Yongkang Chen

Temperature and magnetism bi-responsive molecularly imprinted polymers: Preparation, adsorption mechanism and properties as drug delivery system for sustained release of 5-fluorouracil.

Temperature and magnetism bi-responsive molecularly imprinted polymers (TMMIPs) based on Fe3O4-encapsulating carbon nanospheres were prepared by free radical polymerization, and applied to selective adsorption and controlled release of 5-fluorouracil (5-FU) from an aqueous solution. Characterization results show that the as-synthesized TMMIPs have an average diameter of about 150 nm with a typical core-shell structure, and the thickness of the coating layer is approximately 50 nm. TMMIPs also displayed obvious magnetic properties and thermo-sensitivity. The adsorption results show that the prepared TMMIPs exhibit good adsorption capacity (up to 96.53 mg/g at 25 °C) and recognition towards 5-FU. The studies on 5-FU loading and release in vitro suggest that the release rate increases with increasing temperature. Meanwhile, adsorption mechanisms were explored by using a computational analysis to simulate the imprinted site towards 5-FU. The interaction energy between the imprinted site and 5-FU is -112.24 kJ/mol, originating from a hydrogen bond, Van der Waals forces and a hydrophobic interaction between functional groups located on 5-FU and a NIPAM monomer. The electrostatic potential charges and population analysis results suggest that the imprinted site of 5-FU can be introduced on the surface of TMMIPs, confirming their selective adsorption behavior for 5-FU.

A Study of surface modifications of carbon nanotubes on the properties of polyamide 66/multiwalled carbon nanotube composites

The effects of surface modification of carbon nanotube on the properties of polyamide 66/multiwalled carbon nanotube composites have been investigated. Polyamide 66 (PA66) and multiwalled carbon nanotube (MWCNT) composites were prepared by melt mixing. The surfaces of MWCNTs were modified with acid- and amine-groups. Field emission scanning electron microscopy analyses revealed that amine-MWCNTs (D-MWCNTs) dispersed better in the PA66 matrix than pristine- and acid-MWCNTs. However, an introduction of D-MWCNTs into PA66 matrix induced heterogeneous nucleation and affected the crystal growth process during the crystallization of PA66/MWCNT composites. Both nanoindentation and friction analyses were carried out in a study of the effect of the introduction of modified MWCNTs on both mechanical and friction properties of the composites. With the introduction of D-MWCNTs, both nanohardness and elastic modulus of the composites were significantly improved, but it was observed that the maximum depth, nanohardness, and elastic modulus of the composites showed no distinct change before and after a friction test. It is evident that PA66/D-MWCNT composites have the least friction coefficient of the PA66/MWCNT composites of all the approaches of carbon nanotube surface modification.

P3HT/Dodecylamine Functioned Carbon Microspheres Composite Films for Polymer Solar Cells

P3HT/dodecylamine functioned carbon microspheres (D-CMSs) composite films were prepared by spin-coating method with D-CMSs and P3HT mixture chloroform solution, and the photovoltaic devices with structures ITO/PEDOT:PASS/P3HT:D-CMSs/Al were also fabricated. Morphology and structure of the composite films were characterized by field emission scanning electron microscopy, atomic force microscopy, Fourier transformation infrared spectrometry and X-raydiffractometry. Ultraviolet-visible spectrophotometry and photoluminescence spectrometry were used to characterize the optical property of the composite films. The results show that composite films with 1:1 ratio of D-CMSs to P3HT had optimum morphology and optical performance. The absorption of annealed P3HT:D-CMSs composite films was enhanced with a red-shift, and the crystallinity of film enhanced after annealing. The polymer solar cells based on P3HT:D-CMSs composite films exhibited a high Voc of 0.840 V, suggesting D-CMSs is a promising acceptor for polymer cells. This would lay an experimental and theoretical foundation for further researching the fabricating polymer solar cells with new acceptors.

Preparation and characterization of 5-fluorouracil surface-imprinted thermosensitive magnetic microspheres

Abstract5-Fluorouracil surface-imprinted thermosensitive magnetic microspheres were prepared by using Fe3O4-encapsulating carbon microspheres as cores, N-isopropylacrylamide as thermosentitive monomer, ammonium persulfate as initiator, N,N′-methylenebisacrylamide as crosslinker, and 5-fluorouracil as template molecule. The formation of these hybrid microspheres was verified by field emission scanning electron microscopy, transmission electron microscopy, Fourier transformation infrared spectroscopy, thermogravimetry, and dynamic light scattering. The results of the latter measurements show that the as-synthesized microspheres have a hydrodynamic diameter of 326xa0nm with the lower critical solution temperature of around 43xa0°C. The obtained microspheres are magnetic and show good potential for controlled loading and release of 5-fluorouracil.Graphical abstract

Surface Morphology Evolution Mechanisms of InGaN/GaN Multiple Quantum Wells with Mixture N2/H2-Grown GaN Barrier

Surface morphology evolution mechanisms of InGaN/GaN multiple quantum wells (MQWs) during GaN barrier growth with different hydrogen (H2) percentages have been systematically studied. Ga surface-diffusion rate, stress relaxation, and H2 etching effect are found to be the main affecting factors of the surface evolution. As the percentage of H2 increases from 0 to 6.25%, Ga surface-diffusion rate and the etch effect are gradually enhanced, which is beneficial to obtaining a smooth surface with low pits density. As the H2 proportion further increases, stress relaxation and H2 over- etching effect begin to be the dominant factors, which degrade surface quality. Furthermore, the effects of surface evolution on the interface and optical properties of InGaN/GaN MQWs are also profoundly discussed. The comprehensive study on the surface evolution mechanisms herein provides both technical and theoretical support for the fabrication of high-quality InGaN/GaN heterostructures.

CFD-RANS model validation of turbulent flow: A case study on MAAT airship

The Computational Fluid Dynamic (CFD) has a wide application in aerodynamic design of airship. In CFD simulations, a turbulence model plays a significantly important role in accuracy and resource cost. In this paper, a configuration of MAAT airship was investigated with different turbulence models under various angles of attack. Three most widely used turbulence models, Standard Spalart-Almaras, Realizable k-ε and SST k-ω, were tested and compared. The resource consumption study was based on the benchmark of 3000 iterations. According to the results, it is proved that Spallart-Allmaras model is the best model for steady-state airship simulation.

The use of pseudo-inverse methods in reconstructing loads on a missile structure

A missile during air carriage is subjected to high vibratory forces. These forces consequently impose high levels of stress on the attachment points to the aircraft. A repetitive application of stress causes fatigue. However, since the vibratory forces cannot be measured directly at the interface, an inverse method utilising missile accelerometer data has been used to determine the forces. This paper presents two frequency domain techniques of reconstructing loads. Both techniques utilise the Moore-Penrose pseudo-inverse method, although the second procedure incorporating a normal modes analysis is perhaps better suited for embedding within a health and usage monitoring system (HUMS). Both techniques enable discrete dynamic loads, which are applied to a finite element model in the time domain, to be successfully reconstructed. Consequently, by identifying forces on a missile structure successfully, the presented techniques enable a better structural integrity assessment to be undertaken.

Simulation of near-tip crack behaviour and its correlation to fatigue crack growth with a modified strip-yield model

A modified strip-yield model has been developed to simulate the plasticity-induced crack closure under the constant amplitude (CA) and a single overload loading conditions. The paper focuses on the simulation of the near tip crack profiles and stress distributions during the fatigue process. Detailed information on near-tip stress and displacement fields at the maximum load (Pmax), the minimum load (Pmin), and the crack opening load (Pop) of a fatigue load cycle have been presented. The correlation of the crack closure to the near-tip material fatigue damage has been investigated and used to rationalise the crack growth behaviour under the CA and a single overload loading conditions.

A Simulation Study of PEMFC Flow Channels Using a New Hybrid Method

Among the number of fuel cells in existence, the proton-exchange membrane fuel cell (PEMFC) has been favoured because of its numerous applications. Computational fluid dynamics (CFD) plays an important role in the development by providing in-depth analysis of PEMFCs gained from studying fluid flow and heat and mass transfer phenomena. The output obtained is useful for reducing the need for expensive prototypes and cutting down test time by a substantial amount. This study is aimed at investigating the advances made in the use of CFD as a technique for the optimization of PEMFCs and studying the effect of some parameters on the performance of the fuel cell (FC) model, by using a new hybrid approach of CFD and Simultaneous Hybrid Exploration that is Robust, Progressive and Adaptive (SHERPA) to study, evaluate and improve the performance. Observations from the CFD results showed that a serpentine-type channel with curved bends would be required for efficient water removal. While further optimization of the model in HEEDS recommended the channel be modified to a 1 × 1 channel (width × depth) for best performance of the fuel cell.

Deposition of Ag nanoparticles on carbon microspheres surface: Evaluation of structures, electrochemical and optical properties

A hybrid material of carbon microspheres (CMSs) with Ag decoration (Ag/CMSs) was developed. Poly (3-hexylthiophene):Ag/CMSs composite film was prepared by spin-coating. Scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectrometry, X-ray diffraction, thermogravimetric analysis and cyclic voltammetry were employed to analyze the morphologies, structures, thermal properties and energy levels of Ag/CMSs. The optical property of the composite films was characterized by ultraviolet-visible spectrophotometry and fluorescent spectrometry. The results indicate that silver nanoparticles (Ag NPs, d = 10-20 nm) are distributed on the surface of CMSs. LUMO and HOMO energy levels of Ag/CMSs are -3.97 and -5.52 eV, below the vacuum energy level, respectively, indicating that it is feasible to use Ag/CMSs as an electron acceptor. Ag NPs are blended into the active layer to trigger localized surface plasmon resonance, and consequently enhance light harvesting. The coupling of surface plasmons and excitons increased the probability of exciton dissociation.