Liquid Crystal Spinning Research Articles

Nanoscale Kevlar Liquid Crystal Aerogel Fibers.

Aerogel fibers, the simultaneous embodiment of aerogel porous network and fiber slender geometry, have shown critical advantages over natural and synthetic fibers in thermal insulation. However, how to control the building block orientation degree of the resulting aerogel fibers during the dynamic sol–gel transition process to expand their functions for emerging applications is a great challenge. Herein, nanoscale Kevlar liquid crystal (NKLC) aerogel fibers with different building block orientation degrees have been fabricated from Kevlar nanofibers via liquid crystal spinning, dynamic sol–gel transition, freeze-drying, and cold plasma hydrophobilization in sequence. The resulting NKLC aerogel fibers demonstrate extremely high mechanical strength (41.0 MPa), excellent thermal insulation (0.037 W·m–1·K–1), and self-cleaning performance (with a water contact angle of 154°). The superhydrophobic NKLC aerogel fibers can cyclically transform between aerogel and gel states, while gel fibers involving different building block orientation degrees display distinguishable brightness under polarized light. Based on these performances, digital textiles woven or embroidered with high- and low-orientated NKLC aerogel fibers enable up to 6.0 Gb information encryption in one square meter and on-demand decryption. Therefore, it can be envisioned that the tuning of the building blocks’ orientation degree will be an appropriate strategy to endow performance to the liquid crystal aerogel fibers for potential applications beyond thermal insulation.

Construction of Aramid Engineering Materials via Polymerization-Induced para-Aramid Nanofiber Hydrogel.

The processing of poly(p-phenylene terephthalamide) (PPTA) has long been a great challenge. This work reports a simple "monomers-nanofibers-macroscopic product" (MNM) hierarchical self-assembly approach to build 3Dall-PPTA engineering materials. This approach mainly includes the preparation of polymerization-induced aramid nanofibers (PANFs) from monomers and the fabrication of all-PPTA materials from PANF hydrogel. Various 3D architectures, including simple solid bulks and sophisticated honeycombs (HCs), are obtained after the dehydration and shrinking of the PANF hydrogel. The tensile strength and compressive yield strength of PANF bulk are more than 62 and 90MPa, respectively, which are comparable to typical engineering plastics. The compressive strength of PANF HC with a density of 360kgm-3 is more than 24MPa. The thermal stability of PANF bulk and PANF HC are as good as that of Kevlar fiber and almost no decomposition occurred before 500°C in a nitrogen atmosphere. Furthermore, the MNM process is performed under mild conditions, without high temperature, high pressure, or corrosive solvent. The MNM process is a novel strategy for the processing of all aromatic polyamide materials with complex structures and high performances and would be another development since the breakthrough of liquid crystal spinning technology of PPTA.

Fabrication of Ultrahigh‐Strength Polybenzimidazole Fibers via a Novel and Green Integrated Liquid Crystal Spinning Process

AbstractHerein, the first example of ultrahigh‐strength polybenzimidazole (PBI) fibers using a PBI solution in liquid crystal state is reported via a novel and green integrated spinning technology. Microwave‐assisted polycondensation is utilized to synthesize the polybenzimidazole/polyphosphoric acid liquid crystal spinning solution and pure water is employed as the coagulating and washing bath to afford a green fabrication process. The green integrated spinning technology is eco‐friendly, cheap, and conducive for the large‐scale production of PBI fibers. The as‐prepared PBI fibers display superb flame retardancy, and the outstanding thermal stability of PBI fiber enables it to preserve structural integrity at temperatures as high as 600 °C. More significantly, it prepared the ultrahigh‐strength of PBI fiber up to 0.91 GPa, which is two times than that of the reported PBI fibers, marking a significant breakthrough for the high‐performance PBI fibers.

Continuous graphene fibers prepared by liquid crystal spinning as strain sensors for Monitoring Vital Signs

Perfect graphene sheets are zero-gap semiconductors (semi-metals) with extremely high electron mobility and have considerable potential in electronics and optics, high sensitivity sensors, supercapacitors and biodevices. Practically applying the semiconductor properties of graphene has become the focus of research. We prepared a microscopically ordered graphene oxide fiber by liquid crystal spinning. The high concentration (50 mg ml−1) graphene oxide dispersion is favorable for forming highly ordered nematic phase in the spinning process. In a liquid crystal, graphene inside a fiber has an ordered regular structure arranged in parallel along the axial direction. High-strength (432.6 ± 12.7 MPa) and highly conductive (4.9 × 104 S/m) graphene fibers are obtained by chemical reduction, in which a strong π-π bonds forms between parallel graphene layers. Given that strain can change graphene band gap and affect electron transport, it is inherited to the graphene fiber, which is macroscopically conductive. Variations, strain response sensors made from this graphene fiber with high sensitivity, and strain range (2%–8%) can be used in the detection of body health signals (speech and pulse waves). These parameters have potential use in artificial electronics skin and wearable health detection.

Preparation and improved mechanical properties of nano‐TiO2 filled Poly (p‐phenylene benzobisoxazole) fiber

AbstractWith in‐situ bending various contents of nano‐sized titanium dioxide (TiO2) were introduced into the solution polymerization system of poly (p‐phenylene benzobisoxazole) (PBO), and the blends were spun into high performance fibers via liquid crystal spinning. The dispersion of TiO2 in matrix was observed by the scanning electron microscopy. The mechanical and thermal properties of PBO and TiO2/PBO fibers were tested by a tensilon and a thermogravimetric analyser. The results show that the tensile strength and modulus of the PBO/TiO2 fiber containing 1.5 wt % TiO2 is 4.62 GPa and 109.99 GPa, which is approximately 36% and 18% higher than that of the pure PBO fiber. The decomposition temperature of the composites is also improved from 697.6°C to 701.8°C. The effect of TiO2 nanoparticles on the structure of PBO is also studied. Copyright © 2009 John Wiley & Sons, Ltd.

Self-Organization Phenomena in Liquid Crystal Spinning

Self-Organization Phenomena in Liquid Crystal Spinning

New horizons in advanced oriented fiber

AbstractAchievement of exceptional properties in films/fibers generally requires very high to ultra high molecular weights and very high degrees of orientation. A brief description of the fiber related technologies‐used to maximize orientation in high performance fibers, e.g., solid state extrusion, special drawing methods gel spinning, and liquid crystal spinning are reviewed. A detailed comparison of the fiber properties resulting from these technologies is also shown. Particular emphasis is.placed on describing the upgrading of polyethylene to a high performance fiber product through several of these technologies. Gel/solution spinning of ultra high molecular weight polyethylene (UHMWPE) is especially highlighted. The latest worldwide efforts to commercialize gel spun fibers are discussed as well as the applicability of the process to other thermoplastics. Applications illustrating the use of high performance fibers in various end use areas are summarized. The primary properties critical to each are also outlined.

Mechanism of the Silk Spinning in terms of Liquid Crystal Spinning

Mechanism of the Silk Spinning in terms of Liquid Crystal Spinning

Director dynamics and NMR applications of nematic liquid crystals spinning at various angles from the magnetic field

The dynamics of the director of a nematic liquid crystal spinning in a magnetic field are studied. A simple average potential theory which gives a qualitative understanding of the director behavior is presented along with an exact quantitative treatment of situations in which the director is stationary in the laboratory frame. NMR spectra of an A2 spin system, 19F in CF2CBr2, are used to verify the theory. For nematic liquid crystals in which the magnetic susceptibility anisotropy Δχ = (χ∥−χ⊥) is positive, the director aligns along the spinning axis when the sample is spun at a rate much greater than that characteristic of director reorientation and the angle between the spinning axis and the magnetic field is less than the magic angle ϑm = 54.74°. Past the magic angle the director distributes in the plane perpendicular to the spinning axis. For liquid crystals in which Δχ is negative, alignment parallel to the spinning axis occurs for angles greater than ϑm and distribution in the plane occurs for angles less than ϑm. By spinning very close to the magic angle the averaged dipolar coupling between the nuclei of a molecule dissolved in the nematic phase can be reduced by up to two orders of magnitude. This reduction is used to convert the ABC pattern of 19F in CF2CFBr to a first order spectrum. Such simplification removes one of the most severe limitations of the chemical application of NMR in liquid crystal solvents. Also obtained is a 13C spectrum of a liquid crystal with the proton dipolar couplings almost totally eliminated by spinning alone.

Rheology and Rheo-optics of Liquid Crystal Polymers

Studies on deformations and flow mechanisms of polymer liquid crystals are expected to afford us fundamental knowledges to clarify the technologically important phenomena, including fiber formation in liquid crystal spinning. A rheological study alone, however, cannot tell the full story of deformation mechanisms of polymer liquid crystalline systems, because the systems usually form complicated super-structures or textures, the unstability of which have been prevented us from studing the relationship between the physical properties and structures. The author and his coworkers have developed new rheo-optical techniques and investigated the relations between structure and rheological properties of various liquid crystals, including liquid crystalline polymers. In this paper, these techniques and some recent experimental results are introduced.After a brief introduction to liquid crystals in general and their rheological properties, the rheology of liquid crystalline polymers is summarized by the three-region flow curve. And then rheo-optical properties of these liquid crystalline polymers are introduced. Spectro-photometric method is very effective for studing deformation and flow mechanism of cholesteric liquid crystals. Polarized-light method is expected to be developed for more general use. Both the rheo-optical and rheological properties of a liquid crystalline polymers may be interpreted by supposing three typical structural models for bulk structure of the polymer liquid crystalline system proposed before.

EPR study of a spinning nematic liquid crystal in a tilted magnetic field

Electron paramagnetic resonance measurements of the lag angle between the director and an external magnetic field for a nematic liquid crystal spinning about an axis oriented arbitrarily with respect to the field are reported. It is shown that the rotational frequency range in which the director distribution is essentially uniform increases rapidly as the rotation axis-applied field angle is reduced from 90°. The results indicate that magnetic torque measurements should be sufficient to determine both the rotational viscosity coefficient and the anisotropic part of the diamagnetic susceptibility.