Design Rules for Graphene and Carbon Nanotube Solvents and Dispersants

Highly Reactive Graphene Dispersant and Its Effective Reinforcement for Phase Change Coatings

High efficient dispersant that meanwhile possesses additional functions is highly desirable for the fabrication of graphene-based composite. In this paper, a new reactive dispersant, multi-silanols grafted naphthalenediamine (MSiND), is synthesized, which shows superiority compared with conventional dispersants. It can not only stabilize graphene in water at a high concentration of up to 16 mg mL-1, but also simultaneously be applicable for ethanol medium, in which the graphene concentration can be as high as 12 mg mL-1 at the weight ratio of 1:1 (MSiND:graphene). The dispersion is compatible with multi-matrixes and affinity to various substrates. In addition, MSiND exhibits excellent reactivity due to the existence of high-density silanol groups. Tough graphene coatings are constructed on glass slides and non-woven fabric simply by direct painting and dip-coating. Moreover, with the assistance of MSiND, graphene-doped phase-change coatings on hydrophobic non-woven fabric (e.g., functional mask) are prepared via the spray method. The composite coatings show enhanced mechanical strength and excellent energy storage performance, exhibiting great potential in heat preservation and thermotherapy.

Neutron Activation Analysis of Rare Earth Element Extraction from Solution through a Surfactant-Assisted Dispersion of Carbon Nanotubes

We report the preparation of surfactant-assisted carbon nanotube dispersions using gum arabic, Triton X-100, and graphene oxide as dispersing agents for removing rare earth elements in an aqueous solution. The analytical tools, including (a) scanning electron microscopy and (b) neutron activation analysis, were utilized for qualitative and quantitative examinations, respectively. Neutron activation analysis was employed to quantitatively determine the percent of extraction of nuclides onto the carbon structure, while the images produced from the scanning electron microscope allowed the morphological structure of the surfactant-CNT complex to be analyzed. This report tested the effects responsible for nuclide removal onto CNTs, including the adsorbent to target mass ratio, the CNT concentration and manufacturing process, the pH, and the ionic radius. Observable trends in nuclide extraction were found for each parameter change, with the degree of dispersion displaying high dependency.

Photo-Cross-Linked Polymeric Dispersants of Comb-Shaped Benzophenone-Containing Poly(ether amine)

Efficient dispersion of nanoparticles (NPs) is a crucial challenge in the preparation and application of composites that contain NPs, particularly in coatings, inks, and related materials. Physical adsorption and chemical modification are the two common methods used to disperse NPs. However, the former suffers from desorption, and the latter is more specific and has limited versatility. To address these issues, we developed a novel photo-cross-linked polymeric dispersant, comb-shaped benzophenone-containing poly(ether amine) (bPEA), using a one-pot nucleophilic/cyclic-opening addition reaction. The results demonstrated that the bPEA dispersant forms a dense and stable shell on the surface of pigment NPs through physical adsorption and subsequent chemical photo-cross-linking, which effectively overcome the drawbacks of the desorption occurred in physical adsorption and the specificity of the chemical modification. By means of the dispersing effect of bPEA, the obtained pigment dispersions show high solvent, thermal, and pH stability without flocculation during storage. Moreover, the NPs dispersants show good compatibility with screen printing, coating, and 3D printing, endowing the ornamental products with high uniformity, color fastness, and less color shading. These properties make bPEA dispersants ideal candidates in fabrication dispersions of other NPs.

Gas-to-nanotextile: high-performance materials from floating 1D nanoparticles

Suspended in the gas phase, 1D inorganic nanoparticles (nanotubes and nanowires) grow to hundreds of microns in a second and can be thus directly assembled into freestanding network materials. The corresponding process continuously transforms gas precursors into aerosols into aerogels into macroscopic nanotextiles. By enabling the assembly of very high aspect ratio nanoparticles, this processing route has translated into high-performance structural materials, transparent conductors and battery anodes, amongst other embodiments. This paper reviews progress in the application of such manufacturing process to nanotubes and nanowires. It analyses 1D nanoparticle growth through floating catalyst chemical vapour deposition (FCCVD), in terms of reaction selectivity, scalability and its inherently ultra-fast growth rates (10⁷-10⁸ atoms per second) up to 1000 times faster than for substrate CVD. We summarise emerging descriptions of the formation of aerogels through percolation theory and multi-scale models for the collision and aggregation of 1D nanoparticles. The paper shows that macroscopic ensembles of 1D nanoparticles resemble textiles in their porous network structure, high flexibility and damage-tolerance. Their bulk properties depend strongly on inter-particle properties and are dominated by alignment and volume fraction. Selected examples of nanotextiles that surpass granular and monolithic materials include structural fibres with polymer-like toughness, transparent conductors, and slurry-free composite electrodes for energy storage.

Adenine derived reactive dispersant and the enhancement of graphene based composites

HYPOTHESIS

Homogeneous dispersion of graphene is the precondition for constructing high performance graphene based composites. However, most of the current dispersants reported in literature still suffer excess usage to reach a desired graphene concentration. Residual of dispersant in composite may seriously affect its properties. Hence, it is expected to obtain effective dispersant with high reactivity to diminish its adverse impacts on graphene composites.

EXPERIMENTS

A highly reactive graphene dispersant (DSiA) was synthesized by grafting silanol groups (Si-OH) onto adenine. Molecular structure and the performance of the dispersant were systematically characterized. Composites were fabricated by direct writing of the graphene dispersion on various substrates, and their features were evaluated by resistance, solvent erosion and tensile testing.

FINDINGS

Graphene concentration can reach up to 6 mg mL^-1 in the presents of DSiA at the weight ratio of 1:1 (DSiA: graphene). DSiA also exhibited good performance for stabilizing multi-walled carbon nanotubes (MWCNTs). Moreover, the dispersant is highly reactive. The graphene based composites showed good mechanical strength and excellent solvent resistance. Overall, the new dispersant provides an ideal choice to uniformly disperse graphene and suitable for fabricating high performance nanocarbon based composites.

Enhancing the Strengthening Effect of Graphene-Nanoplates in Al Matrix Composites by Heterogeneous Matrix Design

In the present work, the properties of graphene-nanoplates/aluminum (GNPs/Al) composites with a heterogeneous matrix design were investigated. The advantage of the heterogeneous matrix was investigated by the finite element method. Then, 0.6 wt.% (GNPs/6061Al)/2024Al (heterogeneous matrix) and 0.6 wt.% GNPs/6061Al composites were prepared by ball milling, pressure infiltration technology, and hot extrusion. The aggregation of GNPs was eliminated and the interlayer slide of GNPs was observed. Mechanical property test results show that the mechanical properties of the heterogeneous matrix composite are better than that of a homogeneous matrix composite, including strength, elastic modulus, and plasticity. It is assumed that the heterogeneous matrix design enhances the non-uniform stress field during the deformation treatment. This improves the dispersion of GNPs, grain refinement, and produces the few-layer graphene (FLG), thus enhancing the strengthening effect of GNPs. Meanwhile, heterogeneous matrix design is thought to introduce more hardening mechanisms to increase the plasticity of materials and improve the intrinsic trade-off of strength and toughness.

The production of graphene using impinging jet exfoliation in a binary system of CO2 and N-methyl pyrrolidone

High quality and high quantity few-layer graphene was successfully prepared using a new impinging jet method. Natural graphite flakes were first agitated in N-methyl pyrrolidone (NMP) with the assistance of supercritical CO₂, then the half-exfoliated graphite was further stripped using the shear stress derived from the impinging jets. After the energy conversion and stress analysis of the graphite particles during the whole exfoliation process, it was revealed that the size of the target mesh, the distance between the nozzle and the target, the decompression rate, and the size of the raw materials had a significant influence on the exfoliation process. Additionally, a microscopic view of the exfoliation and dispersion mechanism of graphene in the CO₂-NMP system was investigated using molecular dynamics simulation, and CO₂ was found to be beneficial for the penetration of NMP into the graphite sheets. Finally, the concentration and quality characteristics of the prepared graphene were characterized using ultraviolet-visible spectroscopy, transmission electron microscopy, Raman spectroscopy, and atomic force microscopy. The maximum concentration was as high as 0.689 mg ml^-1, the thickness of 68% of the product was less than 2.5 nm, and the lateral dimension was from 0.5 to 3.0 μm. These results indicate that this impinging jet method is promising for large-scale industrial production.

Molecular insights into the dispersion stability of graphene oxide in mixed solvents: Theoretical simulations and experimental verification

HYPOTHESIS

Improving the dispersion stability of graphene oxide (GO) suspensions is of great importance in many potential applications of GO, such as GO-based laminated membranes used for separation, printable electronics, and aqueous liquid crystals.

EXPERIMENTS

Molecular dynamics (MD) simulations and quantum chemistry (QC) calculations along with complementary experiments were performed to study the dispersion stability of GO in the mixtures of water and polar organic solvents (dimethyl sulfoxide (DMSO), ethanol, and acetone).

FINDINGS

GO exhibits better dispersion stability in a solvent mixture than in pure water. The MD simulations uncover the underlying mechanism that mixed solvent layers are formed steadily on the surface of GO sheets and screen the interactions between them. QC calculations reveal that both DMSO and water form hydrogen bonds with the oxidized regions of GO. X-ray diffraction experiments confirm that the GO sheets are intercalated by DMSO and water molecules. Furthermore, the optimal ratio of the organic solvent to water is determined to achieve the best dispersion stability of GO through MD simulations. And such ratio is also verified by ultraviolet absorption spectral experiments. Thus, our findings provide a facile method to prepare GO suspensions with high dispersion stability.

Exfoliation of Two-Dimensional Materials: The Role of Entropy

Liquid-phase exfoliation (LPE) is the best-known method for the synthesis of two-dimensional (2D) nanosheets. Compared to enthalpy, entropy is hardly considered to be a factor in choosing energy-efficient solvents and has not even been verified to be negligible. In this Letter, we explore the entropy contribution in LPE by performing molecular dynamics (MD) simulation of the structural flexibility effect in graphene, hexagonal boron nitride (hBN), and molybdenum disulfide (MoS₂). Our results show that surface vibration favors the exfoliation of graphene and hBN and destabilizes the reaggregation of nanosheets in water at 300 K, whereas the opposite is found for MoS₂. The entropy change is found to be 41%, 48%, and 4% of the enthalpy gain for graphene, hBN, and MoS₂ in LPE, respectively, and 64%, 32%, and 56% in reaggregation, which amounts to a step advancement for solvent screening in LPE of 2D materials.

Stabilization of aqueous graphene dispersions utilizing a biocompatible dispersant: a molecular dynamics study

Investigation of the high efficiency of flavin mononucleotide sodium salt (FMNS) for the stabilization of aqueous graphene dispersions using all-atom molecular dynamics simulations.

Debundling, Dispersion, and Stability of Multiwalled Carbon Nanotubes Driven by Molecularly Designed Electron Acceptors

Carbon nanotubes (CNTs) have attracted significant attention because of their outstanding physical and chemical properties, and yet, their high natural tendency to form bundles, ropes, or aggregates, as a consequence of their strong π-π interactions, limits their solvent processing and further applications. Efficient processing solvents, mostly amide-based, that partially compensate for these strong inter-CNT π-π interactions have been widely reported. However, the yield of debundled/dispersed CNTs and the stability of subsequent dispersions in these solvents remain key challenges. Moreover, there are major concerns related to the large-scale use of conventional solvents, as they are fossil fuel based and intrinsically highly toxic, hence the need to identify environmentally friendly and safer alternatives. Herein, we address these challenges by using a ternary system composed of multiwalled CNTs (MWCNTs), tailored electron-deficient acceptors, and an organic solvent. Not only do the electron-deficient acceptors interrupt the inter-CNTs π-π interactions, thereby enabling the subsequent debundling and dispersion of MWCNTs aggregates in the solvent, they also act as stabilizers, after dispersion, by inhibiting inter-CNT π-π interactions and re-agglomeration. The use of electron acceptors increases the yield by a factor of 165 in N-methyl 2-pyrrolidone, improves the long-term stability of the debundled and dispersed MWCNTs, and reduces the energy input to only 30 min of mild bath sonication, compared with prolonged high-energy sonication reported in the literature. We also report for the first time, the use in MWCNT processing of a "green" biosolvent, dihydrolevoglucosenone, as an environmentally friendly and nontoxic alternative to the more conventional amide-based solvents.