Facile, Energy‐Efficient Microscale Fibrillation of Polyacrylamides under Ambient Conditions

Abstract

Insight into fiber formation can provide new rationale for the design and preparation of fibers with programmed mechanical properties. While synthetic bioinspired fibers have shown impressive tensile properties, the fiber formation process remains poorly understood. Moreover, these systems are highly complex and their formation is environmentally and economically costly. Controlled fiber formation under ambient conditions from polyacrylamide solutions with properties comparable to natural fibers such as wool and coir is demonstrated. Photopolymerization and subsequent microscale fibrillation of different acrylamides in water/ethanol mixtures yield a simple and energy‐efficient route to fiber formation. This strategy reduces required processing energy by two‐to‐three orders of magnitude. Through extensive experimental elucidation, insight into precise fiber forming conditions of polymeric solutions is achieved. Ethanol is utilized as a chain transfer agent to control the molecular weight of the polyacrylamides, and the entanglement regimes of the solutions are determined through rheological characterization showing fiber formation above the entanglement concentration. Unique from previously reported hydrogel microfibers, it is shown that fibers with good mechanical properties can be obtained without the need for composites or crosslinkers. The reported approach offers a platform for fiber formation under ambient conditions with molecular‐level understanding of their assembly.

Aqueous spinning of robust, self-healable, and crack-resistant hydrogel microfibers enabled by hydrogen bond nanoconfinement

“…Nevertheless, despite great efforts that have been made to produce various hydrogel fibers by 3D printing 10 , pultrusion/draw spinning [11][12][13][14][15][16][17][18][19] , wet spinning 2,20,21 , microfluidic spinning 22,23 , reactive spinning 24 , and tube templating 25,26 , none of these previous hydrogel fibers are reported to synergize the properties of high mechanical strength, crack resistance, and self-healability. Additionally, the complexity and organic solvents involving in many spinning processes also largely contradict to the energy-efficient aqueous production of natural fibers with ultralow carbon footprint 27 .…”

Recent developments in artificial spider silk and functional gel fibers

“…Reproduced with permission: Copyright 2022, Wiley-VCH GmbH. 32 (B) Schematic of the fabrication of rTRM7 fiber by the drawing process. Reproduced with permission: Copyright 2022, Nature.…”

“…Synthetic bioinspired fibers have exhibited impressive tensile properties, but the fiber formation process is still not well understood. Moreover, these systems are highly complex, and the formation process used for the process is expensive, 32 (Figure 1A). Spinning of artificial spider silk from protein and polypeptides is a typical, well‐developed method in which fibers are produced from a solution and are subsequently converted first into a gel‐like state either by wet spinning or dry spinning and finally to fibers.…”

“…(A) Gradient map showing samples that easily formed stable fibers (green) and unstable fibers (yellow) and that did not form fibers (red). Reproduced with permission: Copyright 2022, Wiley‐VCH GmbH 32 . (B) Schematic of the fabrication of rTRM7 fiber by the drawing process.…”

Ambient-conditions spinning of functional soft fibers via engineering molecular chain networks and phase separation

“…Among these spinning techniques, forming functional fibers under ambient conditions—room temperature and atmospheric pressure—with combined features beyond mechanical attributes (i.e., stimuli-responsive behavior 21 , self-sensing deformations 13 , and anti-freezing 22 ) is challenging. Although some favorable results have been reported on developing new spinning methods 9 , 16 , 19 , few of them are capable of producing functional fibers under ambient conditions 23 – 25 . These precursor dope materials are usually not drawable under ambient conditions.…”