The role of interfacial interactions on the glass-transition and viscoelastic properties of silica/polystyrene nanocomposite

Filler surface properties and polymer-filler interactions have dominate influence on viscoelastic behavior of polymeric matrix composites. When the filler-filler spacing is on the order of the polymeric matrix molecular size, fillers may agglomerate through direct short-range interactions, also by overlapping of interfacial layers of neighboring fillers. In this work the effect of interfacial layer on the viscoelastic properties of silica/polystyrene composite was investigated.The Si/Ps nanocomposites were prepared by solution mixing method, and dynamic rheometry was employed to determine the viscoelastic behavior in the melt state. Experimental results show that, addition of silica nanoparticles to polystyrene matrix would increase the glass-transition temperature of polymer. This increasing will be accelerated by presence of nanoparticles with more filler-polymer adhesion energy, because of more interfacial layer volume fraction. It is helpful in evaluating the volume fraction and equivalent thickness of interfacial layer in polymer nanocomposites. Likewise it is shown that, the dynamic moduli of nanocomposite is enhanced associated with the increase in the glass-transition temperature. This study implies that the main source of increment in both dynamic modulus and glass-transition temperature of polymer nanocomposites is the presence of the immobilized interfacial layer and the secondary filler network.     

Investigation of the fracture mechanism and mechanical properties of polystyrene/silica nanocomposite in various silica contents

There is limited research on the effect of silica on the mechanical properties of polystyrene. For this lack of information, this study has focused on the fracture mechanism and mechanical properties of Polystyrene/silica nanocomposite. Transmission electron microscopy showed proper dispersion of nanoparticles in PS matrix in both low and high filler loadings. Scanning electron microscopy, TOM micrography, and non-contact surface profiler were used to study the fracture surface and fracture mechanism characteristics of the nanocomposite. It seems that the debonding mechanism is an important mechanism in toughening of Polystyrene/silica nanocomposites. In addition, mechanical behavior of the samples was investigated. Tensile, flexural, and compressive strength and also impact and plain-strain fracture toughness of nanocomposite samples showed different behaviors in low and high nanoparticle loadings and interestingly, we found an optimum value less than 2% for nanoparticle loading in which we observed the highest improvement in mechanical properties of the nanocomposite.     

The effect of process parameters on physical and mechanical properties of commercial low density polyethylene/ORG-MMT nanocomposites

Polyethylene/organo-montmorillonite clay (org-MMT) nanocomposites were prepared utilizing PP-g-MA as a compatibilizer by melt intercalation method. In order to increase the miscibility of polyethylene (PE) with nanoparticle surface at firs, a primary masterbatch consist of compatibilizer and org-MMT was prepared then, this compound was melt intercalated with PE to synthesis the PE/org-MMT nanocomposites. In this study, the presence of commercial low density polyethylene in Nanocomposites structure and also the effect of process parameters such as: amount of nanoparticles, mixing rate and mixing time on nanocomposite structure and properties have been investigated. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that the interlayer distance of nanoparticle layers increased and a partially intercalated structure was prepared by melt intercalation method. Interaction between polyethylene chains and nanoparticle layers could be improved if the control of above parameters causes to penetrate the chains into nanoclay layers; by an optimization, this effect could improve the physical and mechanical properties. The DSC data revealed that melting temperature has slowly increased and crystalinity has lightly decreased. Consequently we can claim the thermal properties of LDPE/clay nanocomposite did not considerably change with clay content. A rise in the mechanical properties such as yield stress and modulus was observed by tension test; by addition of 5% clay content the tensile strength increased about 7%, the tensile modulus enhanced about 60% and the yield stress increased about 16% in comparison with the pure LDPE.     

Electromechanical response of semiconducting carbon–polyimide nanocomposite thin films

Electromechanically responsive polymer nanocomposite thin films can provide embedded microscale sensing elements for unobtrusive monitoring of strain, torque and pressure particularly for composite structures. Thin nanocomposite carbon–polyimide films with thicknesses up to 90 μm were produced with carbon contents that yield semiconducting behaviour attributable to distance dependent electron hopping between isolated nanoparticles. The tensile modulus and the strain at break indicated minimum interaction between polymer and nanoparticle surfaces. A decreasing storage modulus with increasing temperature indicated increasing free volume inducing polymer chain motions.     

Characterization of carbon nanotube/nanofiber-reinforced polymer composites using an instrumented indentation technique

An instrumented indentation technique was tested on three types of carbon nanotube/nanofiber-reinforced composites to investigate its applicability for measuring mechanical properties (elastic modulus and hardness). There was good agreement in the measured elastic modulus between the instrumented indentation and uniaxial tension tests for the case of a nanocomposite with a harder epoxy matrix material. In contrast, there was a considerable difference in elastic modulus between the two tests for the case of a nanocomposite with a softer polystyrene matrix material. A modified area function was then developed for the nanocomposite with the softer polystyrene matrix material, and this eliminated the difference in elastic modulus between the two test techniques. Thus, the instrumented indentation technique can be used for evaluating the mechanical properties of polymer matrix nanocomposites with an added advantage that a small sample size can be used. The instrumented indentation test was also utilized in the case of a patterned nanotube array-reinforced epoxy matrix composite. This clearly showed the modulus of the array nanocomposite improved considerably compared to that of the neat epoxy resin.     

Al2O3/TiO2纳米复合粉体爆炸喷涂层微结构及纳米压痕力学特性

研究了纳米复合涂层(NCC)和传统涂层(MCC)的微观结构及纳米压痕力学性能. NCC孔洞小,具有良好的均质分布特征.MCC中存在多级尺度分布的孔洞及微裂纹等缺陷, 呈现明显的非均质分布特征.NCC中大量晶界、亚晶界和微裂纹使得涂层中Al2O3基质相细化为纳米晶粒,但MCC中存在大量未熔片层颗粒.NCC和MCC具有各向异性的弹性、塑性、硬度和弹性模量.NCC比MCC相应的断面和表面具有更优良的抵抗外加负载性能、弹性恢复能力,更高的纳米压痕硬度和弹性模量.     

The effective Young's modulus of carbon nanotubes in composites

A detailed study has been undertaken of the efficiency of reinforcement in nanocomposites consisting of single-walled carbon nanotubes (SWNTs) in poly(vinyl alcohol) (PVA). Nanocomposite fibers have been prepared by electrospinning and their behavior has been compared with nanocomposite films of the same composition. Stress transfer from the polymer matrix to the nanotubes has been followed from stress-induced Raman band shifts, which are shown to be controlled by both geometric factors such as the angles between the nanotube axis, the stressing direction and the direction of laser polarization, and by finite length effects and bundling. A theory has been developed that takes into account all of these factors and enables the behavior of the different forms of nanocomposite, both fibers and films, to be compared in different polarization configurations. The effective modulus of the SWNTs has been found to be in the range 530-700 GPa which, while being impressive, is lower than the generally accepted value of around 1000 GPa as a result of factors such as finite length effects and nanotube bundling. This value of effective modulus has, however, been shown to be consistent with the contribution of nanotubes to the 20% increase in Young's modulus found for the nanocomposite films with a loading of only 0.2% of SWNTs. Hence a self-consistent method has been developed which enables the efficiency of reinforcement by nanotubes, and potentially other high-aspect-ratio nanoparticles, to be evaluated from stress-induced Raman bands shifts in nanocomposites independent of the specimen geometry and laser polarization configuration.     

Microstructural characterization of Mg-SiC nanocomposite synthesized by high energy ball milling

High-energy ball milling is successfully used to produce magnesium matrix nanocomposites reinforced with SiC nanoparticles. Changes in morphology and microstructural features of the milled powders were characterized in order to highlight advantages of the mechanical milling process and evaluate the role of the SiC nanoparticles. It was observed that with increasing volume fraction of SiC nanoparticles, a finer nanocomposite powder with more uniform particle size distribution is obtained. A homogeneous distribution of SiC nanoparticles, even up to 10% volume fraction, in magnesium matrix after 25?h milling was confirmed by elemental mapping and TEM results. The analysis of the XRD patterns accompanied by dark-field TEM images revealed that magnesium crystallites refine to fine nanocrystalline sizes after the mechanical milling. The results showed that the crystallite size of the magnesium matrix reduced with increasing SiC nanoparticle content in addition to the induced lattice strain.     

Conformation of intramolecularly cross-linked polymer nanoparticles on solid substrates

The conformation of cross-linked, monomolecular, polystyrene nanoparticles on a solid substrate is considered as a function of cross-linking degree and substrate surface free energy. It is found that an extreme amount of cross-linking is necessary for the ca. 5-10 nm diameter nanoparticles to retain their original spherical shape, regardless of surface free energy. A lesser amount of cross-linking produces a nanoparticle that collapses to a pancake-like conformation on a high-energy substrate yet remains spherical on a low-energy surface. A simple model is developed to reveal the relationship between nanoparticle modulus and surface free energy to define the nanoparticle conformation.     

The influence of poly(acrylic acid) molar mass and concentration on the properties of polyalkenoate cements Part II Young''s modulus and flexural strength

The Young's modulus and flexural strength were determined for glass polyalkenoate cements as a function of poly(acrylic acid), PAA molar mass, concentration, glass volume fraction and cement ageing time. The Young's modulus was independent of PAA molar mass. The Young's modulus increased dramatically with the PAA concentration of the cement until concentrations greater than 50% m/m were reached. The modulus increased with time for nearly all the cements investigated consistent with a continuing ionic cross-linking process in the cement matrix. The modulus increased with an increase in the volume fraction of the higher modulus glass phase. Increasing the glass volume fraction provides more surface area for acid attack resulting in a more cross-linked polysalt matrix, as well as increasing the volume fraction of residual glass particles. Flexural strength was highly dependent on molar mass of the PAA and its concentration. The molar mass dependence of the flexural strength was greatest at higher PAA concentrations.     

Transforming an intrinsically hydrophilic polymer to a robust self-cleaning superhydrophobic coating via carbon nanotube surface embedding

A single-step method, including surface embedding of nanoparticles into a polymer matrix, was employed to fabricate superhydrophobic thermoplastic polyurethane (TPU)/carbon nanotube (CNT) nanocomposite coatings. The main aim was to prove that surface roughness plays a more important role in designing superhydrophobic surfaces as compared with the surface energy. Therefore, TPU was used as the model hydrophilic polymer and CNTs were employed as non-hydrophobic nanoparticles. It was found that, at a certain pressing time, CNTs form an efficient hair-like morphology which is able to highly enclose air within its as-formed pores leading to superhydrophobic behavior. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and confocal microscopy were utilized for characterization of samples. SEM and confocal microscopy results proved that surface roughness played the key role in the final wettability behavior. Based on XPS results, it was also found that a very long pressing time led to partial migration of TPU macromolecules into the CNTs' pores, and hence, superhydrophobicity was reduced. The effects of mechanical abrasion and nanoparticle type on wettability behavior of samples were evaluated as well. In conclusion, it is suggested that surface roughness factor should be highly considered in designing superhydrophobic nanocomposite coatings rather than surface energy.     

Deformation and fracture behavior of electrocodeposited alumina nanoparticle/copper composite films

Electrocodeposition of alumina nanoparticles and copper thin film on silicon wafers was performed. The volume fraction of the nanoparticle is about 5% and the size is about 50 nm. Comparison between the static tensile behaviors of specimens with and without nanoparticles reveals that the Young’s modulus is significantly increased by incorporating nanoparticles into the copper film. However, the ultimate tensile strength of the nanocomposite (235 MPa) is slightly lower than that of the pure copper reference specimen (250 MPa). For the nanocomposite, the strain at failure is 7.8%, which is lower than that of the pure copper film (10.5%). Distinct microscale deformation mechanisms are observed: the main deformation mechanism of the pure copper film is slip followed by strain hardening, whereas for the nanocomposite, multistage failure behaviors are found due to the debonding at the nanoparticle/copper interface. Notched specimens were also tested and compared with the unnotched specimens. In addition, cyclic loading tests on the nanocomposite were conducted to show its hardening behavior.     

Fabrication of thermoplastic polyester elastomer/layered zinc hydroxide nitrate nanocomposites with enhanced thermal,mechanical and combustion properties

The objective of this study is to explore the potential of layered zinc hydroxide nitrate modified with sodium benzoate as nanoparticle in thermoplastic polyester elastomer (TPEE). The organically modified zinc hydroxide nitrate was compounded with TPEE using solution blending method. The nanocomposite structure was characterized by means of X-ray diffraction and transmission electron microscopy. The results showed that the nanoparticle was homogenously dispersed in TPEE matrix, and partially exfoliated structure was formed. The thermal behavior, mechanical and thermal combustion properties of the novel nanocomposite were studied respectively through differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA) and microscale combustion calorimeter (MCC). For the nanocomposite containing 7 wt% nanoparticle, the crystallization temperature evaluated by DSC was increased by 10 °C. The storage modulus at −95 °C measured by DMA was improved by around 26%. The heat release capacity (an indicator of a material fire hazard) from MCC testing was reduced by about 56% (compared to the results of neat TPEE).     

碳纤维和SiO2纳米颗粒增强环氧树脂复合材料的压缩性能

纤维增强聚合物复合材料的压缩性能与聚合物基体力学性质密切相关。本文利用连续碳纤维（CF）和含有均匀分散的SiO₂纳米颗粒改性的环氧树脂基体,制备了CF-nano SiO₂/Epoxy微纳米多相复合材料单向层合板,并对其轴向压缩性能进行了系统的研究。试验表明,将纳米颗粒引入基体能够有效提高纤维增强聚合物基复合材料的压缩强度,占nano SiO₂/Epoxy体积为8.7%的纳米颗粒可将复合材料的压缩强度提升约62.7%。基于单向层合板的弹塑性微屈曲模型对纳米颗粒的增强效应进行了理论分析。根据含纳米颗粒的环氧树脂在压缩过程中的损伤行为,提出了一套基于加卸载试验建立纳米复合材料基体压缩本构关系的方法。将模型获得的基体本构关系与经典复合材料弹塑性微屈曲模型耦合,能够较为准确地预测本研究制备的微纳米多相复合材料的压缩强度。经试验检验,预测结果与实测数值达到很好的一致性。      

Temperature-dependent gas transport and its correlation with kinetic diameter in polymer nanocomposite membrane

Activation energies for permeation of polymer nanocomposite membrane have not been reported so far. A trade-off relation between permeability and selectivity shows that as permeability increases, the selectivity decreases. Attempts have been made to see this trade-off relation at relatively higher temperature. It is found that selectivity decreases drastically with increasing temperature. A polymer–matrix composite was prepared by adding silica nanoparticles using casting method. Pure gas permeability was measured using a constant volume–variable pressure method at different temperature ranges from 35 to \(70^{\circ }\hbox {C}\). The Van’t Hoff relation was used to estimate the activation energy for permeation. It is found to decrease as compared with virgin polycarbonate and it increases with kinetic diameter. For the first time, the permeability and selectivity for nanocomposite membrane are reported as a function of temperature. Activation energies for different gases have been calculated for nanocomposite membrane and compared with that of virgin polymer membrane. Decrease in activation energies for permeation (\(E_\mathrm{p}\)) with increasing kinetic diameter has been observed for both the membranes. Selectivity reduces with temperature for both the membranes. Mechanical and thermal properties of nanocomposite membrane have been investigated using a dynamic mechanical analyser and differential scanning calorimetry, respectively. Scanning electron microscopy has been used to study surface morphology. The results show modification in physical properties due to incorporation of silica nanoparticles.     

Anelastic behaviour of materials under multiaxial strains

Data on Young's modulus and Poisson's ratio obtained in AISI-1080 steel, in the temperature region between about 300 and 600 K, are presented. The measurements have been performed in longitudinal excitation and several harmonics were used, to obtain Poisson's ratio from the measured resonant frequencies. The maximum observed in the temperature dependence of Young's modulus, for the fundamental resonant frequency, is attributed to a stress-induced disordering of carbon atoms in the octahedral interstices of the martensitic matrix. The increases of Young's modulus with temperature are described in terms of expressions deduced in the paper, which are based on Landau theory of second-order phase transitions. The critical temperature is related to theM _s temperature which characterizes the martensitic phase transition. Finally, the temperature dependence of Poisson's ratio is described in terms of a theory of anelastic behaviour under multiaxial strains, based on the standard anelastic solid model.     

Fabrication of Fe(3)O(4) nanoparticle arrays via patterned template assisted self-assembly

Magnetic nanoparticle arrays have been fabricated by combining chemically synthesized Fe(3)O(4) nanoparticles with a diblock copolymer template substrate consisting of self-assembled polystyrene (PS) dots in a polymethylmethacrylate (PMMA) matrix. The influence of the volume fraction of the Fe(3)O(4) suspending solution and the withdrawal speed of the template on the formation of array structures was investigated. A small volume fraction of the nanoparticles and low withdrawal speed play an important role in the fabrication of the patterned arrays of nanoparticles via template assisted self-assembly. Below a withdrawal speed of 0.5?mm?s(-1) and a nanoparticle volume fraction below 0.05?vol% (in particular, at extremely high dilutions of less than 0.01?vol%), the selective deposition of one to several nanoparticles on every single PS dot becomes possible.     

Mechanical properties of thin glassy polymer films filled with spherical polymer-grafted nanoparticles

It is commonly accepted that the addition of spherical nanoparticles (NPs) cannot simultaneously improve the elastic modulus, the yield stress, and the ductility of an amorphous glassy polymer matrix. In contrast to this conventional wisdom, we show that ductility can be substantially increased, while maintaining gains in the elastic modulus and yield stress, in glassy nanocomposite films composed of spherical silica NPs grafted with polystyrene (PS) chains in a PS matrix. The key to these improvements are (i) uniform NP spatial dispersion and (ii) strong interfacial binding between NPs and the matrix, by making the grafted chains sufficiently long relative to the matrix. Strikingly, the optimal conditions for the mechanical reinforcement of the same nanocomposite material in the melt state is completely different, requiring the presence of spatially extended NP clusters. Evidently, NP spatial dispersions that optimize material properties are crucially sensitive to the state (melt versus glass) of the polymeric material.     

Microstructure changes in TiB2-Cu nanocomposite under sintering

Stability and growth of nanoparticulate reinforcements in metal matrix composites during heating are widely studied for dispersion-strengthened alloys, which contain several volume percent of reinforcing phase. When high volume content of nanoparticles distributed within a matrix is concerned results of particles aggregation and growth as well as crystallization mechanisms are not so evident. In this work microstructural evolution under sintering in metal-matrix composite TiB₂-Cu with high volume content (up to 57%) of titanium diboride nanoparticles 30-50 nm in size was investigated. The nanocomposite powders were produced through synthetic method combining preliminary mechanical treatment of initial powder mixtures in high-energy ball mill, self-propagating exothermic reaction and subsequent mechanical treatment of the product. We focused on microstructure changes in TiB₂-Cu nanocomposite consolidated by Spark-Plasma Sintering and conventional sintering and showed that in the former case fine-grained skeleton of titanium diboride is formed with connectivity between particles well established. In the latter case behavior of nanoparticles is surprising: at low temperatures fiber-like structures are formed while increasing temperature causes appearance of faceted crystals. These unusual results allow us to propose the direct involvement of nanoparticles in the processes of crystallization by moving as a whole in the matrix.     

Size effects on silver nanoparticles' properties

In this work a systematic study of the dependence of the structural, electronic, and vibrational properties on nanoparticle size is performed. Based on our total energy calculations we identified three characteristic regimes associated with the nanoparticle's dimensions: (i)?below 1.5?nm (100?atoms) where remarkable molecular aspects are observed; (ii)?between 1.5 and 2.0?nm (100 and 300?atoms) where the molecular behavior is influenced by the inner core crystal properties; and (iii)?above 2.0?nm (more than 300?atoms) where the crystal properties are preponderant. In all considered regimes the nanoparticle's surface modulates its properties. This modulation decreases with the increasing of the nanoparticle's size.