均匀分布纳米粒子系近场辐射热扩散特性

当粒子系中粒子平均间距接近甚至小于热辐射特征波长时,由于倏逝波贡献,其辐射换热热流可远超黑体辐射极限热流。由于存在复杂近场作用,密集粒子系内近场辐射热扩散特性尚不清晰。本文基于涨落电磁理论研究了均匀分布纳米粒子系的近场辐射热扩散特性。研究发现:通过与离散尺度多体辐射换热理论及动理学理论关于金属及电介质粒子链近场辐射换热结果对比,常规热扩散理论可更准确地用于研究粒子系近场辐射热扩散特性,SiC纳米粒子链辐射等效导热系数随温度增大而增大,且温度只影响辐射等效导热系数的大小,而对其光谱峰值频率则无影响。当粒子间距一定时,粒子系辐射等效导热系数随粒子尺寸的增大而增大,更多能量可以在大颗粒构成的粒子链上传递。紧密堆积的粒子系内近场光子隧穿作用较强,其辐射等效导热系数也大于较稀疏粒子系的辐射等效导热系数。

聚酰亚胺/纳米钛系粒子杂化膜制备与性能

采用原位聚合法和流延成膜法制备了系列纳米钛系粒子含量的聚酰亚胺(PI)/TiO_(2)和PI/BaTiO_(3)杂化膜,以γ-巯丙基三甲氧基硅烷偶联剂(KH590)对纳米钛系粒子进行表面处理以提高有机-无机相之间的界面相容性,通过傅里叶变换红外光谱、广角X射线衍射对杂化膜的结构进行研究,同时分析了TiO_(2)和BaTiO_(3)对杂化膜热性能、亲水性、介电性和力学性能的影响。杂化膜结构研究表明,原位聚合法成功地将纳米钛系粒子引入PI基体中,纳米钛系粒子的掺杂没有破坏PI分子链的有序排列;PI/TiO_(2)杂化膜的热失重5%温度(T5%)较纯PI膜都有所降低,而PI/BaTiO_(3)杂化膜的T5%普遍高于纯PI膜,纳米钛系粒子质量分数达到5%时,PI/TiO_(2)和PI/BaTiO_(3)杂化膜的T5%达到最大,分别为540℃和584℃。杂化膜的亲水性和介电强度较纯膜均得到了较大提高,但力学性能均有不同程度的降低,当纳米钛系粒子质量分数为15%时,PI/TiO_(2)和PI/BaTiO_(3)杂化膜的接触角最小,分别为79.3°和77.3°,且PI/BaTiO_(3)杂化膜的力学性能、亲水性和介电强度均高于PI/TiO_(2)杂化膜。

pH-responsive mesoporous silica nanoparticles employed in controlled drug delivery systems for cancer treatment

In the fight against cancer, controlled drug delivery systems have emerged to enhance the therapeutic efficacy and safety of anti-cancer drugs. Among these systems, mesoporous silica nanoparticles （MSNs） with a functional surface possess obvious advantages and were thus rapidly developed for cancer treatment. Many stimuli-responsive materials, such as nanopartides, polymers, and inorganic materials, have been applied as caps and gatekeepers to control drug release from MSNs. This review presents an overview of the recent progress in the production of pH-responsive MSNs based on the pH gradient between normal tissues and the tumor microenvironment. Four main categories of gatekeepers can respond to acidic conditions. These categories will be described in detail.

Heat transfer characteristics of nanofluid through circular tube

Nano fluid is considered to be a class of high efficient heat transfer fluid created by dispersing some special solid nanoparticles (normally less than 100 nm) in traditional heat transfer fluid. The present experiment was conducted aiming at investigating the forced heat transfer characteristics of aqueous copper (Cu) nanofluid at varying concentration of Cu nano-particles in different flow regimes (300<Re≤16 000). The forced convective heat transfer enhancement is available both in the laminar and turbulent flow with increasing the concentration. Especially, the enhancement rate increases dramatically in laminar flow regime, for instance, the heat transfer coefficient of Cu/water nanofluid increases by two times at around Re=2 000 compared with that of base fluid water, and averagely increases by 62% at 1% volume fraction. However, the heat transfer coefficient of Cu/water decreases sharply in the transition flow regime. Furthermore, it has the trend that the heat transfer coefficient displays worse with increasing the concentration.

Research progress in nanoparticles as anticancer drug carrier

Nanoparticles drug delivery system has sustained and controlled release features as well as targeted drug delivery, which can change the characteristics of drug distribution in vivo. It can increase the stability of the drug and enhance drug bioavailability. The selective targeting of nanoparticles can be achieved through enhanced permeability and retention effect and a conjugated specific ligand or through the effects of physiological conditions, such as pH and temperature. Nanoparticles can be prepared by using a wide range of materials and can be used to encapsulate chemotherapeutic agents to reduce toxicity, which can be used for imaging, therapy, and diagnosis. In this research, recent progress on nanoparticles as a targeted drug delivery system will be reviewed, including positive-targeting, negative-targeting, and physicochemical-targeting used as anticancer drug carriers.

Intensification of levofloxacin sono-degradation in a US/H_2O_2 system with Fe_3O_4 magnetic nanoparticles

Fe3O4 magnetic nanoparticles(MNPs) were synthesised, characterised, and used as a peroxidase mimetic to accelerate levofloxacin sono-degradation in an ultrasound(US)/H2O2 system. The Fe3O4 MNPs were in nanometre scale with an average diameter of approximately 12 to 18 nm. The introduction of Fe3O4 MNPs increased levofloxacin sono-degradation in the US/H2O2 system. Experimental parameters, such as Fe3O4 MNP dose, initial solution p H, and H2O2 concentration, were investigated by a one-factor-at-a-time approach. The results showed that Fe3O4 MNPs enhanced levofloxacin removal in the p H range from 4.0 to 9.0. Levofloxacin removal ratio increased with Fe3O4 MNP dose up to 1.0 g·L-1and with H2O2 concentration until reaching the maximum. Moreover, three main intermediate compounds were identified by HPLC with electrospray ionisation tandem mass spectrometry, and a possible degradation pathway was proposed. This study suggests that combination of H2O2, Fe3O4 MNPs and US is a good way to improve the degradation efficiency of antibiotics.

Influence factors on thermal conductivity of ammonia-water nanofluids

In order to investigate the mechanism of nanoparticles enhancing the heat and mass transfer of the ammonia-water absorption process,several types of binary nanofluids were prepared by mixing Al2O3 nanoparticles with polyacrylic acid(PAA),TiO2 with polyethylene glycol(PEG 1000),and TiN,SiC,hydroxyapatite(noodle-like) with PEG 10000 to ammonia-water solution,respectively.The thermal conductivities were measured by using a KD2 Pro thermal properties analyzer.The influences of surfactant and ammonia on the dispersion stabilities of the binary nanofluids were investigated by the light absorbency ratio index methods.The results show that the type,content and size of nanoparticles,the temperature as well as the dispersion stability are the key parameters that affect the thermal conductivity of nanofluids.For the given nanoparticle material and the base fluid,the thermal conductivity ratio of the nanofluid to the ammonia-water liquid increases as the nanoparticle content and the temperature are increased,and the diameter of nanoparticle is decreased.Furthermore,the thermal conductivity ratio increases significantly by improving the stabilities of nanofluids,which is achieved by adding surfactants or performing the proper ammonia content in the fluid.

Investigation of Influence of Magnetic Nanoparticles on the Quality-Factor of the Oscillatory Circuit

In this study, author investigated the spectral response of EM （electromagnetic） energy absorption in a colloidal system of Fe3O4 nanoparticles with an average size of 9.50 nm immersed in a 2% aqueous solution of SDS （sodium dodeci[ sulfate）. The temperature of the nanoparticles and the SDS solution was evaluated by a novel method based on measuring the Q-factor （quality-factor） of a resonant circuit. The Q-factor of the investigated system as a function of the frequency of the EM field was obtained. The nanoparticles-SDS liquid system exhibited a resonance-like behavior of the absorption, where the resonance frequency was about 170 MHz, and the absorption rise up to the resonance frequency was rather slow. The observed absorption of EM energy was accompanied by a small temperature increasing of the system. Measurements of the ESR （electron spin resonance） spectrum of the Fe3O4 nanoparticles have presented a slightly asymmetric singlet with the proportionality factor g = 2 and a line-width of the magnetic field strength △H = 0.1 mT. It was shown that the observed absorption spectrum corresponds to paramagnetic behavior of the investigated nanoparticles.

Morphology and Properties of Hybrid Systems Comprising Gold Nanoparticles in CuPc Matrices

Transmission electron microscopy and surface- and bulk-sensitive spectroscopic methods were used to study the morphology and the electronic structure of a hybrid organic-inorganic system composed of gold nanoparticles （NP＇s） which were distributed in an organic matrix. Au atoms deposited onto a copper phthalocyanine （CuPc） surface diffuse into the organic matrix and self-assemble in well defined NP＇s with metallic properties. No formation of a continuous metallic Au film on top of the CuPc film is observed up to nominal coverages as large as 130 A.

Defect-free surface of quartz glass polished in elastic mode by chemical impact reaction

Removal of brittle materials in the brittle or ductile mode inevitably causes damaged or strained surface layers containing cracks, scratches or dislocations. Within elastic deformation, the arrangement of each atom can be recovered back to its original position without any defects introduced. Based on surface hydroxylation and chemisorption theory, material removal mechanism of quartz glass in the elastic mode is analyzed to obtain defect-free surface. Elastic contact condition between nanoparticle and quartz glass surface is confirmed from the Hertz contact theory model. Atoms on the quartz glass surface are removed by chemical bond generated by impact reaction in the elastic mode, so no defects are generated without mechanical process. Experiment was conducted on a numerically controlled system for nanoparticle jet polishing, and one flat quartz glass was polished in the elastic mode. Results show that scratches on the sample surface are completely removed away with no mechanical defects introduced, and microroughness(Ra) is decreased from 1.23 nm to 0.47 nm. Functional group Ce — O — Si on ceria nanoparticles after polishing was detected directly and indirectly by FTIR, XRD and XPS spectra analysis from which the chemical impact reaction is validated.

Nanofluid Heat Transfer Enhancement for Nuclear Reactor Applications

Colloidal dispersions of nanoparticles are known as ＇nanofluids＇. Such engineered fluids offer the potential for enhancing heat transfer, particularly boiling heat transfer, while avoiding the drawbacks （e.g., erosion, settling, clogging） that hindered the use of particle-laden fluids in the past. At Massachusetts Institute of Technology （MIT）, the authors have been studying the heat transfer characteristics of nanofluids for the past five years, with the goal of evaluating their benefits for and applicability to nuclear power systems （e.g., primary coolant, safety systems, severe accident mitigation strategies）. This paper summarizes the MIT research in this area with particular emphasis to boiling behavior, including, prominently, the Critical Heat Flux limit and quenching phenomena.

Transformation optics applied to van der Waals interactions

The van der Waals force originates from the electromagnetic interaction between quantum fluctuationinduced charges. It is a ubiquitous but subtle force which plays an important role and has a wide range of applications in surface related phenomena like adhesion, friction,and colloidal stability. Calculating the van der Waals force between closely spaced metallic nanoparticles is very challenging due to the strong concentration of electromagnetic fields at the nanometric gap. Especially, at such a small length scale, the macroscopic description of the dielectric properties no longer suffices. The diffuse nonlocal nature of the induced surface electrons which are smeared out near the boundary has to be considered. Here,we review the recent progress on using three-dimensional transformation optics to study the van der Waals forces between closely spaced nanostructures. Through mapping a seemingly asymmetric system to a more symmetric counterpart, transformation optics enables us to look into the behavior of van der Waals forces at extreme length scales,where the effect of nonlocality is found to dramatically weaken the van der Waals interactions.

Recent progress in the application of microfluidic systems and gold nanoparticles in immunoassays

Immunoassays are useful for many bioassays. Many new techniques and materials are introduced into the immunoassay to improve the efficiency. This paper reviews recent progress in the application of microfluidic systems and gold nanoparticles in immunoassay. The micro/nano technologies and materials can offer good sensitivity, fast detection, cost-effectiveness and easy signal readout. In particular, the miniaturization of microfluidics and colorimetric assays based on gold nanoparticles have dramatically improved the efficiency of immunoassays.

Nanoparticle-based oral delivery systems for colon targeting: principles and design strategies

Colon-targeted oral delivery is crucial for the treatment of colon-related diseases, as this delivery strategy enables precise drug administration to the diseased site, enhances drug bioavailability, and improves patient com- pliance. In particular, nanoparticle-based oral formulations shield drugs from the harsh gastrointestinal environment, and selectively increase drug colon cells, thus elevating concentration inside diseased therapeutic efficacy while reducing systemic toxicity. In this review, we elaborate recent progress in this area, with emphasis on the patho- physiological characteristics of colon site and design strategies to take advantage of these characteristics for colon targeting.

Dendrimer-based strategies for cancer therapy:Recent advances and future perspectives

This review reports some recent advances on the use of dendrimer-based systems for cancer therapy. Dendrimers are emerging as promising carriers or stabilizers for drugs and nanoparticles（NPs） due to their highly branched 3-dimensional globular shape, internal hydrophobic cavity and multiple peripheral functional groups. The fabricated nanoplatforms loaded with therapeutic agents such as drugs,siRNAs or NPs can be further modified to have targeting specificity, antifouling properties and good biocompatibility.In particular, recent advances in the surface modifications of dendrimers and the application of dendrimers as versatile platforms for different therapeutic treatments to cancer including chemotherapy, radiotherapy, photothermal therapy,photodynamic therapy, gene therapy, and combination therapy will be introduced in detail.

Simple colorimetric detection of dopamine using modified silver nanoparticles

Dopamine(DA) plays an important role in health and peripheral nervous systems. Colorimetric detection of DA has the advantage of color change and simplicity in operation and instrumentation. Herein, we report a highly sensitive and selective colorimetric detection of DA by using two specific ligands modified Ag nanoparticles, where the DA molecules can make dual recognition with high specificity. The colloidal suspension of modified Ag nanoparticles was agglomerated after interacting with DA, while the color of Ag nanoparticles suspension changed from yellow to brown, arising from the interparticle plasmon coupling during the aggregation of Ag nanoparticles. The modified Ag nanoparticles suspension and agglomeration were confirmed by transmission electron microscope images. The optical properties behind the color change were thoroughly investigated by using UV-Vis and Raman techniques. The changes in p H, zeta potential, particle size and surface charge density by adding DA were also determined by using dynamic light scattering measurements. The detection limits of modified Ag probes for DA was calculated to be 6.13′10^(-6) mol L^(-1)(S/N=2.04) and the correlation co-efficient was determined to be 0.9878. Because of the simplicity in operation and instrumentation of the colorimetric method, this work may afford a feasible, fast approach for detecting and monitoring the DA levels in physiological and pathological systems.

Three-dimensional melamine sponge loaded with Au/ceria nanowires for continuous reduction of p-nitrophenol in a consecutive flow system

Herein, we report a versatile strategy to fabri- cate three-dimensional melamine sponge （MS）-Au/ceria nanowire （NW） networks to realize in situ continuous reduction of p-nitrophenol in a consecutive flow system. This system has proven to be high activity and stability. The ceria NW networks with large surface area can stabi- lize tiny Au nanoparticles dispersed on the ceria NWs, which are loaded on the framework of MS by dip-coating, and enhance the synergistic effect between ceria NWs networks and Au nanoparticles, leading to extremely high activity and good stability for catalytic application. The low-cost raw materials and catalyst with high activity and stability may make this three-dimensional MS-Au/ceria NWs composite material promising for continuous cat- alytic reaction application in industry or other fields.

Theoretical investigation on tunneling magnetoresistance in ferromagnetic/anti-ferromagnetic core/shell system

Based on Monte Carlo simulations,the effect of structural configuration on the hysteresis behavior and tunneling magnetoresistance(TMR) of composite nanoparticles with ferromagnetic(FM) core/anti-ferromagnetic(AFM) shell is investigated.The simulated results indicate that the coercive field(H c) of composites increases with the decreasing ratio of core-radius(r core) to shell-radius(r shell).When the ratio of r shell to r core is approaching 4:3,H c decreases with increasing AFM thickness.In addition,TMR is found to increase with the decreasing ratio of r core to r shell,resulting from the enhancement of resistance changes in disordered AFM shell.

Size and composition dependence of melting temperature of binary nanoparticles

Based on the ideal solution approximation, the model for size-dependent melting temperature of pure metal nanoparticles is extended to binary alloy systems. The developed model, free of any adjustable parameter, demonstrates that the melting temperature is related to the size and composition of alloy nanoparticles. The melting temperature of CuNi, PbBi and Snln binary alloy nanocrystals is found to be consistent with the experiments and molecular dynamics simulations. The research reveals that alloy nanocrystals have similar melting nature as pure metal.