纳米颗粒的测量与表征

介绍了纳米颗粒测量的各种方法,有电镜观察法,X射线衍射线宽法,激光粒度分析法,比表面积法,颗粒沉降法,拉曼散射法,扫描探针显微术以及小角X射线散射等,并对其测量原理,测量过程,适用范围及测量方法优缺点进行了讨论.

纳米颗粒的测量与表征

介绍了用于纳米颗粒测量的电镜观察法、X射线衍射线宽法、激光粒度分析法、比表面积法、颗粒沉降法、扫描探针显微术以及小角X射线散射等,并对其测量原理、测量过程、适用范围及测量方法的优缺点进行了讨论。

Effect of Mo and ZrO_(2)nanoparticles addition on interfacial properties and shear strength of Sn58Bi/Cu solder joint

The influence of Mo and ZrO_(2)nanoparticles addition on the interfacial properties and shear strength of Sn58Bi solder joint was investigated.The interfacial microstructures of Sn58Bi/Cu,Sn58Bi+Mo/Cu and Sn58Bi+ZrO_(2)/Cu solder joints were analysed using a scanning electron microscope(SEM)coupled with energy dispersive X-ray(EDX)and the X-ray diffraction(XRD).Intermetallic compounds(IMCs)of MoSn_(2)are detected in the Sn58Bi+Mo/Cu solder joint,while SnZr,Zr_(5)Sn_(3),ZrCu and ZrSn_(2)are detected in Sn58Bi+ZrO_(2)/Cu solder joint.IMC layers for both composite solders comprise of Cu_(6)Sn_(5) and Cu_(3)Sn.The SEM images of these layers were used to measure the IMC layer’s thickness.The average IMC layer’s thickness is 1.4431μm for Sn58Bi+Mo/Cu and 0.9112μm for Sn58Bi+ZrO_(2)/Cu solder joints.Shear strength of the solder joints was investigated via the single shear lap test method.The average maximum load and shear stress of the Sn58Bi+Mo/Cu and Sn58Bi+ZrO_(2)/Cu solder joints are increased by 33%and 69%,respectively,as compared to those of the Sn58Bi/Cu solder joint.By comparing both composite solder joints,the latter prevails better as adding smaller sized ZrO_(2)nanoparticles improves the interfacial properties granting a stronger solder joint.

New strategy of S,N co‐doping of conductive‐copolymer‐derived carbon nanotubes to effectively improve the dispersion of PtCu nanocrystals for boosting the electrocatalytic oxidation of methanol

Efficacious regulation of the geometric and electronic structures of carbon nanomaterials via the introduction of defects and their synergy is essential to achieving good electrochemical performance.However,the guidelines for designing hybrid materials with advantageous structures and the fundamental understanding of their electrocatalytic mechanisms remain unclear.Herein,superfine Pt and PtCu nanoparticles supported by novel S,N‐co‐doped multi‐walled CNT(MWCNTs)were prepared through the innovative pyrolysis of a poly(3,4‐ethylenedioxythiophene)/polyaniline copolymer as a source of S and N.The uniform wrapping of the copolymer around the MWCNTs provides a high density of evenly distributed defects on the surface after the pyrolysis treatment,facilitating the uniform distribution of ultrafine Pt and PtCu nanoparticles.Remarkably,the Pt_(1)Cu_(2)/SN‐MWCNTs show an obviously larger electroactive surface area and higher mass activity,stability,and CO poisoning resistance in methanol oxidation compared to Pt/SN‐MWCNTs,Pt/S‐MWCNTs,Pt/N‐MWCNTs,and commercial Pt/C.Density functional theory studies confirm that the co‐doping of S and N considerably deforms the CNTs and polarizes the adjacent C atoms.Consequently,both the adsorption of Pt1Cu2 onto the SN‐MWCNTs and the subsequent adsorption of methanol are enhanced;in addition,the catalytic activity of Pt_(1)Cu_(2)/SN‐MWCNTs for methanol oxidation is thermodynamically and kinetically more favorable than that of its CNT and N‐CNT counterparts.This work provides a novel method to fabricate high‐performance fuel cell electrocatalysts with highly dispersed and stable Pt‐based nanoparticles on a carbon substrate.

Production and mechanical properties of nano SiC particle reinforced Ti-6Al-4V matrix composite

Different mass fractions （0, 5%, 10%, and 15%） of the synthesized nano SiC particles reinforced Ti-6Al-4V （Ti64） alloy metal matrix composites （MMCs） were successfully fabricated by the powder metallurgy method. The effects of addition of SiC particle on the mechanical properties of the composites such as hardness and compressive strength were investigated. The optimum density （93.33%） was obtained at the compaction pressure of 6.035 MPa. Scanning electron microscopic （SEM） observations of the microstructures revealed that the wettability and the bonding force were improved in Ti64 alloy/5% nano SiCp composites. The effect of nano SiCp content in Ti64 alloy/SiCp matrix composite on phase formation was investigated by X-ray diffraction. The correlation between mechanical parameter and phase formation was analyzed. The new phase of brittle interfaced reaction formed in the 10% and 15% SiCp composite specimens and resulted in no beneficial effect on the strength and hardness. The compressive strength and hardness of Ti64 alloy/5% nano SiCp MMCs showed higher values. Hence, 5% SiCp can be considered to be the optimal replacement content for the composite.

Effect of Zr additions and annealing temperature on electrical conductivity and hardness of hot rolled Al sheets

The influence of annealing cycles up to 650 °C on the specific conductivity and hardness（HV） of hot-rolled sheets of Al alloys containing up to 0.5% Zr（mass fraction） was studied.Using analytical calculations of phase composition and experimental methods（scanning electron microscopy,transmission electron microscopy,electron microprobe analysis,etc）,it is demonstrated that the conductivity depends on the content of Zr in the Al solid solution which is the minimum after holding at 450 °C for 3 h.On the other hand,the hardness of the alloy is mainly caused by the amount of nanoparticles of the L12（Al3Zr） phase that defines the retention of strain hardening.It is shown that the best combination of electrical conductivity and hardness values can be reached within an acceptable holding time at the temperature about 450 °C.

Flow of Casson nanofluid with viscous dissipation and convective conditions: A mathematical model

The magnetohydrodynamic(MHD) boundary layer flow of Casson fluid in the presence of nanoparticles is investigated.Convective conditions of temperature and nanoparticle concentration are employed in the formulation. The flow is generated due to exponentially stretching surface. The governing boundary layer equations are reduced into the ordinary differential equations. Series solutions are presented to analyze the velocity, temperature and nanoparticle concentration fields. Temperature and nanoparticle concentration fields decrease when the values of Casson parameter enhance. It is found that the Biot numbers arising due to thermal and concentration convective conditions yield an enhancement in the temperature and concentration fields. Further, we observed that both the thermal and nanoparticle concentration boundary layer thicknesses are higher for the larger values of thermophoresis parameter. The effects of Brownian motion parameter on the temperature and nanoparticle concentration are reverse.

Effect of TiC nanoparticle on friction and wear properties of TiC/AA2219 nanocomposites and its strengthening mechanism

TiC nanoparticles reinforced 2219 aluminum matrix composites were successfully prepared by ultrasonic casting, followed by forging and T6 heat treatment. The friction and wear properties of the disc-to-column were studied under four separate normal values of 5, 10, 20 and 30 N. The increasing hardness value of the nanocomposite may be attributed to the large amount of TiC(i.e., 1.3 wt.% and 1.7 wt.%) introduced to the composites. The friction coefficient of the nanocomposite decreased with the increase of TiC nanoparticles(0-1.7 wt.%) under the same load. But the wear resistance of the TiC/AA2219 nanocomposite increased by 30%-90% as compared to the 2219 matrix alloy. And it decreased with the increasing load. The composite with 0.9 wt.% TiC produced the best results in terms of friction and wear because of its relatively higher hardness and perfect ability to retain a transfer layer of a comparatively larger thickness. On the wear surface, some Al2O3particles were found which aided in the development of protective shear regions and improved the wear resistance. The wear mechanism for the TiC/AA2219 nanocomposite was a combination of adhesive and oxidative wear, with the composites containing hard TiC nanoparticles being mainly abrasive.

Size-dependent melting properties of Sn nanoparticles by chemical reduction synthesis

Tin nanoparticles with different size distribution were synthesized using chemical reduction method by applying NaBH4 as reduction agent.The Sn nanoparticles smaller than 100 nm were less agglomerated and no obviously oxidized.The melting properties of these synthesized nanoparticles were studied by differential scanning calorimetry.The melting temperatures of Sn nanoparticles in diameter of 81,40,36 and 34 nm were 226.1,221.8,221.1 and 219.5？欲espectively.The size-dependent melting temperature and size-dependent latent heat of fusion have been observed.The size-dependent melting properties of tin nanoparticles in this study were also comparatively analyzed by employing different size-dependent theoretical melting models and the differences between these models were discussed.The results show that the experimental data are in accordance with the LSM model and SPI model,and the LSM model gives the better understanding for the melting property of the Sn nanoparticles.

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.

Mesoporous Silica Nanoparticles for the Analytical Extraction of Triphenyltin from Water

A rapid, precise, sensitive and simple method has been developed for the extraction and determination of TPT （triphenyltin）, DPT （diphenyltin） and MPT （monophenyltin） in seawater samples. The procedure is based on the use of the dual functionalization of mesoporous silica with diol and Cl6 alkane groups for the collection of TPT and its derivatives, DPT and MPT, from seawater samples, followed by ethylation of the target matrices using sodium tetraethylborate （NaBEt4） and quantification by gas chromatography with pulsed flame photometric detection. The modified extraction method replaces conventional solid- and liquid-phase extraction with solid dispersion of silica nanoparticles. The partitioning of the analyte between a carefully size-selected silica nanoparticles （solid phase） and a liquid phase occurs as the solid moves through the sample as a colloidal sol. By tailoring the size of the particles to approximately 250 nm in diameter, they can be easily dispersed in aqueous solution, without the need for any mechanical or hand shaking and the solid can then be readily recovered, together with the analytes, by simple filtration or centrifugation. Recoveries of TPT, DPT and MPT chloride spiked matrices rang from 87.3±1.1 to 98.1±1.3 in seawater samples （n = I 1 samples）. The limit of detection obtained was typically in the range of 0.1-3 ng Sn/L. The proposed method shows excellent linearity in the range of 0.5-2 ng Sn/L and good repeatability （RSD 〈 5% at 0.02 ng TPT （as Sn）/L）. The method performance is demonstrated with real seawater samples.

Surface properties of encapsulating hydrophobic nanoparticles regulate the main phase transition temperature of lipid bilayers： A simulation study

The main phase transition temperature of a lipid membrane, which is vital for its biomedical applications such as controllable drug release, can be regulated by encapsulating hydrophobic nanoparticles into the membrane. However, the exact relationship between surface properties of the encapsulating nanoparticles and the main phase transition temperature of a lipid membrane is far from clear. In the present work we performed coarse-grained molecular dynamics simulations to meet this end. The results show the surface roughness of nanoparticles and the density of surface-modifying molecules on the nanoparticles are responsible for the regulation. Increasing the surface roughness of the nanoparticles increases the main phase transition temperature of the lipid membrane, whereas it can be decreased in a nonlinear way via increasing the density of surface-modifying molecules on the nanoparticles. The results may provide insights for understanding recent experimental studies and promote the applications of nanoparticles in controllable drug release by regulating the main phase transition temperature of lipid vesicles.

High densities of magnetic nanoparticles supported on graphene fabricated by atomic layer deposition and their use as efficient synergistic microwave absorbers

An atomic layer deposition （ALD） method has been employed to synthesize Fe3O4/graphene and Ni/graphene composites. The structure and microwave absorbing properties of the as-prepared composites are investigated. The surfaces of graphene are densely covered by Fe3O4 or Ni nanoparticles with a narrow size distribution, and the magnetic nanoparticles are well distributed on each graphene sheet without significant conglomeration or large vacancies. The coated graphene materials exhibit remarkably improved electromagnetic （EM） absorption properties compared to the pristine graphene. The optimal reflection loss （RL） reaches -46.4 dB at 15.6 GHz with a thickness of only 1.4 mm for the Fe3O4/graphene composites obtained by applying 100 cycles of Fe2O3 deposition followed by a hydrogen reduction. The enhanced absorption ability arises from the effective impedance matching, multiple interfacial polarization and increased magnetic loss from the added magnetic constituents. Moreover, compared with other recently reported materials, the composites have a lower filling ratio and smaller coating thickness resulting in significantly increased EM absorption properties. This demonstrates that nanoscale surface modification of magnetic particles on graphene by ALD is a very promising way to design lightweight and high-efficiency microwave absorbers.

Combustion characteristics of nanofluid fuels in a half-opening slot tube

Combustion characteristics of nanofluid fuels containing aluminum nanoparticles were investigated in half-opening slot tubes from the fundamental view. The effects of particle loading rates(0.25% and 2.5% by weight), type of base fuels(ethanol and butanol),and fuel flow rates(0.2, 0.6, and 1 mL/min) were studied in details. The combustion characteristics of the nanofluid fuels and pure based fuels were also examined to provide a comparison. Flame was unstable with reignition, stable state, nearly extinguishment repeatedly at low flow rate. At medium flow rate, flame height was increased and flame tended to be stable. At high flow rate,flame became unstable and was disturbed by the droplet forming and dripping significantly. Al atoms inside the oxide layer should be melted before the particles combustion, while Al oxide layer should be melted before the particles aggregates combustion. The effects of particles on the combustion characteristics, especially on the evaporation rate of base fuel, were discussed. The reasons for various combustion phenomena of nanofluid fuels were given, which can provide the useful guidance for the experimental research and practical applications of nanofluid fuels.

Solvent switching and purification of colloidal nano- particles through water/oil Interfaces within a density gradient

Traditional post-treatment of colloidal nanoparticles （NPs） usually involves repeated centrifugation-wash-sonication processes to separate NPs from the original synthetic environment; however, such separation processes have either high energy cost or low efficiency and tend to cause aggregation. Here we show a general and scalable colloid post-processing technique based on density gradient centrifugation through water/oil interfaces. Such a one-step technique can switch the solvent in a colloid at almost any concentration without aggregation, and meanwhile purify colloidal nanoparticles by separating them from by-products and environmental impurities. Droplet sedimentation was shown to be the mechanism of this one-step concentration/purification process, and mathematical modeling was established to quantify the accumulation and sedimentation velocities of different NPs.

1.3 μm emitting SrF2：Nd^3＋ nanoparticles for high contrast in vivo imaging in the second biological window

Novel approaches for high contrast, deep tissue, in vivo fluorescence biomedical imaging are based on infrared-emitting nanoparticles working in the so-called second biological window （1,000-1,400 nm）. This allows for the acquisition of high resolution, deep tissue images due to the partial transparency of tissues in this particular spectral range. In addition, the optical excitation with low energy （infrared） photons also leads to a drastic reduction in the contribution of autofluorescence to the in vivo image. Nevertheless, as is demonstrated here, working solely in this biological window does not ensure a complete removal of autofluorescence as the specimens diet shows a remarkable infrared fluorescence that extends up to 1,100 nm. In this work, we show how the 1,340 nm emission band of Nd3. ions embedded in SrF2 nanoparticles can be used to produce autofluorescence free, high contrast in vivo fluorescence images. It is also dem- onstrated that the complete removal of the food-related infrared autofluorescence is imperative for the development of reliable biodistribution studies.

Formation of copper oxide nanowires and nanoparticles via electrospinning

Copper oxide nanowires and nanoparticles were fabricated through electrospinning followed by calcinations in different heating conditions.It was found that the solution viscosity and environment humidity had great impact on the morphologies of precursor nanowires,and the parameters of heat treatment,including final temperature and heating rate,significantly affected the product morphologies.

Improving the sensitivity for DNA sensing based on doubleanchored DNA modified gold nanoparticles

DNA modified nanoparticles(Au NPs) are an established and widely used type of nucleotide sensor. We sought to improve the design by applying short rigid DNA duplexes near the surface of the Au NPs forming a so called double-anchored Au NP sensor, and compared it with other conventional DNA modified Au NPs. The improved design exhibited higher assembly efficiency, and consequently increased its sensitivity to target DNA.

Humidity-responsive nanocomposite of gold nanoparticles and polyacrylamide brushes grafted on Ag film: synthesis and application as plasmonic nanosensor

A general stepwise strategy for the preparation of new humidity-responsive plasmonic nanosensor was described for the first time, based on Ag film functionalization by polyacrylamide（PAAM） brushes via surface-initiated atom transfer radical polymerization（SI-ATRP） method and then assembled with gold nanoparticles（Au NPs）. We designed by this way a new plasmonic device made of Au NPs embedded in a humid vapor responsive polymer layer on Ag film and extensively characterized by surface-enhanced Raman scattering（SERS）. When the relative humidity（RH） is above 50%, the number of plasmonic hotspots decreases, causing SERS signal reduced noticeably, for the volume expansion of PAAM brushes varied the nano-gap between closely spaced Au NPs, and between Au NPs and Ag film. The reversible optical properties of the prepared nanocomposite tuned by RH were probed through SERS using 4-mercaptopyridine（4-Mpy） as a molecular probe, and the decrease of the RH reversibly induces a significant enhancement of the 4-Mpy SERS signal. By means of the high reversibility, the RH responsive nanocomposite developed in this paper provides a dynamic SERS platform and can be applied as plasmonic nanosensor which is proved to be stable for at least two months.

Molecule bridged graphene/Ag for highly conductive ink

Printing is a method of additive manufacturing that can reduce material costs and environmental contamination during the fabrication process.Ag ink is commonly used in printed electronics,such as interconnects,inductors,and antennas.However,the high cost of noble Ag restricts its massive applications.To reduce the cost of the state-of-the-art Ag ink and realize large-scale manufacturing,we develop a molecule-bridged graphene/Ag(MB-G/A)composite to produce highly conductive and cost-effective paperbased electronics.Graphene can be used to substitute part of Ag nanoparticles to reduce costs,form a conducive percolation network,and retain a reasonable level of conductivity.We adopt cysteamine as a molecular linker,because it anchors on the surface of graphene via the diazonium reaction.Additionally,the thiol functional group on the other end of cysteamine can bond to a Ag atom,forming a molecular bridge between graphene and Ag and promoting electron transport between Ag and graphene.As a result,the maximum conductivity of MB-G/A inks can reach 2.0×10^(5)S m^(−1),enabling their successful application in various printable electronics.In addition,the optimum MB-G/A ink costs less than half as much as pure Ag inks,showing the great potential of MB-G/A ink in commercial electronic devices.