Supramolecular Crystallization of Monodispersed Silica Spherical Particles (MSSP) in Concentrated Suspensions

The supramolecular crystallization of MSSP concentrated suspensions in alcohol and ethyl ether with various ammonia concentrations is found to occur as a phase transition, with appearence of a pre-transitional state. The temperature dependence of the time, it takes for this state to be established, evidences for the presence of processes of nucleation and activation character.     

Kinetics of supramolecular crystallization of concentrated suspensions of monodisperse spherical silica particles

The kinetics of supramolecular crystallization of concentrated suspensions is three-dimensional and follows the Avrami-Erofeev equation: A=1-exp[-(kt)^m], where m=4. The rate constant k is proportional to the probability of the appearance of a crystallization center in unit volume in unit time and the linear crystal growth rate, which is determined experimentally.     

Synthesis and Characterization of Monodisperse Spherical Zirconia Particles

Monodisperse zirconia spherical particles are prepared by hydrolysis of zirconium propoxide in 2-methoxyethanol in presence of decanoic acid as a shape stabilizer. The powder is analyzed by computer image analysis on TEM micrographs, TG-DSC, FTIR, X-ray diffraction and nitrogen adsorption isotherms. A competition phenomenon between aggregation and individual growth of the particles during precipitation is deduced from the observations.     

由硅溶胶生长单分散颗粒的研究

针对现行单分散二氧化硅颗粒制备方法的粒径预见性差、步骤繁琐、收率低等问题，研究了一种用硅溶胶作为种子，在氨、水和乙醇的混合溶液中通过水解正硅酸乙酯（ＴＥＯＳ）生长出单分散颗粒的简便方法。该方法仅在初始的悬浮液中滴加ＴＥＯＳ即可使种子正常生长，无须补充氨水以修正体系浓度的变化。最终的分散相浓度可达１０％（质量分数）。可选择生长的粒径范围在１微米以内并可精确控制。所得颗粒粒径分布偏差于Ｓｔｏｂｅｒ方法     

由硅溶胶生长单分散颗粒的研究

针对现行单分散二氧化硅颗粒制备方法的粒径预见性差、步骤繁琐、收率低等问题，研究了一种用硅溶胶作为种子，在氨、水和乙醇的混合溶液中通过水解正硅酸乙酯（TEOS）生长出单分散颗粒的简便方法．该方法仅在初始的悬浮液中滴加TEOS即可使种子正常生长，无须补充氨水以修正体系浓度的变化．最终的分散相浓度可达10％（质量分数）．可选择生长的粒径范围在1微米以内并可精确控制．所得颗粒粒径分布偏差优于Stber方法．讨论了种子数密度、生长环境和TEOS滴加速度对生长最终颗粒粒径分布偏差的影响     

Parametric Analysis of Kinetic Models. Xiii. Catalytic Trigger in a Flow System

The thickness of the concentrated layer in the MSSP suspensions, which is sufficient to initiate phase transition into supramolecular crystals, has been experimentally determined and calculated. When the electrostatic repulsion predominates over molecular attraction, the transition occurs only if gravitational forces, which virtually act as molecular attracting forces, are involved.     

Nucleation of Supramolecular Crystals in Suspensions of Monodispersed Spherical Silica Particles During Sedimentation

Growth of supramolecular crystals (SC) was studied during sedimentation in suspensions of monodisperse spherical silica particles (MSSP). The number of growth centers was found to decrease depending on the deionization of the dispersion. The process is accompanied by the corresponding enlargement of the crystals. The volume and surface components of the Gibbs energy of nucleation do not determine the probability of nucleation. The energy of electrostatic repulsion of ions covering structural units (SU), which exceeds the MSSP molecular gravitation, was the only parameter found to correlate with the number of crystallization centers.     

Synthesis of Monodisperse α-Fe2O3 Particles in Short Periods

Asanimportantmaterialusedformagnetic,pigment,catalysis,gas-sensitiveandmedicalimagingapplications,monodispersehematite(a-Fe2O3)particleshaveattractedmoreattentionsinrecentyears1,2.Althoughvariousmorphologica-Fe2O3particleshavebeensynthesizedbyforcedhydrolysisprocess3,4,inwhichthepropertiesofa-Fe2O3particlesvaryconsiderablywithalargenumberofsynthesisparameterssuchaspH,theconcentrationofreactants,thecoexistentanionsetc.,thereisalackofmethodforpreparingmonodispersea-Fe2O3particlesinshortperiod…     

Thixotropic destruction and secondary cluster growth of supramolecular crystals in suspensions of monodisperse spherical silica particles

Supramolecular crystals (SC) which appear in concentrated suspensions of monodisperse spherical silica particles (MSSP) can be mechanically destroyed. This destruction occurs because the bonding of structural units (SU) in SC is weak and the interaction forces of SU become locally unbalanced. The SC are destroyed into microblocks with the initial SC structure. The nascent secondary suspension consists of these blocks (clusters). The secondary crystals grow from the clusters and when these clusters are large, the growth is of a dendritic character.     

Synthesis and Characterization of the Organic Surface Modifications of Monodisperse Colloidal Silica

Monodisperse colloidal silica spheres were prepared from tetraethylorthosilicate in mixtures of water, ammonia and ethanol. The surfaces of the spheres were successfully modified by chemical reaction with silane coupling agents. Several qualitative and quantitative methods were employed to analyse the organic surface modifications. As a result, the surface coverage of silica spheres with silane coupling agents could be calculated using different characterization methods.     

Preparation of Silver Nanoshells on Silica Particles by a Simple Two-step Process

A simple two-step method was developed to prepare silver nanoshells coated on silica paticles. The method involves two steps: concentration of reaction precursor (AgNO3) on particle surfaces and subsequent reduction by formaldehyde. The obtained composite particles were characterized by TEM, ED, and SEM-EDS measurements. The results show that the silver nanoshell is coated on silica particle surface in the form of a polycrystalline (cubic structure) layer with average thickness of 20 nm and weight percentage of 1.9%.     

Mechanism of the growth of monodispersed spherical silica particles to the submicron size

Summary Monodispersed spherical submicron silica particles were obtained by the precipitation of soluble silica on the surface of preliminary obtained smaller particles. Silica was added into the system at low concentrations to prevent both its polymerization in the solution and the formation of new particles. The kinetics of the particle growth is controlled by the diffusion of soluble silica through the double diffusion layer.     

The Effect of Gelatin on the Preparation of Silica Coated Iron Particles

A method is described for coating fine iron particles(～1μm) with a uniform silica layer,produced by the hydrolysis of tetraethyl orthosilicate.The presence of a small amount of gelatin on the surface of the iron particles facilitates this process.The X-ray photoelectron measurements indicated that the gelatin interacted with the surface of the iron particles by means of both nitrogen(in -NH2 groups) and oxygen(in -COOH groups) and then bound to the silica.The silica coating increases the resistance of the iron particles to oxidation on heating in air,which makes the temperature at which an observable oxidization occurs from 330 ℃ to 400 ℃ raised.     

单分散SiO2体系制备中TEOS水解动力学研究

采用一种与他人不同的萃取－冷冻分离－气相色谱法，跟踪形成单分散二氧化硅体系条件下正硅酯乙酯（TEOS）的水解过程，考察了温度（25～45℃）、氨浓度（0．5～0．2mol•L－1）、水浓度（6．0～15．0mol•L－1）等实验条件范围内，以上实验参数对TEOS水解速度的影响；并回归得到目前适用于在乙醇介质中氨催化下，形成单分散二氧化硅微粒常用实验条件范围内，唯一的较完整的水解动力学方程式．     

Spherical Polyolefin Particles from Olefin Polymerization in the Confined Geometry of Porous Hollow Silica Particles

Porous hollow silica particles (HSPs) are presented as new templates to control the product morphology in metallocene‐catalyzed olefin polymerization. By selectively immobilizing catalysts inside the micrometer‐sized porous hollow silica particles, the high hydraulic forces resulting from polymer growth within the confined geometries of the HSPs cause its supporting shell to break up from the inside. As the shape of the support is replicated during olefin polymerization, perfectly spherical product particles with very narrow size distribution can be achieved by using HSPs exhibiting a monomodal size distribution. Furthermore, the size of the obtained product particles can be controlled not only by the polymerization time but also by the size of the support material.

     

Supramolecular crystal growth in concentrated suspensions of charged monodisperse spherical silica particles

Concentrated suspensions of charged monodisperse spherical silica particles (MSSP) stabilized by alkalis or ammonia are able to crystallize at a certain destabilization. Crystal structures with the particles fixed at certain distances from each other show an isotropic normal mechanism of continuous growth with a rough phase boundary. The crystallization is determined by three parameters,víz. the concentration of particles, temperature, the thickness of the ion atmosphere around the particles and the concentration of counterions. The crystallization of MSSP suspensions is considered as a model of the supramolecular crystallization in the field of synthesis of mesoporous structures.     

Mechanism of Reversible Thixotropic Transformation in Concentrated Suspensions of Monodisperse Spherical Silica Particles: Analysis in Terms of Colloidal Crystal Formation and Growth

The mechanism of thixotropic transformation of concentrated suspension of monodisperse spherical silica particles into gel made of blocks with regular structure was considered in terms of colloidal crystal formation and the Alder–Hoover model of phase transition. The kinetics of linear growth of colloidal crystals as structural blocks was experimentally studied. This process was shown to have the activation nature determined by the diffusion of structural units at the interface and can be described in terms of Frenkel's kinetic theory of liquids.     

One‐Pot Fabrication of Supramolecular Polymer Particles via Situ Polymerization Stringed Assembly of a Two‐Monomer Microemulsion

Summary: A novel method, situ polymerization stringed assembly (SPSA), is proposed to prepare stable solid or hollow supramolecular polymer particles, which are assembled by numerous nanoparticles. By this method, the fabrication of primary nanoparticles (poly(methyl methacrylate), PMMA), the linkers (polyvinylpyrrolidone, PVP, chains) between the nanoparticles, and the final assembled solid or hollow particles could be achieved in just one‐pot by methyl methacrylate (MMA)/N‐vinylpyrrolidone (NVP) microemulsion polymerization under UV irradiation. The structures of the supramolecular particles can be changed from solid to hollow by tuning the mass ratio of MMA/NVP in the microemulsion. AFM, TEM, and SEM experiments are performed to identify the results.

AFM image of the PMMA/PVP solid particles obtained from the photopolymerization of the microemulsion containing 20 wt.‐% MMA, 10 wt.‐% NVP, and 5 × 10⁻² wt.‐% BP.     

In Situ Monitoring of the Generation of Monodisperse Silica Particles during the Hydrolysis of Tetraethyl Orthosilicate with Piezoelectric Quartz Crystal Impedance Analyzer

The piezoelectric quartz crystal(PQC)impedance analyzer was used to monitor in situ the generation of monodisperse silica particles during the hydrolysis of tetraethyl orthosilicate (TEOS) and their adsorption onto and Au electrode in alcohol solutions containing water(6-15mol/L)and ammonia(0.2-2.0 mol/L).The equivalent circuit parameters,the resonance frequencies and the half-peak width values of the conductance spectra of the PQC resonance were obtained.The resonant frequency decreased notably while the motional resistance changed very slightly(within 1Ω during the hydrolysis reaction,suggesting that the mass effect dominated the adsorption of generated monodisperse silica particles on the gold electrode in this system.Changes in f0 indicated that the ammonia concentration affected the hydrolytic reaction obviously,and the influence of water concentration on the reaction was small while the water was significantly excessive.Kinetics of monodisperse silica particle adsorption occurring at the electrode i solution interface was analyzed using a first-order reaction scheme.In addition,the electrolyte-induced precipitation of the monodisperse silica of adsorbed particles per area and the converge of monodisperse silica particles were obtained from scanning electron nicroscope(SEM)observations.