Nanocomposite polymeric materials with 3D graphene-based architectures: from design strategies to tailored properties and potential applications

Ultra-Low Loading of Ultra-Small Fe3 O4 Nanoparticles on Nonmodified CNTs to Improve Green EMI Shielding Capability of Rubber Composites

From a material design perspective, the incorporation of Fe3 O4 @carbon nanotube (Fe3 O4 @CNT) hybrids is an effective approach for reconciling the contradictions of high shielding and low reflection coefficients, enabling the fabrication of green shielding materials and reducing the secondary electromagnetic wave pollution. However, the installation of Fe3 O4 nanoparticles on nonmodified and nondestructive CNT walls remains a formidable challenge. Herein, a novel strategy for fabricating the above-mentioned Fe3 O4 @CNTs and subsequently assembling segregated Fe3 O4 @CNT networks in natural rubber (NR) matrices is proposed. The advanced and unique structure, magnetism, and lossless conductivity endow the as-obtained Fe3 O4 @CNT/NR with a shielding effectiveness (SE) of 63.8 dB and a low reflection coefficient of 0.24, which indicates a prominent green-shielding capability that surpasses those of previously reported green-shielding materials. Moreover, the specific SE reaches 531 dB cm-1 , exceeding that of those of previously reported carbon/polymer composites. Meanwhile, the outstanding conductivity enables the composite to reach a saturation temperature of ≈95 °C at a driving voltage of 1.5 V with long-term stability. Therefore, the as-fabricated Fe3 O4 @CNT/rubber composites represent an important development in green-shielding materials that are applied in cold environment.

Selective Laser Sintering of Polydimethylsiloxane Composites

Conductive silicone elastomer carbon nanotubes (CNTs) composites possess potential applications in a variety of fields, including electronic skin, wearable electronics, and human motion detection. Based on a novel self-made covalent adaptable network (CANs) of polydimethylsiloxane (PDMS) containg dynamic steric-hindrance pyrazole urea bond (PDMS-CANs), CNTs wrapped PDMS-CANs (CNTs@PDMS-CANs) powders were prepared by a liquid phase adsorption and deposition, and were successfully used for selective laser sintering (SLS) three-dimensional printing. SLS-printed PDMS-CANs/CNTs nanocomposites possess high electrical conductivity and low percolation threshold as SLS is one kind of quasi-static processing, which leads to the formation of conductive segregated CNTs network by using the PDMS powders with special CNTs wrapped structure. The introduction of dynamic pyrazole urea bond endows the materials self-healing capability under electrothermal and photothermal stimulus. In addition, due to the resistance difference of the damaged and intact areas, crack diagnosing can be realized by infrared thermograph under electricity. In an application demonstration in strain sensor, the composite exhibits a regular cyclic electrical resistance change at cyclic compression and bending, indicating a relative high reliability.

Advances in Graphene-Polymer Nanocomposite Foams for Electromagnetic Interference Shielding

With the continuous advancement of wireless communication technology, the use of electromagnetic radiation has led to issues such as electromagnetic interference and pollution. To address the problem of electromagnetic radiation, there is a growing need for high-performance electromagnetic shielding materials. Graphene, a unique carbon nanomaterial with a two-dimensional structure and exceptional electrical and mechanical properties, offers advantages such as flexibility, light weight, good chemical stability, and high electromagnetic shielding efficiency. Consequently, it has emerged as an ideal filler in electromagnetic shielding composites, garnering significant attention. In order to meet the requirements of high efficiency and low weight for electromagnetic shielding materials, researchers have explored the use of graphene-polymer nanocomposite foams with a cellular structure. This mini-review provides an overview of the common methods used to prepare graphene-polymer nanocomposite foams and highlights the electromagnetic shielding effectiveness of some representative nanocomposite foams. Additionally, the future prospects for the development of graphene-polymer nanocomposite foams as electromagnetic shielding materials are discussed.

3D printing of flexible strain sensor based on MWCNTs/flexible resin composite

The flexible strain sensor is an indispensable part in flexible integrated electronic systems and an important intermediate in external mechanical signal acquisition. The 3D printing technology provides a fast and cheap way to manufacture flexible strain sensors. In this paper, a MWCNTs/flexible resin composite for photocuring 3D printing was prepared using mechanical mixing method. The composite has a low percolation threshold (1.2%ωt). Based on the composite material, a flexible strain sensor with high performance was fabricated using digital light processing technology. The sensor has a GF of 8.98 under strain conditions ranging between 0% and 40% and a high elongation at break (48%). The sensor presents mechanical hysteresis under cyclic loading. With the increase of the strain amplitude, the mechanical hysteresis becomes more obvious. At the same time, the resistance response signal of the sensor shows double peaks during the unloading process, which is caused by the competition of disconnection and reconstruction of conductive network in the composite material. The test results show that the sensor has different response signals to different types of loads. Finally, its practicability is verified by applying it to balloon pressure detection.

The construction of bio-inspired hierarchically porous graphene aerogel for efficiently organic pollutants absorption

Three-dimensional graphene aerogel shows a wide application in many frontier domains, which have attracted extensive research interest owing to its large specific surface area and high porosity. However, it is still a great challenge to construct the ideal hierarchical pore structure while guaranteeing excellent absorption and mechanical performance. In this paper, inspired by the bio-based porous material, a hierarchical graphene aerogel with inter-connected micro-/nano-scale pore structure was constructed. The micro and nano-scale pores are generated by the bubble and nanoparticles (NPs) template, respectively. The resulting graphene aerogel (GA) presents low density, increased interfacial areas, high mechanical performance, and excellent absorption performance towards a mass of organic solvents. In combination with its high compressibility, a diverse organic solvent can be absorbed efficiently and recycled by extrusion conveniently. Besides, owing to the scattered hydrophilic sites of functional groups and NPs on the surface of GA-b/NP, it shows high adhesion properties for water droplets, thus presents great potential in high-efficiency fog collecting materials. In a word, the proposed approach presents a novel strategy for the construction of the hierarchical aerogel with light-weight and elasticity, as well as the achievement of efficient functionalization, which has great potential for the preparation of diverse functional composites.

Effect of carbonaceous fillers on adsorption behavior of multifunctional diatomite-based foams for wastewater treatment

Nowadays the study of the potential applications of multifunctional materials for environmental remediation is one of the main goals of the materials engineering. Multifunctional porous materials, MPMs, incorporate, all in once, different and multiple functionalities that make them suitable for several uses and can satisfy many purposes at the same time. Multifunctional diatomite-based foams with a hierarchical porosity, already produced and characterized to be applied in building as well as aerospace sectors, are proposed as adsorbents for inorganic and organic pollutants removal from wastewaters. Then, the effect of the addition of different carbonaceous nanofillers (graphite, graphene and graphene oxide) on the water purification efficiency of the adsorbent was evaluated. Firstly, pristine MPM showed the best performance in adsorbing Indigo Carmine due to its intrinsic chemism and hierarchical porosity (at macro-, micro- and nano-level), but it is not the best with respect to the Cd²⁺ adsorption, if compared with the nanocomposites. Among the nanocomposite products, both graphene- and graphene oxide-MPM samples showed a significantly improved adsorption capacity towards Cd²⁺. This behavior is due to the synergistic effect of the finer morphology, higher available foam surface, and the highly exfoliated fillers, graphene and graphene oxide, which permit a better dispersion into the matrix.

MWCNT/rGO/natural rubber latex dispersions for innovative, piezo-resistive and cement-based composite sensors

The present study is focused on the development and characterization of innovative cementitious-based composite sensors. In particular, multifunctional cement mortars with enhanced piezoresistive properties are realized by exploiting the concept of confinement of Multiwall Carbon Nanotubes (MWCNTs) and reduced Graphene Oxide (rGO) in a three-dimensional percolated network through the use of a natural-rubber latex aqueous dispersion. The manufactured cement-based composites were characterized by means of Inelastic Neutron Scattering to assess the hydration reactions and the interactions between natural rubber and the hydrated-cement phases and by Scanning Electron Microscopy and X-Ray diffraction to evaluate the morphological and mineralogical structure, respectively. Piezo-resistive properties to assess electro-mechanical behavior in strain condition are also measured. The results show that the presence of natural rubber latex allows to obtain a three-dimensional rGO/MWCNTs segregate structure which catalyzes the formation of hydrated phases of the cement and increases the piezo-resistive sensitivity of mortar composites, representing a reliable approach in developing innovative mortar-based piezoresistive strain sensors.

Mechanism of Heterogeneous Bubble Nucleation in Polymer Blend Foaming

A three-dimensional heterogeneous bubble nucleation model is constructed to provide a reasonable explanation at the molecular level for the foaming mechanism of polypropylene (PP) and polystyrene (PS) blends. CO₂ solubilities and supersaturation rations are quantitatively calculated to help interpret the contribution of each phase of the blend in the CO₂ dissolution stage. The spatial density profiles of polymer/CO₂ binary melt around different polymer chains are presented to give an intuitive perspective to the thermodynamic driving force. The predicted interfacial tension and contact angles of critical bubbles provide valid evidence to distinguish the wettability of CO₂ in different regions. The values of predicted free-energy barriers, critical radii, and nucleation number densities imply that bubbles that nucleate in the PP and PS blend interfacial region attached to the PS-rich phase achieve the smallest size and largest number density. The reliability of the theoretical model has been tested by partial available experimental data.

Mesoporous silica nanoparticles as carriers of active agents for smart anticorrosive organic coatings: a critical review

Mesoporous silica nanoparticles (MSN) have attracted increasing interest for their applicability as smart nanocarriers of corrosion inhibitors, due to their porous structure, resistance to main corrosive environments and good compatibility with polymer coatings. In this review, the main synthetic routes to obtain MSN with tailored textural properties, the design of different loading and stimuli-induced release strategies, the development of advanced organic nanocomposite coatings with MSN and the validation of their anticorrosive performances are reviewed and compared. Through a critical analysis of the literature, the most promising research trends and perspectives to exploit the highly interesting properties of MSN in advanced organic coatings are proposed.

Engineering Segregated Structures in a Cross-Linked Elastomeric Network Enabled by Dynamic Cross-Link Reshuffling

Construction of segregated structures in polymer composites is an efficient way to improve the electrical conductivity and reduce the percolation threshold by confining conductive fillers into the interstitial areas between polymer domains. Yet, it remains a great challenge to engineer segregated structures into thermosets as the cross-linked structure prohibits the "sintering" of polymer domains into a coherent material. Thus far, the state of art approaches to create segregated network in cross-linked polymers involve tedious procedures and are limited to latex mixing technology. Here, inspired by solid state plasticity of vitrimers, we present a simple method to create segregated structures in covalently cross-linked networks by compression molding of conductive filler-coated vitrimer granules. Specifically, dynamic boronic ester-cross-linked styrene-butadiene rubber vitrimers was ground into granules and then mechanically mixed with carbon nanotubes (CNTs) to coat CNTs onto vitrimer granules, followed by hot-press molding. During the molding process, the transesterifications of boronic esters enable cross-linked granules to adhere together through molecular bonding, and the high viscosity of granules forces CNTs to selectively localize at their boundary region. As a result, coherently segregated composites with an ultralow percolation threshold, good flexibility, and healing capability are obtained. With this example, we envisage that this work provides a conceptual method to create segregated structures in cross-linked polymers.

Electric Heating Behavior of Reduced Oxide Graphene/Carbon Nanotube/Natural Rubber Composites with Macro-Porous Structure and Segregated Filler Network

Conductive polymer composites with carbonaceous fillers are very attractive and play a significant role in the field of electric heaters owing to their lightweight, corrosion resistance, and easy processing as well as low manufacturing cost. In this study, lightweight reduced oxide graphene/carbon nanotube/natural rubber (rGO/CNT/NR) composites were fabricated by a facile and cost-effective approach, which consists of rGO assembling on rubber latex particles and hydrogels formation due to the interaction network established between carbonaceous fillers and subsequent mild-drying of the resulting hydrogels. Thanks to the amphiphilic nature of GO sheets, which can serve as a surfactant, the hydrophobic CNTs were easily dispersed into water under ultrasound. On the basis of both the high stable rGO and CNTs suspension and the assembling of rGO on rubber latex, a three-dimensional segregated network of CNT and rGO were easily constructed in macro-porous composites. Either the segregated network and macro-porous structure endowed the resulting composites with low density (0.45 g cm-3), high electrical conductivity (0.60 S m-1), and excellent electric heating behavior, when the weight content of rGO and CNTs are 0.5% and 2.5%, respectively. For electric heating behavior, the steady-state temperature of the above composites reaches 69.1 °C at an input voltage of 15 V.

Synthesis and Electrochemical Study of Three-Dimensional Graphene-Based Nanomaterials for Energy Applications

Graphene is an attractive soft material for various applications due to its unique and exclusive properties. The processing and preservation of 2D graphene at large scales is challenging due to its inherent propensity for layer restacking. Three-dimensional graphene-based nanomaterials (3D-GNMs) preserve their structures while improving processability along with providing enhanced characteristics, which exhibit some notable advantages over 2D graphene. This feature article presents recent trends in the fabrication and characterization of 3D-GNMs toward the study of their morphologies, structures, functional groups, and chemical compositions using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Owing to the attractive properties of 3D-GNMs, which include high surface areas, porous structures, improved electrical conductivity, high mechanical strength, and robust structures, they have generated tremendous interest for various applications such as energy storage, sensors, and energy conversion. This article summarizes the most recent advances in electrochemical applications of 3D-GNMs, pertaining to energy storage, where they can serve as supercapacitor electrode materials and energy conversion as oxygen reduction reaction catalysts, along with an outlook.

An anisotropic layer-by-layer carbon nanotube/boron nitride/rubber composite and its application in electromagnetic shielding

Multifunctional polymer composites with anisotropic properties are attracting interest as they fulfil the growing demand of multitasking materials. In this work, anisotropic polymer composites have been fabricated by combining the layer-by-layer (LBL) filtration method with the alternative assembling of carbon nanotubes (CNTs) and hexagonal boron nitride flakes (hBN) on natural rubber latex particles (NR). The layered composites exhibit anisotropic thermal and electrical conductivities, which are tailored through the layer formulations. The best composite consists of four layers of NR modified with 8 phr (parts per Hundred Rubber) CNTs (∼7.4 wt%) and four alternate layers with 12 phr hBN (∼10.7 wt%). The composites exhibit an electromagnetic interference (EMI) shielding effectiveness of 22.41 ± 0.14 dB mm^-1 at 10.3 GHz and a thermal conductivity equal to 0.25 W m^-1 K^-1. Furthermore, when the layered composite is used as an electrical thermal heater the surface reaches a stable temperature of ∼103 °C in approx. 2 min, with an input bias of 2.5 V.

Multifunctional Role of MoS2 in Preparation of Composite Hydrogels: Radical Initiation and Cross-Linking

This paper describes the multifunctional effect of molybdenum disulfide (MoS₂) that enables the rapid and accessible preparation of nanocomposite hydrogels via a bottom-up design. The MoS₂ nanoplatelet forms radical species through a redox reaction with persulfate under aqueous conditions while initiating the polymerization of acrylic monomers and providing noncovalent cross-linking points without requiring external stimuli or extra cross-linkers, leading to the formation of hydrogels that are in situ embedded with inorganic flakes. Furthermore, the addition of MoS₂ could induce more rigid and elastic networks compared to those in control hydrogels using a typical cross-linker at the same level; for example, 0.08 wt % MoS₂ resulted in a composite hydrogel of which the elastic modulus was 2.5 times greater than that from a hydrogel using N,N'-methylenebis(acrylamide) as the showing phase transition during polymerization. The composite hydrogels are self-healable, taking advantage of reversible physical cross-links. Thus, two cut hydrogel strips could be readily rejoined by heating at 70 °C, and the resulting whole strip showed mechanical strength similar to that of the pristine sample before it was cut. This synthetic approach would give way to the modular design of MoS₂-containing composite hydrogels.

Constructing Oriented Two-Dimensional Large-Sized Modified Graphene Oxide Barrier Walls in Brominated Butyl Rubber to Achieve Excellent Gas Barrier Properties

Brominated butyl rubber (BIIR) is widely used as tire lining, medical sealing material, and so on, due to its merits like high strength, low permeability, and high vulcanization activity. However, the gas barrier properties of BIIR need to be improved further to meet the requirements of certain special conditions such as high pressure (aircraft tire: 1.5 MPa). In this work, oriented two-dimensional (2D) large-sized modified graphene oxide (mGO) barrier walls in BIIR are successfully constructed based on the following processes: three-dimensional (3D) large-sized mGO hollow spherical shells in BIIR matrix are achieved from the core (water)-shell (mGO) structure in BIIR solution, which is obtained through the Pickering emulsion template method, and then are pressed into oriented 2D large-sized mGO barrier walls in the BIIR matrix. Such oriented 2D large-sized mGO barrier walls not only have an extremely large size between 50 and 120 μm but also are aligned perpendicular to the gas diffusion direction. Thus, even only with 0.7 wt % mGO, the nitrogen permeability of the BIIR composite is reduced by 91% relative to pristine BIIR and by 40% relative to the comparing sample with small mGO sheets. Therefore, this work provides a route to regulate the distribution of GO and thus can be a useful reference to fabricate rubber composites with superior gas barrier properties.

Versatile Aerogels for Sensors

Aerogels are unique solid-state materials composed of interconnected 3D solid networks and a large number of air-filled pores. They extend the structural characteristics as well as physicochemical properties of nanoscale building blocks to macroscale, and integrate typical characteristics of aerogels, such as high porosity, large surface area, and low density, with specific properties of the various constituents. These features endow aerogels with high sensitivity, high selectivity, and fast response and recovery for sensing materials in sensors such as gas sensors, biosensors and strain and pressure sensors, among others. Considerable research efforts in recent years have been devoted to the development of aerogel-based sensors and encouraging accomplishments have been achieved. Herein, groundbreaking advances in the preparation, classification, and physicochemical properties of aerogels and their sensing applications are presented. Moreover, the current challenges and some perspectives for the development of high-performance aerogel-based sensors are summarized.