Scalable Formation of Concentrated Monodisperse Lignin Nanoparticles by Recirculation-Enhanced Flash Nanoprecipitation

A highly controllable and scalable process for fabrication of large amounts of concentrated lignin nanoparticles (LNPs) is reported. These lignin core nanoparticles are formed through flash nanoprecipitation, however, scaling up of the fabrication process requires fundamental understanding of their operational formation mechanism and surface properties. It is shown how a semicontinuous synthesis system with a recirculation loop makes it possible to produce flash precipitated lignin nanoparticles in large amounts for practical applications. The roles of the process parameters, including flow rates and lignin concentration, are investigated and analyzed. The results indicate that the LNPs are formed by a process of continuous burst nucleation at the point of mixing without diffusive growth, which yields nanoparticles of highly uniform size following a modified LaMer nucleation and growth mechanism. This mechanism makes possible facile process control and scale-up. Effective control of the resulting nanoparticle size is achieved through the initial concentration of lignin in the injected solution. The impressive capability to produce suspensions of any predesigned multimodal distribution is demonstrated. The resulting nanofabrication technique can produce large volumes of concentrated LNP suspensions of high stability and tightly controlled size distributions for biological or agricultural applications.     

光谱法研究等离子体粒子循环和输运

介绍了三高斯拟合技术,首先用单高斯选点拟合了Hα线形分布的远翼,由谱线的多谱勒展宽得出等离子体离子温度为170 eV,再对剩余量进行双高斯拟合,从多谱勒频移求出反射和解吸粒子入射速度分别为3.0×104 m/s和1×104 m/s,从谱线辐射强度推出再循环粒子由60%反射粒子和40%解吸粒子组成。在简化模型下讨论了粒子的输运行为,算出了氢原子密度、体发射系数和粒子约束时间的分布,均与实验结果相符。分析了粒子入射速度大小对粒子约束时间的影响,结果表明,正常放电下,HT 6M托卡马克粒子约束时间在4~8 ms;反射粒子的速度大小直接决定粒子约束时间的大小和空间分布。     

A Method of Separation of Polydisperse Particles in the Plasma of Radio‐Frequency Discharge

A method of separation of polydisperse dust particles in the plasma of radio‐frequency (RF) capacitive discharge is considered. Investigations of plasma equipotential field enabled us to determine conditions for separation of polydisperse dust particles. The simplicity of the technology made it possible to obtain small dispersed particles of different materials. Samples of small dispersed microparticles of silica and alumina were obtained. The size and chemical composition of samples were examined using a Quanta 3D 200i scanning electron microscope (SEM, FEI, USA). The average size of separated silica nanoparticles was 600 nm, that of silica and alumina microparticles was 5 μm. Two separation methods were developed: the first one used a special trap and shape of the bottom electrode of RF discharge (for separation of microparticles) and the second used an electrical trap (for separation of nanoparticles). The graphs of particle size distribution were constructed using graphical and mathematical calculations. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

修正的Landau 流体力学模型与Cu+Cu 碰撞末态带电粒子赝快度分布

采用修正的Landau 流体力学模型,并考虑到带头粒子效应,对高能重离子碰撞末态带电粒子的赝快度分布进行了讨论。指出:带头粒子的快度分布应为高斯形式,其正规化常数为参与者数。研究表明:流体力学模型本身与BNL-RHIC-PHOBOS 合作组在(NN)½ =200 GeV 的Cu+Cu 碰撞中的实验测量符合得不是很好,只有将参与者的贡献包括在内,实验结果才能得到很好的描述。By using the revised Landau hydrodynamic model and taking into account the effect of leading particles, we discussed the pseudorapidity distributions of final charged particles in high energy heavy ion collisions. We argued that the rapidity distributions of leading particles have the Gaussian form with the normalization constant being equal to the number of participants. The investigations show that the results from the hydrodynamic model alone are not consistent with the experimental data carried out by BNL-RHIC-PHOBOS Collaboration in Cu+Cu collisions at (NN)½ = 200 GeV. Only after the contributions from leading particles are included, can the experimental measurements be described well.     

Nanoparticle Tracking Analysis of Polymer Nanoparticles in Blood Plasma

A successful drug delivery system must overcome complex biological barriers. For particles injected into the blood, one of the first and most critical barriers pertains to blood stability to circulate through the human body. To effectively design drug delivery vehicles, interactions between the particles and blood, as well as the aggregation behavior, must be understood. This work presents a method to analyze particle size and aggregation in blood plasma using a commercially available nanoparticle tracking analysis (NTA) system. As a model system, fluorescently labeled polystyrene nanoparticles are incubated in goat blood plasma and analyzed using NTA. The particles incubated in plasma are found to have a protein corona that is larger than what has been observed by dynamic light scattering (DLS) in diluted plasma. Particles that are decorated with a PEG layer are also found to have large protein coronas in undiluted plasma. Because NTA is based on a unique visualization method, large multicomponent aggregates could be observed and quantified in a manner not feasible with other techniques. PEGylation of the particles is found to decrease the multicomponent aggregation from 1000 ± 200 particles for unmodified to 200 ± 30 particles for 1K PEGylated per 1 × 10⁵ total particles.     

胶体金纳米颗粒的表面等离子体发射特性

利用电化学方法制备出粒径为20-80 nm的胶体金纳米颗粒。研究其荧光发射光谱特性,在485nm处观察到表面自由电子集体激发导致的表面等离子体共振发射峰,其位置不随激励光波长的变化而移动。当激励光波长为485 nm时,观察到最强的发射峰。在240和640 nm处,还观察到倍频发射峰和3/4分频发射峰。增加金纳米颗粒粒径,观察到发射谱的峰值增大而发射峰的位置只有很小的红移。     

Research in Korea on Gas Phase Synthesis and Control of Nanoparticles

Research activity into the gas phase synthesis of nanoparticles has witnessed rapid growth on a worldwide basis, which is also reflected by Korean research efforts. Nanoparticle research is inherently a multi-disciplinary activity involving both science and engineering. In this paper, the recent studies undertaken in Korea on the gas phase synthesis and control of nanoparticles are reviewed. Studies on the synthesis of various kinds of nanoparticles are first discussed with a focus on the different types of reactors used. Recent experimental and theoretical studies and newly developed methods of measuring and modeling nanoparticle growth are also reviewed.     

Gold Nanoparticles: Production,Reshaping, and Thermal Charging

Gold nanoparticles are of great interest for various nanoelectronic applications, e.g., for making single electron transistors or very fine leads to molecular size entities. For this and other applications, it is important that all particles have controllable size and shape. In this paper, we describe the production of size-selected gold aerosol particles in the 20nm range made by evaporation in a high-temperature tube furnace and subsequent size selection. To obtain spherical particles, it was necessary to reshape the particles at high temperature, which was investigated for temperatures between 25°C and 1200°C. High-resolution transmission electron microscopy showed that the degree of crystallinity became higher for higher reshaping temperature. During reshaping at high temperature, an anomalous charging behavior was discovered, whereby negatively as well as positively charged particles became multiply negatively charged. Possible mechanisms for explaining this thermally activated phenomenon are discussed.     

Numerical Study on the Coagulation and Breakage of Nanoparticles in the Two-Phase Flow around Cylinders

The Reynolds averaged N-S equation and dynamic equation for nanoparticles are numerically solved in the two-phase flow around cylinders, and the distributions of the concentration M₀ and geometric mean diameter d_g of particles are given. Some of the results are validated by comparing with previous results. The effects of particle coagulation and breakage and the initial particle concentration m₀₀ and size d₀ on the particle distribution are analyzed. The results show that for the flow around a single cylinder, M₀ is reduced along the flow direction. Placing a cylinder in a uniform flow will promote particle breakage. For the flow around multiple cylinders, the values of M₀ behind the cylinders oscillate along the spanwise direction, and the wake region in the flow direction is shorter than that for the flow around a single cylinder. For the initial monodisperse particles, the values of d_g increase along the flow direction and the effect of particle coagulation is larger than that of particle breakage. The values of d_g fluctuate along the spanwise direction; the closer to the cylinders, the more frequent the fluctuations of d_g values. For the initial polydisperse particles with d₀ = 98 nm and geometric standard deviation σ = 1.65, the variations of d_g values along the flow and spanwise directions show the same trend as for the initial monodisperse particles, although the differences are that the values of d_g are almost the same for the cases with and without considering particle breakage, while the distribution of d_g along the spanwise direction is flatter in the case with initial polydisperse particles.     

Coagulation of Charged Aerosols

We consider the coagulation of an aerosol embedded in a stationary atmosphere of bipolar ions. Particles respond to the ionic environment by developing an instantaneous charge the fluctuations of which may produce attraction or repulsion between the particles. The governing parameter is the charge asymmetry factor which quantifies the relative charging efficiency of positive and negative ions. We use a Monte Carlo method to solve the coagulation equation in the free-molecule regime. We perform simulations for conditions ranging from symmetric and nearly symmetric environments (e.g. flames, ionizers), which result in particles that are on the average neutral to highly asymmetric conditions (low-pressure plasmas), which produce a substantial non-zero net charge. In symmetric ionic atmospheres we find that electrostatic interactions are unimportant and particles grow as if in the absence of charging ions. In asymmetric bipolar atmospheres, electrostatic interactions between particles are repulsive, the mean particle size grows logarithmically in time and the resulting size distributions are significantly narrower than the classical self preserving distributions.     

Electron Acceleration by Beating of Two Intense Cross-Focused Hollow Gaussian Laser Beams in Plasma

This paper presents propagation of two cross-focused intense hollow Gaussian laser beams(HGBs) in collisionless plasma and its effect on the generation of electron plasma wave(EPW) and electron acceleration process,when relativistic and ponderomotive nonlinearities are simultaneously operative. Nonlinear differential equations have been set up for beamwidth of laser beams, power of generated EPW, and energy gain by electrons using WKB and paraxial approximations. Numerical simulations have been carried out to investigate the effect of typical laser-plasma parameters on the focusing of laser beams in plasmas and further its effect on power of excited EPW and acceleration of electrons. It is observed that focusing of two laser beams in plasma increases for higher order of hollow Gaussian beams,which significantly enhanced the power of generated EPW and energy gain. The amplitude of EPW and energy gain by electrons is found to enhance with an increase in the intensity of laser beams and plasma density. This study will be useful to plasma beat wave accelerator and in other applications requiring multiple laser beams.     

Colloidal Suspensions of Platinum Group Metal Nanoparticles (Pt,Pd, Rh) Synthesized by Dielectric Barrier Discharge Plasma (DBD)

Atmospheric‐pressure plasmas produced by dielectric barrier discharge can be used to grow nanoparticles from aqueous solutions containing ions from the platinum group metals (PGM: Pt, Pd, and Rh). The technology could also be applied to recover PGM from waste solutions. In plasma electrochemistry, PGM solutions act as a liquid electrode, and a counter electrode located near the surface of the liquid is used to generate the plasma (e.g., hydrogen, argon). The treatment synthesizes nanoparticles within minutes, which can be separated from the treated solutions. In the present study, small concentrations of PGM ions (1 × 10⁻³m ) are recuperated from aqueous solutions containing chloride ions. The efficiency of the process is quantified by elemental analysis, and the size of the colloids, measured by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Very high recovery yields are found for palladium (>99%), as well as for rhodium (>75%) and for platinum (>51%). Plasma electrochemistry is a very efficient and rapid process to recuperate PGM ions from water solutions (faster than conventional electrowinning) such as industrial waste, acid leach, and related effluents. The very fine and surfactant‐free nanoparticles could find promising applications as industrial and automotive catalysts.     

Variable Frequency Microwave Synthesis of Silver Nanoparticles

Synthesis of silver nanoparticles based on a polyol process and variable frequency microwave (VFM) was investigated. Comparing to a thermal method, the reaction by VFM radiation was much faster. The effects of silver nitrate concentration, poly(N-vinylpyrrolidone) (PVP) concentration, reaction time and reaction temperature were studied. It was found that the higher concentration of silver nitrate, longer reaction time and higher temperature increased the particle size while the higher concentration of PVP decreased the particle size.     

Screening of a Test Charge in Plasma

Nonlinear screening of a test charge in plasma by electrons trapped or untrapped is studied. The obtained results are in rigorous estimations mathematically in comparison with the corresponding Debye screening forms. Meanwhile their validity is physically discussed and some confusions in literature are clarified.     

粒子-转子模型和推转壳模型中的能谱统计分析

用粒子–转子模型和推转壳模型研究了6个粒子分别填充在单j壳和双j壳上的混沌行为.分析了单j壳和双j壳情况下能谱的最近邻能级间距分布和谱刚度随自旋及推转频率的变化,结果表明,当组态空间大小不变时,系统在双j壳(g_7/2+d_5/2)情况下比在单j壳(i_13/2)情况下更规则,而当组态空间从单j壳(i_13/2)扩大到双j壳(i_13/2+g_9/2)时,系统的混沌程度变化不大.同时比较了将6个粒子的两体相互作用分别取为δ力和对力时的系统的混沌行为     

Relative Distribution of Au48 ～ Au52 in Au Plasma by Ionization Dynamics

The present work proposes a theoretical method called ionization dynamics to derive the ionic charge state distribution. Using relativistic quantum mechanics to calculate the energy level lifetime and average ionic lifetime of each ion, the first-order ionization rate constant can be obtained. Based on these data, from the solution of differential equations for consecutive-irreversible ionization reactions, one will be able to derive the ionic charge state distribution.The calculated average positive charge 49.24 of Au48 ～ Au52 and their relative distribution are in good agreement with the results of Lawrence Livermore National Laboratory.     

负离子对等离子体鞘层特性影响的数值研究

构造强电负性等离子体中平板电极处鞘层形成的模型,使用流体动力学方程组研究等离子体鞘层.得到空间电势、空间静电荷分布和鞘层宽度作为距离函数的数值结果.结果表明,强电负性鞘层中,在等离子体区和鞘层区之间几乎没有过渡的预鞘区,在靠近极板附近鞘层里的电子、负离子和正离子的分布形成一个纯正离子鞘区.在靠近鞘边附近,空间静电荷密度分布有一个很尖的峰.发现同电正性情形相比,强电负性鞘层的宽度要窄很多,空间电势下降得快得多.     

Plasma synthesis of semiconductor nanocrystals for nanoelectronics and luminescence applications

Functional nanocrystals are widely considered as novel building blocks for nanostructured materials and devices. Numerous synthesis approaches have been proposed in the solid, liquid and gas phase. Among the gas phase approaches, low pressure nonthermal plasmas offer some unique and beneficial features. Particles acquire a unipolar charge which reduces or eliminates agglomeration; particles can be electrostatically confined in a reactor based on their charge; strongly exothermic reactions at the particle surface heat particles to temperatures that significantly exceed the gas temperature and facilitate the formation of high quality crystals. This paper discusses two examples for the use of low pressure nonthermal plasmas. The first example is that of a constricted capacitive plasma for the formation of highly monodisperse, cubic-shaped silicon nanocrystals with an average size of 35 nm. The growth process of the particles is discussed. The silicon nanocubes have successfully been used as building blocks for nanoparticle-based transistors. The second example focuses on the synthesis of photoluminescent silicon crystals in the 3–6 nm size range. The synthesis approach described has enabled the synthesis of macroscopic quantities of quantum dots, with mass yields of several mg/hour. Quantum yields for photoluminescence as high as 67% have been achieved.     

Structural and Optical Properties of Gold/Silica “Mushroom” Particles Prepared by Interfacial Templating

Complex shaped nanoparticles featuring structural or surface chemical patchiness are of special interest in both fundamental and applied research areas. This study reports the preparation and optical properties of gold/silica “mushroom” nanoparticles, where a gold particle is only partially covered by the silica cap. The synthetic approach allows precise control over the particle structure. The interfacial preparation method relies on partially embedding the gold particles in a polystyrene layer that masks the immersed part of the gold particle during silica shell growth from an aqueous solution. By adjusting sacrificial polystyrene film thickness and silica growth time, precise control over the coverage and cap thickness can be achieved. Correlative electron microscopy and single particle scattering spectroscopy measurements underline the high precision and reproducibility of the method. The good agreement between the measured and simulated single particle spectra supported by near‐field calculations indicates that the observed changes in the dipolar plasmon resonance are influenced by the extent of coverage of the gold core by the silica cap. The straightforward methods readily available for gold and silica surface modification using range of different (bio)molecules make these well‐defined nanoscale objects excellent candidates to study fundamental processes of programmed self‐assembly or application as theranostic agents.     

Copolymer Particles with Incorporated Gold and Silver Nanoparticles to Absorb Short‐Wavelength Scattering in Full‐Color Photonic Glasses

Photonic glasses (PGs) have fascinated researchers because the structural colors that are reflected from PGs are angle independent. However, low color saturation, especially for colors at longer wavelengths, is an obstacle for realizing full‐color PGs. It is reported that the form‐factor‐(FF)‐derived reflections that degrade the color saturation of PGs can be removed by embedding Ag and Au nanoparticles (NPs) into copolymers. Styrene and 4‐vinylpyridne copolymer particles are prepared and used as nanotemplates to synthesize AgNPs and AuNPs. The wavelength of the FF‐derived reflections in relation to the diameter of the particles is estimated. NPs with an absorption spectrum corresponding to the calculated values are then selectively embedded in the copolymer particles. PGs fabricated with AgNP‐ and AuNP‐embedded copolymer particles exhibit fewer FF‐derived reflections owing to the surface‐plasmon‐resonance‐induced absorption of the embedded NPs. Using these FF‐reduced PGs, angle‐independent full‐color PG pigments are realized.