Project description:Colloidal liquid crystals (LCs) formed by nanoparticles hold great promise for creating new structures and topologies. However, achieving highly ordered hierarchical architectures and stable topological configurations is extremely challenging, mainly due to the liquid-like fluidity of colloidal LCs in nature. Herein, an innovative synchronous nanofluidic rectification (SNR) technique for generating ultralong graphene oxide (GO) liquid crystal (GOLC) fibers with hierarchical core-skin architectures is presented, in which the GO sheet assemblies and hydrogel skin formation are synchronous. The SNR technique conceptually follows two design principles: horizontal polymer-flow promotes the rapid planar alignment of GO sheets and drives the chiral-reversing of cholesteric GOLCs, and in situ formed hydrogel skin affords some protection against environmental impact to maintain stable topological configurations. Importantly, the dried fibers retain the smooth surface and ordered internal structures, achieving high mechanical strength and flexibility. The linear and circular polarization potential of GOLC fibers are demonstrated for optical sensing and recognition. This work may open an avenue toward the scalable manufacture of uniform and robust, yet highly anisotropic, fiber-shaped functional materials with complex internal architectures.
Project description:Combining polymers with small amounts of stiff carbon-based nanofillers such as graphene or graphene oxide is expected to yield low-density nanocomposites with exceptional mechanical properties. However, such nanocomposites have remained elusive because of incompatibilities between fillers and polymers that are further compounded by processing difficulties. Here we report a water-based process to obtain highly reinforced nanocomposite films by simple mixing of two liquid crystalline solutions: a colloidal nematic phase comprised of graphene oxide platelets and a nematic phase formed by a rod-like high-performance aramid. Upon drying the resulting hybrid biaxial nematic phase, we obtain robust, structural nanocomposites reinforced with graphene oxide.
Project description:In contemporary manufacturing, the processing of structural materials plays a pivotal role in enabling the creation of robust, tailor-made, and precise components suitable for diverse industrial applications. Nonetheless, current material forming technologies face challenges due to internal stress and defects, resulting in a substantial decline in both mechanical properties and processing precision. We herein develop a processing strategy toward graphene superstructure with a curvature gradient, which allows us to fabricate robust structural materials with meticulously designed functional shapes. The structure consists of an arc-shaped assembly of graphene nanosheets positioned at co-axial curvature centers. During the dehydration-based evaporate-casting process, the assembly is tightened via capillary effect, inducing local bending. By precisely tuning the axis-center distance and tilt angle, we achieve accurate control over the shape of obtained structure. Notably, internal stress is harnessed to reinforce a designed mortise and tenon structure, resulting in a high joining strength of up to ~200 MPa. This innovative approach addresses the challenges faced by current material forming technologies and opens up more possibilities for the manufacturing of robust and precisely shaped components.
Project description:The dispersions containing two kinds of layered solids-graphene oxide (GO) and exfoliated montmorillonite (MMT) were mainly prepared, following which the binary aerogels were synthesized. The results indicate that the formation of liquid crystals (LCs) occurs at lower GO concentration and the birefringence becomes stronger when MMT is introduced into GO dispersion. Sol-gel transition forms in the binary suspensions with different mass fractions of MMT and GO. LCs with highly ordered alignment are observed in the gel and the fraction of LCs obviously increases with the increase in GO concentration. Moreover, the birefringence is observed in MMT-GO binary aerogels with the interconnected three-dimensional porous network, which is attributed to the ordered arrangement of MMT and GO nanosheets in pore walls. Among the aerogels with different MMT/GO ratios, the samples at the ratio of 10 : 1 show better adsorption capacity and removal percentage of cationic and anionic dyes.
Project description:Enhancing the electrical conductivity of liquid crystal (LC) circumvents challenges for application in advanced electronic components. Toward this, using additives made of different nanostructures that could result in functional LCs is suggested. In this paper, various concentrations of graphene (Gr)/metal-oxide (Fe3O4) nanocomposite (GMN) (0.0001-1 w%) were added to E7 nematic LC. We found that the role of anisotropic Gr flakes, their edges as well as surface-decorated-metal-oxide-additives have significant impact on electrical properties of E7. A range of appropriate additives of such a nanocomposite enhances the electrical conductivity of LCs. This effect can be traced through the decrease in the formation of GMN aggregates in the E7 and increase in the electrostatic field at the edges of the Gr sheets. Moreover, the presence of metal-oxide nanoclusters due to the presence of oxygen vacancies and defects facilitates the construction of conductive network for improving the charge transfer pathways and contributes to a stronger interaction of the Gr surface with charged species. These factors can provide Gr layers as dipole moments and lead to signal propagation in the dielectric medium. Our finding conveys a pathway toward significant enhancement of electrical conductivity in the LC family which can be useful for functional applications.
Project description:Graphene-based membranes demonstrating ultrafast water transport, precise molecular sieving of gas and solvated molecules shows great promise as novel separation platforms; however, scale-up of these membranes to large-areas remains an unresolved problem. Here we demonstrate that the discotic nematic phase of graphene oxide (GO) can be shear aligned to form highly ordered, continuous, thin films of multi-layered GO on a support membrane by an industrially adaptable method to produce large-area membranes (13 × 14 cm(2)) in <5 s. Pressure driven transport data demonstrate high retention (>90%) for charged and uncharged organic probe molecules with a hydrated radius above 5 Å as well as modest (30-40%) retention of monovalent and divalent salts. The highly ordered graphene sheets in the plane of the membrane make organized channels and enhance the permeability (71 ± 5 l m(-2) hr(-1) bar(-1) for 150 ± 15 nm thick membranes).
Project description:Graphene flakes with giant shape anisotropy are extensively used to establish connectedness electrical percolation in various heterogeneous systems. However, the percolation behaviour of graphene flakes has been recently predicted to be far more complicated than generally anticipated on the basis of excluded volume arguments. Here we confirm experimentally that graphene flakes self-assemble into nematic liquid crystals below the onset of percolation. The competition of percolation and liquid crystal transition provides a new route towards high-k materials. Indeed, near-percolated liquid-crystalline graphene-based composites display unprecedented dielectric properties with a dielectric constant improved by 260-fold increase as compared with the polymer matrix, while maintaining the loss tangent as low as 0.4. This performance is shown to depend on the structure of monodomains of graphene liquid-crystalline phases. Insights into how the liquid crystal phase transition interferes with percolation transition and thus alters the dielectric constant are discussed.
Project description:We report the role of chemically expanded graphite in the fabrication of high-performance graphene oxide fibers by wet spinning. X-ray diffraction peak showed that the interplanar distance of the expanded graphene oxide (EGO) fiber was more than that of graphene oxide (GO) fiber due to the expanded graphite. X-ray photon spectroscopy analysis revealed that EGO was more oxidized than GO. The hydrogen bonding network and secondary intermolecular interaction made the EGO aqueous solution more stable and crystalline, and it was able to be stretched in the coagulation bath. Morphological analysis showed the excellent alignment and compactness of EGO sheets in the fibers. The increased interplanar distance between the EGO sheets favored the edge-to-edge interaction more than the basal plane interaction within the fiber, thus resulting in high mechanical strength (492 MPa) and increased elongation (6.1%).
Project description:Three-dimensional (3D) graphene oxide aerogel (GOA) is one of the best fillers for composites for microwave absorption. However, its further development has been hindered by the poor mechanical properties. Methodology to improve the mechanical properties of the aerogel remains an urgent challenge. Herein, graphene oxide/carbon nanotube/epoxy resin composite aerogel (GCEA) was successfully prepared by a facile method. The results showed that the prepared GCEA with the hierarchical and 3D cross-linked structures exhibited excellent compression performance, structural and thermal stability, high hydrophilicity, and microwave absorption. The prepared GCEA recovered from multiple large strain cycles without significant permanent deformation. The minimum reflection loss (RL) was -39.60 dB and the maximum effective absorption bandwidth (EAB) was 2.48 GHz. The development of the enhanced GO aerogels will offer a new approach to the preparation of 3D microwave-absorbing skeletal materials with good mechanical properties.
Project description:Blue phase (BP) liquid crystals are chiral fluids wherein millions of molecules self-assemble into cubic lattices that are on the order of hundred nanometers. As the unit cell sizes of BPs are comparable to the wavelength of light, they exhibit selective Bragg reflections in the visible. The exploitation of the photonic properties of BPs for technological applications is made possible through photopolymerization, a process that renders mechanical robustness and thermal stability. We review here the preparation and characterization of stimuli-responsive, polymeric photonic crystals based on BPs. We highlight recent studies that demonstrate the promise that polymerized BP photonic crystals hold for colorimetric sensing and dynamic light control. We review using Landau-de Gennes simulations for predicting the self-assembly of BPs and the potential for using theory to guide experimental design. Finally, opportunities for using BPs to synthesize new soft materials, such as highly structured polymer meshes, are discussed.