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.     

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.     

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.     

Rheology modification of montmorillonite dispersions by colloidal silica

We have studied the effect of additions of both anionic and cationic spherical silica colloids of different sizes on the rheology of dispersions of a well-characterised montmorillonite clay, SWy-2. The systems have been studied above and below the critical hydrodynamic overlap concentration, c*, of the clay. For dispersions at c < c* on replacement of ～10 % w/w of the clay content by silica, it was found that whereas a cationic silica additive transformed a liquid-like, non-gelling montmorillonite dispersion into a substantial gel, anionic silica destroyed any nascent structure in the fluids, reducing the effective viscosity and virtually eliminating the rheological hysteresis characteristic of structured fluids. On the other hand, in the regime of c > c*, replacement of ～10 % w/w of the clay content by silica leads to enhancements of all the rheological parameters characteristic of a gelling system, for the addition of both anionic and cationic silica. A simple tentative microstructural model for this complex behaviour is presented. This work, alongside our previous studies, confirms significant rheological modification by the addition of small quantities of nanoparticles as a general phenomenon of clay-colloid systems. It further suggests that viscosity enhancement and control of the rates of sol-gel transitions for product applications can be achieved using relatively low-cost, commercially available materials, such as silica nanoparticles and natural clays of different mineralogy.     

Effects of laponite and silica nanoparticles on the cleaning performance of amylase towards starch soils

This work aims to understand the effect of nanoparticle-enzyme interactions and how such interactions affect starch based soil removal. Silica and laponite are used as the model nanoparticles, and s-amylase is employed as the model enzyme. The results show that, if the nanoparticles and enzyme are added simultaneously, laponite enhances the enzyme performance toward starch soil removal, whereas silica imposes a small effect on the enzymatic activity towards the same soil substrates. However, when nanoparticles are added first, the enzyme activity is not affected much by laponite but is hindered significantly by silica nanoparticles. Furthermore, sequential addition of the enzyme followed by silica nanoparticles improves soil removal. Electron microscopic analyses, measurements of the enzyme activity in suspen- sions of nanoparticles, and particle size characterisation suggest that dense coverage of soil surface by the silica nanoparticles be likely a mechanism for the experimentally observed hindrance of soil removal when silica nanoparticles are added before enzyme.     

Effect of fumed silica nanoparticles on the morphology and rheology of immiscible polymer blends

We examined the effect of interfacially active particles on the morphology and rheology of droplet/matrix blends of two immiscible homopolymers. Experiments were conducted on polybutadiene/polydimethylsiloxane (10/90) blend and the inverse system. The effects of fumed silica nanoparticles, at low particle loadings (0.1–2.0 wt%), were examined by direct flow visualization and by rheology. Fumed silica nanoparticles were found to significantly affect the morphology of polymer blends, inducing droplet cluster structure and decreasing the droplet size, regardless of which phase wets the particles preferentially. This is surprising in light of much past research that shows that particles are capable of bridging and thus induce droplet cluster structure in droplet/matrix systems only when they are preferentially wetted by the continuous phase. Therefore, there should exist other possible mechanisms responsible for these droplet cluster structures except for the bridging mechanism. We proposed a particle-flocculating mechanism based on the fact that fumed silica particles readily flocculate due to their high aspect ratio, fractal-like shape, or interparticle attractions. Optical microscopy also reveals that the clustering structure becomes more extensive, and the droplet sizes in the clusters become smaller when the particle loading is increased. Rheologically, the chief effect of particles is to change the flow behavior from a liquid-like rheology to gel-like behavior. This gel-like behavior can be attributed to droplet clustering. Moreover, it should be emphasized that such gel-like behavior can be seen in the blends regardless of which phase wets the particles preferentially, suggesting that, once again, bridging is not the only cause of droplet clustering.     

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.     

表面修饰SiO2纳米微粒对锂基脂抗磨性能影响的研究

合成了表面修饰SiO2纳米微粒,利用四球摩擦磨损试验机考察了SiO2纳米微粒作为锂基脂添加剂的摩擦磨损行为,用扫描电子显微镜、能量色散谱仪和X射线光电子能谱仪对钢球磨损表面进行了分析.结果表明:SiO2纳米微粒作为锂基脂添加剂具有良好的抗磨损性能,能够显著提高锂基脂的失效载荷.这是由于在摩擦过程中,SiO2纳米微粒富集在磨损表面并形成边界润滑膜,对磨损表面起到修复作用,从而使得锂基脂的抗磨和承载能力明显提高.     

Rheology and structure of precipitated silica and poly(dimethyl siloxane) system

The reinforcing capability of precipitated silica in poly(dimethyl siloxane: PDMS) was characterized by means of bound rubber formation, solvent swelling, yield stress, rheological and dynamic properties. Volume concentration of precipitated silica in PDMS was varied from 0 to 0.16. The homogeneity of the compounds after mixing was confirmed by studying a uniformity of dispersion of silica particles in PDMS via SEM morphology of vulcanizates. Bound rubber measurements of the compounds and solvent swelling studies of vulcanizates showed that the precipitated silica exhibited much stronger interaction with PDMS than that of typical carbon black with rubbers but less than that of fumed silica with PDMS. At high volume concentrations of silica (0.128 and 0.160), a yield behavior was evident from the storage modulus measurements. The network formation due to an interaction between the precipitated silica and PDMS was visualized via dynamic property measurements.     

Effect of polymer bridging on rheological properties of dispersions of charged silica particles in the presence of low-molecular-weight physically adsorbed poly(ethylene oxide)

 The effect of a low-molecular-weight physically adsorbed poly(ethylene oxide) on the rheological behavior of aqueous dispersions of silica particles (as a model system) has been investigated. Particular attention is given to the evolution of the rheological behavior with increasing polymer concentration in the system at different volume fractions of the particles. Experiments were performed in the absence of salt and just the pH of the dispersion was adjusted to 9.5, a condition at which the system is electrostatically stable and electrostatic repulsive forces are long range in nature. It was observed that the shear viscosity and the linear viscoelastic functions of the dispersion at 55 vol% increase initially through the addition of polymer, reach a maximum, and then decrease to a minimum with further addition of polymer to the system. At higher polymer concentrations, there may be an increase in the viscosity of the dispersion owing to an increase in the concentration of free polymer chains in the medium causing depletion flocculation in the system. The increase in the rheological behavior of the dispersion at low polymer coverage is attributed to polymer bridging flocculation caused by a low-molecular-weight poly(ethylene oxide) in the system. Comparison of the data given here with the results of earlier studies on the viscosity behavior of the system in the presence of salt (0.01 M) indicates that the range of the electrostatic repulsion has a significant role in the rheological behavior of the system. Received: 7 February 2001 Accepted: 18 October 2001     

Experimental and numerical study of the effect of silica filler on the tensile strength of a 3D-printed particulate nanocomposite

Polymers are commonly found to have low mechanical properties, e.g., low stiffness and low strength. To improve the mechanical properties of polymers, various types of fillers have been added. These fillers can be either micro- or nano-sized; however; nano-sized fillers are found to be more efficient in improving the mechanical properties than micro-sized fillers. In this research, we have analysed the mechanical behaviour of silica reinforced nanocomposites printed by using a new 5-axis photopolymer extrusion 3D printing technique. The printer has 3 translational axes and 2 rotational axes, which enables it to print free-standing objects. Since this is a new technique and in order to characterise the mechanical properties of the nanocomposites manufactured using this new technique, we carried out experimental and numerical analyses. We added a nano-sized silica filler to enhance the properties of a 3D printed photopolymer. Different concentrations of the filler were added and their effects on mechanical properties were studied by conducting uniaxial tensile tests. We observed an improvement in mechanical properties following the addition of the nano-sized filler. In order to observe the tensile strength, dog-bone samples using a new photopolymer extrusion printing technique were prepared. A viscoelastic model was developed and stress relaxation tests were conducted on the photopolymer in order to calibrate the viscoelastic parameters. The developed computational model of nano reinforced polymer composite takes into account the nanostructure and the dispersion of the nanoparticles. Hyper and viscoelastic phenomena was considered to validate and analyse the stress–strain relationship in the cases of filler concentrations of 8%, 9%, and 10%. In order to represent the nanostructure, a 3D representative volume element (RVE) was utilized and subsequent simulations were run in the commercial finite element package ABAQUS. The results acquired in this study could lead to a better understanding of the mechanical characteristics of the nanoparticle reinforced composite, manufactured using a new photopolymer extrusion 5-axis 3D printing technique.     

Characterization of the bubbling fluidization of nanoparticles

The dynamic features of an agglomerate bubbling fluidization of nanoparticles were investigated through the analysis of pressure fluctuations. Experiments were carried out in a lab-scale fluidized bed at ambient conditions using 10-15 nm silica nanoparticles without any surface modification. Pressure fluctuation signals were processed in both frequency and time-frequency domains to characterize the behavior of various scales of phenomena （i.e.. macro-, meso-, and micro-structures） during fluidization. Due to the aggregation of nanoparticles, three separate broad peaks were observed in the frequency spectra of the pressure signals measured in the bubbling fluidized bed of nanoparticles. A non-intrusive method based on the decoupling of pressure fluctuations recorded simultaneously in the plenum and in the bed was used to determine the approximate size of the bubbles in the bed.     

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,...     

纳米SiO2颗粒增强镍基复合镀层的组织与微动磨损性能研究

采用电刷镀技术在45#钢表面制备了纳米SiO2颗粒增强镍基复合镀层,用扫描电子显微镜和透射电子显微镜观察分析了复合镀层的表面形貌和微观组织形貌,用纳米压痕仪测试了复合镀层的微观力学性能,并采用PLINT型高温微动疲劳试验机考察了复合镀层在室温至500 ℃下的微动磨损行为.结果表明:纳米SiO2颗粒促进了镀层的晶粒细化,提高了镀层的力学性能,复合镀层的硬度和弹性模量分别比镍镀层提高了2.01GPa和5 GPa,从而改善了镀层的微动磨损性能;复合镀层的耐磨性能约为镍镀层的2倍,这是由于纳米SiO2颗粒对复合镀层具有超细晶强化、硬质点弥散强化以及高密度位错强化机制所致.     

Nanofluids thermal behavior analysis using a new dispersion model along with single-phase

A numerical study has been performed to analyze nanofluids convective heat transfer. Laminar α-Al₂O₃-water nanofluid flows in an entrance region of a horizontal circular tube with constant surface temperature. Numerical analysis has been carried out using two different single-phase models (homogenous and dispersion) and two-phase models (Eulerian–Lagrangian and mixture). A new model is developed to consider the nanoparticles dispersion. The transport equations for the tube with constant surface temperature were solved numerically using a control volume approach. The effects of nanoparticles volume fraction (0.5, 1 %) and Reynolds number (650 ≤ Re ≤ 2300) on nanofluid convective heat transfer coefficient were studied. The results are compared with the experimental data and it is shown that the homogenous single-phase model is underestimated and the mixture model is overestimated. Although the Eulerian–Lagrangian model gives a reasonable prediction for the thermal behavior of nanofluids, the dispersion single-phase model gives more accurate prediction despite its simplicity.     

Dispersion stabilization of antimony-doped tin oxide（ATO）nanoparticles used for energy-efficient glass coating

Nano-antimony-doped tin oxide（ATO） was synthesized using the sol-gel method.A colloidal dispersion of ATO nanoparticles in distilled water was achieved using a milling process in which different dispersants were studied.In this paper,different factors that affect the stability of ATO nanoparticles were discussed,such as zeta potential,dispersant,and pH value.Sodium polyphosphate was a suitable dispersant for stabilizing ATO nanoparticles in distilled water.A stable dispersion of ATO nanoparticles in distilled water was prepared.The stable dispersion of ATO nanoparticles was used to prepare nano-thermal insulation glass paint to block near-infrared rays of sunlight.     

油酸表面修饰PbO纳米微粒作为润滑油添加剂的摩擦学性能研究

利用四球摩擦磨损试验机考察了油酸修饰PbO纳米微粒作为润滑油添加剂的摩擦学行为,并用X射线光电子能谱仪（XPS）、扫描电子显微镜（SEM）和能量散射谱仪（EDS）等现代分析工具对钢球磨损表面进行了分析,摩擦磨损试验结果表明,油酸修饰PbO纳米微粒作为润滑油添加剂能够明显提高基础油的减摩抗磨能力,当添加质量分数为0.30%时,与基础油相比可以使摩擦系数和钢球磨厂主 直径降低30%左右。XPS、SEM及EDS分析结果表明,钢球表面在摩擦过程中形成了一层富含PbO的边界润滑膜,这使得油酸修饰PbO纳米微粒作为润滑油添加剂表现出良好的摩擦学性能。     

铋纳米微粒添加剂的摩擦学性能研究

采用液相分散法制备了平均粒径为60 nm的油溶性铋纳米微粒,用四球摩擦磨损试验机考察了所制备的铋纳米微粒作为润滑油添加剂的减摩抗磨性能.结果表明,当添加量处于0.04%～1.00%范围内时,铋纳米微粒表现出良好的减摩抗磨性能,并能显著提高基础油的失效负荷.     

Dispersion stabilization of antimony-doped tin oxide (ATO) nanoparticles used for energy-efficient glass coating

Nano-antimony-doped tin oxide (ATO) was synthesized using the sol–gel method. A colloidal dispersion of ATO nanoparticles in distilled water was achieved using a milling process in which different dispersants were studied. In this paper, different factors that affect the stability of ATO nanoparticles were discussed, such as zeta potential, dispersant, and pH value. Sodium polyphosphate was a suitable dispersant for stabilizing ATO nanoparticles in distilled water. A stable dispersion of ATO nanoparticles in distilled water was prepared. The stable dispersion of ATO nanoparticles was used to prepare nano-thermal insulation glass paint to block near-infrared rays of sunlight.     

Validation of surface coating with nanoparticles to improve the flowability of fine cohesive powders

Fluidization of fine cohesive powders is seriously restricted by the strong interparticle cohesion. The rational combination of nanoparticles with fine cohesive powders is expected to obtain composite particles with improved flowability. In this work, we firstly reviewed the sandwich and three-point contact models regarding the fundamental principles of nano-additives in reducing cohesiveness. Based on these previous models, the effects of the size of nanoparticles, their agglomeration and coverage on the surface of cohesive powders in reducing interparticle forces were theoretically analyzed. To validate the theory effectiveness for the irregularly shaped cohesive powders, an extreme case of cubic powders coated with silica nanoparticles was fabricated, and the flowability of the composite particles was determined experimentally. Ultimately, based on force balance of a single particle, a semi-theoretical criterion for predicting the fluidization behavior of coated powders was developed to guide the practical applications of improving the flowability of cohesive powders through structural design and modulation.