DISPERSION AND NUCLEATION FOR ULTRAFINE PARTICLES OF SILICA AND SILICATE IN POLY（ETHYLENE TEREPHTHALATE） BASED COMPOSITES

In this paper,the dispersion and nucleation behavior of ultrafine particles of silica and layered silicate (LS) in poly(ethylene terephthalate) (PET) matrix are investigated and characterized by Transmission Electron Microscopy (TEM),Wide Angle X-ray Diffraction (WAXD),Dynamic Scanning Calorimetry (DSC),and Atomic Force Microscopy (AFM).The solid precursors based on silica and LS are suggested originally for preparing nanocomposites with good dispersion morphology.Results show that the initial sub-micron (1000-500nm) LS particles are exfoliated or dispersed into nanometer-scale particles (30-70nm) during their polymerization with PET monomers.These dispersed nanoparticles form an ordered morphology in their nucleation and growth during annealing nanocomposites.DSC patterns reveal that the double melting peaks of annealed PET-LS nanocomposites disappear,while they have shrunken in PET-silica ones.These findings strongly demonstrate that the dispersed nanoparticles accelerate the crystallization of PET.The dispersed LS particles have higher percolation and nucleation performance than those of silica.The homogeneous distribution morphology of ultrafine particles is easily obtained by controlling the load of their corresponding precursors.Such a dispersion obviously improves PET properties in that its heat distortion temperature (HDT)increases from 76℃ to 103℃, and crystallization increases 2-4 times more than that of PET.Especially,the nanocomposite films keep themselves transparent when particle load is within 2 wt.% though there are 3 wt.% or so of agglomerated particles in the nanocomposites.     

Effects of polyethyleneimine-functionalized MCM-41 on flame retardancy and thermal stability of polyvinyl alcohol

Hyperbranched polyethylenimine (PEI)-functionalized mesoporous silica (MCM@PEI) was synthesized and used to produce poly(vinyl alcohol) (PVA) nanocomposites. The modified nanofiller was characterized with infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N₂ adsorption. When compared with pure mesoporous silica (MCM), the MCM@PEI nanoparticles exhibited better dispersion in the PVA matrix. The effects of MCM@PEI on the thermal and flame properties of PVA nanocomposites were also studied. Improvement in the thermal properties was confirmed by enhanced thermal stability and char yield. Incorporation of MCM@PEI in PVA led to a significant drop in the heat release rate and the total heat release.     

Coalescence suppression in model immiscible polymer blends by nano-sized colloidal particles

The effect of nanometer sized silica particles (R16 nm) on the flow-induced morphology of immiscible polymer blends is studied. Polydimethylsiloxane (PDMS) and polyisobutylene (PIB) are chosen as model components. A stable droplet/matrix microstructure is obtained for blends of 30% PIB in 70% PDMS or vice versa. Rheological measurements are used to show that the silica particles alter the sensitivity of the of dispersed phase/matrix microstructure to shear flow. Coalescence is suppressed or at least slowed down on a practical time scale, especially when PDMS is the matrix phase. The effect of mixing conditions, pre-shear rate and particle concentration on the blend morphology are studied. Cryo-SEM is used to observe the accumulation of the particles at the interface. Blends stabilized by solid particles could provide an interesting alternative to blends compatibilized by block-copolymers.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.     

The structure of colloidal polyethylenimine–silica nanocomposite microparticles

Deposition of silica from an organosilane tetraethoxysilane (TEOS) onto parent polyethylenimine (PEI) microgel particles produces a novel PEI–silica nanocomposite, which possesses greater adsorption capacity for copper ions than either parent material. This study explores factors governing interactions of silica with the PEI matrix, along with structural features of resulting PEI–silica composite particles, to explain their properties and determine their application potential. The influence of initial TEOS/PEI mass ratio and the duration of silica deposition on the final silica content and distribution in the composite are studied. A comparative analysis of the structural architecture of chemically etched silica remnants, original PEI–silica composite particles and the parent PEI-microgel is carried out using X-ray photoelectron spectroscopy, small-angle X-ray scattering, and electron microscopy techniques. It is found that silica sol nanoparticles are evenly distributed throughout the PEI-microgel framework and interlinked with it via electrostatic interactions, enabling a structural model of the PEI–silica nanocomposite to be proposed. The chemical stability of resulting nanocomposite particles in parallel with the parent PEI-microgel is tested and shown to be robust for more than 100 days of storage in aqueous dispersions across a range of pH conditions, highlighting the application potential for these particles in copper capture.     

Design of new HDPE/silica nanocomposite and its enhanced melt strength

Linear polymers are restricted to use in processes that involve severe extensional deformation, such as fiber spinning, film blowing, and thermoforming. To extend their applicability, the extensional properties of polymer melts should be enhanced such that strain hardening, which is defined as an increase in extensional viscosity under a large strain that deviates from the linear viscoelastic curve, is pronounced. In this study, a novel preparation method of linear polymer/inorganic nanocomposites was proposed with a main focus on enhanced melt strength. The design of molecular structure consists of three components—linear polymer, compatibilizer, and surface-modified particles. High-density polyethylene was used as a linear polymer while polyethylene grafted with maleic anhydride was used as a compatibilizer. Silica particles were synthesized and modified on their surfaces by 3-aminopropyltriethoxysilane. The strain hardening behavior of the surface-modified silica composites was pronounced. However, such a result was not observed for the composites of the same composition with pure-silica. In addition, the dispersion of the modified silica was much better than that of pure-silica.     

POROUS SILICA NANO-TUBE AS HOST FOR ENZYME IMMOBILIZATION

With their hollow morphology and large openings, the as-synthesized porous silica nano-tubes (NTPS), prepared through a sol-gel routine by using nano-sized needle-shaped CaCO3 particles as templates, were used as host for enzyme immobilization. Bioimmobilization study showed that enzyme molecules could not only be adsorbed on the external surface of NTPS but also entrapped in their inner hollow cores, leading to higher enzyme loading capacities of NTPS (more than 350 mg/g silica) in a shorter time, as compared to common porous silica (less than 50 mg/g) and most conventional mesoporous silica materials (less than 100 mg/g).     

PREPARATION AND MICROSTRUCTURE CHARACTERIZATION OF Ni／TiO2 NANOCOMPOSITE

Homogeneous Ni^2 -doped titania gel was synthesized by a sol-gel process,and the xerogel was then obtained through aging and drying,leading to the formation of Ni/TiO2 nanocomposite after heat treatment under a suitable reducing atmosphere.The resulting nanocomposite was characterized by TGA-DSC,TEM,XRD and BET methods.The results show that the structure and grain size of the nanocomposites could be manipulated by altering the heat-treatment conditions,and that the nanocomposite possesses a mesoporous structure with a pore radius of ca.28nm and a specific surface area of 49.1 m^2.g^-1.It is demonstrated that the nanosized Ni dispersion in the titania matrix significantly affects the anatase-rutile phase transformation.     

SYNTHESIS AND COATING OF ORDERED MESOPOROUS SILICA

1,3,5-trimethyl benzene (TMB) was used as organic swelling agent in O/W emulsions to template ultra-large mesoporous materials using the hydrothermal method. The silicas with well-defined mesopores and hydrothermally robust framework were characterized by X-ray diffraction, transmission electron microscopy and BET surface area analysis. The influence of the quantity of TMB during preparation was studied. It has been found that the TMB/CTAB ratio must be controlled for producing high pore volume materials. Polysulfone (PSU), as the usual extraction agent, was coated on the silicas with the solvent evaporation method to produce a solid separation medium. The adsorptivity and the surface area of the coated MCM were determined: 10% PSU coated MCM adsorbed twice as much phenol as the uncoated material, reaching 0.5 mg/g silica. It was found that the surface area of the coated material decreased rapidly with an increase of the PSU Ioadina.     

非均匀微极介质的有效性质分析

首先讨论了不同尺度关系下宏细观过渡方法,然后重点介绍了尺度关系满足L>>l>>A ≈lm时(适用于金属基复合材料,泡沫基复合材料和纳米复合材料等),构元材料看作微极介质,而均质化后的材料仍可看作传统Cauchy介质时的解析弹塑性细观力学方法.在这样的理论框架下,细观结构的尺度影响可作为变量引入细观力学模型,并且当A>>lm 时,该方法自然退化成传统的细观力学方法.      

Modification of silica with PMMA via ultrasonic irradiation and its application for reinforcement of polyacrylates

Polymethyl methacrylate （PMMA） encapsulated silica nanocomposite particles were prepared by ultra- sonically induced in situ polymerization of methyl methacrylate （MMA） on the surface of silica sol. The nanoparticles were characterized by Fourier transform infrared spectroscopy （FFIR）, transmission electron microscopy （TEM）, thermogravimetry （TG）, scanning electron microscopy （SEM）. The results showed that core-shell structure nanocomposite particles with an average size of 36 nm were obtained, and the thickness of polymer encapsulating layer was about 8 nm. The pretreatment of silica sol with tert-butyl hydroperoxide （TBHP） and the addition of ~-methacryloxypropyl trimethoxysilane （MAPTS） significantly enhanced the encapsulation effect. Modified by the polymer layer, the silica particles could be well dispersed in matrices and utilized to improve the mechanical performance of polyacrylates.     

Micromechanics-based modelling of stiffness and yield stress for silica/polymer nanocomposites

Establishing structure–property relationships for nanoparticle/polymer composites is a fundamental task for a reliable design of such new systems. A micromechanical analytical model is proposed in the present work, in order to address the problem of stiffness and yield stress prediction in the case of nanocomposites consisting of silica nanoparticles embedded in a polymer matrix. It takes into account an interphase corresponding to a perturbed region of the polymer matrix around the nanoparticles. Its modulus is continuously graded from that of the silica nanoparticle to that of the polymer matrix. Considering the thickness of the third phase as a characteristic length scale, the influence of particle size on the overall nanocomposite behaviour is examined. The key role of the interphase on both the overall stiffness and yield stress is studied and the model output is compared to experimental data of various silica spherical nanoparticle/polymer composites extracted from the literature. The model is also used to examine the influence of interphase features on the overall nanocomposite behaviour. A finite element analysis is then achieved and the numerical results are validated using the analytical predictions. Local stress and strain distributions are analysed in order to understand the phenomena occurring at the nano-scale.     

Preparation and functionalization of mesoporous silica spheres as packing materials for HPLC

This paper presents the integrated results of a series of new methods for preparing mesoporous silica spheres as high-performance liquid chromatography (HPLC) packing materials. The separation performance of the mesoporous spheres materials has also been determined. Micrometersized silica spheres with uniform spherical morphologies and ordered mesostructures were first successfully synthesized by the method employing a water-soluble polymer-assisted assembly. Then the templates for getting ordered mesoporous materials with high-density silanol groups were removed by using hydrothermal oxidation. Finally the silica spheres were functionalized with C8 alkyl groups by surface modification under hydrothermal conditions. The resultant functionalized silica spheres were demonstrated to be excellent packing materials for HPLC.     

Preparation and functionalization of mesoporous silica spheres as packing materials for HPLC

This paper presents the integrated results of a series of new methods for preparing mesoporous silica spheres as high-performance liquid chromatography （HPLC） packing materials. The separation performance of the mesoporous spheres materials has also been determined. Micrometer- sized silica spheres with uniform spherical morphologies and ordered mesostructures were first successfully synthesized by the method employing a water-soluble polymer-assisted assembly. Then the templates for getting ordered mesoporous materials with high-density silanol groups were removed by using hydrothermal oxidation. Finally the silica spheres were functionalized with C8 alkyl groups by surface modification under hydrothermal conditions. The resultant functionalized silica spheres were demonstrated to be excellent oacking materials for HPLC.     

纳米颗粒改性环氧树脂的力学性能与断裂机理

采用高度分散的纳米二氧化硅颗粒增韧/增强高性能环氧树脂.研究结果表明,高性能环氧树脂的力学性能随着纳米颗粒的添加能够得到明显的改善;填充14wt％的纳米二氧化硅时,复合材料的弹性模量、拉伸强度和断裂韧性分别提高了21％、17％和49％.断面观察分析发现,纳米颗粒的存在会导致环氧树脂基体发生塑性变形,如剪切带和空穴增长,...     

PREPARATION AND CHARACTERIZATION OF SUPERPARAMAGNETIC FUNCTIONAL POLYMERIC MICROPARTICLES

Superparamagnetic poly(styrene-divinylbenzene-glycidyl methacrylate) (Pst-DVB-GMA) microparticles were prepared via a modified suspension polymerization process. A magnetic fluid was first prepared by a chemical co-precipitation method. Then magnetic microparticles were produced by mixing the monomers and the magnetic fluid with water in the presence of a stabilizer poly(vinyl pyrrolidone) (PVP) to form a suspension, and finally benzoyl peroxide was added to initiate the co-polymerization. The morphology and magnetic properties of the microparticles were examined by TEM and VSM. The spherically shaped microparticles, with a size range of 4 to 7 pm, showed distinct superparamagnetic characteristics. XRD was used to investigate the structure of the magnetite particles dispersed in the polymer matrix. The microparticles with epoxy groups on their surface can be applied directly to the seoaration of biomolecules.     

Homogeneous nanoparticle dispersion prepared with impurity-free dispersant by the ball mill technique

The homogeneous dispersion of nanoparticles in solvents or polymer matrices is essential for practical application of nanocomposites. In this study, the planetary ball milling technique was used to de-agglomerate silica nanoparticles in butyl acetate. The size of the nanosilica aggregates was evaluated by TEM and SEM. With the addition of polyacrylate polymer to the organic solvent, the nanoparticle agglomerates were effectively broken up by planetary ball milling at the proper milling time; however, re-agglomeration occurred after a longer milling time. The results of TGA and FTIR indicated that the polyacrylate molecules could be adsorbed in situ onto the nanoparticles. Behaving similar to a dispersant, the adsorbed polyacrylate reduced the blend viscosity significantly and prevented re-agglomeration of the nanoparticles. Utilizing the polyacrylate polymer both as the dispersant and the polymer matrix, the polyacrylate-based nanocoatings were further prepared. The optical transmittance and haze value of the nanocoatings were found to be sensitive to the dispersion level of the nanoparticles, and the elastic modulus and hardness of the nanocoatings were improved in comparison with those of the neat polymer coating.     

Influence of suspension stability on wet grinding for production of mineral nanoparticles

Grinding behavior of nanoparticles in an attritor mill and the minimum achievable particle size are strongly influenced by the suspension stability. In the present work, suspension stability (i.e. (-potential) of nanoparticles was studied by measuring pH as a function of grinding time in the wet milling process. It was found that after a certain time in an attritor mill, there is no further size reduction and the average product particle size increases monotonically. One of the reasons is that the production of submicron particles leads to more particle-particle interactions and consequently pH of the suspension decreases with grinding time. Usually pH value is related to suspension stability and it can be enhanced by addition of NaOH solution. The maximum negative (-potential of -51.2 mV was obtained at pH of 12 for silica. The higher the (-potential with the same polarity, higher will be the electrostatic repulsion between the particles. Hence, the maximum electrostatic repulsion force was maintained by the adjustment of pH value in wet milling. The experiments were conducted at different pH conditions which were maintained constant throughout the experiments and nanosized particles were obtained consequently.     

Effect of poly(ethylene oxide) on the rheological behavior of silica suspensions

The steady-shear viscosity, dynamic viscoelasticity, and sedimentation behavior were measured for silica suspensions dispersed in aqueous solutions of poly(ethylene oxide) (PEO). For suspensions prepared with polymer solutions in which the transient network is developed by entanglements, the viscosity at a given shear rate decreases, shows a minimum, and then increases with increasing particle concentration. Because the suspensions are sterically stabilized under the conditions where the particle surfaces are fully covered with by a thick layer of adsorbed polymer, the viscosity decrease can be attributed to the reduction of network density in solution. But under the low coverage conditions, the particles are flocculated by bridging and this leads to a viscosity increase with shear-thinning profiles. The polymer chains with high molecular weights form flexible bridges between particles. The stress-dependent curve of storage modulus measured by a stress amplitude sweep shows an increase prior to a drastic drop due to structural breakdown. The increase in elastic responses may arise from the restoring forces of extended bridges with high deformability. The effect of PEO on the rheological behavior of silica suspensions can be explained by a combination of concentration reduction of polymer in solution and flocculation by bridging.     

Effect of matrix viscoelasticity on the electrorheological properties of particle suspensions

We have investigated the electrorheological properties of dispersions of semi-conducting particles in oils and elastomers. We focused on how the dynamic mechanical properties measured under oscillatory shearing change with the viscosity of the oil or the elasticity of the elastomer. The dependence on electric field and strain amplitude were also investigated. We found that the largest increment of the mechanical properties under electric fields was obtained when using oils of low viscosity and elastomers of low elasticity. The strain amplitude which produced the largest variation with electric field was found to be 0.1% for the elastomer systems, but significantly larger (1%) for the oil systems. These results are interpreted in terms of a model based on the competition between the dipole–dipole electrostatic interaction (which acts to maintain neighbouring particles together) and the shearing force due to the deformation of the matrix (which acts to separate the particles). We find that there are parallels between the electrorheological behaviour of particles dispersed in elastomers and the behaviour of particles dispersed in oils. These results should find application in the selection of suitable matrix materials for electrorheological suspensions.     

Rheology of carbon black suspensions. II. Well dispersed system

Linear viscoelastic properties were investigated for the suspensions of carbon black (CB) particles having covalently-fused aggregate structures of an average diameter a=120 nm. The suspending medium, an alkyd resin (AR), had a high affinity toward the CB particles, and the aggregates of these particles were well dispersed to form no higher-order agglomerates. Consequently, the suspensions obeyed the time-temperature superposition and their Arrhenius-type activation energy was identical to that of the medium. From comparison of the zero shear viscosity η₀ for the CB suspensions and hard-sphere silica suspensions, an effective volume fraction φ_eff of the CB particles was found to be 2.7 times larger than the bare volume fraction of the particles. The CB particles exhibited a slow relaxation process, and the terminal relaxation time of this process was close to the Peclet time (Brownian diffusion time) evaluated from the aggregate size a and a high frequency viscosity. Furthermore, the terminal relaxation mode distribution of the CB suspensions was well scaled with an intensity factor H_t that was evaluated from the φ_eff in a way utilized for the hard-sphere silica suspensions. These results demonstrated that the slow relaxation in the CB suspensions was dominated by the Brownian diffusion of the CB aggregates, as similar to the situation for the silica suspensions.