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Injectable hydrogels based on various functional biocompatible materials have made rapid progress in the field of bone repair. In this study, a self-healing and injectable polysaccharide-based hydrogel was prepared for bone tissue engineering. The hydrogel was made of carboxymethyl chitosan (CMCS) and calcium pre-cross-linked oxidized gellan gum (OGG) cross-linked by the Schiff-base reaction. Meanwhile, magnetic hydroxyapatite/gelatin microspheres (MHGMs) were prepared by the emulsion cross-linking method. The antibacterial drugs, tetracycline hydrochloride (TH) and silver sulfadiazine (AgSD), were embedded into the MHGMs. To improve the mechanical and biological properties of the hydrogels, composite hydrogels were prepared by compounding hydroxyapatite (HAp) and drug-embedded MHGMs. The physical, chemical, mechanical and rheological properties of the composite hydrogels were characterized, as well as in vitro antibacterial tests and biocompatibility assays, respectively. Our results showed that the composite hydrogel with 6% (w/v) HAp and 10 mg/mL MHGMs exhibited good magnetic responsiveness, self-healing and injectability. Compared with the pure hydrogel, the composite hydrogel showed a 38.8% reduction in gelation time (196 to 120 s), a 65.6% decrease in swelling rate (39.4 to 13.6), a 51.9% increase in mass residual after degradation (79.5 to 120.8%), and a 143.7% increase in maximum compressive stress (53.6 to 130.6 KPa). In addition, this composite hydrogel showed good drug retardation properties and antibacterial effects against both S. aureus and E. coli. CCK-8 assay showed that composite hydrogel maintained high cell viability (87%) and rapid cell proliferation after 3 days, indicating that this smart hydrogel is expected to be an alternative scaffold for drug delivery and bone regeneration. STATEMENT OF SIGNIFICANCE: Biopolymer hydrogels have been considered as the promising materials for the treatment of tissue engineering and drug delivery. Injectable hydrogels with and self-healing properties and responsiveness to external stimuli have been extensively investigated as cell scaffolds and bone defects, due to their diversity and prolonged lifetime. Magnetism has also been involved in biomedical applications and played significant roles in targeted drug delivery and anti-cancer therapy. We speculate that development of dual cross-linked hydrogels basing biopolymers with multi-functionalities, such as injectable, self-healing, magnetic and anti-bacterial properties, would greatly broaden the application for bone tissue regeneration and drug delivery.

Biopolymer-based hydrogels with sustained drug release capability and antibacterial activity have exhibited great potential in clinical application in drug delivery and wound healing. In this study, a new type of composite wound dressing hydrogel aiming at avoiding wound infection was developed through embedding drug loaded gellan gum microspheres (GMs) into a doubly crosslinked hydrogel, which was constructed by Schiff-base crosslinking of oxidized gellan gum (OG) (pre-crosslinked by calcium ion) and carboxymethyl chitosan (CMCS). The gelation time, swelling index, degradation rate and mechanical properties of the blank hydrogel was optimized by varying the ratios of CMCS/OG (w/w) with fixed OG/calcium (w/w) ratio. The best overall performance of the hydrogel was obtained when CMCS/OG is 16/7 (w/w), with a 139 s gelation time, swelling index remained above 30 after swelling equilibrium, 100.5% degradation rate on the seventh day, and 8.8 KPa compressive modulus. After being embedded with cargo-loaded GMs, the aforementioned performance of the blank hydrogel was improved, and the sustained release of cargoes (antibacterial drugs, tetracycline hydrochloride and silver sulfadiazine) was observed. Moreover, the excellent antibacterial activity of the composite hydrogel was also demonstrated in vitro. These results support the bioactive composite hydrogel can be employed as a promising injectable scaffold for promoting wound regeneration and drug delivery.

Chronic HBV infection, the main cause of liver cirrhosis and hepatocellular carcinoma, has become a global health concern. Machine learning algorithms are particularly adept at analyzing medical phenomenon by capturing complex and nonlinear relationships in clinical data. Our study proposed a predictive model on the basis of 55 routine laboratory and clinical parameters by machine learning algorithms as a novel non-invasive method for liver fibrosis diagnosis. The model was further evaluated on the accuracy and rationality and proved to be highly accurate and efficient for the prediction of HBV-related fibrosis. In conclusion, we suggested a potential combination of high-dimensional clinical data and machine learning predictive algorithms for the liver fibrosis diagnosis.

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In the calibration application of airborne inertial sensor, turntable based angular rate measurement is mainly focused on static and constant angular rate test. Relatively little research has been done on the dynamic performance testing under changes in angular rate and angular acceleration rate. A wavelet analysis-based turntable dynamic angular rate measurement method and device are proposed, which can accurately acquire the instantaneous angular rate under turntable speed variation. The dynamic rate experiments were validated for three different angular acceleration situations. The results show that the measurement accuracy of the dynamic angular rate is better than 0.38% during the rapid variation of the velocity, and reaches 0.03% during the steady phase of the rotational speed.

In the aerospace applications, the cases of radio irregularity, obstacle, asymmetrical distribution are disadvantageous for node localization of wireless sensor networks. In this paper, the related principles and methods of Graph Theory is introduced to minimize the localization error caused by radio irregularity. The model of asymmetry communication is established based on Graph Theory. Through the analysis to communication path between nodes in directed network, solution schemes are put forward for locating nodes in case of asymmetric communication. The localization performance is compared in different scenes and conditions. For node localization with radio irregularity, the accuracy can be improved 10% by our solutions when the network topology is regular. While the network topology is irregular, the localization accuracy can also be improved when strongly connected graph comes into being.

The chaotic and intrinsic complexity of wind speed time series calls for an appropriate model to accurately predict the moving tendency. In this study, we proposed a single dendritic neuron model (S-DNM) using a back-propagation algorithm to accomplish wind speed forecasting. First, based on mutual information method and false nearest neighbor method, the time delay and embedding dimension are calculated. Second, the phase space is reconstructed by time delay and embedding dimension, and the characteristics of wind speed time series are analyzed. Then, the maximum Lyapunov exponent is applied to confirm the chaotic properties of the wind speed time series. Finally, using wind speed data from Sotavento located in Galicia, Spain, the performance of the forecasting method is evaluated for short-term horizons (1 hour ahead). Experimental results show that the proposed S-DNM performed better than the traditional ELMAN model and classic multi-layered perceptron network. Thus, it is concluded that the proposed model is suitable for wind speed forecasting.

In this study, a new idea is proposed to analyze the financial market and detect price fluctuations, by integrating the technology of PSR (phase space reconstruction) and SOM (self organizing maps) neural network algorithms. The prediction of price and index in the financial market has always been a challenging and significant subject in time-series studies, and the prediction accuracy or the sensitivity of timely warning price fluctuations plays an important role in improving returns and avoiding risks for investors. However, it is the high volatility and chaotic dynamics of financial time series that constitute the most significantly influential factors affecting the prediction effect. As a solution, the time series is first projected into a phase space by PSR, and the phase tracks are then sliced into several parts. SOM neural network is used to cluster the phase track parts and extract the linear components in each embedded dimension. After that, LSTM (long short-term memory) is used to test the results of clustering. When there are multiple linear components in the m-dimension phase point, the superposition of these linear components still remains the linear property, and they exhibit order and periodicity in phase space, thereby providing a possibility for time series prediction. In this study, the Dow Jones index, Nikkei index, China growth enterprise market index and Chinese gold price are tested to determine the validity of the model. To summarize, the model has proven itself able to mark the unpredictable time series area and evaluate the unpredictable risk by using 1-dimension time series data.

An antibacterial and biodegradable composite hydrogel dressing integrated with microspheres is developed for drug delivery and wound healing. The mechanism of gelation is attributed to the Schiff-base reaction between aldehyde and amino groups of oxidized alginate (OAlg) and carboxymethyl chitosan (CMCS). To enhance antibacterial and mechanical properties, tetracycline hydrochloride (TH) loaded gelatin microspheres (GMs) were fabricated by an emulsion cross-linking method, followed by integrating into the OAlg-CMCS hydrogel to produce a composite gel dressing. In vitro gelation time, swelling, degradation, compressive modulus and rheological properties of the gel dressing were investigated as the function of microsphere ratios. With increasing ratios of microspheres from 10 to 40mg/mL, the composite dressing manifested shorter gelation time and lower swelling ratios, as well as higher mechanical strength. Comparing to other formulations, the gel dressing with 30mg/mL microspheres showed more suitable stabilities and mechanical properties for wound healing. Also, in vitro drug release results showed that the loaded TH could be sustained release from the composite gel dressing by contrast with pure hydrogels and microspheres. Furthermore, powerful bacteria growth inhibition effects against Escherichia coli and Staphylococcus aureus suggested that the composite gel dressing, especially the one with 30mg/mL GMs containing TH, has a promising future in treatment of bacterial infection.

In this paper, we propose a switchable bi-functional metamaterial device based on a hybrid gold-vanadium dioxide (VO2) nanostructure. Utilizing the property of a metal-to-insulator transition in VO2, perfect absorption and asymmetric transmission (AT) can be thermally switched for circularly polarized light in the near-infrared region. When VO2 is in the metallic state, the designed metamaterial device behaves as a chiral-selective plasmonic perfect absorber, which can result in an optical circular dichroism (CD) response with a maximum value ∼ 0.7. When VO2 is in the insulating state, the proposed metamaterial device exhibits a dual-band AT effect. The combined hybridization model and electromagnetic field distributions are presented to explain the physical mechanisms of chiral-selective perfect absorption and AT effect, respectively. The influences of structure parameters on CD response and AT effect are also discussed. Moreover, the proposed switchable bi-functional device is robust against the incident angle for obtaining perfect absorption and strong CD response as well as the AT effect. Our work may provide a promising path for the development of multifunctional optoelectronic devices, such as thermal emitters, optical modulators, CD spectroscopy, optical isolator, etc.

In recent years, artificial intelligence and machine learning have become increasingly involved in the treatment of prevalent human diseases. Acute ischemic stroke (AIS) is an increasingly severe d...

As a complicated dynamic system, financial time series calls for an appropriate forecasting model. In this study, we propose a neuron model based on dendritic mechanisms and a phase space reconstruction (PSR) to analyze the Shanghai Stock Exchange Composite Index, Deutscher Aktienindex, N225, and DJI Average. The PSR allows us to reconstruct the financial time series, so we can prove that attractors exist for the systems constructed. Thus, the attractors obtained can be observed intuitively in a three-dimensional search space, thereby allowing us to analyze the characteristics of dynamic systems. In addition, using the reconstructed phase space, we confirmed the chaotic properties and the reciprocal to determine the limit of prediction through the maximum Lyapunov exponent. We also made short-term predictions based on the nonlinear approximating dendritic neuron model, where the experimental results showed that the proposed methodology which hybridizes PSR and the dendritic model performed better than traditional multi-layered perceptron, the Elman neural network, the single multiplicative neuron model and the neuro-fuzzy inference system in terms of prediction accuracy and training time. Hopefully, this hybrid technology is capable to advance the research for financial time series and provide an effective solution to risk management.

Injectable and biodegradable alginate-based composite gel scaffolds doubly integrated with hydroxyapatite (HAp) and gelatin microspheres (GMs) were cross-linked via in situ release of calcium cations. As triggers of calcium cations, CaCO3 and glucono-D-lactone (GDL) were fixed as a mass ratio of 1:1 to control pH value ranging from 6.8 to 7.2 during gelation. Synchronously, tetracycline hydrochloride (TH) was encapsulated into GMs to enhance bioactivity of composite gel scaffolds. The effects of HAp and GMs on characteristics of gel scaffolds, including pH value, gelation time, mechanical properties, swelling ratio, degradation behavior and drug release, were investigated. The results showed that HAp and GMs successfully improved mechanical properties of gel scaffolds at strain from 0.1 to 0.5, which stabilized the gel network and decreased weight loss, as well as swelling ratio and gelation time. TH could be released from this composite gel scaffold into the local microenvironment in a controlled fashion by the organic/inorganic hybrid of hydrogel network. Our results demonstrate that the HAp and GMs doubly integrated alginate-based gel scaffolds, especially the one with 6% (w/v) HAp and 5% (w/v) GMs, have suitable physical performance and bioactive properties, thus provide a potential opportunity to be used for bone tissue engineering. The potential application of this gel scaffold in bone tissue engineering was confirmed by encapsulation behavior of osteoblasts. In combination with TH, the gel scaffold exhibited beneficial effects on osteoblast activity, which suggested a promising future for local treatment of pathologies involving bone loss.

Heat removal and “simultaneous” thermal stability are vitally important for the high performance and the long-term reliability of printed electronics. However, such a demand is challenging, because heat-conductive reinforcements also “simultaneously” encourage the thermal expansion/degradation of polymeric materials. To restrict the motion of polymer chains (the key for achieving increased glass transition temperature (Tg) and thus enhancing thermal stability), chemical modifications are often used to intensify the reinforcement/polymer interfacial interactions, but they deteriorate the intrinsic conductivity of the reinforcements. Herein, this deadlock is broken. Moreover, no chemicals are needed. We reveal an inherent superiority of ‘thick’ graphene oxide nanoplatelet (GONP) in enhancing both the thermal conductivity and also the Tg and its associated dimensional and structural thermal stability of epoxy, with a particular emphasis on enabling the thermal conductivity-reinforcing capability of GONPs to make a “positive” contribution to the thermal stability enhancement of epoxy. The strong GONP/epoxy interfacial interaction formed was verified by “local” mechanical properties investigated using nanoindentation. The superiority of the ‘thick’ GONP is based on the specialty of layered-structure and thus can be extended to various GONP-like reinforcements for endowing polymeric materials with high overall thermal properties for printed electronics.

Dual-crosslinked alginate/carboxymethyl chitosan (CMC) based hydrogels containing in situ synthesized calcium phosphate (CaP) particles were developed by combining two physical crosslinking, the ionic crosslinking of alginate with divalent cation (Ca2+), and the electrostatic interaction between cation of amino groups on CMC and anion of carboxyl groups on alginate. The calcium phosphate particles were in situ synthesized by using the excess Ca2+ of ionic crosslinking. The developed hydrogels were investigated the rheological properties, swelling behavior, degradation, and drug released performance in both water-soluble and insoluble drug models. The results showed that the viscoelasticity and swelling capacity of dual-crosslinked hydrogels were enhanced comparing the single-crosslinked alginate-based hydrogel. The in situ gelation of the developed hydrogel provided the injectable ability and drug-encapsulated capacity. Beside, calcium phosphate, including hydroxyapatite (HAp) was in situ synthesized during the gelation. Biocompatibility of this injectable hydrogel was studied by encapsulation behavior of human adipose-derived stem cells (ASCs). With these qualities, the developed hydrogel may have potential for medical providers such as hydrogel injections and drug providers.

By adding 2 wt% multi-layer graphene oxide (MGO) to an epoxy resin, the thermal conductivity of the compos- ite reached a maximum, 2.03 times that of the epoxy. The presence of 2 wt%MGO percolating chains leads to an unprece- dentedly sharp rise in energy barrier at final curing stage, but an increased epoxy curing degree (!IR) is observed; however, this !IR difference nearly disappears after aging or thermal annealing. These results suggest that the steep concentration gra- dient of -OH, originated from the 2 wt%MGO percolating chains, exerts the vital driving force on the residual isolated/ trapped epoxy to conquer barrier for epoxy-MGO reaction. A modified Shrinking Core Model customized for the special layered-structure of MGO sheet was proposed to understand the resistance variation during the intercalative epoxy-MGO reaction. It shows that the promoted intercalative crosslinking is highly desirable for further improving the thermal conduc- tivity of the composite, but it meets with increased resistance. Guided by the kinetic studies, targeted optimization on the cure processing strategy was accordingly proposed to promote the intercalative crosslinking, a thermal conductivity, 2.96 times that of the epoxy, was got with only a small amount (30°C) increase of the post-heating temperature.

Multi-layer graphene oxide (MGO) has attracted considerable interest in conductive polymer composites. However, in most cases the optimal MGO content is determined using a complex procedure. Avoiding the complicated work of processing polymerized samples followed by testing various properties, here a facile strategy is proposed to directly identify the critical MGO content among formulations for epoxy composites with optimal thermal properties, simply by monitoring the “unusual” nonlinear MGO content-dependent cure behaviors, as well as the “unusual” pattern of double-peak curing curves. The formation mechanism of the double-peak pattern was explored, with emphasis on studying the epoxy/MGO reaction using a modified Shrinking Core Model. The optimal content determined in this work (2 wt% MGO) was verified by the thermal properties (thermal conductivity, structural thermal stability and coefficient of thermal expansion) of MGO/epoxy composites. Based on the inherent relationship between the effect of MGO percolating chains on the thermal polymerization behavior and the resulting thermal properties, this strategy can be easily extended to different kinds of conductive MGO/polymer composites.

The result of Chinese housing market continues to prosper or not is related to the development of China, and further it also has an impact on the world finance. Thus forecasting the house price index is very important and challenging. In this paper we propose an unsupervised learnable neuron model (DNM) by including the nonlinear interactions between excitation and inhibition on dendrites. We use DNM to fit the House Price Index (HPI) data and then forecast the trends of Chinese housing market. To verify the effectiveness of the DNM, we use a traditional statistical model (i.e., the exponential smoothing (ES) model) to make a performance comparison. Three quantitative statistical metrics including normalized mean square error, absolute percentage of error, and correlation coefficient are used to evaluate the forecasting performance of the two models. Experimental results demonstrate that the proposed DNM is better than ES in all of the three quantitative statistical metrics.

Transparent and flexible alginate-based membranes containing antibacterial drugs were prepared by a casting/solvent evaporation method from alginate solution mixed with chitosan floccule (CSF) and oxidized sodium alginate (OAlg). To improve the properties of the membranes, CSF and OAlg were added to the alginate solution in different ratios. The mechanism of membrane formation is attributed to two aspects: Schiff-base cross-linking between CSF and OAlg; ion cross-linking between sodium alginate and CaCl2. The results showed that the incorporation of CSF and OAlg had a significant effect on the properties of the alginate membrane. With the change in the ratio between CSF and OAlg, the tensile strength, swelling rate, water vapor permeability, wettability and degradation stability of the membranes were significantly changed. In order to enhance the anti-bacterial properties, clindamycin (DA) and silver sulfadiazine (AgSD), which represent water-soluble and water-insoluble drug models, were integrated into the membrane, respectively. The results of controlled release effects and inhibition zones indicate that the alginate membranes containing drugs have a promising future in treatment of bacterial infection as wound dressing.

Thin-film electronics are urged to be directly laminated onto human skin for reliable, sensitive biosensing together with feedback transdermal therapy, their self-power supply using the thermoelectric and moisture-induced-electric effects also has gained great attention (skin and on-skin electronics (On-skinE) themselves are energy storehouses). However, "thin-film" On-skinE 1) cannot install "bulky" heatsinks or sweat transport channels, but the output power of thermoelectric generator and moisture-induced-electric generator relies on the temperature difference (∆T ) across generator and the ambient humidity (AH), respectively; 2) lack a routing and accumulation of sweat for biosensing, lack targeted delivery of drugs for precise transdermal therapy; and 3) need insulation between the heat-generating unit and heat-sensitive unit. Here, two breathable nanowood biofilms are demonstrated, which can help insulate between units and guide the heat and sweat to another in-plane direction. The transparent biofilms achieve record-high transport// /transport⊥ (//: along cellulose nanofiber alignment direction, ⊥: perpendicular direction) of heat (925%) and sweat (338%), winning applications emphasizing on ∆T/AH-dependent output power and "reliable" biosensing. The porous biofilms are competent in applications where "sensitive" biosensing (transporting// sweat up to 11.25 mm s-1 at the 1st second), "insulating" between units, and "targeted" delivery of saline-soluble drugs are of uppermost priority.

Graphite nanoplatelets (GNPs) were utilized to improve the electrical conductivity of pristine bacterial cellulose (BC) membranes. By physical and chemical methods, flake-shaped GNPs, weaving through the surface layer of web-like cellulose nanofibrils, were indeed fixed or trapped by the adjacent nanofibrils in the BC surface network, for comparison, rod-shaped multi-walled carbon nanotubes (MWCNTs) were homogeneously inserted into BC membrane through the pore structures and tunnels within the BC membrane. Strong physical and chemical interaction exists between the BC nanofibrils and the particles of GNP or MWCNT even after 15 h sonication. BC membrane with 8.7 wt% incorporated GNPs reached the maximum electrical conductivity of 4.5 S/cm, while 13.9 wt% MWCNT/BC composite membrane achieved the maximum electrical conductivity of 1.2 S/cm. Compared with one dimensional (1-D) MWCNTs, as long as GNPs inserted into BC membranes, the 2-D reinforcement of GNPs was proven to be more effective in improving the electrical conductivity of BC membranes thus not only break the bottleneck of further improvement of the electrical conductivity of BC-based composite membranes but also broaden the applications of BC and GNPs.

The main purpose of this paper is to propose a neuron model based on dendritic mechanisms and a phase space reconstruction (PSR) to analyze XAUUSD (Gold/U.S. Dollar), EURUSD (Euro Fx/U.S. Dollar), GBPJPY (British Pound/Japanese Yen), and USDJPY (U.S. Dollar/Japanese Yen). We reconstruct the time series of exchange rate by using the PSR to prove that attractors exist for the systems constructed. In this way, it is able for us to observe the attractors obtained intuitively in a three-dimensional search space, which make it easier to analyze the characteristics of dynamic systems. In the forecasting procedure, we employ the maximum Lyapunov exponent to identify the chaotic properties and the reciprocal to determine the limit of prediction, by using the reconstructed phase space. Short-term predictions are also made based on the dendritic neuron model after the experiment, which resulted that the proposed methodology performed better than the traditional multi-layered perceptron and the Elman neural network in the light of prediction accuracy and training time.

Magnetic protein microspheres with core-shell structure were prepared through a novel approach based on the sonochemical method and the emulsion solvent evaporation method. The microspheres are composed of the oleic acid and undecylenic acid modified Fe3O4 cores and coated with globular bovine serum albumin (BSA). Under an optimized condition, up to 57.8 wt% of approximately 10 nm superparamagnetic Fe3O4 nanoparticles could be uniformly encapsulated into the BSA microspheres with the diameter of approximately 160 nm and the high saturation magnetization of 38.5 emu/g, besides of the abundant functional groups. The possible formation mechanism of magnetic microspheres was discussed in detail.

Thin-film wearable electronics are required to be directly laminated on to human skin for reliable, sensitive bio-sensing but with minimal irritation to the user after long-time use. Excellent heat management films with strongly anisotropic thermal conductivity (K) and adequate breathability are increasingly desirable for shielding the skin from heating while allowing the skin to breathe properly. Here, interfacial self-assembly of a graphene oxide (GO) film covering an ambient-dried bacterial cellulose aerogel (AD-BCA) film followed by laser reduction was proposed to prepare laser-reduced GO (L-rGO)/AD-BCA bilayered films. The AD-BCA substrate provides low cross-plane K (K ⊥ ≈ 0.052 W mK−1), high breathability, and high compressive and tensile resistance by 'partially' inheriting the pore structure from bacterial cellulose (BC) gel. The introduction of an upper L-rGO film, which is only 0.31 wt% content, dramatically increases the in-plane K (K // ) from 0.3 W mK−1 in AD-BCA to 10.72 W mK−1 owing to the highly in-plane oriented, continuous, uniform assembling geometry of the GO film; while K ⊥ decreases to a lower value of 0.033 W mK−1, mainly owing to the air pockets between L-rGO multilayers caused by the laser reduction. The bilayered films achieve a K // /K ⊥ of 325, which is substantially larger even than that of graphite and similar polymer composites. They permit high transmission rates for water vapor (416.78 g/m2/day, >204 g/m2/day of normal skin) and O2 (449.35 cm3/m2/day). The combination of strongly anisotropic thermal conductivity and adequate breathability facilitates applications in heat management in on-skin electronics.

By adding 6 wt% multi-walled carbon nanotubes (MWCNTs) or 71.7 wt% micro-SiC to an epoxy resin the thermal conductivities of the composites reached maxima that were respectively 2.9 and 20.7 times that of the epoxy alone. To further improve the thermal conductivity a method that partially replaces microfiller with nanofiller was used, and a thermal conductivity, 24.3 times that of the epoxy, was obtained with 5 wt% MWCNTs + 55 wt% micro-SiC.

The influence of carboxylic functionalization (COOH-functionalization) of multi-walled carbon nanotubes (MWCNTs) on the thermal properties of MWCNTs/diglycidyl ether of bisphenol A/2-ethyl-4-methylimidazole (MWCNTs/DGEBA/EMI-2,4) nanocomposites was studied using DSC and TGA. The results showed that, at the initial curing stage, activation energy E decreases with increasing curing degree α, moreover, COOH-functionalization of MWCNTs decreases E. Therefore, COOH-functionalization of MWCNTs does not change the autocatalytic cure reaction mechanism of MWCNTs/DGEBA/EMI-2,4 system and has catalytic effect on the curing process. Then, at the later curing stage, carboxylated MWCNTs (COOH-MWCNTs) increase the inflexions of the curves of E vs. α less than purified MWCNTs, indicating that COOH-MWCNTs delay the vitrification less than purified MWCNTs. Furthermore, COOH-functionalization of MWCNTs also improves the thermal stability of nanocomposites.

The effect of multi-walled carbon nanotubes (MWCNTs) on the cure behavior of diglycidyl ether of bisphenol-A glycidol ether epoxy resin/2-ethyl-4-methylimidazole (DGEBA/EMI-2,4) system during the cure process was studied with dynamic differential scanning calorimetry. The results showed that, at the initial curing stage, MWCNTs act as catalyst and facilitate the curing, moreover, this accelerating effect is already noticeable at the lowest content of MWCNTs investigated (1 wt%) with slightly further effect at higher contents, suggesting a saturation of catalyzing action at higher contents investigated (3.5 wt%). Then, at the later curing stage, MWCNTs prevent from the occurrence of vitrification. The cure acceleration effect caused by MWCNTs could bring positive effect on the processing of composite since it needs shorter pre-cure time or lower pre-temperature, however, the hindrance effect to vitrification phenomena would bring negative effect as it needs longer post-cure time or higher post-temperature. Furthermore, it was also found that the addition of MWCNTs does not change the autocatalytic cure reaction mechanism of the DGEBA/EMI-2,4 system, but decreases the overall degree of cure, as evidenced by lower total heat of reaction and lower glass transition temperatures of the cured composites compared to neat epoxy.

BACKGROUND: The aim of this work was to study, using differential scanning calorimetry, the effect of carboxylic functionalization of multi-walled carbon nanotubes (MWCNTs) on the cure reaction of MWCNTs/diglycidyl ether of bisphenol A/2-ethyl-4-methylimidazole (MWCNTs/DGEBA/EMI-2,4) nanocomposites. This is important for the practical design, analysis and optimization of novel materials processing. RESULTS: Comparing the influence of non-functionalized MWCNTs and carboxyl-functionalized MWCNTs, it was found that, at the initial curing stage, both MWCNTs act as catalyst and COOH functionalization of MWCNTs has a catalytic effect on the curing process. Then, at the later curing stage, non-functionalized MWCNTs prevent the occurrence of vitrification, whereas COOH functionalization of MWCNTs promotes vitrification. Non-functionalized MWCNTs decrease the degree of curing, as evidenced by lower total heat of reaction and lower glass transition temperatures of nanocomposites compared to neat epoxy; however, COOH functionalization of MWCNTs increases the degree of curing. CONCLUSION: For the development of composites, COOH functionalization of MWCNTs could bring a positive influence to the composite process. Its acceleration of cure could help shorten pre-cure time or lower pre-treatment temperature, and its effect of promoting vitrification could help shorten post-cure time or lower post-treatment temperature. Copyright © 2009 Society of Chemical Industry

This report covers the results of a study on evaluating the effect of nano-SiC particles on mechanical, thermal and electrical properties of epoxy by lap shear, TGA, DSC and electrical tests. Epoxy composites filled with micro-SiC particles were also studied for comparison. The mechanisms of performance improvement were discussed in detail. The results showed that with identical loading, silane treated nano-SiC filled nanocomposites have the best properties. The volume resistivity decrease, dielectric constant e increase and loss tangent tan(δ) increase by addition of silane treated nano-SiC particles are smaller than those by the other fillers. Silane treatment of nanoparticles improves each performance, including increases shear strength, thermal stability, volume resistivity and decreases e and (δ). The addition of nano-SiC particles remarkably improves shear strength, e and tan(δ), while slightly enhances thermal stability of epoxy. 8 vol. % silane treated nano-SiC/epoxy composite has the highest shear strength 10.6 MPa with the maximum enhancement, 80%, over the neat resin. It also has good temperature independence of dielectric properties and enough volume resistivity, which meet the demand of some microelectronics materials.

This report covers the results of a study on identifying the thermal conduction mechanism of nano-sized SiC/diglycidyl ether of bisphenol-A glycidol ether epoxy resin/2-ethyl-4-methylimidazole (nano-SiC/DGEBA/EMI-2,4) composites. The analysis using FTIR provided an in-depth understanding about how the pretreatment of micro/nano-sized SiC (micro/nano-SiC) particles affects the surface structure of the two different-sized particles, and thereby results in the difference in particles/resin interface structures, which determine different thermal conduction mechanisms. The surface modification approaches included: (1) silane treatment using γ-aminopropyl-triethoxysilane (A1100) and (2) oxidation followed by silane treatment. The results showed that, it is the structure of cross-linked SiC particles/resin three-dimensional network, established by chemical bonding, dominates the thermal conduction mechanism of nano-SiC/DGEBA/EMI-2,4 composites, and leads to the nanocomposites with high thermal conductivity at low filler content. Meanwhile, thermal conduction chains, the prevailing thermal conduction mean in the micro-SiC/DGEBA/EMI-2,4 composites, are the secondary means to conduct thermal diffusion in the nanocomposites.

The influence of nano-sized carborundum (nano-SiC) particles and amino silane coupling agent on the curing kinetics of bisphenol-A glycidol ether epoxy resin (DGEBA) initiated with 2-ethyl-4-methylimidazole (EMI-2,4) was studied by means of non-isothermal differential scanning calorimetry (DSC). Besides decreasing the heat of reaction Δ H , the presence of nano-SiC particles results in delayed cure reactions, which is also manifested by the increased values of exothermic peak temperature T p and cure reaction activation energy E of the filled systems. Meanwhile, the amino silane coupling agent could increase Δ H , and decrease slightly the degree of delayed cure reactions caused by nano-SiC particles, and thereby decreasing T p of the filled systems. The presence of nano-SiC particles prevents from the occurrence of vitrification, so does the amino silane coupling agent when the nano-SiC particle content is low (≲15 wt%). As the nano-SiC particle content is high (≳15 wt%), the presence of amino silane coupling agent promotes the occurrence of vitrification. Besides E , the presence of nano-SiC particles could increase the overall order of reaction m + n and the frequency factor A , meanwhile, the amino silane coupling agent decreases these three parameters.

Curing kinetics of a bisphenol-A glycidol ether epoxy resin (DGEBA)/2-ethyl-4-methylimidazole (EMI-2,4)/nano-sized SiC(nano-SiC) system was investigated with two kinetic methods by means of differential scanning calorimetry (DSC). Methods I and II were deduced by assuming a constant E and a variable E , respectively. With method I, the cure reaction activation energy E , the frequency factor A and the overall order of reaction m + n are calculated to be 71.75 kJ mol −1 , e 20.55 and 2.20, respectively. These results were used to have a simple qualitative comparison with the DGEBA/EMI-2,4 system. With method II, E is proved to decrease initially, and then increase as the cure reaction proceeds. The value of E spans from 42.4 to 95.8 kJ mol −1 . Furthermore, the variations of E were also used to study the cure reaction mechanism, and the shrinking core model was used to study the resin–particle reaction. Methods I and II are effective as long as they are used in proper aspects. With these two methods used all together, we can have a comprehensive and in-depth understanding of the curing kinetics of the DGEBA/EMI-2,4/nano-SiC system and the effect of nano-SiC particles on the curing kinetics of the DGEBA/EMI-2,4 system.

The curing kinetics of the diglycidyl ether of bisphenol-A (DGEBA)/2-ethyl-4-methylimidazole (EMI-2,4)/nano-sized carborundum (nano-SiC) system was studied by means of nonisothermal differential scanning calorimetry (DSC). An isoconversional method of kinetic analysis yields a dependence of the effective activation energy E on the extent of conversion that decreases initially, and then increases as the cure reaction proceeds. The variations of E were used to study the cure reaction mechanisms, and the Shrinking Core Model was used to study the resin-particle reaction. The results show that the presence of nano-SiC particles prevents the occurrence of vitrification, as well as inhibits the cure reaction.

Visible light responsive zinc ferrite doped titania photocatalyst (TiO2(ZnFe2O4)) was prepared by sol–gel method and was calcined at different temperatures. Diffuse reflectance spectroscopy (DRS) results show that the absorption edge of TiO2(ZnFe2O4) has moved to the visible spectrum range in comparison with the undoped titania. The photocatalytic experimental result demonstrates that TiO2(ZnFe2O4) powder can effectively photodegrade methyl orange (MO) under visible light irradiation. Effect of calcination temperature on the photocatalytic activity of TiO2(ZnFe2O4) was also investigated. Zeta potential measurements indicate that the isoelectric point (IEP) of the TiO2(ZnFe2O4) powder shifts to lower pH units with the increase of calcination temperature. Brunauer–Emmett–Teller (BET) surface area decreases with the rise of calcination temperature. It is concluded that the surface charge and BET surface area are the key factors for the higher photoactivity of zinc ferrite doped titania photocatalyst calcined at 400 °C.

Natural sponge was used as a template to produce carbon/epoxy resin and (carbon+silicon carbide)/epoxy resin composites with interpenetrating network structures. Carbon with a network structure was first obtained by pyrolysis of the natural sponge. The composites were then obtained by injecting epoxy resin and silicone resin into the carbon. Their microstructures and wear properties were analyzed. The results show that the natural structure of sponge controlled the interpenetrating network structures of the composites. The netlike carbon in the composites reduced the wear rate of the epoxy resin. Compared with the carbon/epoxy resin composite, the (carbon+silicon carbide)/epoxy resin composite shows better wear resistance.