Investigation of charging behavior of PS particles in nonpolar solvents

The charging behavior of PS (polystyrene) particles dispersed in nonpolar solvent containing surfactant AOT (sodium di-2-ethylhexylsulfosuccinate) was researched by phase angle light scattering (PALS). The effects of the AOT concentration, the particle concentration and the particle size on the zeta potential of the particles were analyzed systemically. The results showed, at different particle concentrations (expressed in the volume fraction of 10(-5)-10(-3)), that the zeta potential could be adjusted by surfactant AOT over a wide concentration range of 0.001-100 mM. An obvious difference of zeta potential on particle concentration was revealed between the high AOT concentrations (beyond 10 mM) and the low ones (below 1 mM). Meantime, it was found that the relationship of particle size to zeta potential showed a great discrepancy between the dilute particle concentrations (below 10(-4)) and the concentrated ones (beyond 6 × 10(-4)). These findings were consistent with the mechanism of preferential adsorption of the charged micelles in nonpolar solvent.     

Preparation of colloidal Fe3O4 ultrafine particles in microemulsions

The preparation of magnetite particles is reported from the precipitation of Fe²⁺/Fe³⁺ with NH₄OH in several kinds of microemulsions: AOT/n-heptane/water microemulsions and a new non-toxic microemulsion system whose phase behaviour and structure has been recently studied. It is shown that both the droplet size and the presence of interactions in the dispersed phase greatly influence the final size of the obtained particles. In addition, the size of the particles can be increased by successive repetition of the reaction inside the droplets of the microemulsion.     

Pressure anomaly in the paramagnetic region of bcc solid3He

The isochoric pressure of bcc Solid³He in the vicinity of the triple point has been measured by changing the temperature stepwisely and waiting for thermal equilibrium. We observed anomalous pressure kinks of the temperature dependence in the paramagnetic region near the triple point. This anomaly appeared at 0.37 to 0.40 tesla, and disappeared below 0.36 tesla. Moreover, critical phenomena at the transition point from the paramagnetic phase (PP) to the high field phase was observed and the phase line curves toward the PP side.     

The nonlinear influence of an electric field on phase transitions in ferromagnetic semiconductors: Lanthanum manganite

We investigate nonequilibrium processes of self-heating induced by electric current in ferromagnetic semiconductors exhibiting colossal magnetoresistance (CMR) in the vicinity of the Curie temperature. The heat balance equation is solved taking into consideration localized states that appear as a result of scattering from magnetic inhomogeneities and are characterized by a percolation threshold proportional to the amplitude of spin fluctuations. The appearance of N-shaped current-voltage characteristics and hysteresis in the dependence of magnetization on electric potential difference, which are caused by the emergence of a “hot” (with respect to internal temperature) semiconductor paramagnetic phase, is revealed in the steady-state regime. The possibility of suppression of the effect of colossal magnetoresistance with increasing potential difference is indicated. The onset of self-oscillation of current and magnetization with decreasing transverse dimensions of the sample is demonstrated.     

Dependence of the beginning of chain activation of boiling sites on superheating of droplets in the dispersed phase of the emulsion

The features characteristic of boiling of emulsions with a low-boiling dispersed phase are studied. The phenomenon of chain boiling up of droplets of the dispersed phase is considered. The dependence of the moment of emergence of chain activation of boiling sites and the subsequent chain boiling up of droplets of the dispersed phase on the temperature of the surface being heated (cooled) is obtained.     

Selection of microemulsion composition via study of phase behavior for synthesis of stable monodisperse platinum nanoparticles and optimization of experimental parameters

ABSTRACT

Monodisperse platinum nanoparticles were synthesized by microemulsion technique. Feasibility of formation of microemulsion with chosen proportions of components is a common problem with this method. Here, prior to preparation of microemulsion for synthesis purpose, systematic study was carried to check the suitability of selected microemulsion system by establishing phase diagram for ternary system at constant temperature on triangular coordinates. Temperature dependency of microemulsion was studied by preparing phase diagram of temperature against mass fraction of aqueous phase in ternary mixture. Both these triangular coordinate diagram at constant temperature and temperature dependency plots helped to choose proper concentrations of components in the system. Effects of molar concentration of water-to-surfactant ratio, platinum salt concentration, continuous oil phase concentration, and presence of cosurfactant with surfactant on particle size were investigated for selected system of components. Synthesized platinum nanoparticles were characterized by dynamic light scattering and transmission electron microscope. Light backscattering profiles obtained by Turbiscan were used to judge the stability of microemulsions. Further, partial weightage of affecting parameters on size of synthesized particle were studied by Taguchi orthogonal array method.     

Critical Behavior of the Liquid Gas Transition of 4He Confined in a Silica Aerogel

We have studied ⁴He confined in a 95 % porosity silica aerogel in the vicinity of the bulk liquid gas critical point. Both thermodynamic measurements and light scattering experiments were performed to probe the effect of a quenched disorder on the liquid gas transition, in relation with the Random Field Ising Model (RFIM). We find that the hysteresis between condensation and evaporation present at lower temperatures disappears at a temperature T _ch between 25 and 30 mK below the critical point. Slow relaxations are observed for temperatures slightly below T _ch , indicating that some energy barriers, but not all, can be overcome. Above T _ch , no density step is observed along the (reversible) isotherms, showing that the critical behavior of the equilibrium phase transition in presence of disorder, if it exists, is shifted to smaller temperatures, where it cannot be observed due to the impossibility to reach equilibrium. Above T _ch , light scattering exhibits a weak maximum close to the pressure where the isotherm slope is maximal. This behavior can be accounted for by a simple model incorporating the compression of ⁴He close to the silica strands.     

AOT/正丁醇正庚烷/水四元微乳液体系中纳米FeNi3合金制备及表征

考察了室温下AOT，正丁醇，正庚烷，水的四元微乳液体系的相图．在此微乳液体系中制备了Fe-Ni合金的前驱体，于适当的温度下热处理，在400℃形成了物相单一的FeNi3纳米合金．X射线电子衍射，能谱，透射电子显微镜等分析表明，此合金的组成为FeNi3，粒径小于25nm．质量磁化率测定表明，随着磁场强度的增加其质量磁化率增大．     

Large n-Expansion Limit of the Three-Dimensional Ferromagnetic Quantum Phase Transition

We use the large n-expansion method to study the role of the long-range interaction, topological and dissipation effects for the case of an itinerant quantum ferromagnet in the limit of the Landau–Ginzburg–Wilson theory. In the one-loop approximation, we calculate the explicit form of the electronic self-energy as a result of electron–fluctuation interaction and extract the temperature dependence of the scattering time. The temperature dependence of the relative resistivity shows that both the dissipative and topological terms of the action determine the non-Fermi behavior of the system in the critical region around the quantum phase transition.      

短切碳纤维导电复合材料渗流和PTC行为的唯象分析

为研究短切碳纤维含量和温度对导电复合材料渗流行为的影响,通过Landau相变理论导出了复合材料电导率与填料体积分数及温度的方程,并用该方程分析了短切碳纤维/乙烯基酯树脂复合材料的渗流和PTC行为。结果表明:复合材料的渗流阈值随温度升高而增加,PTC温度随碳纤维含量增加而上升。当温度由24.6℃上升到108.4℃时,其渗流阈值的理论值由1.06%增加到1.60%;当碳纤维体积分数由3.1%增加到4.6%时,其PTC温度的理论值由120℃上升到170℃。复合材料渗流阈值和PTC温度理论值与实验值符合得很好。      

A computational analysis of the percolation threshold and the electrical conductivity of carbon nanotubes filled polymeric materials

Percolation of individual single walled carbon nanotubes (SWCNTs) and of SWCNT bundles dispersed in a non-interacting polymeric matrix has been analyzed computationally using an analytical model and a numerical simulation method. While the analytical model used is strictly valid only in the limit of an infinite length-to-diameter aspect ratio of the dispersed phase, good agreement is found between its predictions and the ones obtained using a computationally-intensive numerical method for the aspect ratios as small as 350. Since the aspect ratio of the individual SWCNTs is on the order of 1,000–10,000, this finding suggests that the analytical model can be used to study SWCNT percolation phenomena.An electrical network model is also applied to the percolating and near-percolating SWCNT clusters in order to compute the dc electrical conductivity of a CP2 polyimide + SWCNT composite material. A reasonably good agreement is obtained between the computational and the experimental results with respect to both the magnitude of the electrical conductivity and to its behavior in the vicinity of the percolation threshold.     

微乳液法制备纳米羟基磷灰石的机理

采用二已基琥珀酰磺酸钠(aerosol OT,AOT)作为表面活性剂,正辛醇作为助表面活性剂,异辛烷为油相,将Ca(H2PO4)2·H2O水溶液和Ca(OH)2饱和溶液作为水相制成反相微乳液,并使两种微乳液反应,制备出呈单分散的球形纳米羟基磷灰石颗粒.通过系统性试验绘制了AOT/异辛烷/Ca(H2PO4)2·H2O水溶液和AOT/异辛烷/Ca(OH)2饱和溶液微乳液的局部三元拟相图,确定了该体系的反相微乳液单相区.采用动态激光散射原理分析了上述微乳液的胶束直径,确定了胶束直径与体系含水量的线性关系,并计算了微乳液胶束的有关参数.分析了羟基磷灰石的反应机理和颗粒的形成过程,并采用紫外可见光吸收光谱,研究了体系含水量对羟基磷灰石超细颗粒形成过程的影响.     

Enhancement of the Skin Permeation of Clindamycin Phosphate by Aerosol OT/1-Butanol Microemulsions

Microemulsions of water/isopropyl palmitate (IPP)/Aerosol OT (AOT)/1-butanol were developed as alternative formulations for topical delivery of clindamycin phosphate. Effect of AOT:1-butanol ratios on microemulsion region existence in the pseudoternary phase diagrams was investigated. The 2:1 AOT:1-butanol provided the largest microemulsion region. Five microemulsions of 1% w/w clindamycin phosphate were prepared and characterized. The permeation through human epidermis of the microemulsions was evaluated and compared with the 70% isopropanol solution using modified Franz diffusion cells. The drug permeation from all microemulsions was found to be significantly greater than that from the solution, indicating the enhancement of the skin permeation by the microemulsions. Within the same microemulsion type, the drug permeation increased with increasing the amount of AOT:1-butanol. The drug permeation from oil-in-water (o/w) microemulsions was relatively higher than that from water-in-oil (w/o) microemulsions. In addition, all microemulsions were stable for at least three months at 30 ± 1°C.     

Enhancement of the skin permeation of clindamycin phosphate by Aerosol OT/1-butanol microemulsions

Microemulsions of water/isopropyl palmitate (IPP)/Aerosol OT (AOT)/1-butanol were developed as alternative formulations for topical delivery of clindamycin phosphate. Effect of AOT:1-butanol ratios on microemulsion region existence in the pseudoternary phase diagrams was investigated. The 2:1 AOT:1-butanol provided the largest microemulsion region. Five microemulsions of 1% w/w clindamycin phosphate were prepared and characterized. The permeation through human epidermis of the microemulsions was evaluated and compared with the 70% isopropanol solution using modified Franz diffusion cells. The drug permeation from all microemulsions was found to be significantly greater than that from the solution, indicating the enhancement of the skin permeation by the microemulsions. Within the same microemulsion type, the drug permeation increased with increasing the amount of AOT:1-butanol. The drug permeation from oil-in-water (o/w) microemulsions was relatively higher than that from water-in-oil (w/o) microemulsions. In addition, all microemulsions were stable for at least three months at 30 ± 1°C.     

新型磁性海藻酸钠复合微球的制备与表征

以碳包铁(Fe@C)纳米粉作为磁性内核,用海藻酸钠作表层高分子,以正庚烷为油相,AOT为表面活性剂,氯化钙、环氧氯丙烷作交联剂,通过反相微乳法制备出了碳包铁/海藻酸钠核壳微球,系统考察了海藻酸钠的浓度、交联剂用量等对所制复合纳米微球性质的影响,并对产物进行了初步的性能表征.结果表明,选择合适的海藻酸钠的浓度、交联剂用量和其它相关参数,可以制备出外观为球形、分散性好、平均粒径约为250nm、具有强磁响应性的复合微球.     

Simulation and numerical investigations of the kinetics of atmospheric aerosol droplets in the wake behind a flat plate

Within the framework of the physicomathematical model of evolution of a polydisperse condensate, numerical investigations of the kinetics of atmospheric aerosol droplets in a supersonic two-phase flow past a flat plate were carried out. The gas flow was described by the Reynolds equations with the use of the two-parameter turbulence model. In view of the smallness of the condensate mass fraction in the incoming flow, the inverse effect of the dispersed phase on the gas was not considered. For various regimes of exposure to a flow, the characteristic features of the spatial distribution of the main parameters of the condensate fractions have been studied: the number densities, radii, temperatures, and averaged velocities of microdrops. The dependence of the dispersed phase dynamics on the Mach number and the incoming flow angle of attack has been investigated and the influence of the allowance for the processes of coagulation/fragmentation on the mass spectrum of droplets is shown. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 2, pp. 331–341, March–April, 2009.     

Percolation and the resistive transition of the critical temperature Tc of Nb3Sn

The relationship between the distribution of the critical temperature, the percolation function, and the resistive transition of the critical temperature is explored for polycrystalline Nb₃Sn. In the neighborhood of the critical temperature, Nb₃Sn is assumed to be a random mixture of superconducting and normal grains. Percolation concepts are applied to a study of the resistivity. A general analysis is made showing that the onset and shape of the resistive transition for composite conductors are determined by the percolation function and the distribution of the critical temperature. An approximate form of the percolation function is determined based on a linear FEM analysis. Example resistive transitions are calculated for an assumed normal distribution of the critical temperature. An argument is presented that relates grain orientation and strain dependence in Nb₃Sn. It is noted that a dependence of the distribution of T_c with strain, in addition to the usual shift in T_c with strain, would be the result of a strain dependence that is a function of grain orientation. The analysis shows the extent to which the slope of the resistive transition is a measure of the distribution of the critical temperature, and therefore a measure of the grain orientation strain sensitivity. Finally, a method is described to determine the percolation function experimentally.     

Percolative behavior of transient photoconductivity in metal-free phthalocyanine nanocrystals

Transient photoconductivity in metal-free phthalocyanine (H₂Pc) nanocrystals dispersed in a polyester matrix is investigated. The H₂Pc nanocrystals concentration dependence of transient photoconductivity is examined above the percolation threshold at different temperatures. It is found that the disorder parameter is independent of temperature and increases with concentration of H₂Pc nanocrystals. These findings can successfully be explained by percolative behavior of photocarriers on geometric fractals.     

石墨热压还原Cu/Cu_(2)O金属陶瓷电导逾渗行为与微观结构分形表征EI北大核心CSCD

采用石墨热压还原法制备Cu/Cu_(2)O金属陶瓷复合材料,并测试不同导通相(Cu)体积含量Cu/Cu_(2)O金属陶瓷复合材料的直流电导率。为了实现对导通相形状、大小和分布状态的定量表征,通过对复合材料微观结构图像的二值化处理进行导通相分形维数计算,结合Cu/Cu_(2)O金属陶瓷复合材料的电逾渗行为,分析复合材料微观结构与电性能之间的对应关系。结果表明:随着导通相体积分数的增加,逾渗无限团簇和逾渗骨架的总量随之增大,但逾渗骨架密度在逾渗阈值附近波动。此外,Cu/Cu_(2)O金属陶瓷复合材料垂直热压方向与平行热压方向的分形维数相差约0.1。分形计算为定量表征导体/绝缘体双相复合材料中导通相的微观结构提供了一种计算方法,有助于对第二相随机分布的复合材料实现微观结构定量表征。     

Interpretation of T(m) and T* in relaxor ferroelectric 0.93Pb(Zn₁/₃Nb₂/₃)O₃-0.07PbTiO₃

The dielectric property of relaxor ferroelectric 0.93Pb(Zn?/?Nb?/?)O?-0.07PbTiO? single crystals (PZN-0.07PT) is studied to investigate the ferroelectric phase transition. The temperature dependence of the susceptibility of the central peak in the light scattering shows a very similar behavior to the real part of the dielectric constant, indicating that the diffuse peak in the temperature dependence of the dielectric constant is induced by relaxation of the polarization. We suggest that the origin of the relaxation above T(m) is the non-180° polarization flipping of a small polar nanoregion (PNR). Additionally, the behavior of the PNRs is interpreted through both the Brillouin spectra and high-energy synchrotron-radiation powder diffraction patterns. Our results reveal that T*~ 499K is the temperature below which the growth rate of the dynamic polarization fluctuation is suppressed by the additional random electric field induced by the generation of the static PNRs.