Production of graphene quantum dots by ultrasound-assisted exfoliation in supercritical CO2/H2O medium

Synthesis, properties and potential applications of photoluminescent carbon nanoparticles: A review

Photoluminescent-carbon nanoparticles (PL-CNPs) are a new class of materials that received immense interest among researchers due to their distinct characteristics, including photoluminescence, high surface-to-volume ratio, low cost, ease of synthesis, high quantum yield, and biocompatibility. By exploiting these outstanding properties, many studies have been reported on its utility as sensors, photocatalysts, probes for bio-imaging, and optoelectronics applications. From clinical applications to point-of-care test devices, drug loading to tracking of drug delivery, and other research innovations demonstrated PL-CNPs as an emerging material that could substitute conventional approaches. However, some of the PL-CNPs have poor PL properties and selectivity due to the presence of impurities (e.g., molecular fluorophores) and unfavourable surface charges by the passivation molecules, which impede their applications in many fields. To address these issues, many researchers have been paying great attention to developing new PL-CNPs with different composite combinations to achieve high PL properties and selectivity. Herein, we thoroughly discussed the recent development of various synthetic strategies employed to prepare PL-CNPs, doping effects, photostability, biocompatibility, and applications in sensing, bioimaging, and drug delivery fields. Moreover, the review discussed the limitations, future direction, and perspectives of PL-CNPs in possible potential applications.

Top-down synthesis and enhancing device adaptability of graphene quantum dots

Quantum dots (QD) are rapidly making their way into several application sectors including optoelectronics, and there is a strong need to focus on non-toxic QDs. In this work, we have synthesized graphene QDs in the size range of 1.4-4.2 nm from inexpensive graphite by oxidative cleavage using a sulphuric and nitric acid mixture. A subsequent hydrogen peroxide oxidation step, investigated using two thermal budgets, has resulted in QDs with excellent photoluminescence (PL) intensity. Prolonged, higher temperature oxidation results in smaller size GQDs. X-ray photoelectron spectroscopy analysis confirmed the role of ·OH radicals in the oxidation process and Raman analysis revealed that the higher thermal budget oxidation results in lower defect density. To overcome the challenges in device adaptability due to the inherent acidity in the QDs, a post-synthesis neutralization process was devised. The neutralized GQDs were formed into a film to be used as the active layer in a photodetector device. Fluorescence decay analysis showed there is no significant change in lifetime because of the film formation process. The fabricated GQD photodetector device exhibited high photocurrent under ultraviolet illumination with an ON/OFF ratio of 400% at an applied bias of ±1 V. The device performance underlines the high potential for the non-toxic, top-down synthesized GQDs for application in optoelectronic devices.

Eco-Friendly and Sustainable Pathways to Photoluminescent Carbon Quantum Dots (CQDs)

Carbon quantum dots (CQDs), a new family of photoluminescent 0D NPs, have recently received a lot of attention. They have enormous future potential due to their unique properties, which include low toxicity, high conductivity, and biocompatibility and accordingly can be used as a feasible replacement for conventional materials deployed in various optoelectronic, biomedical, and energy applications. The most recent trends and advancements in the synthesizing and setup of photoluminescent CQDs using environmentally friendly methods are thoroughly discussed in this review. The eco-friendly synthetic processes are emphasized, with a focus on biomass-derived precursors. Modification possibilities for creating newer physicochemical properties among different CQDs are also presented, along with a brief conceptual overview. The extensive amount of writings on them found in the literature explains their exceptional competence in a variety of fields, making these nanomaterials promising alternatives for real-world applications. Furthermore, the benefits, drawbacks, and opportunities for CQDs are discussed, with an emphasis on their future prospects in this emerging research field.

Functionalization of Graphene Derivatives with Conducting Polymers and Their Applications in Uric Acid Detection

In this article, we review recent progress concerning the development of sensorial platforms based on graphene derivatives and conducting polymers (CPs), alternatively deposited or co-deposited on the working electrode (usually a glassy carbon electrode; GCE) using a simple potentiostatic method (often cyclic voltammetry; CV), possibly followed by the deposition of metallic nanoparticles (NPs) on the electrode surface (ES). These materials have been successfully used to detect an extended range of biomolecules of clinical interest, such as uric acid (UA), dopamine (DA), ascorbic acid (AA), adenine, guanine, and others. The most common method is electrochemical synthesis. In the composites, which are often combined with metallic NPs, the interaction between the graphene derivatives-including graphene oxide (GO), reduced graphene oxide (RGO), or graphene quantum dots (GQDs)-and the CPs is usually governed by non-covalent functionalization through π-π interactions, hydrogen bonds, and van der Waals (VW) forces. The functionalization of GO, RGO, or GQDs with CPs has been shown to speed up electron transfer during the oxidation process, thus improving the electrochemical response of the resulting sensor. The oxidation mechanism behind the electrochemical response of the sensor seems to involve a partial charge transfer (CT) from the analytes to graphene derivatives, due to the overlapping of π orbitals.

Graphene quantum dots: synthesis, properties, and applications to the development of optical and electrochemical sensors for chemical sensing

GQDs exhibits exceptional electrochemical activity owing to their active edge sites that make them very attractive for biosensing applications. However, their use in the design of new biosensing devices for application to the detection and quantification of toxins, pathogens, and clinical biomarkers has so far not investigated in detail. In this regard, herein we provide a detailed review on various methodologies employed for the synthesis of GQDs, including bottom-up and top-down approaches, with a special focus on their applications in biosensing via fluorescence, photoluminescence, chemiluminescence, electrochemiluminescence, fluorescence resonance energy transfer, and electrochemical techniques. We believe that this review will shed light on the critical issues and widen the applications of GQDs for the design of biosensors with improved analytical response for future applications. HIGHLIGHTS: • Properties of GQDs play a critical role in biosensing applications. • Synthesis of GQDs using top-down and bottom-up approaches is discussed comprehensively. • Overview of advancements in GQD-based sensors over the last decade. • Methods for the design of selective and sensitive GQD-based sensors. • Challenges and opportunities for future GQD-based sensors.

A Size-Controlled Graphene Oxide Materials Obtained by One-Step Electrochemical Exfoliation of Carbon Fiber Cloth for Applications to In Situ Gold Nanoparticle Formation and Electrochemical Sensors—A Preliminary Study

A simple, one-step and facile method has been introduced to prepare fluorescent and electrochemically active carbon nanoparticles with single-size distribution and good long-term stability by electrochemical exfoliation of polyacrylonitrile-based carbon fibers in an alkaline solution-phase condition. The preparation condition was systematically optimized by studying the effect of temperature and electrolytes. It has been found that an electrochemical exfoliation reaction carried out at an applied potential of 2 V vs. Ag/AgCl in a phosphate-ion-containing alkaline solution at a temperature of 40 °C is an ideal condition for the preparation of 14 ± 4 nm-sized carbon nanoparticles. Unlike the literature protocols, there are no filtration and membrane dialysis-based off-line sample pretreatments adopted in this work. The as-prepared carbon nanoparticles were characterized by fluorescence, Raman spectrum, transmission electron microscope, and X-ray photoelectron spectroscopic characterization methods. It was found that the carbon–oxygen functional group rich in graphene–oxide quantum dots (GOQDs) such as carbon nanoparticles were formed in this work. A preliminary study relating to simultaneous electrochemical oxidation and the sensing of uric acid and ascorbic acid with well-resolved peaks was demonstrated as a model system to extend the new carbon material for electroanalytical applications. Furthermore, in situ synthesis of 2 nm-sized gold nanoparticles stabilized by GOQDs was presented. The carbon nanoparticles prepared by the direct method in this work have shown good stability over 6 months when stored at room temperature. The electrochemical exfoliation reaction has been found to be highly reproducible and suitable for bulk synthesis of luminescence-effective carbon nanoparticles to facilitate fundamental studies and practical applications.

Two-Dimensional Quantum Dot-Based Electrochemical Biosensors

Two-dimensional quantum dots (2D-QDs) derived from two-dimensional sheets have received increasing interest owing to their unique properties, such as large specific surface areas, abundant active sites, good aqueous dispersibility, excellent electrical property, easy functionalization, and so on. A variety of 2D-QDs have been developed based on different materials including graphene, black phosphorus, nitrides, transition metal dichalcogenides, transition metal oxides, and MXenes. These 2D-QDs share some common features due to the quantum confinement effects and they also possess unique properties owing to their structural differences. In this review, we discuss the categories, properties, and synthetic routes of these 2D-QDs and emphasize their applications in electrochemical biosensors. We deeply hope that this review not only stimulates more interest in 2D-QDs, but also promotes further development and applications of 2D-QDs in various research fields.

Shedding Light on Graphene Quantum Dots: Key Synthetic Strategies, Characterization Tools, and Cutting-Edge Applications

During the last 20 years, the scientific community has shown growing interest towards carbonaceous nanomaterials due to their appealing mechanical, thermal, and optical features, depending on the specific nanoforms. Among these, graphene quantum dots (GQDs) recently emerged as one of the most promising nanomaterials due to their outstanding electrical properties, chemical stability, and intense and tunable photoluminescence, as it is witnessed by a booming number of reported applications, ranging from the biological field to the photovoltaic market. To date, a plethora of synthetic protocols have been investigated to modulate the portfolio of features that GQDs possess and to facilitate the use of these materials for target applications. Considering the number of publications and the rapid evolution of this flourishing field of research, this review aims at providing a broad overview of the most widely established synthetic protocols and offering a detailed review of some specific applications that are attracting researchers’ interest.

Ultrasonic cavitation in CO2-expanded N, N-dimethylformamide (DMF)

Due to the tunability in mass transfer, solvation and solubility, gas-expanded liquids show advantages over traditional organic solvents in many characteristics. Ultrasonication is a commonly used method to promote heat and mass transfer. The introduction of ultrasonic technology into the gas-expanded liquid system can promote the polymerization of polymer monomers, enhance extraction efficiency, and control the growth size of nanocrystals, etc. Although acoustic cavitation has been extensively explored in aqueous solutions, there are still few studies on cavitation in organic liquids, especially in gas-expanded liquid systems. In this article, the development of cavitation bubble cloud structure in CO₂-expanded N, N-dimethylformamide (DMF) was observed by a high-speed camera, and the cavitation intensity was recorded using a spherical hydrophone. It was found that the magnitude of the transient cavitation energy was not only related to input power, but also closely related to CO₂ content. The combination of ultrasound (causing a rapid alternation of gas solubility) and gas-expanded liquid system (causing a decrease in viscosity and surface tension of liquids) is expected to provide a perfect platform for high-speed mass transfer.

Influence of ultrasonic combined supercritical-CO2 electrodeposition process on copper film fabrication: Electrochemical evaluation

Introducing ultrasound irradiation to the electrodeposition process can significantly improve the physical and chemical properties of deposited films. Meanwhile, the beneficial effects from supercritical-CO_2, such as high diffusivity, high permeability, low surface tension, etc., would improve the electrodeposition process with better surface quality. In the shed of the light, the present work deals with the preparation of copper (Cu) films using the integrated techniques, i.e., ultrasonic-assisted supercritical-CO₂ (US-SC-CO₂) electrodeposition approach. For comparison, Cu films were also prepared by normal supercritical-CO₂ (SC-CO₂) and conventional electrodeposition methods. To investigate the characteristics of Cu films, surface morphology analysis, roughness analysis, X-ray diffraction studies (XRD), Linear polarization, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were performed. In this work, EIS analysis was utilized for interfacial charge transfer resistance analysis with 5 mM [Fe(CN)₆]^-3/-4 redox system and corrosion analysis with 3.5 wt% NaCl solution. The observed results revealed that the film prepared with the US-SC-CO₂ method have superior properties than those produced by normal SC-CO₂ and conventional methods. Due to the combination of US-SC-CO₂, the cavitation implosion occurs rapidly that enriches the deposited film quality, such as sufficient grain size, smoother surface, enhanced corrosion resistance, and charge carrier dynamics. On the other hand, the ultrasound effect with SC-CO₂ helped to remove the weakly adhered metal ions on the electrode's surface.

Ultrasonic-assisted supercritical-CO2 electrodeposition of Zn-Co film for high-performance corrosion inhibition: A greener approach

The ultrasonic-assisted electrodeposition process significantly improves the mechanical and electrochemical properties. Meanwhile, supercritical fluid technology also enhances the electrodeposition process with increased benefits, such as low surface tension, permeability, high diffusivity, and density, which improves the surface quality through grain refinement. In this study, Zn-Co films were prepared using the ultrasonic-assisted supercritical-CO2 (US-SC-CO2) electrodeposition approach, and its pressure effect on the film was evaluated. The films were also prepared by the conventional and typical supercritical-CO2 (SC-CO2) methods for a comparison study. All the prepared films were characterized by morphological studies, elemental composition, crystal structure orientation, and microhardness tests. Later, the fabricated films were examined by potentiodynamic polarization technique and electrochemical impedance technique (EIS) with 3.5 wt.% NaCl solution for corrosion evaluation. Based on results, Zn-Co film prepared through the US-SC-CO2 process shows a spherical nodule like structure with reduced grain size and significantly enhanced hardness property. In XRD studies, the shift in diffracted peak's position reveals the increased proportion of Co ions. Further, EDX results also confirm the same with the characteristic peaks. Finally, compared to the other methods, the corrosion resistance was more efficient in the US-SC-CO2 process by 73.75%.

Synthesis of graphene quantum dots and their applications in drug delivery

This review focuses on the recent advances in the synthesis of graphene quantum dots (GQDs) and their applications in drug delivery. To give a brief understanding about the preparation of GQDs, recent advances in methods of GQDs synthesis are first presented. Afterwards, various drug delivery-release modes of GQDs-based drug delivery systems such as EPR-pH delivery-release mode, ligand-pH delivery-release mode, EPR-Photothermal delivery-Release mode, and Core/Shell-photothermal/magnetic thermal delivery-release mode are reviewed. Finally, the current challenges and the prospective application of GQDs in drug delivery are discussed.

Dispersed graphene materials of biomedical interest and their toxicological consequences

Graphene is one-atom thick nanocarbon displaying a unique honeycomb structure and extensive conjugation. In addition to high surface area to mass ratio, it displays unique optical, thermal, electronic and mechanical properties. Atomic scale tunability of graphene has attracted immense research interest with a prospective utility in electronics, desalination, energy sectors, and beyond. Its intrinsic opto-thermal properties are appealing from the standpoint of multimodal drug delivery, imaging and biosensing applications. Hydrophobic basal plane of sheets can be efficiently loaded with aromatic molecules via non-specific forces. With intense biomedical interest, methods are evolving to produce defect-free and dispersion stable sheets. This review summarizes advancements in synthetic approaches and strategies of stabilizing graphene derivatives in aqueous medium. We have described the interaction of colloidal graphene with cellular and sub-cellular components, and subsequent physiological signaling. Finally, a systematic discussion is provided covering toxicological challenges and possible solutions on utilizing graphene formulations for high-end biomedical applications.

Blue- and green-emitting hydrophobic carbon dots: preparation, optical transition, and carbon dot-loading

In the past decade, hydrophobic fluorescent carbon dots (OCDs) have received little attention, and its potential application and light transition mechanism is seldom explored. Here we report a novel one-step approach for synthesizing blue- and green-emitting hydrophobic fluorescent carbon dots (OCD_b and OCD_g) by calcinating with the uses of citric acid and hexadecylamine as initial reactants. The optimal conditions for preparing OCD_b and OCD_g were obtained by using the Taguchi L25 (3⁵) orthogonal array. The highest quantum yield and product yield of OCDs reached 80.2% and 57.1%, respectively, larger than those from most of all the known reports. The fluorescent stability of OCD_b and OCD_g was excellent under UV irradiation (30 W) for days. The luminescent color of OCDs showed a great dependence on reaction conditions. It is easier to get OCD_g via a reaction kept at a high temperature for a long time. The optical transition mechanism was studied for the two kinds of color OCDs, and therefore proposed in combination with their optical properties and surface groups. The reason for light transition is probably related to an appropriate critical ratio and surface density of the C=O and N-H bond in the surface structure of the product. For the OCD_g, the concentration matching ratio of N-H and C=O bonds in the surface structure of the green-emitting product is approximately between d/2 and 3d/2, where d is a fixed constant. Lower than or higher than this critical ratio range, the product emits blue light. Based on their high fluorescence quantum efficiency and the advantages mentioned above, these OCDs were then respectively used for preparing hydrophobic fluorescent carbon dot-loading liposomes and acrylate films, both exhibiting a perfect performance with no fluorescence quenching.

Graphene Quantum Dots in Electrochemical Sensors/Biosensors

Background:

Graphene and its derivatives, as most promising carbonic nanomaterials have been widely used in design and making electrochemical sensors and biosensors. Graphene quantum dots are one of the members of this family which have been mostly known as fluorescent nanomaterials and found extensive applications due to their remarkable optical properties. Quantum confinement and edge effects in their structures also cause extraordinary electrochemical properties.

Objective:

Recently, graphene quantum dots besides graphene oxides and reduced graphene oxides have been applied for modification of the electrodes too and exposed notable effects in electrochemical responses. Here, we are going to consider these significant effects through reviewing some of the recent published works.

A one-step ultrasonic irradiation assisted strategy for the preparation of polymer-functionalized carbon quantum dots and their biological imaging

Fluorescent carbon nanoparticles (FCNs) have gradually become the most promising alternative candidates to other traditional fluorescent nanomaterials for biological applications on account of their excellent fluorescence property and remarkable biocompatibility. Although many methods have reported on the preparation of FCNs, to date, no studies have reported the preparation of polymers of functionalized FCNs. A high-efficiency method was developed in this work to synthesize high-quality poly(ethylene oxide) (PEG)-functionalized FCNs from cigarette ash and thiol group-containing PEG via a facile one-pot ultrasonic irradiation treatment. A series of characterization techniques demonstrated the uniform nanoscale size, good fluorescence stability, high water dispersibility and remarkable biocompatibility of the generated FCNs. Furthermore, cell imaging was easily achieved at high resolution using the synthetic FCNs as probes, which validates their potential for bioimaging applications. In summary, an efficient one-pot strategy is reported for the first time on the preparation of PEG-functionalized FCNs with the assistance of ultrasonic irradiation. This method should be of great research interest for the fabrication of other polymer-functionalized FCNs with designable properties and functions.

High-Efficiency Production of Graphene by Supercritical CO2 Exfoliation with Rapid Expansion

In this study, direct nonequilibrium molecular dynamics simulations based on the density-functional tight-binding potential were performed to investigate the mechanism of graphite exfoliation by supercritical CO₂ in the depressurization process. We found that the graphite peeling rate and the graphene yield depended on the number of inserted CO₂ molecules in our simulations, and the appropriate pressure or density of CO₂ is a prerequisite to achieve graphite exfoliation. Our theoretical results proposed that the graphite peeling occurred till the pressure or the density of CO₂ was larger than 12.2 MPa or 0.21 g/cm³. This is confirmed by the experimental observations. Furthermore, we declared that the essential effect of the pressure or density of CO₂ was attributed to the competition between the van der Waals attraction in the graphite interlayer and repulsion of CO₂ and graphite, which resulted from the steric hinder effect. The current theoretical observations provide potential scientific evidence to control graphite exfoliation by supercritical CO₂.

Graphene nanosheets preparation using magnetic nanoparticle assisted liquid phase exfoliation of graphite: The coupled effect of ultrasound and wedging nanoparticles

This study aims to investigate a novel technique to improve the yield of liquid phase exfoliation of graphite to graphene sheets. The method is based on the utilization of magnetic Fe₃O₄ nanoparticles as "particle wedge" to facilitate delamination of graphitic layers. Strong shear forces resulted from the collision of Fe₃O₄ particles with graphite particles, and intense ultrasonic waves lead to enhanced exfoliation of graphite. High quality of graphene sheets along with the ease of Fe₃O₄ particle separation from graphene solution which arises from the magnetic nature of Fe₃O₄ nanoparticles are the unique features of this approach. Initial graphite flakes and produced graphene sheets were characterized by various methods including field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectroscopy, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Zeta potential analysis. Moreover, the effect of process factors comprising initial graphite concentration, Fe₃O₄ nanoparticles concentration, sonication time, and sonication power were investigated. Results revealed that graphene preparation yield and the number of layers could be manipulated by the presence of magnetic nanoparticles.

High-Performance Supercapacitor of Graphene Quantum Dots with Uniform Sizes

Graphene quantum dots (GQDs) with uniform sizes of less than 5 nm are synthesized by a novel top-down strategy. Nitric acid as a strong oxidant can be used to cut graphene oxide via sonication and hydrothermal processes. Moreover, purified GQDs are obtained from removing oxygen-containing functional groups in a heat treatment process. Both nanoscale size and edge effect of GQDs improve their abundant active sites and restrain the restack of graphene nanosheets. Meanwhile, their electrochemical performance demonstrates the properties of the GQDs for practical application in energy storage. The GQD electrode material shows an ideal electric double-layer capacitance behavior such as a high specific capacitance of 296.7 F g^-1, a satisfactory energy density of 41.2 W h kg^-1 at 1 A g^-1, a low internal resistance, a small relaxation time, and an excellent cycling stability. The results illustrate excellent electrochemical activity, high conductivity, and enhanced ion transport rate on the surface of electrolyte and electrode. The advantages of GQDs confirm their unique characteristics for potential applications in the field of electrode materials for supercapacitors.

Ultrasound coupled with supercritical carbon dioxide for exfoliation of graphene: Simulation and experiment

Ultrasound coupled with supercritical CO₂ has become an important method for exfoliation of graphene, but behind which a peeling mechanism is unclear. In this work, CFD simulation and experiment were both investigated to elucidate the mechanism and the effects of the process parameters on the exfoliation yield. The experiments and the CFD simulation were conducted under pressure ranging from 8MPa to 16MPa, the ultrasonic power ranging from 12W to 240W and the frequency of 20kHz. The numerical analysis of fluid flow patterns and pressure distributions revealed that the fluid shear stress and the periodical pressure fluctuation generated by ultrasound were primary factors in exfoliating graphene. The distribution of the fluid shear stress decided the effective exfoliation area, which, in turn, affected the yield. The effective area increased from 5.339cm³ to 8.074cm³ with increasing ultrasonic power from 12W to 240W, corresponding to the yield increasing from 5.2% to 21.5%. The pressure fluctuation would cause the expansion of the interlayers of graphite. The degree of the expansion increased with the increase of the operating pressure but decreased beyond 12MPa. Thus, the maximum yield was obtained at 12MPa. The cavitation might be generated by ultrasound in supercritical CO₂. But it is too weak to exfoliate graphite into graphene. These results provide a strategy in optimizing and scaling up the ultrasound-assisted supercritical CO₂ technique for producing graphene.

The effects of ultrasonic agitation on supercritical CO2 copper electroplating

Applying ultrasound to the electroplating process can improve mechanical properties and surface roughness of the coating. Supercritical electroplating process can refine grain to improve the surface roughness and hardness. However, so far there is no research combining the above two processes to explore its effect on the coating. This study aims to use ultrasound (42kHz) in supercritical CO₂ (SC-CO₂) electroplating process to investigate the effect of ultrasonic powers and supercritical pressures on the properties of copper films. From the results it was clear that higher ultrasonic irradiation resulted in higher current efficiency, grain refinement, higher hardness, better surface roughness and higher internal stress. SEM was also presented to verify the correctness of the measured data. The optimal parameters were set to obtain the deposit at pressure of 2000psi and ultrasonic irradiation of 0.157W/cm³. Compared with SC-CO₂ electroplating process, the current efficiency can be increased from 77.57% to 93.4%, the grain size decreases from 24.34nm to 22.45nm, the hardness increases from 92.87Hv to 174.18Hv, and the surface roughness decreases from 0.83μm to 0.28μm. Therefore, this study has successfully integrated advantages of ultrasound and SC-CO₂ electroplating, and proved that applied ultrasound to SC-CO₂ electroplating process can significantly improve the mechanical properties of the coating.

Preparation of waterborne dispersions of epoxy resin by ultrasonic-assisted supercritical CO2 nanoemulsification technique

Waterborne nanoemulsion of diglycidyl ether of bisphenol A type epoxy resin (DGEBA) with droplet size of around 124nm was prepared by using an ultrasonic-assisted supercritical carbon dioxide (scCO₂) technique in an autoclave reactor at a low temperature (32°C). A view cell positioned in-line with the ultrasonic probe allowed observation of the emulsification process. From the image analysis and droplet size measurement, the influence mechanisms of the ultrasonic power, the degree of mixing of scCO₂ with DGEBA, the adding amount of emulsifier, and the system pressure on emulsification process and emulsion droplet size were investigated. In the emulsification process, scCO₂ penetrated into the mixture and absorbed on the DGEBA molecular. The interactions between CO₂ and the functional groups of DGEBA reduced the chain-chain interactions of polymer segments and therefore efficiently reduced the viscosity of DGEBA at a low temperature. Meantime, the cavitation and acoustic streaming of ultrasound provided a shear force for the nanoemulsification and a disturbance force for the homogeneity of the emulsion. Therefore, the combination of scCO₂ and ultrasonication made it possible to prepare a long-term stable nanoemulsion under a low temperature. This ultrasonic-assisted scCO₂ emulsification method provides an efficient and solvent-free process for the preparation of waterborne nanoemulsions of, for example, some heat-sensitive and water-insoluble active substances at low temperature.

RGO and Three-Dimensional Graphene Networks Co-modified TIMs with High Performances

With the development of microelectronic devices, the insufficient heat dissipation ability becomes one of the major bottlenecks for further miniaturization. Although graphene-assisted epoxy resin (ER) display promising potential to enhance the thermal performances, some limitations of the reduced graphene oxide (RGO) nanosheets and three-dimensional graphene networks (3DGNs) hinder the further improvement of the resulting thermal interface materials (TIMs). In this study, both the RGO nanosheets and 3DGNs are adopted as co-modifiers to improve the thermal conductivity of the ER. The 3DGNs provide a fast transport network for phonon, while the presence of RGO nanosheets enhances the heat transport at the interface between the graphene basal plane and the ER. The synergy of these two modifiers is achieved by selecting a proper proportion and an optimized reduction degree of the RGO nanosheets. Moreover, both the high stability of the thermal conductivity and well mechanical properties of the resulting TIM indicate the potential application prospect in the practical field.