attributed to the flow-induced phase separation under extension [ 31 ].…”

Solubility, Rheology, and Coagulation Kinetics of Poly-(O-Aminophenylene)Naphthoylenimide Solutions

“…As is seen from these data, only when the polymer concentration is above 12–15% the values of the Newtonian viscosity reach 100 Pa·s and at 23% the viscosity approaches 1000 Pa·s. In other words, both strategies, i.e., an increase in the molecular weight of the polymer or concentration of the pre-polymer solution do not allow producing of the dopes with viscoelastic properties suitable for dry-wet or mechanotropic spinning [ 19 , 20 ].…”

Compositions Based on PAN Solutions Containing Polydimethylsiloxane Additives: Morphology, Rheology, and Fiber Spinning

“…1-a fiber-optic illuminator along the jet axis; 2-back lighting; 3-a syringe with the solution; 4-a lens to focus the light into the center of an extended jet; 5-a camera; 6-a jet. This is according to [30,31].…”

“…The corresponding experimental results are presented in Figure 15. The images show the comparative kinetics of the thinning of the liquid filament and the phase separation process according to the mechanism described in detail in [30,31]. For a PAN solution, a noticeable change in the shape of the jet begins from the 30th second and is accompanied by the release of solvent to the jet surface.…”