Graphene Oxide Liquid Crystals Research Articles

Dry Spin Graphene Oxide Fibers: Mechanical/Electrical Properties and Microstructure Evolution

Dry-spinning method is extensively employed in fiber industry, comparing to the counter-part of wet-spinning process, it has advantages of environmentally friendly, high yield rate and no need for purification. Here, we report the synthesis of graphene oxide (GO) fibers via dry spinning GO inks with extremely high concentrations. The proper rheology properties of such GO inks allow us to dry spin GO fiber directly. Various dry spinning conditions are investigated, and the relationship between mechanical performance and micro-structure of the obtained GO fiber are established. We found that the existence of larger GO liquid crystal domains does not necessarily result to higher mechanical properties, and it is because those large GO liquid crystal domains evolve into thick GO films during drying process and thus prevent the intimate compaction of the whole GOF and leave behind gaps. This is detrimental for the mechanical properties, and thus the dry spin GOF are much weaker than that of wet spin ones. Importantly, Barus effects, that generally arise during the melt spinning of polymers, were not observed, indicating that caution must be taken when classical polymer rheology theories are applied to investigate the dynamic behaviors of GO solution.

(Invited) Graphene Oxide Liquid Crystals and Relevant Functional Nanostructures

Graphene Oxide Liquid Crystal (GOLC) is a newly emerging graphene based material, which exhibits nematic type colloidal discotic liquid crystallinity with orientational ordering of graphene oxide flakes in good solvents, including water. Since our first discovery of GOLC in aqueous dispersion at 2009, this interesting mesophase has been utilized over world-wide for many different application fields, such as liquid crystalline graphene fiber spinning, highly ordered graphene membrane/film production, prototype liquid crystal display and so on. Interestingly, GOLC also allow us a valuable opportunity for the highly ordered molecular scale assembly of functional nanoscale structures. This presentation will introduce our current status of GOLC research particularly focusing on the nanoscale assembly of functional nanostructures. Besides, relevant research works associated to the nanoscale assembly and chemical modification of various nanoscale graphene based materials will be presented.

Graphene oxide liquid crystals: a frontier 2D soft material for graphene-based functional materials.

Graphene, despite being the best known strong and electrical/thermal conductive material, has found limited success in practical applications, mostly due to difficulties in the formation of desired large-scale highly organized structures. Our discovery of a liquid crystalline phase formation in graphene oxide dispersion has enabled a broad spectrum of highly aligned graphene-based structures, including films, fibers, membranes, and mesoscale structures. In this review, the current understanding of the structure-property relationship of graphene oxide liquid crystals (GOLCs) is overviewed. Various synthetic methods and parameters that can be optimized for GOLC phase formation are highlighted. Along with the results from different characterization methods for the identification of the GOLC phases, the typical characteristics of different types of GOLC phases introduced so far, including nematic, lamellar and chiral phases, are carefully discussed. Finally, various interesting applications of GOLCs are outlined together with the future prospects for their further developments.

Graphene-based cellular materials with extremely low density and high pressure sensitivity based on self-assembled graphene oxide liquid crystals

A flexible strain sensor based on an ultralow density cellular material exhibits extremely high sensitivity.

Conductive Tough Hydrogel for Bioapplications.

Biocompatible conductive tough hydrogels represent a new class of advanced materials combining the properties of tough hydrogels and biocompatible conductors. Here, a simple method, to achieve a self-assembled tough elastomeric composite structure that is biocompatible, conductive, and with high flexibility, is reported. The hydrogel comprises polyether-based liner polyurethane (PU), poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(4-styrenesulfonate) (PSS), and liquid crystal graphene oxide (LCGO). The polyurethane hybrid composite (PUHC) containing the PEDOT:PSS, LCGO, and PU has a higher electrical conductivity (10×), tensile modulus (>1.6×), and yield strength (>1.56×) compared to respective control samples. Furthermore, the PUHC is biocompatible and can support human neural stem cell (NSC) growth and differentiation to neurons and supporting neuroglia. Moreover, the stimulation of PUHC enhances NSC differentiation with enhanced neuritogenesis compared to unstimulated cultures. A model describing the synergistic effects of the PUHC components and their influence on the uniformity, biocompatibility, and electromechanical properties of the hydrogel is presented.

Nanostructured Electrospun Hybrid Graphene/Polyacrylonitrile Yarns.

Novel nanostructured hybrid electrospun polyacrylonitrile (PAN) yarns with different graphene ratios were prepared using liquid crystal graphene oxide (LCGO) and PAN. It was found that the well-dispersed LCGO were oriented along the fiber axis in an electrified thin liquid jet during electrospinning. The graphene oxide sheets were well dispersed in the polar organic solvent, forming nematic liquid crystals upon increasing concentration. Twisted nanofibers were produced from aligned nanofibrous mats prepared by conventional electrospinning. It was found that the mechanical properties of the twisted nanofiber yarns increased even at very low LCGO loading. This research offers a new approach for the fabrication of continuous, strong, and uniform twisted nanofibers which could show promise in developing a novel carbon fiber precursor.

Graphene Oxide Liquid Crystals Special Issue, Editorial

Graphene Oxide Liquid Crystals Special Issue, Editorial

Graphene Oxide: Liquid Crystals of Graphene Oxide: A Route Towards Solution‐Based Processing and Applications (Part. Part. Syst. Charact. 9/2017)

Graphene Oxide: Liquid Crystals of Graphene Oxide: A Route Towards Solution‐Based Processing and Applications (Part. Part. Syst. Charact. 9/2017)

Confinement effects on lyotropic nematic liquid crystal phases of graphene oxide dispersions

Graphene oxide (GO) forms well ordered liquid crystal (LC) phases in polar solvents. Here, we map the lyotropic phase diagram of GO as a function of the lateral dimensions of the GO flakes, their concentration, geometrical confinement configuration and solvent polarity. GO flakes were prepared in water and transferred into other polar solvents. Polarising optical microscopy (POM) was used to determine the phase evolution through the isotropic-biphasic-nematic transitions of the GO LC. We report that the confinement volume and geometry relative to the particle size is critical for the observation of the lyotropic phase, specifically, this determines the low-end concentration limit for the detection of the GO LC. Additionally, a solvent with higher polarisability stabilises the LC phases at lower concentrations and smaller flake sizes. GO LCs have been proposed for a range of applications from display technologies to conductive fibres, and the behaviour of LC phase formation under confinement imposes a limit on miniaturisation of the dimensions of such GO LC systems which could significantly impact on their potential applications.

Wet-Spun Superelastic Graphene Aerogel Millispheres with Group Effect.

Graphene aerogel has attracted great attention due to its unique properties, such as ultralow density, superelasticity, and high specific surface area. It shows huge potential in energy devices, high-performance pressure sensors, contaminates adsorbents, and electromagnetic wave absorbing materials. However, there still remain some challenges to further promote the development and real application of graphene aerogel including cost-effective scalable fabrication and miniaturization with group effect. This study shows millimeter-scale superelastic graphene aerogel spheres (GSs) with group effect and multifunctionality. The GSs are continuously fabricated on a large scale by wet spinning of graphene oxide liquid crystals followed by facile drying and thermal annealing. Such GS has an unusual core-shell structure with excellent elasticity and specific strength. Significantly, both horizontally and vertically grouped spheres exhibit superelasticity comparable to individual spheres, enabling it to fully recover at 95% strain, and even after 1000 compressive cycles at 70% strain, paving the way to wide applications such as pressure-elastic and adsorbing materials. The GS shows a press-fly behavior with an extremely high jump velocity up to 1.2 m s-1 . For the first time, both free and oil-adsorbed GSs are remotely manipulated on water by electrostatic charge due to their ultralow density and hydrophobic properties.

Discotic Liquid Crystals with Graphene: Supramolecular Self‐assembly to Applications

In past decades many breakthroughs have been witnessed in research on liquid crystals (LCs) and the application of LCs has spread. On another side graphene is considered as a rapidly rising star on the horizon of materials science, soft condensed matter physics and promising applications. Supramolecular chemistry of LCs and graphene together is described as “chemistry beyond the molecule”. A new class of 2D colloidal graphene oxide liquid crystalline material consisting discotic liquid crystallinity and their interactions with LCs present a platform for number of versatile properties and applications. This review focuses on discotic liquid crystalline (DLC) behavior of graphene oxide/reduced graphene oxide in various solvents, their characterization and application for energy storage, wet‐spinning fibers, electro‐optical devices, and displays etc. In the first part of this review, a brief introduction of discotic graphene oxide liquid crystals (GOLCs), their fundamental, synthesis process, supramolecular structures of graphene‐DLC composites is highlighted. In the second part, some important physical studies and application of this largest polycyclic aromatic core of DLCs are discussed. Finally, an outlook on this emerging two dimensional material in liquid crystal field with relevant scientific application background is presented.

Phase Transition and Liquid Crystalline Organization of Colloidal Graphene Oxide as a Function of pH

This paper discusses the influence of pH on colloidal graphene oxide (GO) liquid crystals. The results indicate that there is a crossing point where suspensions at pH > pKa, the GO sheets have different behavior than suspensions at pH < pKa. This behavior is evidenced by broadening of the biphasic region in the isotropic to nematic phase transition, by observing different shape and internal configurations of the nematic droplets, and in the magnitude of fractionation between large and small sheets in the nematic and isotropic phases. The behavior of GO liquid crystal droplets under the influence of a static magnetic field is studied, and evidence is found in the magnetically induced distortions for the support of our interpretation of the internal configurations of the nematic droplets. This study also demonstrates that magnetic distortions are reversible on a time scale of minutes to hours. This research is based on the LC‐PolScope, a polarized light system, which is found to be a powerful tool for characterization of GO liquid crystals due to its fast and easy image acquisition and analysis.

Secondary Interactions of Graphene Oxide on Liquid Crystal Formation and Stability

Graphene oxide liquid crystals (GO LC) prove their potential usefulness in a new design of carbon scaffold composites with ordered structures from nano to macroscale. This paper highlights the degree of GO functionalization as a notable influencing factor on GO LC formation. The large amount of oxygen functional groups, which cause secondary interactions between GOs, decrease the critical concentration for the phase transitions from isotropic to biphasic to nematic phases. In the biphasic state where isotropic and anisotropic phases coexist, highly oxidized GO sheets spontaneously develop LC phases among themselves. Furthermore, the strong hydrogen bonding networks between GO sheets govern the stabilization of the GO aqueous dispersion for a long period. This unique behavior can be used to design GO‐based architecture with controllable density and ordering.

Liquid Crystals of Graphene Oxide: A Route Towards Solution‐Based Processing and Applications

The liquid crystalline behavior of graphene oxide (GO) has enabled the design of facile and effective solution processing methods for assembling highly ordered macroscopic graphene structures, further expanding the development of novel graphene‐based devices. In this progress report, first the preparation of liquid crystalline graphene oxide (LCGO) with a particular emphasis on different approaches to improve the oxidation efficiency and to control the GO sheet size is discussed. Then the use of LCGO dispersions in the solution processing of 1D, 2D and 3D architectures with highly tailored microstructures is covered. The LCGO composites are also reviewed as an important part of novel graphene‐based multi‐functional materials. Finally, various applications of LCGO are discussed to highlight the critical role of LCGO in expanding the applications of graphene. Based on these systematic discussions, an outlook on the future directions, challenges, and opportunities in this field is provided.

Dielectrophoretic Condensation and Tailored Phase Separation in Graphene Oxide Liquid Crystals

The authors demonstrate electric‐field‐induced isotropic–nematic or biphase–nematic phase separation using dielectrophoretic condensation of graphene oxide (GO) particles in a dispersion medium. Phase separation using dielectrophoresis (DEP) has several advantages over gravity‐induced phase separation: the concentration of a DEP‐induced nematic can be controlled over a wider range, the spatial shape of phase separation can be arbitrary tailored through electrode design, and the GO particles are better aligned. Using optical absorption and birefringence of wet samples and microscopy observations of freeze‐dried fracture samples, the alignment and density modulation of GO particles in the DEP cell are investigated. This work demonstrates that DEP is a simple and useful tool to control the local phases, density, and GO alignment in wet dispersions.

Amorphous Molybdenum Sulfide Deposited Graphene Liquid Crystalline Fiber for Hydrogen Evolution Reaction Catalysis

Amorphous Molybdenum Sulfide Deposited Graphene Liquid Crystalline Fiber for Hydrogen Evolution Reaction Catalysis

Polycaprolactone-templated reduced-graphene oxide liquid crystal nanofibers towards biomedical applications

Here, we report a facile method to generate electrically conductive nanofibers by coating and subsequently chemically reducing graphene oxide (GO) liquid crystals on a polycaprolactone (PCL) mat.

Controlling wrinkles and assembly patterns in dried graphene oxide films using lyotropic graphene oxide liquid crystals

ABSTRACTWe fabricated graphene oxide (GO) films on glass substrates by blade coating a lyotropic GO liquid crystal dispersion. Substrate temperature and blading speed were precisely controlled to manipulate the surface morphologies of GO films. The temperature and blade speed influenced the drying rate of film and the amount GO dispersion supplied. By controlling these parameters, film-thickness modulation and three types of surface wrinkle patterns were selectively achieved. We also plotted the wrinkle patterns diagram as functions of the film fabrication conditions. The films exhibited different optical anisotropies depending on wrinkle patterns. GO films with controlled wrinkles can be used as electrodes for supercapacitor applications owing to the large surface areas.

Ionic interactions to tune mechanical and electrical properties of hydrated liquid crystal graphene oxide films

Considerable improvements have been obtained in physical and mechanical properties of free standing liquid crystal graphene oxide (LCGO) films in their hydrated state, by modification of LCGO dispersions with a low quantity of chloride salts. Addition of salts to LCGO dispersions result in an increase of the storage and loss moduli and viscosity through the interaction between cations and functional groups of LCGO, with the magnitude of increase being dependent upon the concentration of the salt added. A viscosity increase of between 30× and 300× (depending on the salt type) is recorded when salt is added at a concentration as low as 80 mM while storage and loss moduli increase up to 23× and 29×, respectively. Free standing films made from the salt treated LCGO dispersions contained up to 26% water in their structure and were observed to have significantly improved mechanical (2× to 5× increase) and electrical properties (decreased surface resistance up to approximately 670×) compared to free standing films prepared without chloride salts. The influence of the salts on properties of LCGO dispersions and their hydrated free standing films is postulated as a complex interplay of many factors such as the size of cations, the valency of positive charge of the cations, ratio of charge and cations size, as well as the hygroscopic nature of the salts.

Role of Graphene Oxide Liquid Crystals in Hydrothermal Reduction and Supercapacitor Performance.

The formation of liquid crystal (LC) phases in graphene oxide (GO) aqueous solution is utilized to develop high-performance supercapacitors. To investigate the effect of LC formation on the properties of subsequently reduced GO (rGO), we compare films prepared through blade-coating of viscous LC-GO solution and ultrasonic spray-coating of diluted GO aqueous dispersion. After hydrothermal reduction under identical conditions, the films show different morphology, oxygen content, and specific capacitance. Trapped water in the LC GO film plays a role in preventing restacking of sheets and facilitating the removal of oxygenated groups during the reduction process. In device architectures with either liquid or polymer electrolyte, the specific capacitance of the blade-coated film is twice as high as that of the spray-coated one. For a blade-coated film with mass loading of 0.115 mg/cm(2), the specific capacitance reaches 286 F/g in aqueous electrolyte and 263 F/g in gelled electrolyte, respectively. This study suggests a route to pilot-scale production of high-performance graphene supercapacitors through blade-coated LC-GO films.