Synthesis of crosslinked poly(styrene-<Emphasis Type="Italic">co</Emphasis>-divinylbenzene-<Emphasis Type="Italic">co</Emphasis>-sulfopropyl methacrylate) nanoparticles by emulsion polymerization: Tuning the particle size and surface charge density

We have synthesized highly charged, crosslinked poly (styrene-co-divinylbenzene-co-sulfopropyl methacrylate) copolymer colloidal particles using emulsion polymerization. The effects of concentration of the emulsifier and the initiator on the particle size and the charge density of the colloidal particles are studied. Colloidal particle size is highly dependent upon the concentration of the emulsifier and the initiator. The colloidal particle diameter decreases with increasing concentration of the emulsifier and increases with increasing concentration of the initiator in the polymerization mixture. Number of particles, surface charge density and charges per particle are also functions of both the emulsifier and the initiator concentration. The surface charge density and the number of charges per sphere increase with increasing particle diameter. These copolymer colloid particles self assemble readily and diffract visible light. Polymer hydrogel imbibed with these colloids shows the light diffraction.     

胶乳型互穿网络聚合物形态结构的研究

用RuO_4染色法研究了LIPN PBA/PS/PMMA乳胶粒的形态结构并用透射电镜和图象分析技术测定了乳胶粒尺寸及其分布。讨论了引发剂、交联剂、反应温度及加料方式对形态结构的影响。     

Effect of grafted polymer species on particle monolayer structure at the air-water interface

We have studied poly(methyl methacrylate)-grafted(PMMA) particle monolayer systems at the air-water interface. In previous papers, we reported that PMMA chains grafted from particles (silica particle and polystyrene latex) were extended on water surfaces. Through observing deposited particle monolayers on substrates using SEM, we have confirmed that PMMA of large molecular weights were either dispersed or arrayed in structure with long inter-particle distances approximately 500 nm. In contrast, low molecular weight PMMA were observed to aggregate upon deposition. We speculated that the difference in morphology in deposited particle monolayers would be attributed to the affinity between the grafted polymer and the substrate. To examine the effect of this affinity three new polymer-grafted silica particles were synthesized with a fairly high graft density of about 0.14 approximately 0.43 nm(-2). As well as PMMA-grafted silica particles (SiO2-PMMA), poly(2-hydroxyethyl methacrylate) and poly(t-butyl methacrylate)--grafted silica particles (SiO2-PHEMA and SiO2-PtBuMA) were also prepared and subjected to pi-A isotherm measurements and SEM observations. These pi-A isotherms indicated that polymer-grafted silica formed monolayer at the air-water interface, and the onset area of increasing surface pressure suggests that the polymer chains are extended on a water surface. However, the morphology of the deposited monolayer is highly dependent on polymer species: SiO2-PHEMA showed that the dispersed particle monolayer structure was independent of grafted molecular weight while SiO2-tBuMA showed an aggregated structure that was also independent of grafted moleculer weight. SiO2-PMMA showed intermediate tendencies: dispersed structure was observed with high grafted molecular weight and aggregated structure was observed with low grafted molecule weight. The morphology on glass substrate would be explaiened by hydrophilic interaction between grafted polymer and hydrophilic glass substrate.     

Particle monolayer formation with arrayed structure by PMMA-grafted polystyrene Latex at the air-water interface

The structure of the particle monolayer formed by the polymer-grafted latex particle at the air-water interface was estimated mainly by pi--A isotherm measurement and SEM observation to examine the effect of core particle characteristics and to generalize the key factors in determining the polymer-grafted particle monolayer structure. Methyl methacrylate (MMA) was polymerized from the polystyrene latex (PSL) surface by atom transfer radical polymerization to give a PMMA-grafted PSL (PSL-PMMA) with a relatively high graft density of about 0.2 nm-2. We obtained PSL-PMMA with PMMA of different molecular weights but almost the same graft density. The onset area of increasing surface pressure in pi-A isotherm was in agreement with the value of effective radius of PSL-PMMA with quite extended PMMA chains. The particle monolayer structure deposited on the substrate was strongly dependent on the molecular weight of the grafted PMMA. The aggregation size was reduced with increasing molecular weight and a lattice-like structure was observed for PSL-PMMA monolayer with a high molecular weight PMMA. The interparticle distance was decreased and structure becomes ordered with increasing surface pressure. The monolayer structure obtained here was consistent with that of the PMMA-grafted silica particle system. We also synthesized polystyrene (PS)-grafted PMMA latex (PML-PS) and compared the two systems. We confirmed that the lattice-like structure depended on the nature of the grafted PMMA chain, not the core particle characteristics.     

Key to analyte migration and retention in electrochromatography

This work identifies electrical field-induced concentration polarization (CP) as a key physical mechanism influencing the retention behavior of charged analytes in electrochromatography with fixed beds of porous adsorbent particles. Due to an insufficient screening of intraparticle surface charge, under most general conditions the porous (permeable) particles become charge-selective. CP is caused by coupled mass and charge transport normal to the charge-selective external surface of the permeable particles, which leads to concentration gradients of ionic species in the adjoining interparticle electrolyte solution. Cation-exchange (cation-selective) particles were employed to investigate the influence of applied voltage on the retention factor of counterionic, i.e., positively charged, analytes. It is demonstrated by macroscopic retention data and microscopic studies resolving the CP phenomenon on a particle scale that the dependence of CP on electrical field and mobile-phase ionic strengths is directly reflected in concomitant changes of analyte retention. The CP zones that develop at the interface between interparticle and intraparticle pore space are recognized by charged, but not electroneutral analytes while entering or leaving the particles. The intensity of these convective-diffusion boundary layers (CP zones) depends on the applied field strength and charge selectivity of a particle. Thus, it is the charge-selective transport between the interparticle and intraparticle pore space in packed beds that prevails under typical experimental conditions in electrochromatography and that forms the physical basis for a general electrical field dependence of the retention factor of charged analytes.     

Monodisperse micron-sized polymethylmethacrylate particles having a crosslinked network structure. V

Highly monodisperse micron-sized polymethylmethacrylate (PMMA) particles crosslinked with carboxylic group-containing urethane acrylates (CUA) were produced by simple dispersion polymerization in methanol. In proper condition, CUA employed as a crosslinker had an excellent ability to achieve the monodisperse PMMA particles to the concentration of about 10 wt%. This arose from the fact that CUA formed monomer-swellable primary particles due to its structurally long tetramethylene oxide groups in the molecule. The influence of the concentrations of the initiator and CUA on the particle diameter (D _n), particle number density (N _p), and polymerization rate (R _p) was found to obey the following approximate relationship, D _n [initiator]^0.41[CUA]^–0.06, N _p [initiator]^–1.22 [CUA]^0.21, and R _p [initiator]^0.34±0.03, respectively. The power law dependence of D _n and N _p on the initiator concentration coincided well with that of linear polymers in the literature. Especially, in this study, it was found that CUA did not have a serious influence on the nucleation. However, the dependence of R _p on the initiator concentration was observed to be higher than that of linear polymers, suggesting that uniquely, the solution polymerization process competed with the heterogeneous polymerization during polymerization, because of the crosslinked network structure of the primary particles.     

Re-electrospraying splash-landed proteins and nanoparticles

FITC-albumin, Lsr-F, or fluorescent polystyrene latex particles were electrosprayed from aqueous buffer and subjected to dispersion by differential electrical mobility at atmospheric pressure. A resulting narrow size cut of singly charged molecular ions or particles was passed through a condensation growth tube collector to create a flow stream of small water droplets, each carrying a single ion or particle. The droplets were splash landed (impacted) onto a solid or liquid temperature controlled surface. Small pools of droplets containing size-selected particles, FITC-albumin, or Lsr-F were recovered, re-electrosprayed, and, when analyzed a second time by differential electrical mobility, showed increased homogeneity. Transmission electron microscopy (TEM) analysis of the size-selected Lsr-F sample corroborated the mobility observation.     

纳米Pd-Ga/PMMA复合体系界面的有序结构

在不使用引发剂和还原剂条件下,用超声辐射工艺双原位合成了纳米钯镓/聚甲基丙烯酸甲酯(PMMA)复合物.XRD和UV-Vis显示,超声还原生成的单质钯和超声粉碎的单质镓在PMMA基体中不是简单的物理分散,而是在生成钯镓合金Ga5Pd/PMMA复合物的同时既有纳米钯又有纳米镓与PMMA形成复合物;XPS表明,镓失去了部分外...     

SYNTHESIS AND CHARACTERIZATION OF CONTROLLED SIZES: POLYSTYRENE LATEXES

Several parameters and their limitations to prepare monodisperse polystyrene particles were discussed. Polystyrene latexes B, C and D of diameter 129.8, 142.8 and 264.5 nm, respectively, were synthesized by emulsion polymerization method. The latex D is almost monodisperse with very low polydispersity of 0.005 while B and C are having polydispersity of 0.1837 and 0.1601. The particle size and particle size distribution of the latexes were determined by a TEM and Brookhaven particle size analyzer. It was observed that the particle size of the latexes decreased with increasing initiator (ammonium persulfate) or surfactant (SDS) concentrations. The surface area of the latexes were calculated by using BET equation on the basis of the amount of nitrogen gas adsorbed at the surface of the particles to form a monolayer. It was observed that the surface area of latex D is less than B and C because of the bigger size of the particles. The average molecular weights, zeta potentials and densities of the latexes were also presented.     

Facile synthesis of silver immobilized-poly(methyl methacrylate)/polyethyleneimine core–shell particle composites

A facile route to synthesize silver-embedded-poly(methyl methacrylate)/polyethyleneimine (PMMA/PEI-Ag) core–shell particle composites was illustrated in this present work. PMMA/PEI core–shell particle templates were first prepared by a surfactant-free emulsion polymerization. PEI on the templates' surface was further used to complex and reduce Ag⁺ ions (from silver nitrate solution) to silver nanoparticles (AgNPs) at ambient temperature, resulting in the PMMA/PEI-Ag particle composites. The formation of AgNPs was affected by the pHs of the reaction medium. The pH of reaction medium at 6.5 was optimal for the formation of PMMA/PEI-Ag with good colloidal stability, which was confirmed by size and size distribution, FTIR spectroscopy, UV–vis spectroscopy and X-ray diffraction. Moreover, the amount of AgNO₃ solution (4.17–12.50 g) was found to affect the formation of AgNPs. Transmission electron microscopy (TEM) indicated that the AgNPs were incorporated in the PMMA/PEI core–shell matrix, and had 6–10 nm in diameter. AgNPs immobilized on PMMA/PEI core–shell particles were also investigated by energy dispersive X-ray spectroscopy analysis mode extended from scanning electron microscopy (SEM/EDS). Furthermore, the presence of AgNPs was found to influence the thermal degradation behavior of PMMA/PEI particle composites as observed through thermogravimetric analysis (TGA).     

乙醇及NaCl存在下甲基丙烯酸甲酯的无皂乳液聚合

以乙醇为助溶剂,在电解质NaCl存在下进行甲基丙烯酸甲酯的无皂乳液聚合。考察了助溶剂、电解质、引发剂及单体的用量时聚甲基丙烯酸甲酯微球粒往及其分布的影响．结果表明,仅加入乙醇,可以使聚合物微球的粒径有所提高。在一定条件下对微球粒径分布影响不大。同时加入乙醇及电解质,能显著提高微球的粒径,得到10μm～100／μm的聚合物微球,但却使其分布变宽。单体用量增加。微球粒径及分布增大,引发剂用量增加,微球粒径及分布也增大。     

Increasing the Morphological Stability of DNA‐Templated Nanostructures with Surface Hydrophobicity

DNA has been extensively used as a versatile template to assemble inorganic nanoparticles into complex architectures; thanks to its programmability, stability, and long persistence length. But the geometry of self‐assembled nanostructures depends on a complex combination of attractive and repulsive forces that can override the shape of a molecular scaffold. In this report, an approach to increase the morphological stability of DNA‐templated gold nanoparticle (AuNP) groupings against electrostatic interactions is demonstrated by introducing hydrophobicity on the particle surface. Using single nanostructure spectroscopy, the nanometer‐scale distortions of 40 nm diameter AuNP dimers are compared with different hydrophilic, amphiphilic, neutral, and negatively charged surface chemistries, when modifying the local ionic strength. It is observed that, with most ligands, a majority of studied nanostructures deform freely from a stretched geometry to touching particles when increasing the salt concentration while hydrophobicity strongly limits the dimer distortions. Furthermore, an amphiphilic surface chemistry provides DNA‐linked AuNP dimers with a high long‐term stability against internal aggregation.     

外加电场气相法制备纳米无机氧化物

气相燃烧法纳米无机氧化物粉体特征一方面取决于前驱体的水解反应速度和粒子的成核生长动力学, 另一方面受到燃烧反应器内物料的流动混合、热质传递等多种过程因素的影响。电场控制气相燃烧法制备纳米 无机氧化物是在原有的基础上外加电场,使火焰的轴向高度降低、径向宽度增大,形成厚度相对均匀的火焰层, 火焰温度梯度也随之增大,抑制粒子表面的生长和粒子之间的烧结,获得“粒径分布较窄的粒子和结构相似的 聚集体”。     

Ionisation density dependence of the optically stimulated luminescence dose-response of AL2O3:C to low-energy charged particles

The optically stimulated luminescence (OSL) response of Al2O3:C to high doses of gamma or beta irradiation can be used to predict the response of this material to charged particles as a function of particle fluence, particle energy and/or linear energy transfer (LET). In particular, it is predicted that track interaction effects at high particle fluences should result in linear-sublinear growth of the OSL signal. Similar considerations also predict a dependence of the fluence at which sublinearity starts upon the energy of the particles. In this work the OSL response of Al2O3:C to low-energy charged particles was investigated using protons (1, 2 and 4 MeV), carbon ions (13 MeV) and oxygen ions (10 MeV). The sublinear growth predicted above was qualitatively confirmed, but the energy dependence prediction was not. Furthermore, the efficiency of OSL production in the material after charged particle irradiation, compared to that obtained for gamma irradiation, is determined from the dose-response curves by fitting to a simple saturating exponential function. The efficiency values so obtained using this method are compared with those obtained from a conventional single-point measurement in the linear portion of the curve and found to be in good agreement. In general, the efficiency decreases as the LET of the particle increases. The present data are compared with published data obtained using high-energy charged particles and the results show that the efficiency is not a unique function of LET.     

Mechanical properties of acrylate-grafted henequen cellulose fibers and their application in composites

The properties of cellulose fiber and PMMA- or PBA-grafted cellulose fibers are investigated as a function of the initiator (ceric-ammonium nitrate) concentration and the amount of grafted polymer onto cellulose fiber. The molecular weight of cellulose decreases while the crystallinity increases with an increment of initiator concentration because of the partial degradation of the amorphous zone of the fibers exposed to the oxidation by the initiator. This results in a reduction of the elastic modulus and tensile strength at high initiator concentrations. Degradation of cellulose is partially inhibited during the grafting process and, therefore, the effect of initiator on the mechanical properties is less notorious in the grafted cellulose fiber. The grafting of PMMA or PBA on the fiber results in lower mechanical properties than those of the ungrafted cellulose fiber. The reduction of the elastic modulus is independent of the amount of grafted PMMA or PBA, but the tensile strength decreases with the PBA content on the PBA-grafted fiber. Either the grafted or the ungrafted cellulose fibers improve the mechanical properties of plasticized PVC composites, and the best results are obtained for PMMA-grafted cellulose fibers because of the better fiber–matrix adhesion. The Halpin–Tsai equation seems to better agree with the experimental data when there is a good fiber–matrix adhesion. In contrast, for poor fiber–matrix adhesion the experimental data has a better agreement with the parallel arrangement equation.     

Hafnium carbide growth behavior and its relationship to the dispersion hardening in tungsten at high temperatures

The growth behavior of hafnium dispersed carbide particles and its relationship the strength of a tungsten-rhenium alloy at temperatures above 2200 K have been examined with transmission electron microscopy. From 2200 to 2600 K, HfC particles grow homogeneously with a relatively slow growth rate. In this temperature region, the activation energy for HfC particle growth is determined to be 50.2 ± 1.0 kcal mol⁻¹. The coarsening of HfC particles is a bulk diffusion-controlled process and hafnium is the less stable element in the HfC decomposition and growth process. Rapid particle growth occurs at temperatures above 2600 K. A bi-modal particle size distribution is observed at 2800 and 3000 K and selective particle growth takes place along dislocation lines and at grain boundaries, indicating that dislocation and boundary enhanced diffusion mechanisms are involved in the HfC particle coarsening process above 2600 K. Based upon the studies on the growth behavior of HfC particles, An Ashby-Orowan dispersion strengthening model is applied to the HfC hardened tungsten. Good agreement is obtained between the calculated resolved shear stress and experimental results.     

乳液聚合合成单分散纳米级PMMA微球

采用乳液聚合法制备了单分散性聚甲基丙烯酸甲酯（PMMA）纳米微球,分析了聚合过程中不同单体滴加时间、不同表面活性剂用量、不同引发剂用量以及不同引发剂种类等因素对聚合体系中微球的粒径以及粒径分布的影响,研究表明,PMMA微球的粒径随单体滴加时间、表面活性剂用量、引发剂用量的增加而减小;采用AIBN引发剂制备的微球的粒径较采用KPS引发剂大。     

缩聚物/加聚物复合胶乳的制备 Ⅰ.环氧树脂/丙烯酸树脂乳液接枝聚合反应

用乳液接枝聚合方法制备环氧树脂／丙烯酸树脂的复合胶乳水分散体系，考察了不同引发剂用量、乳化剂用量、单体浓度对复合胶乳粒径、接枝率、分子量的影响，并对这类复合胶乳体系的接枝机理进行了探讨。实验结果表明，引发剂浓度增大，粒径增大，分子量减小，接枝率增大；乳化剂浓度增大，分子量和接枝率变化不大，粒径则有下降趋势；环氧树脂浓度增大，粒径倾向于增大，分子量和接枝率则显著降低。说明缩聚物／加聚物接枝乳液聚合与一般乳液聚合规律有所不同。     

Influence of electrophoresis waveforms in determining stochastic nanoparticle capture rates and detection sensitivity

Electrophoretic capture and release of charged polystyrene particles at the opening of a membrane pore has been investigated to determine the optimal applied current waveform, iapp(t), for ensuring true stochastic counting rates and to improve detection sensitivity (i.e., Delta(counts per second)/Delta(particle concentration)). In capture and release detection, charged particles are electrophoretically driven to the opening of a small pore ( approximately 60 nm diameter) in a membrane; capture of a single particle at the pore opening at time tau is signaled by a decrease in the flux of a redox species (Fe(CN)(6)4-) through the pore. The captured particle is then released by applying an electrophoretic current in the opposite direction, and the process is repeated to acquire sufficient statistical data to determine the solution particle concentration (Cp) based on the relationship between Cp and the average particle counting rate (tauavg(-1)). Both tauavg(-1) and the method sensitivity are shown, for the detection of 90 nm diameter polystyrene particles, to depend strongly on the applied current waveform. The observed dependence is a consequence of the nonequilibrium distribution of particles in the analyte solution that results from electrostatic forces acting on the particle whenever iapp has a nonzero value. Stochastic capture rates corresponding to an initial uniform distribution of particles are more closely achieved using an applied current waveform that includes an equilibration period (iapp=0) prior to electrophoretic capture. An increase in particle detection sensitivity, relative to the previously reported value, results from this equilibration step.     

分散聚合法制备粒径可控的单分散聚苯乙烯微球

以苯乙烯(St)为单体,偶氮二异丁腈(AIBN)为引发剂,聚乙烯吡咯烷酮(PVP)为分散剂,乙醇/水为分散介质,采用分散聚合法制备了聚苯乙烯(PS)微球。研究了单体、引发剂、分散剂的浓度,分散介质中乙醇与水的比例对制备PS微球粒径及粒径分布的影响。采用傅立叶红外光谱(FT-IR)、透射电子显微镜(TEM)、场发射扫描电镜(FE-SEM)、动态光散射(DLS)等手段,对微球的组成成分、表面形貌、粒径及其分布进行了表征。结果表明,在合适条件下,分散聚合法可以制备粒径200～1000nm范围内可控、球形度良好、表面光滑、互不粘连的单分散PS微球。