Modelling mechanical percolation in graphene-reinforced elastomer nanocomposites

Graphene is considered an ideal filler for the production of multifunctional nanocomposites; as a result, considerable efforts have been focused on the evaluation and modeling of its reinforcement characteristics. In this work, we modelled successfully the mechanical percolation phenomenon, observed on a thermoplastic elastomer (TPE) reinforced by graphene nanoplatelets (GNPs), by designing a new set of equations for filler contents below and above the percolation threshold volume fraction (Vp). The proposed micromechanical model is based on a combination of the well-established shear-lag theory and the rule-of-mixtures and was introduced to analyse the different stages and mechanisms of mechanical reinforcement. It was found that when the GNPs content is below Vp, reinforcement originates from the inherent ability of individual GNPs flakes to transfer stress efficiently. Furthermore, at higher filler contents and above Vp, the nanocomposite materials displayed accelerated stiffening due to the reduction of the distance between adjacent flakes. The model derived herein, was consistent with the experimental data and the reasons why the superlative properties of graphene cannot be fully utilized in this type of composites, were discussed in depth.Comment: 29 pages, 12 figure

On the controlled electrochemical preparation of R4N+ graphite intercalation compounds and their host structural deformation effects

AbstractWe present electrochemical studies of tetraalkylammonium (R4N+) reduction chemistry at Highly Orientated Pyrolytic Graphite (HOPG) and glassy carbon (GC) electrodes. We show that by electrochemically controlled intercalation and formation of a graphite intercalation complex (GIC) into layered HOPG, the irreversible reduction of the tetraalkylammonium cation can be prevented and subsequent de-intercalation of the GIC via the use of potentiostatic control is achievable. R4N+ cations with varying alkyl chain lengths (methyl, ethyl and butyl) have been shown to exhibit excellent charge recovery effects during charge/discharge studies. Finally the effects of electrode expansion on the degree of recovered charge have been investigated and the observed effects of R4N+ intercalation on the graphite cathode have been probed by scanning electron microscopy (SEM) and X-ray diffraction (XRD)

Fabrication and Mechanical Performance of Graphene Nanoplatelet/Glass Fiber Reinforced Polymer Hybrid Composites

From Frontiers via Jisc Publications RouterHistory: collection 2021, received 2021-09-09, accepted 2021-10-20, epub 2021-11-16Publication status: PublishedGlass fiber reinforced polymer (GFRP) composites are promising alternatives for the traditional carbon steel pipes used in the oil and gas industry due to their corrosion and chemical resistance. However, the out-of-plane mechanical properties of GFRPs still need further improvement to achieve this goal. Hence, in this work, two methods combining either vacuum mixing or spray coating with vacuum-assisted resin infusion were studied to fabricate graphene nanoplatelet (GNP)/GFRP hybrid composites. The former method resulted in a severe filtering effect, where the GNPs were not evenly distributed throughout the final composite, whereas the latter process resulted in a uniform GNP distribution on the glass fabrics. The addition of GNPs showed no modest contribution to the tensile performance of the GFRP composites due to the relatively high volume and in-plane alignment of the glass fibers. However, the GNPs did improve the flexural properties of GFRP with an optimal loading of 0.15 wt% GNPs, resulting in flexural strength and modulus increases of 6.8 and 1.6%, respectively. This work indicates how GNPs can be advantageous for out-of-plane mechanical reinforcement in fiber-reinforced composites

Atmospheric Pressure Catalytic Vapor Deposition of Graphene on Liquid In and Cu-In Alloy Substrates

From MDPI via Jisc Publications RouterHistory: accepted 2021-10-24, pub-electronic 2021-10-30Publication status: PublishedLiquid substrates are great candidates for the growth of high-quality graphene using chemical vapour deposition (CVD) due to their atomically flat and defect free surfaces. A detailed study of graphene growth using atmospheric pressure CVD (APCVD) on liquid indium (In) was conducted. It was found that the effect of the growth parameters on the quality of the graphene produced is highly dependent on the properties of the substrate used. A short residence time of 6.8 sec for the reactive gases led to a high graphene quality, indicating the good catalytic behaviour of In. The role of hydrogen partial pressure was found to be crucial, with monolayer and bilayer graphene films with a low defect density obtained at low PH2 (38.6 mbar), whilst more defective, thicker graphene films with a partial coverage being obtained at high PH2 (74.3 mbar). The graphene deposition was insensitive to growth time as the graphene growth on liquid In was found to self-limit to bilayer. For further investigation, five compositions of Cu-In alloys were made by arc-melting. Graphene was then grown using the optimum conditions for In and the quality of the graphene was found to degrade with increasing Cu wt.%. This work will aid the future optimisation of the growth conditions based upon the substrate’s properties

Electrically Conductive 2D Material Coatings for Flexible & Stretchable Electronics: A Comparative Review of Graphenes & MXenes

There is growing interest in transitioning electronic components and circuitry from stiff and rigid substrates to more flexible and stretchable platforms, such as thin plastics, textiles, and foams. In parallel, the push for more sustainable, biocompatible, and cost-efficient conductive inks to coat these substrates, has led to the development of formulations with novel nanomaterials. Among these, 2D materials, and particularly graphenes and MXenes, have received intense research interest due to their increasingly facile and scalable production, high electrical conductivity, and compatibility with existing manufacturing techniques. They enable a range of electronic devices, including strain and pressure sensors, supercapacitors, thermoelectric generators, and heaters. These new flexible and stretchable electronic devices developed with 2D material coatings are poised to unlock exciting applications in the wearable, healthcare and Internet of Things sectors. This review has surveyed key data from more than 200 articles published over the last 6 years, to provide a quantitative analysis of recent progress in the field and shade light on future directions and prospects of this technology. We find that despite the different chemical origins of graphenes and MXenes, their shared electrical properties and 2D morphology, guarantee intriguing performance in end applications, leaving plenty of space for shared progress and advancements in the future

Ice-templated hybrid graphene oxide—graphene nanoplatelet lamellar architectures: tuning mechanical and electrical properties

From IOP Publishing via Jisc Publications RouterHistory: received 2020-10-21, oa-requested 2021-01-07, rev-recd 2021-01-12, accepted 2021-01-25, epub 2021-02-23, open-access 2021-02-23, ppub 2021-05-14Publication status: PublishedFunder: Morgan Advanced Materials and RAEngFunder: Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brasil (CAPES)Funder: Heilongjiang Huasheng Graphite Co., People’s Republic of ChinaAbstract: The traditional freeze-casting route for processing graphene-based aerogels is generally restricted to aqueously dispersed flakes of graphene oxide (GO) and post-processing reduction treatments, which brings restrictions to the aerogels electrical properties. In this work, we report a versatile aqueous processing route that uses the ability of GO todisperse graphene nanoplatelets (GNP) to produce rGO-GNP lamellar aerogels via unidirectional freeze-casting. In order to optimise the properties of the aerogel, GO-GNP dispersions were partially reduced by L-ascorbic acid prior to freeze-casting to tune the carbon and oxygen (C/O) ratio. The aerogels were then heat treated after casting to fully reduce the GO. The chemical reduction time was found to control the microstructure of the resulting aeorgels and thus to tune their electrical and mechanical properties. An rGO-GNP lamellar aerogel with density of 20.8 ± 0.8 mg cm−3 reducing using a reduction of 60 min achieved an electrical conductivity of 42.3 S m−1. On the other hand, an optimal reduction time of 35 min led to an aerogel with compressive modulus of 0.51 ±0.06 MPa at a density of 23.2 ± 0.7 mg cm−3, revealing a compromise between the tuning of electrical and mechanical properties. We show the present processing route can also be easily applied to produce lamellar aerogels on other graphene-based materials such as electrochemically exfoliated graphene

Effect of graphene nanoplatelets on the mechanical and gas barrier properties of woven carbon fibre/epoxy composites

From Springer Nature via Jisc Publications RouterHistory: received 2021-05-14, accepted 2021-08-14, registration 2021-08-23, pub-electronic 2021-09-05, online 2021-09-05, pub-print 2021-12Publication status: PublishedFunder: Engineering and Physical Sciences Research Council; doi: http://dx.doi.org/10.13039/501100000266; Grant(s): EP/K016946/1Abstract: Carbon-fibre-reinforced polymer (CFRP) composites are promising materials for non-metallic pipe applications in the oil and gas industry owing to their high corrosion resistance, specific strength and stiffness. However, CFRP has poor gas barrier performance meaning that a liner has to be inserted. Graphene-based nanomaterials have been demonstrated to improve gas barrier properties in thermoplastic polymers, and thus, a CFRP–graphene hybrid composite could provide an alternative to lined pipes. In this work, a method combining spray coating with vacuum-assisted resin infusion was developed to fabricate CFRP hybrid composites with preferred in-plane aligned graphene nanoplatelets. Tensile and flexural properties, as well as CO2 gas permeability, were evaluated. It was illustrated that both tensile and flexural properties performed better under relatively low GNP loadings (< 0.2 vol%), while gas barrier property was significantly improved with the increasing GNP loadings which fits the Nielsen model with an effective GNP aspect ratio of 350. Graphical abstract