室温交联型硅丙微胶乳的合成研究Ⅱ.改性微胶乳的粒径控制及其微观形态表征

采用种子微乳液聚合法和单体预乳化法分别合成了室温交联型有机硅改性聚丙烯酸酯微胶乳，研究了硅烷单体的添加和氧化反应对改性微胶乳粒子大小及分布的影响．结果表明：采用种子微乳液聚合法得到的硅丙微胶乳粒子大小与硅烷单体的种类．用量和添加顺序无关，平均粒径约为40-60nm．TEM照片显示出，采用种子微乳液聚合法合成的硅丙微胶乳舡子由于内部存在交联结构而导致表面形状不规则，有“乳突”现象；而采用预乳化法合成的硅丙微胶乳粒径粗大，呈规则的球形，氧化后柱径从100nm以上减小到80nm左右，粒子表面出现“绒毛”现象，这是由于硅烷组分的水解反应受到抑制而使粒子内部的交联密度降低的缘故．     

范德华作用和静电作用下的二元粒子自组装

采用简单粗粒化粒子模型,通过郎之万动力学模拟研究了具有范德华作用和静电作用的二元粒子自组装．研究发现,通过改变粒子尺寸和粒子间作用强度,二元粒子能够自发形成各种聚集结构,如球形、堆叠层状与管状结构．利用两亲性分子或两嵌段聚合物自组装理论,解释了二元粒子聚集结构的形成规律．当向溶液中加入反电荷离子时,模拟表明粒了聚集结构在相图中的分布出现了明显偏移．     

无皂乳液聚合制备高浓度单分散聚(苯乙烯-甲基丙烯酸甲酯)胶体粒子

通过添加聚乙烯醇和丙酮，找到了一种无皂乳液聚合制备高浓度单分散苯乙烯－甲基丙烯酸甲酯共聚胶体粒子的新途径，粒子半径达纳米数量级，体系的固含量大于50％，研究了聚乙烯醇和丙酮对反应过程，胶乳粒子大小的影响，结果表明聚乙烯醇和丙酮对高浓度无皂纳米胶乳粒子的形成与稳定起重要作用。     

球形尖晶石型钴铁氧体:合成方法及其影响因素

实现了在低温、常压条件下由含铁水滑石微晶到球形尖晶石型铁氧体的合成。结果表明,所合成的铁氧体系平均粒径为1.0μm的规整球。进一步研究发现,铁氧体微球的成型过程受到很多因素影响,例如,球型铁氧体磁性粒子的大小随着晶化过程中溶液的酸碱度的升高而变大;同时外加磁场的存在不但会使球型铁氧体磁性粒子的粒径变大,而且也会使晶化产物的粒子形貌更加趋于规整。另外,还对不同组成的尖晶石型铁氧体微球的形成进行横向比较时发现,合成初期的化合物投料组成对终产物形貌的影响是巨大的,随着投料组成中Fe2+含量的增加,转化过程变得容易,且在投料金属离子组成nCo2+∶nFe2+∶nFe3+为1∶1∶1时,所得的球型铁氧体磁性粒子的粒径最大。相同条件下不同组成的铁氧体微球粒径差异明显,MgFe2O4不能形成球形颗粒,NiFe2O4和CoFe2O4可以形成球形颗粒,其中CoFe2O4形成的颗粒粒径最大。     

激光光散射表征寡链聚苯乙烯微胶乳粒子的方法

本文阐述了利用激光光散射表征寡链（ｐａｕｃｉ－ｃｈａｉｎ）聚苯乙烯微胶乳的方法。在静态光散射中，可测得微胶乳粒子的重均摩尔质量，结合粒子内所含高分子链的重均分子量，进而计算出每个微胶乳粒子内高分子链的平均数目；在动态光散射中，通过对时间相关光谱的拉普拉斯反演求出粒子的平动扩散系数分布Ｇ（Ｄ），进而得到流体力学半径（Ｒｈ）及分子量的分布。通过综合分析静态与动态光散射的结果，建立了计算球形粒子密度的光散射方法，并发现，寡链聚苯乙烯微胶乳的密度低于通常的胶乳粒子以及本体聚苯乙烯的密度     

计算离子液体溶液汽液相平衡的分子热力学模型

用平均球近似理论、微扰理论和UNIFAC基团贡献方法分别考虑离子之间的长程静电作用、离子与溶剂之间的中程静电作用以及所有粒子之间的短程作用,本文提出了一种新的分子热力学模型,可用于离子液体溶液中溶剂活度系数的计算.通过对含烷基咪唑磷酸酯类离子液体与水、甲醇或乙醇组成的9个二元体系的饱和蒸汽压数据进行关联,获得了相关的模型参数,即溶剂的分子直径和基团之间的交互作用能参数.溶剂活度系数及饱和蒸汽压的计算结果与实验值的平均偏差为1.40%,符合良好,因此本模型可望用于含离子液体体系汽液相平衡的预测.     

应用电子显微镜测定丁苯吡胶乳和丁苯胶乳中胶乳粒子的平均粒径及粒径分布

丁苯吡胶乳和丁苯胶乳粒子的直径一般在1000(?)以下,这样微小的粒子,只有用电子显微镜才能看清它的形态和外貌。我们用电子显微镜观察丁苯吡胶乳及丁苯胶乳中的胶乳粒子,测定了胶乳粒子的平均粒径及粒径分布,为改进工艺、提高质量提供了资料。实验方法简介如下:     

尺寸可控的球型DNA纳米颗粒构筑策略及其应用

为探究球型DNA纳米颗粒的尺寸对细胞摄取的影响，提出了一种新型构筑策略，制备了一系列尺寸精准可控的球型DNA纳米颗粒，并进一步揭示了球型DNA纳米颗粒的尺寸与MCF-7细胞内化效率的关系；此外，该策略还可以与框架诱导策略相结合，构筑尺寸可控的磷脂囊泡.该结果为构建新型高效的DNA纳米颗粒载药系统提供了理论参考，为特定尺寸的药物载体设计和开发拓展了思路.     

Fe3O4@SiO2@YF3:Eu3+磁-光双功能复合粒子的制备与性能

采用水热法合成了Fe3O4@SiO2@YF3:Eu3+磁-光双功能复合粒子,对其结构和性能进行了表征.XRD分析表明:Fe3O4表面包覆上了结晶良好的正交晶系的YF3.TEM照片表明:复合粒子为球形,构成核的Fe3O4颗粒的尺寸在200～350 nm之间,Fe3O4@SiO2@YF3:Eu3+核壳结构复合粒子的尺寸约为230～380 nm,与包覆前的Fe3O4相比较,包覆后,颗粒尺寸增大,并且YF3:Eu3+是以棒状结构连接在Fe3O4球型颗粒的表面.磁性和荧光光谱分析表明:该复合颗粒同时具有良好的发光性和磁性,使其在生物医学领域具有潜在的应用.     

Fe3O4@SiO2@YF3∶Eu3+磁-光双功能复合粒子的制备与性能

采用水热法合成了Fe3O4@SiO2@YF3∶Eu3+磁-光双功能复合粒子,对其结构和性能进行了表征。XRD分析表明:Fe3O4表面包覆上了结晶良好的正交晶系的YF3。TEM照片表明:复合粒子为球形,构成核的Fe3O4颗粒的尺寸在200～350 nm之间,Fe3O4@SiO2@YF3∶Eu3+核壳结构复合粒子的尺寸约为230～380 nm,与包覆前的Fe3O4相比较,包覆后,颗粒尺寸增大,并且YF3∶Eu3+是以棒状结构连接在Fe3O4球型颗粒的表面。磁性和荧光光谱分析表明:该复合颗粒同时具有良好的发光性和磁性,使其在生物医学领域具有潜在的应用。     

SANS and SAXS analysis of charged nanoparticle adsorption at oil-water interfaces

A systematic study of the adsorption of charged nanoparticles at dispersed oil-in-water emulsion interfaces is presented. The interaction potentials for negatively charged hexadecane droplets with anionic polystyrene latex particles or cationic gold particles are calculated using DLVO theory. Calculations demonstrate that increased ionic strength decreases the decay length of the electrostatic repulsion leading to enhanced particle adsorption. For the case of anionic PS latex particles, the energy barrier for particle adsorption is also reduced when the surface charge is neutralized through changes in pH. Complementary small-angle scattering experiments show that the highest particle adsorption for PS latex occurs at moderate ionic strength and low pH. For cationic gold particles, simple DLVO calculations also explain scattering results showing that the highest particle adsorption occurs at neutral pH due to the electrostatic attraction between oppositely charged surfaces. This work demonstrates that surface charges of particles and oil droplets are critical parameters to consider when engineering particle-stabilized emulsions.     

A modeling approach to describe the adhesion of rough, asymmetric particles to surfaces

A combined theoretical and experimental study of the adhesion of alumina particles and polystyrene latex spheres to silicon dioxide surfaces was performed. A boundary element technique was used to model electrostatic interactions between micron-scale particles and planar surfaces when the particles and surfaces were in contact. This method allows quantitative evaluation of the effects of particle geometry and surface roughness on the electrostatic interaction. The electrostatic interactions are combined with a previously developed model for van der Waals forces in particle adhesion. The combined model accounts for the effects of particle and substrate geometry, surface roughness and asperity deformation on the adhesion force. Predictions from the combined model are compared with experimental measurements made with an atomic force microscope. Measurements are made in aqueous solutions of varying ionic strength and solution pH. While van der Waals forces are generally dominant when particles are in contact with surfaces, results obtained here indicate that electrostatic interactions contribute to the overall adhesion force in certain cases. Specifically, alumina particles with complex geometries were found to adhere to surfaces due to both electrostatic and van der Waals interactions, while polystyrene latex spheres were not affected by electrostatic forces when in contact with various surfaces.     

Brownian Dynamics Simulation of Film Formation of Mixed Polymer Latex in the Water Evaporation Stage

Brownian dynamics simulations of the filming process of a mixed polymer latex in the water evaporation stage were performed in order to explore the effect of surface potential on latex particle packing and distribution at a temperature far below the glass transitions of polymers in bulk. Polymer latex particles are modeled as spheres that interact via DLVO potential with various surface charge densities for emulsifier-free emulsion polymerized particles and dispersion polymerized particles. It is found that the distribution of modeled poly(methyl methacrylate) and polystyrene latex particles in the finally formed film exhibits a noticeable dependence of surface potentials of latex particles. When the difference of the surface potentials between binary mixed latex particles is small, the particles distribute randomly. In contrast, when the difference of the surface potentials between binary mixed latex particles is large, heterocoagulation occurs and the polymer latex in which the repulsive electrostatic potential is weak will form clusters in the film. The results are in agreement with laser confocal fluorescence microscopy observations of fluorescent dye labeled poly(methyl methacrylate) and polystyrene mixed latex films. The correlation between latex particles increases with increasing repulsive electrostatic potential, and the spatial order can be obtained at the end of the water evaporation stage. Copyright 2000 Academic Press.     

Electrostatic double-layer interaction between spherical particles inside a rough capillary

Predictions of electrostatic double-layer interaction forces between two similarly charged spherical colloidal particles inside an infinitely long "rough" capillary are presented. A simple model of a rough cylindrical surface is proposed, which assumes the capillary wall to be a periodic function of axial position. The periodic roughness of the wall is characterized by the wavelength and amplitude of the undulations. The electrostatic double-layer interaction force between two spherical particles located axially inside this rough capillary is determined by solving the nonlinear Poisson-Boltzmann equation employing finite element analysis. The effect of surface roughness of the cylindrical enclosure on the interaction force between two particles is extensively studied on the basis of this model. The simulations are carried out for dimensionless amplitudes (amplitude/particle radii) ranging from 0.05 to 0.15 and scaled wavelengths (wavelength/particle radii) ranging from 0.4 to 4.0. The interaction force between the particles is significantly modified by the proximity of the rough capillary wall. Generally, the interaction force for rough capillaries oscillates around the corresponding interaction force in a smooth capillary depending on the magnitudes of the scaled amplitude and wavelength of the roughness. The influence of roughness on the electrostatic interactions becomes more pronounced when the surface potential of the cylinder wall is different from the sphere surface potentials. When the cylinder and the particle surfaces have large potential differences, the axial force experienced by a particle is dominated by the capillary roughness. There are dramatic oscillations of the force, which alternately becomes repulsive and attractive as the particle moves from the crest to the trough of the rough capillary wall. These results suggest that manipulation of colloidal particles in narrow microchannels may be subject to significant force variations owing to the roughness inherent in microfabricated channels etched on metal films.     

The influence of stabilizing agents on the interaction between styrene/butadiene latex and calcium carbonate: a calorimetric and a dynamic electrokinetic study

The role of stabilizing agents in the interaction between styrene/butadiene latex and calcium carbonate particles has been studied using isothermal titration calorimetry (ITC) and an electrokinetic sonic amplitude (ESA) technique. It is demonstrated that the polyacrylate sodium salt (dispersing agent, referred to as NaPA) used as stabilizing agent for the calcium carbonate suspensions principally affects the interfacial properties of the calcite surface. An electrostatic barrier is created and this decreases the attractive interactions between the latex and the negatively charged mineral surface. The total enthalpy change observed when an emulsion of styrene/butadiene particles substantially free from surfactant was added to the dispersed calcium carbonate could be described via a relatively complex path. The process included (i) an exothermic response from the association of the latex particles (adsorption process) with the dispersed calcium carbonate surface and (ii) an endothermic bulk phase effect due to the adsorption on the latex particles of dissolved species originating from the calcium carbonate. Stabilization of the latex particles with sodium dodecyl benzene sulfonate (SDBS) or a non-ionic fatty alcohol ethoxylate surfactant did not significantly change the enthalpy of interaction. It was further demonstrated that SDBS had a very weak affinity for the dispersed calcium carbonate particles and that dissolution of species, such as calcium ions, from the calcium carbonate surface, allows further adsorption of SDBS onto the latex particles.     

Electrostatic interactions between amphoteric latex particles and proteins

The electrostatic interactions between amphoteric polymethyl methacrylate latex particles and proteins with different pI values were investigated. These latex particles possess a net positive charge at low pH, but they become negatively charged at high pH. The nature and degree of interactions between these polymer particles and proteins are primarily controlled by the electrostatic characteristics of the particles and proteins under the experimental conditions. The self-promoting adsorption process from the charge neutralization of latex particles by the proteins, which have the opposite net charge to that of the particles, leads to a rapid reduction in the zeta potential of the particles (in other words colloidal stability), and so strong flocculation occurs. On the other hand, the electrostatic repulsion forces between similarly charged latex particles and the proteins retard the adsorption of protein molecules onto the surfaces of the particles. Therefore, latex particles exhibit excellent colloidal stability over a wide range of protein concentrations. A transition from net negative charge to net positive charge, and vice versa (charge reversal), was observed when the particle surface charge density was not high enough to be predominant in the protein adsorption process.     

Stability in Colloidal Mixtures Containing Particles with a Large Disparity in Size

An experimental approach, based on turbidity measurements, is proposed for studies of the stability in colloidal mixtures containing particles with large disparity in size. The main advantage of this approach is that it permits investigations even under conditions of comparable particle number concentrations of the two colloidal populations. Binary mixtures containing a poly(vinyl acetate) (PVAc) latex and a Ludox AS-40 silica sol were investigated. The silica particles were much smaller than the latex ones. The experimental stability factors were compared with the theoretical values computed on the basis of the Kihira-Ryde-Matijevic model (J. Chem. Soc., Faraday Trans. 88(16), 2379 (1992)) for interaction between spherical particles with unevenly distributed surface charges. All the experimental results support the idea that, even when both sols are negatively charged, the small silica particles are adsorbed onto the latex surface. Under these conditions, the heteroaggregates, which are composed of PVAc cores surrounded with silica particles, can be modeled as PVAc particles having "modified" surface characteristics (i.e., average Stern potential and varying extents of the surface charge segregation). Copyright 2001 Academic Press.     

Interaction between poly(styrene-acrylic acid) latex nanoparticles and zinc oxide surfaces

Latex particles with an average diameter of 70 nm, functionalized at the surface with carboxylic groups, are chemically coated by layer-by-layer deposition onto a spherical probe attached on an atomic force microscope cantilever. The forces between poly(styrene-acrylic acid) latex nanoparticles and differently terminated zinc oxide surfaces are studied by a homemade atomic force microscope based apparatus. The results confirmed a preferred adhesion of the latex particles to zinc-terminated ZnO faces, 0001, compared to oxygen-terminated and apolar faces. The method proposed allows the measurement of the interaction between nanometric particles and planar surfaces, which may be of interest for different applications in surface and colloid sciences.     

Synthesis and characterization of amphoteric latex particles

Stable monodisperse amphoteric latex particles were prepared by the semibatch surfactant-free emulsion copolymerization of methyl methacrylate and methacrylic acid (MAA) initiated by 2,2'-azobis(2-amidinopropane) dihydrochloride (V-50). These submicron particles have a net positive charge, which is attributed to the ionized amino group at low pH. In contrast, they become negatively charged owing to the ionized carboxyl group at high pH. There exists a pH at which these particles exhibit a net charge of zero (pI). At a constant level of V-50, the pI value of these latices decreases with increasing amount of MAA used in the polymerization recipe. The effect of pH on the colloidal stability of these amphoteric latices toward the addition of the negatively charged latex was investigated. The resultant coagulation kinetics was used to study the electrostatic interaction between the amphoteric particles and negatively charged particles.     

Interactions between dextran-modified poly(methyl methacrylate) latex particles and concanavalin A

The electrostatic and affinity interactions between concanavalin A (Con A) and dextran-modified latex particles were investigated. The ratio of the initial number of dextran active sites to that of Con A molecules plays an important role in determining the structure of flocs formed during adsorption and, thereby, has an influence on the amount of adsorbed Con A and the subsequent elution yield. NaCl and d-glucose, used successively in the two-step desorption of Con A, were employed to study the relative importance of electrostatic and affinity interactions involved in the Con A adsorption process. A significant fraction of adsorbed Con A is attributed to the electrostatic interaction mechanism. The feasibility of using the dextran-modified latex products to purify Con A from Jack bean meal was demonstrated. Received: 22 February 2000 Accepted: 19 September 2000