Shear stress mediated scrolling of graphene oxide

© 2018 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license: http://creativecommons.org/licenses/by-nc-nd/4.0/ This author accepted manuscript is made available following 24 month embargo from date of publication (May 2018) in accordance with the publisher’s archiving policyGraphene oxide scrolls (GOS) are fabricated in high yield from a colloidal suspension of graphene oxide (GO) sheets under shear stress in a vortex fluidic device (VFD) while irradiated with a pulsed laser operating at 1064 nm and 250 mJ. This is in the absence of any other reagents with the structure of the GOS established using powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, atomic force microscopy and scanning electron microscopy

Laser-Ablated Vortex Fluidic-Mediated Synthesis of Superparamagnetic Magnetite Nanoparticles in Water Under Flow

ACS AuthorChoice - This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposesSelective formation of only one iron oxide phase is a major challenge in conventional laser ablation process, as is scaling up the process. Herein, superparamagnetic single-phase magnetite nanoparticles of hexagonal and spheroidal-shape, with an average size of ca. 15 nm, are generated by laser ablation of bulk iron metal at 1064 nm in a vortex fluidic device (VFD). This is a one-step continuous flow process, in air at ambient pressure, with in situ uptake of the nanoparticles in the dynamic thin film of water in the VFD. The process minimizes the generation of waste by avoiding the need for any chemicals or surfactants and avoids time-consuming purification steps in reducing any negative impact of the processing on the environment.The authors gratefully acknowledge the financial support from the Australia Research Council and the Government of South Australia; also the expertise, equipment, and support provided by the Australian Microscopy and Microanalysis Research Facility (AMMRF) and the Australian National Fabrication Facility (ANFF) at the South Australian nodes of the AMMRF and ANFF under the National Collaborative Research Infrastructure Strategy

Sub-micron moulding topological mass transport regimes in angled vortex fluidic flow

Shear stress in dynamic thin films, as in vortex fluidics, can be harnessed for generating non-equilibrium conditions, but the nature of the fluid flow is not understood. A rapidly rotating inclined tube in the vortex fluidic device (VFD) imparts shear stress (mechanical energy) into a thin film of liquid, depending on the physical characteristics of the liquid and rotational speed,ω, tilt angle,θ, and diameter of the tube. Through understanding that the fluid exhibits resonance behaviours from the confining boundaries of the glass surface and the meniscus that determines the liquid film thickness, we have established specific topological mass transport regimes. These topologies have been established through materials processing, as spinning top flow normal to the surface of the tube, double-helical flow across the thin film, and spicular flow, a transitional region where both effects contribute. The manifestation of mass transport patterns within the film have been observed by monitoring the mixing time, temperature profile, and film thickness against increasing rotational speed,ω. In addition, these flow patterns have unique signatures that enable the morphology of nanomaterials processed in the VFD to be predicted, for example in reversible scrolling and crumbling graphene oxide sheets. Shear-stress induced recrystallisation, crystallisation and polymerisation, at different rotational speeds, provide moulds of high-shear topologies, as ‘positive’ and ‘negative’ spicular flow behaviour. ‘Molecular drilling’ of holes in a thin film of polysulfone demonstrate spatial arrangement of double-helices. The grand sum of the different behavioural regimes is a general fluid flow model that accounts for all processing in the VFD at an optimal tilt angle of 45°, and provides a new concept in the fabrication of novel nanomaterials and controlling the organisation of matter

Continuous flow laser-induced unzipping of multiwalled carbon nanotubes

Unzipped multiwalled carbon nanotubes (MWCNTs) provide a route to graphene carbon ribbons (GNRs), which have application in electronic devices. Pulsed irradiation using an Nd:YAG laser operating at 1064 nm mediates such unzipping of MWCNTs dispersed in ethanol under shear stress within the vortex fluidic device (VFD). The method is scalable with the thin film device operating under continuous flow, while also avoiding the use of harsh chemicals and auxiliary substances. Unzipped MWCNTs are formed in 90% yield and have been characterized using scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis, X-ray powder diffraction and X-ray photoelectron spectroscopy. The systematically derived optimal laser power for unzipping was 250 mJ and increasing the laser power results in the fragmentation of the MWCNTs.</p

Ordering in Surfactant Foam Films Transferred onto Hydrophilic and Hydrophobic Substrates

Foam films have been formed by aqueous dodecyldimethyl­phosphine oxide (C₁₂DMPO) and aqueous hexadecyl­trimethyl­ammonium bromide (C₁₆TAB) solutions and drained. The surfactant films were transferred onto hydrophilic and hydrophobic substrates at five different drainage times. Angle-resolved X-ray photoelectron spectroscopy and metastable induced electron spectroscopy were used for investigation of the thickness and orientation of the surfactant molecules in the transferred foam film. Of the four combinations only the drained film formed by C₁₆TAB transferred onto hydrophobic surfaces shows a strong degree of orientation of the surfactant molecules in the transferred film. The other three combinations do not show a preferred orientation of the surfactant molecules in the foam film. The phenomenon is discussed based on the interaction of the molecules within the films and the interaction of the formed films with the substrates

Highly Uniform Nanodiamond-Graphene Composites Microspheres for Electrocatalytic Hydrogen Evolution

To progress the clean hydrogen-gas-based energy economy, there is a demand for cost-effective, highly efficient catalysts to facilitate the hydrogen evolution reaction process (HER). Due to the amazing catalytic capabilities of two-dimensional materials, extensive research has been done on these structures. However, most of the described syntheses take a lot of time, are challenging, and are ineffective. The present work demonstrates the performance of the recently reported nanodiamond/graphene composite microsphere ND-GCSs as a catalyst for HER. These spheres were produced via the microwave-irradiation approach. A modified process was adopted to improve the particle size uniformity and yield. The prepared composite spheres showed very interesting catalytic activity for the HER when assembled on a screen-printed carbon electrode. The prepared ND-GCSs@SPCE showed a significant shift of the onset potential to ca. −450 mV and a small Tafel slope value of ca. 85 mV/decade. The electron transfer was drastically enhanced with a tremendous decrease in charge transfer resistance to ca. 265 Ω. The electrocatalyst showed excellent long-term stability for the HER application. Additionally, this novel composite structure might be beneficial for diverse applications including batteries, supercapacitors, catalyst supports, and more

Inverted vortex fluidic exfoliation and scrolling of hexagonal-boron nitride

Exfoliation or scrolling of hexagonal boron nitride (h-BN) occurs in a vortex fluidic device (VFD) operating under continuous flow, with a tilt angle of -45° relative to the horizontal position. This new VFD processing strategy is effective in avoiding the build-up of material that occurs when the device is operated using the conventional tilt angle of +45°, where the h-BN precursor and scrolls are centrifugally held against the wall of the tube. At a tilt angle of -45° the downward flow aided by gravity facilitates material exiting the tube with the exfoliation of h-BN and formation of h-BN scrolls then optimized by systematically varying the other VFD operating parameters, including flow rate and rotational speed, along with concentration of h-BN and the choice of solvent. Water was the most effective solvent, which enhances the green chemistry metrics of the processing

Sub-Micron Moulding Topological Mass Transport Regimes in Angled Vortex Fluidic Flow

Induced mechanical energy in a thin film of liquid in an inclined rapidly rotating tube in the vortex fluidic device (VFD) can be harnessed for generating non-equilibrium conditions, which are optimal at 45o tilt angle, but the nature of the fluid flow is not understood. Through understanding that the fluid exhibits resonance behaviours from the confining boundaries of the glass surface and the meniscus that determines the liquid film thickness, we have established specific topological mass transport regimes. These topologies have been established through materials processing, as circular flow normal to the surface of the tube, double-helical flow across the thin film, and spicular flow, a transitional region where both effects contribute. This includes new phenomenological shear stressed crystallization and molecular drilling. The manifestation of these patterns has been observed by monitoring mixing times, temperature profiles, and film thickness against rotational speed of liquids in the tube. The grand sum of the different behavioural regimes is a general fluid flow model that accounts for all processing in the VFD at an optimal tilt angle of 45o, and provides a new concept in the fabrication of novel nanomaterials and controlling the organisation of matter.</b

Vortex fluidic mediated transformation of graphite into highly conducting graphene scrolls

Two-dimensional graphene has remarkable properties that are revolutionary in many applications. Scrolling monolayer graphene with precise tunability would create further potential for niche applications but this has proved challenging. We have now established the ability to fabricate monolayer graphene scrolls in high yield directly from graphite flakes under non-equilibrium conditions at room temperature in dynamic thin films of liquid. Using conductive atomic force microscopy we demonstrate that the graphene scrolls form highly conducting electrical contacts to highly oriented pyrolytic graphite (HOPG). These highly conducting graphite-graphene contacts are attractive for the fabrication of interconnects in microcircuits and align with the increasing interest in building all sp(2)-carbon circuits. Above a temperature of 450 degrees C the scrolls unravel into buckled graphene sheets, and this process is understood on a theoretical basis. These findings augur well for new applications, in particular for incorporating the scrolls into miniaturized electronic devices