Guoxing Sun

High-impact polystyrene/halloysite nanocomposites prepared by emulsion polymerization using sodium dodecyl sulfate as surfactant

High-impact polystyrene (PS) nanocomposites filled with individually dispersed halloysite nanotubes (HNTs) were prepared by emulsion polymerization of styrene in the presence of HNTs with sodium dodecyl sulfate (SDS) as the emulsifier. The SDS is a good dispersing agent for HNTs in aqueous solution. The emulsion polymerization resulted in the formation of polystyrene nanospheres separating individual HNTs. Transmission electron microscopy revealed that the HNTs were uniformly dispersed in the PS matrix. Differential scanning calorimetry, Fourier-transform infrared spectroscopy and thermogravimetry were used to characterize the PS/HNT nanocomposites. The impact strength of the PS/HNTs nanocomposites was 300% higher than that of the neat PS. This paper presents a simple yet feasible method for the preparation of high-impact PS/halloysite nanocomposites.

Mussel-Inspired Adhesive and Tough Hydrogel Based on Nanoclay Confined Dopamine Polymerization

Adhesive hydrogels are attractive biomaterials for various applications, such as electronic skin, wound dressing, and wearable devices. However, fabricating a hydrogel with both adequate adhesiveness and excellent mechanical properties remains a challenge. Inspired by the adhesion mechanism of mussels, we used a two-step process to develop an adhesive and tough polydopamine-clay-polyacrylamide (PDA-clay-PAM) hydrogel. Dopamine was intercalated into clay nanosheets and limitedly oxidized between the layers, resulting in PDA-intercalated clay nanosheets containing free catechol groups. Acrylamide monomers were then added and in situ polymerized to form the hydrogel. Unlike previous single-use adhesive hydrogels, our hydrogel showed repeatable and durable adhesiveness. It adhered directly on human skin without causing an inflammatory response and was easily removed without causing damage. The adhesiveness of this hydrogel was attributed to the presence of enough free catechol groups in the hydrogel, which were created by controlling the oxidation process of the PDA in the confined nanolayers of clay. This mimicked the adhesion mechanism of the mussels, which maintain a high concentration of catechol groups in the confined nanospace of their byssal plaque. The hydrogel also displayed superior toughness, which resulted from nanoreinforcement by clay and PDA-induced cooperative interactions with the hydrogel networks. Moreover, the hydrogel favored cell attachment and proliferation, owning to the high cell affinity of PDA. Rat full-thickness skin defect experiments demonstrated that the hydrogel was an excellent dressing. This free-standing, adhesive, tough, and biocompatible hydrogel may be more convenient for surgical applications than adhesives that involve in situ gelation and extra agents.

Mechanism of cement paste reinforced by graphene oxide/carbon nanotubes composites with enhanced mechanical properties

This study presents the enhanced mechanical properties of cement paste reinforced by graphene oxide (GO)/carbon nanotubes (CNTs) composites. The UV-vis spectroscopy and optical microscopy results show that the dispersion of CNTs in the GO solution is much better than in an aqueous solution due to the higher electrostatic repulsion, which allows a completely new approach of dispersing CNTs rather than by incorporating a dispersant. More importantly, the GO/CNTs composite plays an important role in improving the compressive and flexural strength of cement paste by 21.13% and 24.21%, which is much higher than cement paste reinforced by CNTs (6.40% and 10.14%) or GO (11.05% and 16.20%). The improved mechanical properties of cement paste are attributed to better dispersed CNTs and enhanced interactions among CNTs by the GO incorporation. Finally, the space interlocking mechanism of the GO/CNTs/cement paste composite with enhanced mechanical properties is proposed.

Co9S8 nanoparticles encapsulated in nitrogen-doped mesoporous carbon networks with improved lithium storage properties

We report the designed synthesis of unique Co9S8 nanoparticles encapsulated in nitrogen-doped mesoporous carbon networks (Co9S8@NMCN nanocomposites). Uniform zeolitic imidazolate framework-67 was first synthesized and then transformed into Co9S8@NMCN nanocomposites by thermal annealing with sulfur powders in an Ar atmosphere. The structural and compositional analysis were conducted by employing X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), which show that each Co9S8 nanoparticle is well encapsulated in nitrogen-doped carbon layers. When evaluated as an anode material for LIBs, the as-prepared composite electrodes delivered superior capacity, excellent cycling stability and rate capability, which are attributed to the advantageous structural features.

Super stretchable hydrogel achieved by non-aggregated spherulites with diameters <5 nm.

The scope of hydrogel applications can be greatly expanded by the improvement of mechanical properties. However, enhancement of nanocomposite hydrogels (NC gels) has been severely limited because the size of crosslinking nanoparticles is too large, at least in one dimension. Here we report a new strategy to synthesize non-aggregated spherulite nanoparticles, with diameters <5 nm, in aqueous solution, and their enhancement to hydrogel. The stress and stretch ratio at rupture of our NC gel are 430 and 121 KPa with only 40-p.p.m. nanoparticle content. The NC gel containing 200-p.p.m. nanoparticles can revert to 90% of its original size after enduring 100-MPa compressive stress. Our results demonstrate that the suppression of nanoparticle size without aggregation helps to establish a super stretchable and high-toughness hydrogel network at very low inorganic content.

A new smart traffic monitoring method using embedded cement-based piezoelectric sensors

Cement-based piezoelectric composites are employed as the sensing elements of a new smart traffic monitoring system. The piezoelectricity of the cement-based piezoelectric sensors enables powerful and accurate real-time detection of the pressure induced by the traffic flow. To describe the mechanical-electrical conversion mechanism between traffic flow and the electrical output of the embedded piezoelectric sensors, a mathematical model is established based on Duhamels integral, the constitutive law and the charge-leakage characteristics of the piezoelectric composite. Laboratory tests show that the voltage magnitude of the sensor is linearly proportional to the applied pressure, which ensures the reliability of the cement-based piezoelectric sensors for traffic monitoring. A series of on-site road tests by a 10 tonne truck and a 6.8 tonne van show that vehicle weight-in-motion can be predicted based on the mechanical-electrical model by taking into account the vehicle speed and the charge-leakage property of the piezoelectric sensor. In the speed range from 20 km h−1 to 70 km h−1, the error of the repeated weigh-in-motion measurements of the 6.8 tonne van is less than 1 tonne. The results indicate that the embedded cement-based piezoelectric sensors and associated measurement setup have good capability of smart traffic monitoring, such as traffic flow detection, vehicle speed detection and weigh-in-motion measurement.

Mechanism of UV-assisted TiO2/reduced graphene oxide composites with variable photodegradation of methyl orange

TiO2/reduced graphene oxide (TiO2/rGO) composites with variable photodegradation efficiency of methyl orange (MO) were synthesized by combining TiO2 and graphene oxide (GO) under ultraviolet (UV) irradiation. In this study, the influences of TiO2 content and UV irradiation time on the reduction degree of GO during fabrication of the TiO2/rGO composite were investigated and characterized by X-ray diffraction (XRD), Raman spectrum, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The experimental results showed that the maximum reduction degree of GO can be achieved by controlling the weight ratio (TiO2/GO) of 10 under 15 min UV irradiation, and the corresponding composite showed 1.71 times the higher photodegradation efficiency of MO over pure TiO2, which results from the newly generated rGO with high electrical conductivity that decreases the recombination rate of excited electrons–holes in TiO2. The results also demonstrated that the photodegradation efficiency of the TiO2/rGO composite was closely related to the reduction of GO during fabrication of the composite. The more UV irradiation during fabrication of the composite, the higher reduction degree of GO, and therefore higher photodegradation efficiency of the TiO2/rGO composite can be achieved, but excessive UV irradiation plays a negative effect on the photodegradation efficiency of the composite. Finally, the mechanism of UV-assisted TiO2/rGO composites with variable photodegradation efficiency was proposed in terms of the reduction degree of GO.

Determination of adsorption mechanism of polycarboxylate-ether based superplasticizers using crystallization, thermal and mass spectrometry methods

In this study, a series of suspensions were fabricated by dispersing calcium carbonate (CaCO3), cement and silica fume into a polycarboxylate-ether plasticizer (PCE)/water solution. The PCE used was a comb-like copolymer containing a sodium polymethacrylate (PMA) backbone partially esterified with polyethyleneglycol (PEG) side chains. Sedimentation and optical microscopy tests indicated that both CaCO3 and cement could form homogeneous suspensions. The crystallization behavior of the PEG side chains revealed that PEG had stronger interactions with CaCO3 than with cement and silica fume particles, which was further confirmed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). A detailed time-of-flight secondary ion mass spectrometry (ToF-SIMS) examination suggested that PEG was mainly located on the surfaces of the CaCO3, and the PMA backbones were mainly located on the surfaces of the cement and silica fume, respectively. The different interactions between copolymer and inorganic particles were associated with their interfacial tensions, and had a remarkable influence on the paste fluidity.

DISPERSION OF PRISTINE MULTI-WALLED CARBON NANOTUBES IN COMMON ORGANIC SOLVENTS

The dispersion of pristine multi-walled carbon nanotubes in various common organic solvents and water has been investigated. Sedimentation tests, optical microscopy, transmission electron microscopy and Tyndall effect tests are employed. The results clearly show that N-methyl-2-pyrrolodone, acetone, tetrahydrofuran and dichloromethane are good solvents to debundle and disperse the multi-walled carbon nanotubes. In contrast, much precipitation can be obviously observed for systems of the carbon nanotubes in water, ethanol and toluene. Additionally, Tyndall effect tests suggest that the upper dispersions of the carbon nanotubes in acetone, tetrahydrofuran and dichloromethane with a concentration of 0.1 mg/mL and the dispersion of carbon nanotubes in N-methyl-2-pyrrolodone with a concentration of 0.05 mg/mL are colloidal systems rather than solutions. Finally, based on the above results, a possible mechanism is briefly discussed.

Constructing aligned γ-Fe2O3 nanorods with internal void space anchored on reduced graphene oxide nanosheets for excellent lithium storage

Unique 1D aligned γ-Fe2O3 nanorods anchored on 2D reduced graphene oxide nanosheets were successfully synthesized by a facile seed-assisted solution reaction and subsequent thermal decomposition method. The structural and compositional analyses by employing X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) show that each γ-Fe2O3 nanorod possesses internal void spaces. The special structural nature of the γ-Fe2O3 nanorods together with the hierarchical nanoarchitectures is responsible for a large specific surface area of ∼193.6 m2 g−1. When evaluated as an anode material for LIBs, the as-prepared composite electrodes delivered superior capacity, better cycling stability and rate capability. The excellent lithium storage properties are attributed to the advantageous structural features.