Liquid Crystalline Graphene Oxide Research Articles

Fundamental Understanding of Ultrathin, Highly Stable Self-Assembled Liquid Crystalline Graphene Oxide Membranes Leading to Precise Molecular Sieving through Non-equilibrium Molecular Dynamics

Self-assembled graphene oxide lyotropic liquid crystal (GO LLC) structures are mostly formed in aqueous medium; however, most GO derivatives are water insoluble, so processing GO LLCs in water poses a practical limitation. The use of polar aprotic solvent (like dimethyl sulfoxide) for the formation of GO LLC structures would be interesting, because it would allow incorporating additives, like photoinitiators or cross-linkers, or blending with polymers that are insoluble in water, which hence would expand its scope. The well-balanced electrostatic interaction between DMSO and GO can promote and stabilize the GO nanosheets' alignment even at lower concentrations. With this in mind, herein we report mechanically robust, chlorine-tolerant, self-assembled nanostructured GO membranes for precise molecular sieving. Small-angle X-ray scattering and polarized optical microscopy confirmed the alignment of the modified GO nanosheets in polar aprotic solvent, and the LLC structure was effectively preserved even after cross-linking under UV light. We found that the modified GO membranes exhibited considerably improved salt rejection for monovalent ions (99%) and water flux (120 LMH) as compared to the shear-aligned GO membrane, which is well supported by forward osmosis simulation studies. Additionally, our simulation studies indicated that water molecules traveled a longer path while permeating through the GO membrane compared to the GO LLC membrane. Consequently, salt ions permeate slowly across the GO LLC membrane, yielding higher salt rejection than the GO membrane. This begins to suggest strong electrostatic repulsion with the salt ions, causing higher salt rejection in the GO LLC membrane. We foresee that the ordered cross-linked GO sheets contributed to excellent mechanical stability under a high-pressure, cross-flow, chlorine environment. Overall, these membranes are easily scalable, exhibit good mechanical stability, and represent a breakthrough for the potential use of polymerized GO LLC membranes in practical water remediation applications.

Nanostructuring Electrode Surfaces and Hydrogels for Enhanced Thermocapacitance

Thermogalvanic cells have the ability to convert low-temperature waste heat energy (<200 °C) into electrical energy. However, these systems cannot store this electrical energy. Thermocapacitors use analogous mechanisms to convert heat into electrical energy, but crucially can store this electrical energy. Previous work has used polyelectrolyte gels to frustrate the mobility of a redox couple, causing an accumulation of charge imbalance at the two electode:gelled electrolyte interfaces, resulting in stored thermocapacitance. Here we report an investigation into two methods of utilizing nanostructuring to increase the thermocapacitance performance of a [Fe(CN)6]3–/4– containing polyacrylate hydrogel; specifically, nanostructuring the bulk of the hydrogel and modifying the electrode with carbon nanotubes and liquid crystalline graphene oxide. Nanomaterial-enhanced carbon cloth electrodes significantly increased the available electroactive surface area and charging–discharging rates of these hydrogels, but only resulted in a modest increase in thermocapacitance. Conversely nanostructuring of the hydrogels by changing the degree of neutralization of the hydrogels resulted in significant improvement in thermocapacitance, but only when high concentrations (1 M) of ferricyanide/ferrocyanide electrolyte are available. This study indicates how two different aspects of the system can be nanostructured to enhance device performance.

The effect of liquid crystalline graphene oxide compared with non-liquid crystalline graphene oxide on the rheological properties of polyacrylonitrile solution

Abstract In this article, polyacrylonitrile (PAN) and two kinds of graphene oxide (GO) with different structural properties are blended in dimethyl sulfoxide (DMSO) according to a certain ratio to prepare stable-spinning solution. One kind of GO is purchased, and we call it GO1. The other is a kind of self-made GO with liquid crystal property in solution, which is called GO2. The effects of two kinds of GO on the rheological properties of PAN/GO spinning solution (15 wt%) were studied. The results show that the viscous activation energy of the liquid crystal GO2/PAN blend solution is significantly higher than that of the nonliquid crystal GO1/PAN blend solution. Moreover, the liquid crystal system is more obviously affected by temperature. The structural viscosity index of the liquid crystalline GO2/PAN solution is obviously lower than that of the GO1/PAN solution. It indicates that the existence of liquid crystallinity is beneficial to the spinning of the solution. In the low-frequency region, the addition of GO1 makes the solution more elastic, and the addition of GO2 makes the solution more viscous.

Platinized graphene fiber electrodes uncover direct spleen-vagus communication

Neural interfacing nerve fascicles along the splenic neurovascular plexus (SNVP) is needed to better understand the spleen physiology, and for selective neuromodulation of this major organ. However, their small size and anatomical location have proven to be a significant challenge. Here, we use a reduced liquid crystalline graphene oxide (rGO) fiber coated with platinum (Pt) as a super-flexible suture-like electrode to interface multiple SNVP. The Pt-rGO fibers work as a handover knot electrodes over the small SNVP, allowing sensitive recording from four splenic nerve terminal branches (SN 1–4), to uncover differential activity and axon composition among them. Here, the asymmetric defasciculation of the SN branches is revealed by electron microscopy, and the functional compartmentalization in spleen innervation is evidenced in response to hypoxia and pharmacological modulation of mean arterial pressure. We demonstrate that electrical stimulation of cervical and sub-diaphragmatic vagus nerve (VN), evokes activity in a subset of SN terminal branches, providing evidence for a direct VN control over the spleen. This notion is supported by adenoviral tract-tracing of SN branches, revealing an unconventional direct brain-spleen projection. High-performance Pt-rGO fiber electrodes, may be used for the fine neural modulation of other small neurovascular plexus at the point of entry of major organs as a bioelectronic medical alternative.

Loading dependency of 2D MoS2 nanosheets in the capacitance of 3D hybrid microfibre-based energy storage devices

This study reports a wet spinning method to spin composite micro-fibres of 2D liquid crystalline graphene oxide (GO) and exfoliated MoS2 nanosheets with very high MoS2 loading. The MoS2 dispersion was found to be isotropic irrespective of solvent type or solute concentration in the dispersion and thus found to be non-spinnable via wet spinning process. The liquid crystallinity of GO induces birefringence in the composite dispersion and enables the spinning of the composite dispersion containing high loading of MoS2 with great flexibility. We were able to spin composite microfibers with 69 wt% MoS2 loading for the first time. The resulting fibres were annealed at high temperature to produce flexible conductive rGO#MoS2 fibres. Scanning electron microscopy (SEM) and Raman analysis strongly suggest homogeneous distribution of MoS2 throughout the fibres. Mechanical properties of the fibres were studied and maximum tensile strength (76.5 MPa) and Young's modulus (13.3 GPa) obtained with 10 wt% MoS2 loading. All solid-state flexible symmetric supercapacitor from these composite fibres was fabricated and the electrochemical performance was studied. The electrochemical study shows high areal capacitance of the produced composite fibres (as high as 282.6 mF cm−2) with good cycling stability (82.5% capacitance retention after 5000 cycles) that indicates high potential of these composite fibres as energy storage system for smart textile of the future.

Concentric/bipolar ordering of liquid crystalline graphene oxide nanosheets confined in microfluidically synthesized spherical droplets

Liquid crystalline ordering of graphene oxide nanosheets inside strongly confined microdroplets has been investigated, which rendered either concentric or bipolar ordering according to the magnitude of physical confinement.

Bidirectional Core Sandwich Structure of Reduced Graphene Oxide and Spinnable Multiwalled Carbon Nanotubes for Electromagnetic Interference Shielding Effectiveness

Thin and flexible electromagnetic shielding materials have recently emerged because of their promising applications in drones, portable electronics, military defense facilities, etc. This research develops an electromagnetic interference (EMI) shielding material by a bidirectional lattice sandwich structure (BLSS), which is formed by liquid crystalline graphene oxide (LCGO) and an orthogonal pattern of spinnable multiwalled (OPSM) nanotubes in consideration of the movement of electromagnetic waves. The average EMI shielding effectiveness (SE) of the developed material with 0.5 wt % reduced LCGO (r-LCGO) and an OPSM nanotube composed of 64 layers was approximately 66.1 dB in the X-band frequency range (8.2-12.4 GHz, wavelength: 3.5-2.5 cm), which corresponds to a shielding efficiency of 99.9999%. Also, its absorption effectiveness is 99.7% of the total EMI SE, indicating that it has a remarkable ability to prevent secondary damage induced by EM reflection. The specific EMI SE (SSE/t) of the composite material considering the contribution of thickness (t) ranged from 21 953 to 2259 dB cm2/g.

Self-assembly and ion transport behaviour of liquid-crystalline graphene oxide multilayer sandwich nanopapers

ABSTRACT The controllability of ion channel size is critical for ion transport and sieving. Graphene oxide (GO) has a planar two-dimensional structure and a rich functional group as a binding site, and the liquid crystal material generally undergoes an orientation change under the action of an external force field. Therefore, this property can be incorporated into GO, and the distance between the layers of GO can be controlled by designing the liquid crystal cell which meets the requirements and adjusting the external force field, thereby controlling the transport of ions. In this paper, multilayer sandwich nanopapers were fabricated by liquid crystals and GO via hydrogen bonding, and the controlled ion transport behaviour was investigated. In the presence of external electric or magnetic field, ion channels in the interlayer distance of sandwich GO nanopapers can be adjusted due to the changes of mesogen orientation; therefore, ion conductivity can be adjusted when a lithium-ion solution pass through the nanopapers. Such nano-paper materials show promise in many fields such as ion transport, separation systems, ion battery and capacitor devices.

Tunable flow rate in textile-based materials utilising composite fibres

Fluid movement is critical in textile-based microfluidic devices with post-processing approaches commonly used to enhance the wicking rate of textile-based microfluidic devices. In this work, for the first time, we have demonstrated composite fibre approach as an effective, easy, tunable and cost-effective technique with long-lasting effect to change the fibres surface chemistry. This approach incorporates commercially sourced polyester yarns and a low-density polyethylene (LDPE) - liquid crystalline graphene oxide (LCGO) composite fibre integrated into a circular knitted structure. Our technique improves the mechanical properties of the resultant fibres and provides a facile route for tuning the wicking properties of textile-based microfluidics constructs. It was shown that the fluid moves up to six times faster in 3D knitted structures containing the composite fibre as compared to equivalent 3D knitted structures made of polyester yarns only, and the flow rate achievable was found to be proportional to the LCGO loading.

ZnO decorated flexible and strong graphene fibers for sensing NO2 and H2S at room temperature

Here we present toxic gas fiber-based sensor, operating at room temperature, which is important in wearable electronics for monitoring the environment and human health. Continuous strong and flexible graphene oxide (GO) fibers, with aligned GO sheets are synthesized by transforming a prealigned liquid crystalline GO solution using a wet spinning assembly. GO fibers are chemically reduced (rGO) for imparting resistance-based gas sensing. ZnO decorated rGO fibers (ZrGO) are synthesized by hydrothermal-assisted chemical reduction of GO fibers. ZnO nanoparticles and flowers, grown on ZrGO fibers, provided more surface area for adsorption of gas molecules compared to rGO fibers. Furthermore, ZrGO fibers provided more catalytic sites for gas interactions to enhance the sensing performance. The fiber-sensor can detect minimum levels of 1.5 and 8 ppm of NO2 and H2S gas, respectively. Interestingly, the sensing performance of ZrGO fiber-sensor is increased by 8 and 24-fold for NO2 and H2S, respectively, compared to rGO. The fiber-sensor shows fast recovery for H2S compared to NO2 gas. This work opens a new way for the application of robust, lightweight, cheap, and room temperature chemical sensors, that can detect hazardous gases.

Scalable Solution Processing MoS2 Powders with Liquid Crystalline Graphene Oxide for Flexible Freestanding Films with High Areal Lithium Storage Capacity.

Freestanding flexible electrodes with high areal mass loading are required for the development of flexible high-performance lithium-ion batteries (LIBs). Currently they face the challenge of low mass loading due to the limited concentrations attainable in processable dispersions. Here, we report a simple low-temperature hydrothermal route to fabricate flexible layered molybdenum disulfide (MoS2)/reduced graphene oxide (MSG) films offering high areal capacity and good lithium storage performance. This is achieved using a self-assembly process facilitated by the use of liquid crystalline graphene oxide (LCGO) and commercial MoS2 powders at a low temperature of 70 °C. The amphiphilic properties of ultralarge LCGO nanosheets facilitates the processability of large-size MoS2 powders, which is otherwise nondispersible in water. The resultant film with an areal mass of 8.2 mg cm-2 delivers a high areal capacity of 5.80 mAh cm-2 (706 mAh g-1) at 0.1 A g-1. This simple method can be adapted to similar nondispersible commercial battery materials for films fabrication or production of more complicated constructs via advanced fabrication technologies.

Effect of pyrolyzed catecholamine polymers for concurrent enhancements of electrical conductivity and mechanical strength of graphene-based fibers

Graphene fibers are regarded as a novel platform material for flexible electronic applications based on their superior electrical conductivity, mechanical properties and potential for mass production. However, properties of graphene fibers are still far from commercial level and considerable effort has been made recently to improve these characteristics. In this paper, we drastically enhanced both the mechanical and electrical properties of graphene-based fibers by converting infiltrated polydopamine (PDA) into N-doped graphitic layers. Graphene-based fibers were fabricated from a liquid crystalline graphene oxide dispersion, and PDA was introduced into the fibers. After pyrolysis, the mechanical properties, i.e., the tensile strength and Young's modulus, of the composite graphene-based fibers exhibited 3.56- and 3.95-fold increases, respectively, compared with those of pristine graphene fibers. Furthermore, the electrical conductivity also dramatically increased to 7.3 × 104 S/m, which is almost 10 times that of pristine graphene fibers. These results show the achievement of advantages superior to those in previously reported studies based on polymer-grafted graphene composite fibers. This hybridized composite fabrication process provides a new way of reinforcing graphene fibers and contributes to expanding the application of graphene-based fibers in flexible electronic devices.

Polyacrylonitrile/liquid crystalline graphene oxide composite fibers – Towards high performance carbon fiber precursors

We have prepared high performance, continuous carbon fiber precursors mimicking the industrial processing by wet spinning technology using polyacrylonitrile (PAN)/liquid crystalline graphene oxide (LCGO) for the first time. This work highlights the unexplored production of novel PAN composite fibers with addition of very low percentage of LCGO without using any surface modifications or coating. Following the coagulation process, as spun PAN/LCGO fibers were passed through a series of wash baths operated at various temperatures and multiple hot stretching baths prior to drying, and taken-up using a traversing winder. Current study also investigates the chemical and microstructural changes of PAN due to the addition of very low amounts of GO without the use of binders or surface treatments. The tensile strength and tensile modulus of the fibers were significantly improved with low filler content up to 1 wt% of LCGO into PAN dope that is, a 115% improvement of tensile strength and 152% increase of tensile modulus were achieved at a filler loading of 0.5 wt% whereas 138% improvement in tensile strength at 1 wt% of LCGO. This study revealed that it is possible to produce high strength precursor fibers by wet spinning with the addition of low filler content by make use of LCGO in PAN solution; this can further provide pathways for making high performance carbon fibers.

A sintered graphene/titania material as a synthetic keratoprosthesis skirt for end-stage corneal disorders

An artificial cornea or keratoprosthesis requires high mechanical strength, good biocompatibility, and sufficient wear and corrosion resistance to withstand the hostile environment. We report a reduced graphene oxide-reinforced titania-based composite for this application. Graphene oxide nanoparticles (GO) and liquid crystalline graphene oxide (LCGO) were the graphene precursors and mixed with titanium dioxide (TiO2) powder. The composites reinforced with reduced GO or LCGO were produced through spark plasma sintering (SPS). The mechanical properties (Young’s modulus and hardness), wear behaviour and corrosion resistance were studied using nanoindentation, anoidic polarization, long-term corrosion assay in artificial tear fluid and tribology assay in corroboration with atomic force microscopy and scanning electron microscopy. Biocompatibility was assessed by human corneal stromal cell attachment, survival and proliferation, and DNA damages. Sintered composites were implanted into rabbit corneas to assess for in vivo stability and host tissue responses. We showed that reduced graphene/TiO2 hybrids were safe and biocompatible. In particular, the 1% reduced LCGO/TiO2 (1rLCGO/TiO2) composite was mechanically strong, chemically stable, and showed better wear and corrosion resistance than pure titania and other combinations of graphene-reinforced titania. Hence the 1rLCGO/ TiO2 bioceramics can be a potential skirt biomaterial for keratoprosthesis to treat end-stage corneal blindness. Statement of SignificanceThe osteo-odonto-keratoprosthesis (OOKP) is an artificial cornea procedure used to restore vision in end-stage corneal diseases, however it is contraindicated in young subjects, patients with advanced imflammatory diseases and posterior segment complications. Hence, there is a need of an improved keratoprosthesisskirt material with high mechanical and chemical stability, wear resistance and tissue integration ability. Our study characterized a reduced graphene oxide-reinforced titania-based biomaterial, which demonstrated strong mechanical strength, wear and corrosion resistance, and was safe and biocompatible to human corneal stromal cells. In vivo implantation to rabbit corneas did not cause any immune and inflammation outcomes. In conclusion, this invention is a potential keratoprosthesis skirt biomaterial to withstand the hostile environment in treating end-stage corneal blindness.

Structuration of lignin-graphene oxide based carbon materials through liquid crystallinity

This paper presents the approach of combining lignin with graphene oxide (GO) flakes in order to introduce a higher structuration inside amorphous carbon materials. Both the phase behavior of lignin-GO solutions and the properties of lignin-GO films are investigated in a first approach. A clear orientation within lignin-based solutions is obtained through the formation of a nematic liquid crystalline GO phase. The impact of the GO flakes on the lignin-GO films after their carbonization is demonstrated via scanning electron microscopy and X-ray diffraction measurements. With increasing GO content inside the composite films, a layer-like morphology and graphitic structures of higher crystallinity are found. The electrical conductivity of the films gradually increases as well. Furthermore, we demonstrate successful spinning trials of lignin-GO solutions into composite fibers by means of coagulation. An increased electrical conductivity of the obtained fibers depending on the GO concentration indicates an increase in crystallinity. The structuration of lignin-based carbon materials may represent an important approach towards bio-based carbon fibers with improved mechanical and electrical properties.

A Novel Sintered Graphene/Titania Material as a Synthetic Keratoprosthesis Skirt for End-Stage Corneal Disorders

An artificial cornea or keratoprosthesis requires high mechanical strength, good biocompatibility, and sufficient wear and corrosion resistance to withstand the hostile environment. We report a novel reduced graphene oxide-reinforced titania-based composite for this application. Graphene oxide nanoparticles (GO) and liquid crystalline graphene oxide (LCGO) were the graphene precursors and mixed with titanium dioxide (TiO2) powder. The composites reinforced with reduced GO or LCGO were produced through spark plasma sintering (SPS). The mechanical properties (Young's modulus and hardness), wear behaviour and corrosion resistance were studied using nanoindentation, anoidic polarization, long-term corrosion assay in artificial tear fluid and tribology assay in corroboration with atomic force microscopy, scanning and transmission electron microscopies. Biocompatibility was assessed by human corneal stromal cell attachment, survival and proliferation, and DNA damages. Sintered composites were implanted into rabbit corneas to assess for in vivo stability and host tissue responses. We showed that reduced graphene/TiO2 hybrids were safe and biocompatible. In particular, the 1% reduced LCGO/TiO2 (1rLCGO/TiO2) composite was mechanically strong, chemically stable, and showed better wear and corrosion resistance than pure titania and other combinations of graphene-reinforced titania. Hence the novel 1rLCGO/ TiO2 bioceramics can be a potential skirt biomaterial for keratoprosthesis to treat end-stage corneal blindness.

Preparation of anisotropic conductive graphene aerogel/polydimethylsiloxane composites as LEGO® modulars

Graphene aerogel (GA), a continuous network constructed by graphene sheets, received tremendous research interests because of its fascinating properties inherited from graphene and continuous network as aerogel. GA with anisotropic structures can be prepared by simple hydrothermal reduction of liquid crystalline graphene oxide, and this ordered GA is a prior candidate to hybrid with polymers to make conductive composites. In this work, a new composite was fabricated by directly infiltrating ordered GA with polydimethylsiloxane (PDMS). Benefit from the presence of GA continuous network, the insulative PDMS turned into electrical conductive composite after intercalated with GA. Furthermore, the conductivity of GA/PDMS composite was anisotropic as a consequence of the ordered microstructure of GA network. Due to the support of PDMS, the obtained composites can be easily fabricated and subsequently assembled into desired shape as LEGO® modulars.

Dynamic assembly of liquid crystalline graphene oxide gel fibers for ion transport.

Colloidal dispersions with liquid crystallinity hold great promise for fabricating their superstructures. As an example, when graphene oxide (GO) sheets are assembled in the liquid crystalline state, they can turn into ordered macroscopic forms of GO such as fibers via the wet spinning process. Here, we report that by reinforcing intersheet interactions, GO liquid crystals (LCs) turn into mechanically robust hydrogels that can be readily drawn into highly aligned fibrillar structures. GO hydrogel fibers with highly aligned sheets (orientation factor, f = 0.71) exhibit more than twice the ionic conductivity compared to those with partially aligned structures (f = 0.01). The hierarchically interconnected two-dimensional nanochannels within these neatly aligned GOLC hydrogel fibers may facilitate controlled transport of charge carriers and could be potentially explored as cables for interconnecting biosystems and/or human-made devices.

Preparation of Anisotropic Conductive Graphene Aerogel/Polydimethylsiloxane Composites as LEGO® Modulars

Graphene aerogel (GA), a continuous network constructed by graphene sheets, received tremendous research interests because of its fascinating properties inherited from graphene and continuous network as aerogel. GA with anisotropic structures can be prepared by simple hydrothermal reduction of liquid crystalline graphene oxide, and this ordered GA is a prior candidate to hybrid with polymers to make conductive composites. In this work, a new composite was fabricated by directly infiltrating ordered GA with polydimethylsiloxane (PDMS). Benefit from the presence of GA continuous network, the insulative PDMS turned into electrical conductive composite after intercalated with GA. Furthermore, the conductivity of GA/PDMS composite was anisotropic as a consequence of the ordered microstructure of GA network. Due to the support of PDMS, the obtained composites can be easily fabricated and subsequently assembled into desired shape as LEGO® modulars.

A Porphyrin/Graphene Framework: A Highly Efficient and Robust Electrocatalyst for Carbon Dioxide Reduction

AbstractDeveloping immobilized molecular complexes, which demonstrate high product efficiencies at low overpotential in the electrochemical reduction of CO2 in aqueous media, is essential for the practical production of reduction products. In this work, a simple and facile self‐assembly method is demonstrated by electrostatic interaction and π–π stacking for the fabrication of a porphyrin/graphene framework (FePGF) composed of Fe(III) tetraphenyltrimethylammonium porphyrin and reduced liquid crystalline graphene oxide that can be utilized for the electrocatalytic reduction of CO2 to CO on a glassy carbon electrode in aqueous electrolyte. The FePGF results in an outstanding robust catalytic performance for the production of CO with 97.0% faradaic efficiency at an overpotential of 480 mV and superior long‐term stability relative to other heterogeneous molecular complexes of over 24 h (cathodic energy efficiency: 58.1%). In addition, a high surface area carbon fiber paper is used as a substrate for FePGF catalyst, resulting in enhanced current density of 1.68 mA cm−2 with 98.7% CO faradaic efficiency at an overpotential of 430 mV for 10 h, corresponding to a turnover frequency of 2.9 s−1 and 104 400 turnover number. Furthermore, FePGF/CFP has one of the highest cathodic energy efficiencies (60.9%) reported for immobilized metal complex catalysts.