Artificial Helical Screws of 2D Materials with Archimedean Spiral Arrangement

Abstract

Helix structures, which are frequently observed in nature, act as versatile structural templates for complex functionalities with asymmetry and anisotropy. However, atomically thin 2D materials, including graphene, transition metal dichalcogenides (TMDs), and MXenes, do not have inherent chirality in their planar geometry and cannot easily form such a structure. This study presents the macroscopic self-assembly of 2D materials for helical screws with an Archimedean spiral arrangement. The naturally triggered spontaneous rotation upon the 1D fiber assembly of 2D materials forms helical screws consisting of multiple helices and perversions. For a clear understanding of the morphological evolution of helical screws, variations in the helical pitch and angle are systematically analyzed considering thermodynamic and kinetic conditions. Subsequently, the influence of spontaneous helix formation on the properties of the 2D assembled fibers is investigated in terms of the solvent-driven actuator performance and electrical and electrothermal properties. The suggested approach provides a new perspective on the directed selfassembly of inherently achiral 2D materials toward chiral helix formation.

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“…Our research group demonstrated a polar solvent-driven graphene fiber actuator (Figure 8d). [205] Due to the spontaneously organized helical screw-like fiber structure achieved through the hierarchical self-assembly of nematic GO liquid crystals, mechanical actuation in the longitudinal direction can be induced under various solvent vapors, including toluene, isopropyl alcohol, ethanol, and acetone. Different polarities and evaporation rates of the solvents yielded different behaviors in the reversible actuation of twisted GO fiber.…”

“…Solvent-based actuators that generate macroscopic mechanical deformation in response to moisture and organic solvents, can be greatly benefited by the incorporation of 2D materials, such as GO, rGO and MXene. [198,205,246] 2D materials with abundant polar functional groups, such as carboxyl and hydroxyl groups, can facilitate a solvent responsiveness by trapping the solvent in their interlayers, leading to the volumetric expansion-based actuation. For instance, an asymmetrical rGO/polypyrrole film has been reported to bend up to 330°while relative humidity increased to 65% with long-term durability over 600 s. [197] Similarly, nacrelike lamellar structure of polydopamine-modified Ti 3 C 2 T x MX-ene/bacterial cellulose nanofiber undergoes the asymmetric water concentration gradient across the film thickness direction in a humid condition, leading to the expansion mismatch and reversible bending of the film.…”

“…2D materials can be employed without any other component [190] or in combination with other materials, such as composites, [191][192][193][194][195][196][197] interface layers, [198][199][200][201][202][203] or electrodes, [204] for the desired actuation properties. By leveraging the exceptional properties of 2D materials, innovative soft actuators in the form of fibers [174,205] and films, [206][207][208][209] can be actuated by either single or a combination of multiple environmental stimuli, including electricity, [206,210] heat, [195,208,211] solvent [198,205] and magnetic fields [194,212] are emerging, paving the way for exciting advancements in the relevant fields.…”

“…d) Polar solvent-responsive helical screw-like graphene fiber actuator. Reproduced with permission [205]. Copyright 2023, John Wiley and Sons.…”

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“…These excellent properties have attracted researchers to mimic nature. Large amounts of artificial helical structures have been exploited by the self-assembled formation based on special DOI: 10.1002/adfm.202305244 geometric features combined with thermal or stress fields during fabrication, including spinning, [3] electrospinning, [4] and biomaterial template manufacturing. [5] With sophisticated structure of helix, various applications have been realized in wide fields such as stimulus-response actuators, [6] remote sensors, [7] helical microrobotics or micromachines, [8] damage resistant composites, [9] 3D crack regulation, [10] etc.…”