Facile Production of Graphene/Polypropylene Composites with Enhanced Electrical and Thermal Properties through In Situ Artificial Latex Preparation

In order to obtain the unique properties of graphene-based composites, to realize homogeneous dispersion of graphene throughout the polymer matrix remains the key challenge. In this work, edge-oxidized graphene/polypropylene (EOGr/PP) composites with well-dispersed EOGr in PP matrix, synchronously exhibiting high electrical conductivity and thermal property, were simply fabricated for the first time using a novel strategy by in situ artificial PP latex preparation in the presence of EOGr based on solution-emulsification technique. The good dispersion state of EOGr in the PP matrix was demonstrated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). A blue shift in Raman G peak of the EOGr nanosheets was observed in the EOGr/PP composites, indicating the strong interactions between the EOGr nanosheets and the PP matrix. The onset crystallization and crystallization peak temperatures increased as the EOGr loading increases due to its good nucleating ability. An improved thermal stability of EOGr/PP composites was observed as evaluated by TGA. The EOGr/PP composites showed an insulator-to-conductor percolation transition in between that of 1 and 2 wt% EOGr content. Such strategy provides a very effective pathway to fabricate high-performance nonpolar polymer/graphene composites with excellent dispersion state of graphene.

The effect of OMMT reinforcement and annealing treatment on mechanical and thermal properties of Polyurethane Copolymer nanocomposites

This study focuses on a new fabrication of nanocomposite based on Polyurethane Copolymer (PUC) intercalated with organo-modified montmorillonite nanoparticles (OMMT), via an efficient combination of solution mixing and melt blending processes. The combination of solution mixing and melt interaction processes produced PUC/OMMT nanocomposites with enhanced properties. The OMMT filled PUC was characterised by TEM and tensile test. The effect of thermal treatment process was also studied due to subsequent microphase separation of PUC resulting from microdomain miscibility. TEM observation recognised a decent dispersion state of OMMT within PUC, owing to their exfoliated and intercalated structure. This morphology was greatly influenced by induced thermal treatment. The dynamic mechanical thermal analysis (DMTA) revealed that storage modulus and glass transition temperature of the nanocomposites increased with OMMT incorporation. The tensile modulus and tensile strength of nanocomposites showed an improvement with the addition of OMMT.

A Simple and Ultrasensitive Colorimetric Biosensor for Anatoxin-a Based on Aptamer and Gold Nanoparticles

Here, we designed a simple, rapid, and ultrasensitive colorimetric aptasensor for detecting anatoxin-a (ATX-a). The sensor employs a DNA aptamer as the sensing element and gold nanoparticles (AuNPs) as probes. Adsorption of the aptamer onto the AuNP surface can protect AuNPs from aggregation in NaCl solution, thus maintaining their dispersion state. In the presence of ATX-a, the specific binding of the aptamer with ATX-a results in a conformational change in the aptamer, which facilitates AuNP aggregation and, consequently, a color change of AuNPs from red to blue in NaCl solution. This color variation is directly associated with ATX-a concentration and can be easily measured using a UV/Vis spectrophotometer. The absorbance variation is linearly proportional to ATX-a concentration across the concentration range of 10 pM to 200 nM, with a detection limit of 4.45 pM and high selectivity against other interferents. This strategy was successfully applied to the detection of ATX-a in lake water samples. Thus, the present aptasensor is a promising alternative method for the rapid detection of ATX-a in the environment.

Investigation and Application of Fractal Theory in Cement-Based Materials: A Review

Cement-based materials, including cement and concrete, are the most widely used construction materials in the world. In recent years, the investigation and application of fractal theory in cement-based materials have attracted a large amount of attention worldwide. The microstructures of cement-based materials, such as the pore structures, the mesostructures, such as air voids, and the morphological features of powders, as well as the fracture surfaces and cracks, commonly present extremely complex and irregular characteristics that are difficult to describe in terms of geometry but that can be studied by fractal theory. This paper summarizes the latest progress in the investigation and application of fractal theory in cement-based materials. Firstly, this paper summarizes the principles and classification of the seven fractal dimensions commonly used in cement-based materials. These fractal dimensions have different physical meanings since they are obtained from various testing techniques and fractal models. Then, the testing techniques and fractal models for testing and calculating these fractal dimensions are introduced and analyzed individually, such as the mercury intrusion porosimeter (MIP), nitrogen adsorption/desorption (NAD), and Zhang’s model, Neimark’s model, etc. Finally, the applications of these fractal dimensions in investigating the macroproperties of cement-based materials are summarized and discussed. These properties mainly include the mechanical properties, volumetric stability, durability (e.g., permeability, frost and corrosion resistance), fracture mechanics, as well as the evaluation of the pozzolanic reactivity of the mineral materials and the dispersion state of the powders.

Influence of the Graphene Filler Nature on the Morphology and Properties of Melt Blended EVOH Based Nanocomposites

In this study, ethylene vinyl alcohol (EVOH) nanocomposites elaborated by melt blending with four different fillers were investigated. Two graphene and two graphite fillers displaying various shapes were selected. The morphology, microstructure, thermal, mechanical, and barrier properties of the nanocomposite films prepared for 2 wt% fillers were analyzed with the aim to establish structure–function properties relationships. The nanocomposites properties significantly depended on the nature of the incorporated filler. The nanocomposite film prepared with the expanded graphite filler exhibited the highest Young modulus value (E = 1430 MPa) and the best barrier properties. Indeed, barrier properties, rarely studied at high water activities, evidenced a significant improvement with a decrease of the water vapor permeability by a factor 1.8 and of the oxygen permeabilities by a factor close to 2, for a critical water activity higher than 0.95. An increase of the thermal stability was also evidenced for this nanocomposite. It was shown that for all studied nanocomposites, the properties could be related to the dispersion state of the fillers and the simultaneous increase of the crystallinity of the matrix. A specific equation was proposed to take into account these both parameters to accurately predict the nanocomposite barrier properties.

Basic Study of Extensional Flow Mixing for the Dispersion of Carbon Nanotubes in Polypropylene by Using Capillary Extrusion

This study evaluated the mixing effect of simple uniaxial extensional flow for the dispersion of multiwalled carbon nanotubes (MWCNTs) into polypropylene (PP) as a nonpolar matrix. An only converging flow allowed for a high strain rate and was suitable for the compounding process. The extensional flow was characterized from the entrance pressure drop (ΔP0) at the converging section. Thus, in this study, capillary extrusion was employed to generate uniaxial extensional flow. Based on the hypothesis that the dispersion of nanofillers depends on the magnitude of flow-induced stress, ΔP0, which related to extensional stress, was measured directly during capillary extrusion by using an orifice die. The influences of the mass flow rate and the hole diameter in the orifice die, which affected ΔP0, on the extrusion of PP nanocomposites with an MWCNT loading of 1.0 wt.% were studied. The extruded samples were collected, and the dispersion state was evaluated based on the melt viscoelastic properties, volume resistivity, and morphological observations by optical microscopy (OM) and transmission electron microscopy (TEM). The agglomeration area of the MWCNTs decreased with higher ΔP0 (higher mass flow rate and smaller hole diameter), which increased the uniformity of the dispersion. Moreover, the influence of the length-to-diameter (L/D) ratio of the hole in the capillary die on the dispersion state of the MWCNTs was investigated. A higher L/D ratio of the capillary die did not improve the dispersion state, although shear and extensional stresses were provided.

Enhanced Tensile Strength of Monolithic Epoxy with Highly Dispersed TiO2-Graphene Nanocomposites

The functionalization of graphene has been reported widely, showing special physical and chemical properties. However, due to the lack of surface functional groups, the poor dispersibility of graphene in solvents strongly limits its engineering applications. This paper develops a novel green “in-situ titania intercalation” method to prepare a highly dispersed graphene, which is enabled by the generation of the titania precursor between the layer of graphene at room temperature to yield titania-graphene nanocomposites (TiO2-RGO). The precursor of titania will produce amounts of nano titania between the graphene interlayers, which can effectively resist the interfacial van der Waals force of the interlamination in graphene for improved dispersion state. Such highly dispersed TiO2-RGO nanocomposites were used to modify epoxy resin. Surprisingly, significant enhancement of the mechanical performance of epoxy resin was observed when incorporating the titania-graphene nanocomposites, especially the improvements in tensile strength and elongation at break, with 75.54% and 176.61% increases at optimal usage compared to the pure epoxy, respectively. The approach presented herein is easy and economical for industry production, which can be potentially applied to the research of high mechanical property graphene/epoxy composite system.

Effect of the Dispersion State in Y5O4F7 Suspension on YOF Coating Deposited by Suspension Plasma Spray

The stable Y5O4F7 suspension for dense yttrium oxyfluoride (YOF) coating by suspension plasma spraying (SPS) was developed. Electrostatically and electrosterically stabilized aqueous Y5O4F7 suspensions were prepared and compared with a commercially available Y5O4F7 suspension without dispersant. The wettability and dispersibility of the Y5O4F7 suspensions were evaluated in terms of the zeta potential, average particle size, and size distribution with electrophoretic light scattering (ELS) and dynamic light scattering (DLS). The viscosity was measured and the sedimentation was tested to examine the fluidity and stability of the Y5O4F7 suspensions. When electrostatic (BYK-154) and electrosteric (BYK-199) dispersants were added to the Y5O4F7 suspension, the isoelectric point (IEP) of Y5O4F7 particles in the suspension shifted to lower pH. The zeta potential of both of electrostatically and electrosterically stabilized Y5O4F7 suspensions were higher than ±40 mV at pH of 8.6, respectively, which were much higher than of the Y5O4F7 suspension without dispersant. Meanwhile, the average particle size of the electrosterically stabilized Y5O4F7 suspension was much smaller than that of the electrostatically stabilized one. The electrosteric stabilization had a great effect on improving the wettability and dispersibility of the Y5O4F7 suspension. The coating rate of the electrosterically stabilized Y5O4F7 suspension was the highest among the three tested suspensions. In addition, the YOF coating deposited with the electrosterically stabilized Y5O4F7 suspension had the highest hardness and the lowest porosity.