Graphene Oxide Liquid Crystals Research Articles

Stable graphene oxide-based lyotropic liquid crystals for interfacial lubrication

Lyotropic liquid crystals have lubricating properties due to their ordered assembly and fluidity, whose mesogens are often characterized by amphiphilic properties. Despite the attention that graphene oxide (GO) has been studied as a novel amphiphilic lyotropic mesogen this decade, and GO applied as a lubrication additive has been demonstrated in both oil and water-based systems, little research reveals the interfacial lubrication of GO liquid crystals yet. This work reports that GO aqueous dispersion can form lyotropic liquid crystals above a specific critical concentration of 5.00 mg/mL, providing a form of stable water-based lubricant, which can keep stable for several months and can reduce friction by 37.3% and wear by 25.24%. The liquid crystal phase was verified by polarizing microscope and synchrotron radiation small-angle X-ray scattering, and its rheological properties and viscoelasticity were studied by interfacial rheometer. The formation of lyotropic liquid crystals can enhance the stability of GO aqueous dispersions at high density, simultaneously ensuring friction decrease and anti-wear effect. It is attributed to the stable nematic network by the ordered GO sheets. The ordered assembly structure bears vertical shear force, therefore, reducing the wear. It is also assumed that the wide lateral size of graphene oxide promotes the nematic phase thus smoothes the graphene oxide film composed spontaneously under the coincidence of lamellar liquid crystal and 2D layered material. Through this work, the interlayer lubrication of GO was optimized, and the problem of GO dispersion sedimentation was solved by self-assembly. The range of interfacial lubrication of GO aqueous dispersion has been expanded and the synergistic effect is conducive to the environmentally friendly lubricants.

A hybrid ionic liquid crystal comprising imidazolium surfactant-graphene oxide

ABSTRACT To produce graphene oxide liquid crystal composites with better controllability, imidazolium surfactant with biphenyl mesogenic core (CBphCM) has been synthesised and used to modify the negatively charged surface of graphene oxide (GO) to obtain a hybrid ionic liquid crystal (CBphCM-GO). The process of GO and CBphCM recombination was monitored by various experimental techniques such as FT-IR, Uv-vis, Raman and XPS. The experimental results indicated that the C=O bonds on GO sheets are all reduced and C−O bonds are partially reduced due to the imidazolium units being electrically active and nitrogen-rich, and the presence of the N−O bonds indicates that a new hybrid is formed between CBphCM and GO. The recombination destroys the electrostatic repulsion balance among the GO lattices, and the CBphCM-GO is observed a fluffy appearance by TEM. The liquid crystal properties of CBphCM and CBphCM-GO were investigated by DSC, polarised optical microscopy (POM) and variable temperature X-ray diffraction, respectively. As an ionic liquid crystal, CBphCM has SmA as well as the rare SmC phases exhibits de Vries-like behaviour with a layer shrinkage. The liquid crystal properties of CBphCM-GO are derived from CBphCM, and the layer shrinkage behaviour from SmA to SmC phase has also been observed.

Directed alignment of graphene-oxide liquid crystals in confined spaces: Effects of flow, pickering stabilization, and phase transition

Because of its versatility for processing, graphene oxide (GO) serves as a superior substance for two-dimensional carbon-based materials. Controlling GO alignment is crucial to augment its inherent anisotropic nature. Here, we report the controlled alignment of GO confined in the rectangular and circular capillary tubes. GO aligns in contrasting orientations according to the phase of GO dispersion during loading into a capillary. Upon GO liquid crystal (LC) loading, GO-layers are oriented tangential to the inner surface of capillary, resulting in a concentric organization of the GO-layers. In the LC phase, the GO orientation is mainly influenced by the flow so that the GOs are aligned tangential to the hydraulic shear plane. However, GO self-assembles parallel to the capillary cross-section when loaded in the isotropic phase and then concentrated into the LC phase. Surprisingly, by excluding flow-induced effects, the GO layer is aligned perpendicular to the inner surface throughout the capillary. This unexpected alignment of the GO-layers is initiated in the meniscus region by the “Pickering effect” (i.e., tangential adsorption of GO along the Air-Liquid interface). Upon solvent evaporation, GO dispersions experience a sequential isotropic to nematic phase transition from the meniscus to the central region. During the phase transition, the orientation of the GO layer is determined by the long-range ordering of the LC phase. As a result, the alignment effect caused by the Air-Liquid interface determines the GO alignment throughout the capillary. Our results provide useful insight into the delicate control of GO alignment in a confined space. Precise control of GO alignment in a confined space can be achieved based on the appropriate directional design of the Air-Liquid interface and the corresponding sequential phase transition.

Nanoporous multilayer graphene oxide membrane for forward osmosis metal ion recovery from spent Li-ion batteries

The recovery of Li and rare metals from the spent electrodes of Li-ion batteries (LIBs) is becoming increasingly important. Herein, nanoporous multilayer graphene oxide (NMG) membranes were fabricated via the confined thermal annealing method to achieve Li-ion selectivity. A graphene oxide (GO) membrane was prepared by coating the membrane with an aqueous layer of GO liquid crystal via the scalable bar coating method, followed by hot-pressing. The influence of the GO interlayer spacing and nanopore presence on the ion separation performance was investigated. The NMG membrane shows different ion permeance phenomena depending on ion concentration. The permeation rate of divalent ions (Co, Ni, Mn) through the NMG membrane was faster than that of Li ions in solution with low ionic strength, whereas the membrane was Li-ion selective in mixed ionic solutions or at high ionic strength. This result indicates that electrostatic interaction by oxygen groups is important at low ionic strength, but size exclusion by interlayer spacing and adsorption by nanopore is critical at high ionic strength. The ion permeation mechanisms were further examined based on molecular calculations, which revealed that the binding energies between the divalent ions and nanopores or basal plane of graphene were high, resulting in slow ion permeation. When the NMG membrane was combined in a forward osmosis system, Li-ion can be separated continuously from the mixture solution simulated from the spent Li-battery electrode. This approach shows the high potential of nanoporous multilayer graphene membrane for Li extraction in particular with dense pore structure and around 7 Å of d-spacing.

Graphene Oxide Based Transparent Resins For Accurate 3D Printing of Conductive Materials

AbstractDigital Light Processing (DLP) allows the fast realization of 3D objects with high spatial resolution. However, DLP is limited to transparent resins, and therefore not well suited for printing electrically conductive materials. Manufacturing conductive materials will significantly broaden the spectrum of applications of the DLP technology. But conductive metals or carbon‐based fillers absorb and scatter light; inhibiting thereby photopolymerization, and lowering resolution. In this study, UV transparent liquid crystal graphene oxide (GO) is used as precursor for generating in situ conductive particles. The GO materials are added to a photopolymerizable resin via an original solvent exchange process. By contrast to earlier contributions, the absence of drying during the all process allows the GO material to be transferred as monolayers to limit UV scattering. The absence of UV scattering and absorption allows for fast and high‐resolution 3D printing. The chosen resin sustain high temperature to enable an in situ efficient thermal reduction of GO into reduced graphene oxide (rGO) that is electrically conductive. The rGO particles form percolated networks with conductivities up to 1.2 × 10−2 S m−1. The present method appears therefore as a way to reconcile the DLP technology with the manufacturing of 3D electrically conductive objects.

Continuous structural deformation of graphene oxide liquid crystal colloids under shear for hydrogel films

In the processing of two-dimensional (2D) liquid crystal (LC), the microstructure of 2D LC colloids is continuously deformed by shearing, which ultimately determines their physical properties. However, it is experimentally difficult to investigate and visualize how the microstructure continuously changes during processing involving shear stress. Thus, controlling the microstructure of 2D LCs using shear forces remains a more difficult problem.Herein, we report the in-situ analysis of structural deformation for 2D colloids liquid crystals focused on the reorientation of the liquid crystal (LC) under oscillatory shear. Graphene oxide (GO) was employed as a model system for 2D LC colloids, and polymers were added to control the 2D colloidal interactions. We found that the GO structure deforms in two steps: The first step is the transition to multi-domains of GO LC and the second transition brings the macroscopic alignment of GO. We additionally found that the added polymer causes the earlier disappearance of multiple GO LC domains and provides a better macroscopic alignment at the same shear condition. The study will be of great interest in the 2D colloidal process accompanying yielding behavior, providing an effective strategy to control the domain orientation and the resulting properties.

Self-Assembly of a Graphene Oxide Liquid Crystal for Water Treatment.

Adsorbents, especially those with high removal efficiency, long life, and multi-purpose capabilities, are the most crucial components in an adsorption system. By taking advantage of the liquid-like mobility and crystal-like ordering of liquid crystal materials, a liquid crystal induction method is developed and applied to construct three-dimensional graphene-based adsorbents featuring excellent shape adaptability, a distinctive pore structure, and abundant surface functional groups. When the monoliths are used for water restoration, the large amount of residual oxygen-containing groups is more susceptible to electrophilic attack, thus contributing to cation adsorption (up to 705.4 mg g-1 for methylene blue), while the connected microvoids between the aligned graphene oxide sheets facilitate mass transfer, e.g., the high adsorption capacity for organic pollutants (196.2 g g-1 for ethylene glycol) and the high evaporation rate for water (4.01 kg m-2 h-1). This work gives a practical method for producing high-performance graphene-based functional materials for those applications that are sensitive to surface and mass transfer properties.

Monodomain Liquid Crystals of Two-Dimensional Sheets by Boundary-Free Sheargraphy

HighlightsMonodomain liquid crystals of graphene oxide over 30 cm is realized by boundary-free sheargraphy.The achieved monodomain liquid crystals have bidirectional sheet ordering, exhibiting unique optical, rheological, and conductive properties.Boundary-free sheargraphy extends to freely design delicate topology of two-dimensional colloids, including topological structures with defect strength from − 2 to + 2 and complex polydomain.

Graphene Oxide Liquid Crystals Aligned in a Confined Configuration: Implications for Optical Materials

Orientation control of two-dimensional (2D) colloidal liquid crystals in both microscopic and macroscopic scales holds massive promise for improved multifield applications. In this respect, graphene oxide (GO) is used as a platform substance for 2D carbon-based lyotropic liquid crystal (LC) materials. Here, we design the directed alignment of aqueous GO-LC dispersion confined in a rectangular capillary tube. The isotropic GO dispersion is loaded into a horizontal capillary and subsequently concentrated to the LC phase by slow water evaporation at open ends of the tube. An obtained surprising result, GO layers organize normal to the inner surfaces of the capillary with a highly ordered orientation of the optic axis over tens of millimeters. Such transverse orientation of GO layers originates from the meniscus region and then moves toward the center, caused by the interfacial effect and the sequential isotropic-to-nematic transition. This aligned mesomorphic system is characterized via optical retardation, nematic order parameter, absorption, and modified Cauchy’s transmission equation about the dependency of both birefringence and wavelength with concentration. Finally, the aligned GO-LC layers are preserved in a polymer composite matrix by photopolymerizing the evaporation-aligned GO/acrylamide-LC dispersion confined in a capillary. This composite shows higher thermal stability than polyacrylamide until 500 °C of about 6.1%. Our experimental findings provide efficient advantages for controlling the orientation of GO-LC and 2D materials, beneficial for diverse optical applications due to their directional ordering.

Polyethylene oxide-intercalated nanoporous graphene membranes for ultrafast H2/CO2 separation: Role of graphene confinement effect on gas molecule binding

H2/CO2 separation is essential for various industrial applications, such as hydrocarbon steam reforming for H2 production. Herein, a layered composite membrane composed of nanoporous graphene (NG) and polyethylene oxide (PEO) is developed. The membrane demonstrates an ultrafast H2 permeability of ca. 32 240 barrer with a moderate H2/CO2 selectivity of 25, which far surpasses the upper bound of the separation performance demonstrated by existing membrane materials. The regularly layered structure is fabricated by facilitating the intercalation of PEO via an aqueous graphene-oxide liquid crystal (GOLC) scaffold. After preparing the layered GO/PEO membrane, hot pressing is conducted to activate dense nanopores on the basal plane of graphene, resulting in an NG/PEO membrane. The permeation of gas molecules is significantly enhanced owing to the presence of nanopores and expansion of the interlayer spacing by PEO. In contrast, CO2 permeation is lower than that of H2 owing to its strong binding interaction with PEO, and molecular simulations demonstrate that this CO2–PEO interaction is significantly enhanced owing to the confinement of PEO in the graphene interlayer spacing, particularly at d-spacing of approximately 7–8 Å.

(Digital Presentation) Chemically Modified Graphene for Real-World Applications: Graphene Oxide Liquid Crystal & Single Atom Catalysts

Graphene Oxide Liquid Crystal (GOLC) is an emerging 2D carbon based soft material, which exhibits nematic type colloidal discotic liquid crystallinity with the 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, including highly oriented 1D fibers, 2D films and 3D nanoporous structures. Besides, relevant research works associated to the nanoscale assembly and chemical modification of various low dimensional materials, including 1D carbon nanotubes, 2D TMDs and MXene, will be presented particularly aiming at energy and environmental applications. In the last part of presentation, our wold-first discovery of single atom catalyst will be introduced also, including other research efforts exploiting customized heteroelement doping of graphene based strucures.

Photocuring Graphene Oxide Liquid Crystals for High-Strength Structural Materials.

Graphene is the strongest known material. However, the challenge of translating that strength from the microscale to the more useful macroscale remains unmet. Preparing solid structures from self-assembled graphene oxide liquid crystals has allowed the creation of paper and fibers with excellent mechanical properties. Conventionally, vacuum filtration, wet spinning, and freeze-drying are used to prepare such structures from graphene oxide liquid crystals. Here, we introduce photocuring as an additional option to create solid structures of self-assembled graphene oxide liquid crystals that allows for thicker samples and other shapes to be realized. The photocured graphene oxide paper prepared here exhibited mechanical properties comparable to those of benchmark samples prepared by vacuum filtration.

Aspect ratio dependent viscoelastic properties of graphene oxide liquid crystals

We present a systematic investigation of the size-dependent viscoelastic properties of aqueous suspensions of graphene oxide (GO). The study is performed on three different size graphene oxide dispersions with an average sheet surface area of 22.89, 126.42 and 173.83 μm2. The viscoelastic properties of the GO suspensions are found to be strongly dependent on the size of GO sheets. Irrespective of the size, all the GO dispersions revealed an isotropic phase at low volume fractions and a nematic liquid crystalline phase above critical volume fractions. The formation of nematic liquid crystalline phase strongly depends on the size of GO sheets. The steady-state flow measurements confirmed the nematic liquid crystalline phase formation at a lower fraction (φ = 0.24%) for ultra-large GO sheet dispersion than small area graphene oxide dispersion (φ = 0.45%). Further, frequency sweep measurements of ultra-large GO suspension exhibit higher storage and loss moduli than small area graphene oxide dispersion for a particular GO concentration. The study also confirmed the gel-like phase formation at a higher GO fraction (φ > 0.73%), where both storage and loss moduli are nearly independent of frequency. The reported size-dependent viscoelastic properties of GO liquid crystals are very important for the fabrication of GO-based materials for various potential applications.

Photonic liquid crystals of graphene oxide for fast membrane nanofiltration

The photonic liquid crystalline (LC) dispersion of graphene oxide (GO) is prepared using centrifugation-induced size-fractionization. Under gravity, a series of successive centrifugations enable large GO sheets to sediment and fractionize into a narrowed size distribution. The resulting large GO sheets display large-area monodomain structures with uniform orientation, forming a photonic LC phase. The single lyotropic LC phase forms at the concentration > 0.34 wt% and structural coloring occurs at the concentration > 0.59 wt%. The structural color with different wavelength is tuned with various concentrations (0.59–0.92 wt%). GO membranes are supported on porous poly(ether sulphone) membranes from photonic LC dispersions by a vacuum-spin method. The photonic GO membrane demonstrates dramatic enhancement of water permeance (169.3 Lm −2 hr −1 bar −1 ), which is 12 times faster than the control GO membrane (13.2 Lm −2 hr −1 bar −1 ). The ion rejection of the photonic GO membrane (45–60%) is also significantly improved, as compared to the control GO membrane (30–48%). Organic dye rejection testing shows that the photonic GO membrane remains as high molecular rejection (> 90%) as the control GO membrane. This work may provide a new way to fabricate ordered GO membranes for fast nanofiltration.

Mechanically strong and highly ion conductive graphene oxide liquid crystal film containing the poly(amic acid) salt

Mechanically strong and highly ion conductive graphene oxide liquid crystal film containing the poly(amic acid) salt

Continuous Structural Deformation of Graphene Oxide Liquid Crystal Colloids Under Shear for Hydrogel Films

Continuous Structural Deformation of Graphene Oxide Liquid Crystal Colloids Under Shear for Hydrogel Films

Self-assembly and antistatic property of poly(styrene sulfonic acid)-based graphene oxide liquid crystal compounds

ABSTRACT Series of poly(styrene sulphonic acid)-based graphene oxide liquid crystals (GOLCs) were synthesised by use of graphene oxide (GO), poly(styrene sulphonic acid), cholesteryl-containing liquid crystal and pyridinyl-based compounds in a self-assembly process. The chemical structure, liquid crystalline behaviour and antistatic property were investigated using appropriate analytical instrument and various experimental techniques. The GOLCs exhibited smectic A phase on heating cycles. The antistatic property was performed by use of a four-probe measuring instrument at different humidity conditions after a liquid crystalline ordering structure were well developed in these GOLC films. All the GOLC films show surface resistivity on the same order of magnitude (kΩ sq−1) at different relative humidity, suggesting that the humidity of the environment is not dominant in the antistatic property. In the microstructure, the GOLC layers are aligned in a liquid-crystalline ordering structure, a hydrogen bonding area of the sulphonic acid- and carboxylic acid-pyridyl linkages around GO is formed continuously without interruption, leading to conduction pathways from the interior cores to the whole surface. It indicates that antistatic property of these GOLCs is not completely dependent on the surface humidity derived from water absorption.

Photo-responsive graphene oxide liquid crystal hybrid modified with imidazolium surfactant containing azobenzene

ABSTRACT A novel photo-responsive imidazolium surfactant containing azobenzene mesogenic cores (CAzoCM) was designed and synthesised to modify graphene oxide, forming imidazolium surfactant-graphene oxide hybrid (CAzoCM-GO), focusing on the correlation between their mesomorphic behaviour, photo-responsive properties and their chemical structure. CAzoCM and CAzoCM-GO were characterised by FT−IR, Raman spectroscopy and XPS, respectively. The results showed that GO was partially reduced by CAzoCM due to the strong electron effect of the imidazole group. The liquid crystal properties of CAzoCM and CAzoCM-GO were investigated by DSC, POM and variable temperature XRD, respectively. CAzoCM exhibited a smectic A phase as well as the rare smectic C phase and the introduction of GO did not destroy the liquid crystal properties of CAzoCM. Furthermore, the photo-responsive behaviour of CAzoCM and CAzoCM-GO had also been studied by UV-vis spectrum. CAzoCM could be switched from trans to cis isomer in 270 s when it was irradiated under ultraviolet light and from cis to trans isomer in 660 s when it was irradiated under visible light. CAzoCM-GO exhibited more sensitive response behaviour, the photo-responsive time from trans to cis isomerisation became 110 s while the photo-responsive time from cis to trans isomerisation became 195 s.

High-Performance Nanofiltration Membranes from Polyphenol–Graphene Oxide Liquid Crystals Prepared Using Natural Extract

High-Performance Nanofiltration Membranes from Polyphenol–Graphene Oxide Liquid Crystals Prepared Using Natural Extract

Enhancing the Mechanical Performance of Reduced Graphene Oxide Aerogel with Cellulose Nanofibers

AbstractUltralight, highly compressible and superelastic carbon materials hold great promise in wearable and flexible electronic devices, but the fabrication remains to be a challenge because of the brittleness nature of carbon. Herein, a carbon aerogel with ultralow density yet high mechanical performance is successfully fabricated from graphene oxide (GO) liquid crystal stabilized bubbles with the enhancement of cellulose nanofiber (CNF). The incorporation of CNF into reduced graphene oxide (rGO) nanosheets enhances the interaction among rGO nanosheets through welding effect, which restricts the slip of rGO nanosheets and the detachment among microspheres, leading to a significant improvement on mechanical properties. The as‐prepared carbon aerogel with tightly packaged cell‐wall architecture displays ultrahigh compressibility (up to 99% strain) and elasticity (90.1% stress retention and 99.0% height retention after 10000 cycles at 50% strain), which are superior to those of the present bubble‐templated carbon aerogels and many other carbon materials through various methods. The structural feature leads to rapid and stable current response and high sensitivity to external strain and pressure, allowing the carbon aerogel to detect very small pressure and various human motions from finger bending to pulse. These advantages make the carbon aerogel promising for flexible electronic devices.