Helical Fibers Research Articles

Assembly and Chiral Memory Effects of Dynamic Macroscopic Supramolecular Helices

Macroscopic enantiomerically pure helical supramolecular fibers are bottom-up assembled in aqueous media from a chiral π-electron donor template and an achiral π-electron acceptor. The helices can be assembled to the sub-millimeter scale with controlled handedness. These dynamic supramolecular architectures allow for a quantitative exchange of the chiral donor template with achiral analogues. During this process, a chiral memory effect was observed, affording enantiomerically pure helices composed entirely of achiral components.

Electromagnetic wave absorption properties of helical carbon fibers and expanded glass beads filled cement-based composites

The cement based composites for electromagnetic (EM) wave absorption were prepared by introducing helical carbon fibers (HCF) and expanded glass beads (EGB), and the influences of HCF mass fraction, EGB volume fraction, and sample thickness on the EM reflection loss were investigated in 2–18 GHz. Results indicate that the EM wave absorption performance increases at first and then decreases with the increase of HCF mass fraction. And the values of absorption peaks and effective bandwidth below −10 dB increase monotonically with the increase of EGB volume fraction. The cement based composites with 2 wt% HCF, 60 vol% EGB, and 20 mm thickness exhibits optimal EM wave absorption performance. The minimum reflection loss can be −17.8 dB and the effective bandwidth for −10 dB reaches 13 GHz. The high EM absorbing capacity and wide effective bandwidth can be attributed to the unique chiral structure of HCF and low permittivity of EGB.

Residual-stress-induced helical long period fiber gratings for sensing applications.

We demonstrate a high-efficiency grating fabrication system, which can be used to inscribe a high-quality helical long period fiber grating (HLPFG) on single-mode fiber by means of hydrogen-oxygen flame. Such the HLPFG can be produced in enormous quantities with a uniform grating parameters and good reproducibility of grating inscription. Possible mechanisms for refractive index modulation in the HLPFG can be attributed to residual stress concentration by solidifying the periodic twisting stress under a fused status of optical fiber. Moreover, the HLPFG exhibits an excellence performance of high temperature sensing with a high sensitivity of ~132.8 pm/°C and a measuring range from room temperature to 900 °C. Comparing to the traditional LPFG fabricated by CO2 laser or arc discharge technique, the HLPFG has a low the bending and tensile strain sensitivity of 1.94 nm/(1/m) and 1.41 pm/με, respectively. So the proposed HLPFG could have a great potential in special applications as optical high-temperature sensors.

Elucidation of the Origin of Thixotropic-Inducing Properties of Additive Amphiphiles and the Creation of a High-Performance Triamide Amphiphile.

The spontaneous growth of helical fibers of amphiphilic diamide derivatives containing hydrocarbons with asymmetric carbon centers in their constituent hydrocarbons was investigated. 12-Hydroxystearic acid and a gemini-type surfactant obtained by the bimolecular condensation of this compound with hexamethylenediamine both impart thixotropic ability to a solvent. Although this thixotropic behavior is based on the growth of hierarchical crystalline nanofibers in the solvents, the degree of fiber growth itself was not the origin of the thixotropy. In this study, it has adopted the methods of the Langmuir monolayer and Langmuir-Blodgett films as technique to selectively and individually evaluate the behavior of 12-hydroxyl stearyl and/or stearyl chains themselves. The ability to impart thixotropy to the solvent via fiber organization was related to the intermolecular hydrogen bonding between the added amphiphiles. Additionally, homogeneous right-handed helical fibers were formed in the spin-cast films of the diamide derivatives, and a positive Cotton effect was observed in their circular dichroism spectra. It is suggested that fibers that do not form helical arrangements cannot impart sufficient thixotropy to the solvent even when extensive fiber growth is achieved, and the structure-dependent development of chirality is the driving force. In addition, to further the development of highly functional thixotropic agents, a trefoil-like triamide derivative containing three chains was synthesized. By using this molecule, solvent gelation occurred at 78% as an addition to the diamide case, and a supramolecular assembly was formed in the corresponding two-dimensional film.

Morphological Control of Coil-Rod-Coil Molecules Containing m-Terphenyl Group: Construction of Helical Fibers and Helical Nanorings in Aqueous Solution.

Rod-coil molecules, composed of rigid segments and flexible coil chains, have a strong intrinsic ability to self-assemble into diverse supramolecular nanostructures. Herein, we report the synthesis and the morphological control of a new series of amphiphilic coil-rod-coil molecular isomers 1-2 containing flexible oligoether chains. These molecules are comprised of m-terphenyl and biphenyl groups, along with triple bonds, and possess lateral methyl or butyl groups at the coil or rod segments. The results of this study suggest that the morphology of supramolecular aggregates is significantly influenced by the lateral alkyl groups and by the sequence of the rigid fragments in the bulk and in aqueous solution. The molecules with different coils self-assemble into lamellar or oblique columnar structures in the bulk state. In aqueous solution, molecule 1a, with a lack of lateral groups, self-assembled into large strips of sheets, whereas exquisite nanostructures of helical fibers were obtained from molecule 1b, which incorporated lateral methyl groups between the rod and coil segments. Interestingly, molecule 1c with lateral butyl and methyl groups exhibited a strong self-organizing capacity to form helical nanorings. Nanoribbons, helical fibers, and small nanorings were simultaneously formed from the 2a-2c, which are structural isomers of 1a, 1b, and 1c. Accurate control of these supramolecular nanostructures can be achieved by tuning the synergistic interactions of the noncovalent driving force with hydrophilic-hydrophobic interactions in aqueous solution.

Peculiar Triarylamine-Based Co-assembled Supramolecular Polymers That Exhibit Two Transition Temperatures in the Formation of a Coiled Helical Bundle.

This paper describes the peculiar co-assembly supramolecular polymerization behavior of triphenylamine trisamide derivatives with d-alanine (T-ala) or glycine (T-gly) moieties. Concentration and temperature-dependent circular dichroism (CD) spectroscopy revealed that the heating curves of co-assemblies obtained at various molar ratios of T-ala to T-gly exhibited two distinct transition temperatures. The first transition was due to the transformation from coiled helical bundles to single helical fibers without handedness. The second was due to a change from typical elongation to nucleation. These phenomena were confirmed by solvent-dependent decoiling of coiled helical structures and concentration-dependent morphological analysis. The two transitioning temperatures were dependent on the concentration of T-ala in the co-assemblies, suggesting that T-ala concentration plays an important role in the formation of coiled helical bundles. Our study demonstrated the first observation of two distinct transition temperatures in supramolecular polymers.

A multiscale numerical approach for the finite strains analysis of materials reinforced with helical fibers

Present study provides a multiscale numerical approach based on representative volume elements (RVE) for the finite strain analyses of materials reinforced with helical fibers. An RVE with wavy-like boundaries bioinspired in the microstructure of tendon fascicles is proposed. Due to the unusual geometry of the RVE, a non-periodic mesh mapping will likely occur, precluding the numerical implementation of the periodic boundary condition in a straightforward manner. Moreover, it is verified that the others classical boundary conditions, namely, the linear boundary displacements model and the minimally constrained model, seem not to be suitable choices for the multiscale analyses of this class of RVEs. Motivated by these facts, two mixed boundary conditions allying characteristics of both, linear and minimal models, are suggested. The kinematic constraints on the RVE are enforced via variational principles and Lagrange multipliers. A displacement-controlled triaxial test performed on a numerical specimen larger than the RVE is proposed as a reference solution for the multiscale responses of the RVE. A set of numerical results concerning microscopic strain fields and macroscopic stress-stretch curves points out that one of the proposed mixed models predicts with great accuracy not only the homogenized quantities but also the kinematic fields developed within the specimen. The computational homogenization strategy addressed in this manuscript can be extended to other fiber-reinforced materials composed of different fiber arrangements also including dissipative effects. Moreover, the boundaries surfaces of the RVE are not restricted to any particular layout and the finite element mesh do not require particular mappings nor additional algorithmic handling.

Twisting Fibers Formation of Cyanobacterial Supra-Polysaccharide through Self-Assembly

Biopolymers such as polysaccharides, cytoskeletal proteins, and DNAs show helical structures in molecular scale and self-orientation in larger scale. Sacran is one of fascinating bacterial polysaccharides which could naturally form incredibly giant fiber in micrometer scale. It is extracted from cyanobacteria, Aphanothece sacrum, which has attached our interest due to the extremely high molecular weight (> 1.6 × 107 g/mol)1 and the self-orienting giant micro-fibers (~1 μm of outer diameter and > 20 μm length)2 during the drying process which cannot encounter in any other soluble polysaccharides. From our previous researches, we found that in drying process of the sacran solution, the rigid polysaccharides exhibit self-orientation and they gather to build a rod-like microdomain in micrometer scale. Moreover, in some conditions, it shows clear twisting structure in micrometer scale. Here, we study the fiber formation using polarized optical microscope and scanning electron microscope to clarify the effect of polymer’s initial concentration, evaporation speed and ionic effect on the fiber formation. This unique formation is significant not only to understand basic fiber natural formation but also to develop for material field applications. The formation mechanism was investigated in micrometer scale from drying process using polarized optical microscope (POM) and scanning electron microscope (SEM). The samples were prepared by drying the 1 μL droplet on a glass substrate at room temperature under control of the initial polymer concentration. From the drying records of a solution (5 × 10-1 wt%), we could confirm three main regions with different morphologies. Around the record of the droplet edge, fibers which oriented apparel to the contact line were clearly observed. In the middle of the record, the twisting fibers in random direction were shown. In the center, dendrite crystal structures could be observed. These results suggest that the sacran forms variety of geometric structures under drying environment and mild condition. Focusing on the fibers at the edge and middle area of sacran droplet, the deposition from 5 × 10-3 wt% solutions showed not only particles but also short fibrous with ~1 μm diameter as main structures. In contrast, deposition from a solution at higher concentration of 5 × 10-2 wt%, giant fibers in micrometer scale were observed. It is clearly seen that self-assembly of loosely-twisting fibers led to form larger structures through snaking or bundling. Considering the different diameter of the micro-rods and the twisting fibers as shown in Fig.1, the loosely-twisting fibers could be observed and they showed a semi-rigid fiber characteristic which causes low orientation around the droplet edge. As for the deposition from 5 × 10-1 wt% solutions, rigid fibers were observed with high orientation around the droplet edge. This might be owing to tightly-twisting fibers at high concentration. The effect of evaporation speed is one of the main factors which effects to the polymer morphology. At low evaporation speed, straight sacran fibers were observed. However, when evaporation speed was increased, the straight fiber transform to snaking or twisting form. The effect on assembly and disassembly of the fibers were also clarified by mixing various kinds of ionic (HCl, NaCl and CaCl2) with various concentrations (1, 5, 10, 60 mM). Sacran fibers were disassembled in all concentration of HCl and NaCl due to carboxylic groups were interacted by monovalent cations. In case of CaCl2, calcium divalent cations could bind with the carboxylate groups as crosslinker. Therefore, it remained fibers assembly of sacran. This unique formation is not only important to understand basic helical natural fiber formation which still being an ambiguous issue but also to develop new environmental friendly material in several fields such as electro optical film, bio-mimic templating and components of medicines in near future. 1) Okajima, M. K., et al., Macromolecules 2009, 42, 3057.2) Okeyoshi, K., et al., Biomacromolecules 2016, 17, 2096. Figure 1

Twist induced plasticity and failure mechanism of helical carbon nanotube fibers under different strain rates

Twist has been well identified as an effective parameter to tune the mechanical behavior of carbon nanotube (CNT) fibers, e.g., tensile strength, strain, modulus and elastic-plastic behaviors. In this contribution, we uncover the twist-induced plastic deformation and failure behaviors of CNT fibers shrunk by ethanol (E-CNT fiber) and polyvinyl alcohol (P-CNT) solutions under low strain rate of 0.001 s−1 and high strain rate of 1300 s−1, which are essentially important for designing high-performance composites with respect to long term stability and short-term collision, respectively. It is found that the strain-induced microstructural evolution processes of CNT fibers depends on twist angle as a result of the strengthening effect of inter-CNT friction and the weakening effect of CNT obliquity. The tensile strength, failure strain and modulus of CNT fibers are more sensitive to strain rate as the twist angle increases. The optimum twist angle provides not only the higher tensile strength, but also the better data repeatability. The numerical results reveal that the brittle/ductile properties of filaments and their interfacial interaction will contribute to the plastic behaviors of a twist fiber. The empirical constitutive equations were built to describe the stress-strain curves of CNT fibers by taking the strain, helical geometry, twist-induced damage and strain rate into consideration.

Voltage-driven nonuniform axisymmetric torsion of a tubular dielectric elastomer actuator reinforced with one family of inextensible fibers

Abstract Dielectric elastomers (DEs) take the advantage of muscles-like voltage-induced giant deformation and have extensive applications in the fields of soft robots, adaptive optics and bioengineering. In the present work, the finite axisymmetric deformation with torsion of a tubular DE actuator reinforced by one family of inextensible helical fibers is studied by using the membrane theory . The voltage-driven torsional behavior of the DE actuator is caused by the asymmetric reinforcement of helical fibers. By adopting the Mooney-Rivlin elasticity model and the ideal dielectric model and accounting for the inextensibility of the helical fibers, a constitutive model is proposed for the fiber-reinforced DE actuator. Based on these modelling assumptions and considering the equilibrium equations and associated boundary conditions, a boundary value problem for the DE actuator is formulated and also solved numerically. Furthermore, the effects of material parameters and the fiber helical angle as well as mechanical loadings, including the internal pressure, axial force and twist moment, on the voltage-induced torsional behavior of the DE actuator are discussed. The developed model and revealed results are expected to aid the design and fabrication of soft actuators and soft robots.

High‐resolution multi‐component distributed acoustic sensing

ABSTRACTDistributed acoustic sensing uses an optical fibre together with an interrogator unit to perform strain measurements. The usage of distributed acoustic sensing in geophysics is attractive due to its dense spatial sampling and low operation cost if the optical fibre is freely accessible. In the borehole environment, optical fibres for distributed acoustic sensing are often readily available as a part of other sensing tools, such as for temperature and pressure. Although the distributed acoustic sensing system promises great potential for reservoir monitoring and surface seismic acquisition, the single axial strain measurement of distributed acoustic sensing along the fibre is inadequate to fully characterise the different wave modes, thus making reservoir characterisation challenging. We propose an acquisition system using five equally spaced helical optical fibres and a straight optical fibre to obtain six different strain projections. This system allows us to reconstruct all components of the 3D strain tensor at any location along the fibre. Analysing the condition number associated with the geometry of the optical fibre, we can systematically search for the optimum design parameters for our configuration. Numerical examples demonstrate the effectiveness of our proposed method to successful reconstruction of the full strain tensor from elastic wavefields of arbitrary complexity.

Sampled Bragg gratings formed in helically twisted fibers and their potential application for the simultaneous measurement of mechanical torsion and temperature.

We propose and demonstrate a novel type of sampled Bragg gratings by combining a helically twisted fiber and a Bragg grating. A comb-like spectrum with a series of harmonic narrow resonances is observed, and the influence of geometrical parameters on the resonances is studied. As a special application, the intrinsic nature of the device that contains the Bragg grating and helical fiber spectral responses permits the temperature to be detected from the former, whereas the mechanical torsion is extracted from the latter, suggesting a potential for the simultaneous measurement of these two parameters. The proposed configuration features simplification, easy fabrication, high flexibility, stability, and low cost, and therefore has good prospects for sensor applications, as well as other applications, such as multi-channel filters, distributed Bragg reflectors, etc.

Helical hollow fibers via rope coiling: Effect of spinning conditions on geometry and membrane morphology

Helical hollow fiber membranes from poly(ether sulfone) were spun via dry-wet spinning, making use of the liquid rope coiling phenomenon. The polymer solution composition was changed by varying the coagulation value and adding PEG400 as pore former. The bore liquid composition, outer coagulation bath temperature, air gap, polymer dope and bore liquid flowrates were varied to map the conditions where helical fibers form. It was observed that increasing air gap changed fiber geometry from straight to helical. Increasing the outer coagulation bath temperature caused helical geometries to become irregular or straight under identical spinning conditions, possibly due to the higher water vapour absorption in the air gap. Regularly helical fibers could, however, be spun with a coagulation bath at 50 °C under a variety of conditions. Comparing fibers spun under the same conditions with different solutions, it was observed that as the solution's viscosity increased, the geometry shifted towards helical. Increasing the bore liquid solvent strength so as to form the skin on the bore side yielded straight fibers due to the fast solidification of the fibers before curling and all helical fibers fabricated had a denser skin on the shell side. During filtrations of yeast suspensions, the helical fibers experienced less fouling with the feed on either the bore or the shell side of the membrane, which shows that using liquid rope coiling to spin helical fibers is a promising, practical method of alleviating fouling in membrane filtrations.

Fabrication of helical microfibers from melt blown polymer blends

ABSTRACTHelical fibers in micro/nanoscale resembling plant tendrils have been of increasing interest due to their unique characteristics. Fabrication of helical microfibers from polymer blends using melt blowing technique is reported in this study. An elastomeric and a stiff polymer are chosen as the raw materials, and a designed swirl‐die melt‐blowing device is used to prepare the microfibrous nonwovens. Focusing on the interfacial interaction between the polymer components induced by the polymer structure and intrinsic properties, airflow field characteristics, and processing parameters, we explore the effects of various parameters on helical fiber formation. Differential scanning calorimeter is employed to examine the rigidity of polymer chains, and the three‐dimensional airflow field simulation is carried out to reveal the airflow field characteristics. This work can provide a promising technique for producing stretchable microfibrous materials which have potential applications in field such as filtration materials and oil sorbents. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2018,56, 970–977

Mode-couplings in two cascaded helical long-period fibre gratings and their application to polarization-insensitive band-rejection filter

Mode-couplings occurring in cascaded single-helix helical long-period fibre gratings (SHLPGs) have been analysed. Using this type of helical long-period fibre grating combined with a cladding-mode stripper, a simple and efficient method of production of a polarization-insensitive flat-top band-rejection filter was proposed and experimentally verified. Unlike the previous SHLPG-based methods in which obtained spectra are strongly dependent on the polarization status of the incident light, the proposed method enables production of a flat-top filter with neither polarization-dependence nor reduction of the rejection depth. As a typical example, a flat-top filter with a rejection depth of ∼17 dB, a bandwidth of ∼14 nm@1 dB, and the maximum polarization-dependent loss (PDL) of ∼1.5 dB was successfully demonstrated.

Two-component gelator isomers with different combination of amine and acid: Helical/non-helical morphology and selective adsorption of dyes

Hydrogels induced by two-component gelator isomers based on the different amine/acid interactions were investigated. Scanning electron microscopy and atomic force microscopy images of the xerogel obtained from the two hydrogels revealed different assembly morphologies. While left-handed helical fibers were observed for the amine-acid based xerogel, acid-amine underwent self-assembly to afford smooth fibers. Fourier transform infrared spectroscopy, fluorescence, and X-ray diffraction measurements combined with density functional theory calculations suggested that the different self-assembly patterns of gelators resulted in opposite electric charges on the xerogel surfaces, in line with Zeta potential measurements. Based on these opposite charges resulting from their different self-assemblies, both xerogels demonstrated efficient dye adsorption abilities with different selectivities. Interestingly, the adsorption performance was not influenced by the salt in the dye solution. Furthermore, the xerogels still showed high dye adsorption efficiency after four cycles. These results provide a two-component hydrogel method for the purification of dye-polluted water systems, while also paving the way for future design of functionalized supramolecular self-assembly systems.

Enhancing the Azimuthal Mode Couplings in a Helical Fiber Grating by Using Phase Sampling

In a single-helix helical long-period fiber grating (SHLPG), due to the inherent one-fold azimuthal symmetric structure of the fiber core, it is very hard to obtain an efficient high-order azimuthal mode coupling. In this letter, we have proposed and demonstrated theoretically a phase-sampling approach to overcome this obstacle, which is realized by periodically inserting phase shifts in the azimuthal direction of the SHLPG. As results of the proposed method, high-efficient couplings between the fundamental mode and the second- and third-order azimuthal modes in a SHLPG have been successfully demonstrated. The proposed method can be applied to generate and convert high-order orbital angular momentum modes even with the SHLPG.

Demonstration of spin and extrinsic orbital-angular-momentum interaction using a few-mode optical fiber

We demonstrate the spin and extrinsic orbital-angular-momentum interaction of light in a few-mode fiber. The interaction of spin and extrinsic orbital angular momentum splits the degeneracy of a degenerate subspace of the higher-order solution of Maxwell's equation and creates correction to the propagating constants of its degenerate eigenmodes that results in the formation of transmitting-length-dependent beat along the propagating trajectory. We examine the interaction of spin and extrinsic orbital angular momentum by the observation of the rotation of the polarization or intensity pattern of the propagating modes which are the combinations of these degenerate eigenmodes when altering the length of this transmitting-length-dependent beat. In experiment, the length of this transmitting-length-dependent beat is altered by the alteration of the pitch of a fiber helix which is made for the production of the extrinsic angular momentum and where the space inversion or mirror symmetry of the mode is broken and the interaction between the spin and extrinsic orbital angular momentum is realized. We demonstrate that the spin and extrinsic orbital-angular-momentum interaction induce the rotation of the polarization or intensity pattern of propagating modes in a way related with the order index of spin and orbital angular momentum carried by their constituent eigencomponents, which are circular vortex modes. This work may contribute to understanding the physical mechanism underlying the evolution of the modes in few-mode fiber or other complex systems for their various applications.

Water-responsive helical graphene-oxide fibers incorporating a continuous carbon nanotube network

Encoding a helical shape into straight fibers could bring unprecedented properties and explore applications in a broad range of areas; this has been difficult for graphene oxide (GO) fibers due to their relatively poor mechanical property and processability. Here, we incorporate a continuous single-walled carbon nanotube (SWNT) network into dispersed GO sheets to fabricate GO/SWNT composite films and helical fibers with an alternating layered structure. Our GO/SWNT fibers combine advantages from both the SWNTs (as a robust and conductive skeleton) and GO (as a hydrophilic matrix), leading to reversible mechanical actuation with axial contraction up to 50% of original fiber length in response to water adsorption. The structural evolution (including increase in fiber diameter and decrease in the helical loop number) is a key factor for generating large axial contraction. Graphene-based helical fibers embedding a continuous carbon nanotube network, as described here, have potential applications in flexible/wearable electronics, sensors and actuators.

Torsion, Strain, and Temperature Sensor Based on Helical Long-Period Fiber Gratings

A novel fiber sensor, which enables us to simultaneously measure the torsion, strain, and temperature, is proposed and experimentally demonstrated, which is based on utilization of two successively cascaded helical long-period fiber gratings (TSC-HLPGs). By using the proposed approach, crosstalk effects among temperature, strain, and torsion can totally be discriminated for the first time to the best of our knowledge. Moreover, not only the torsion angle, but also the torsion direction can be determined simultaneously. Accuracies for the resolved temperature, the strain, and the torsion angle are estimated to be ~0.8 °C within the range of 20 °C–100 °C, $\sim 225~\mu \varepsilon $ within the range of 0- $2600~\mu \varepsilon $ , and ~1.2° (corresponding to a torsion responsivity of 3.54 nm/rad/m in our case) within the rotation angle of −360° ~ 360°, respectively.