Modeling electrical conductivity of polymer nanocomposites with aggregated filler

A mean-field model is developed for the electrical conductivity of microcomposites and nanocomposites with polymer matrices. The model accounts for aggregation of filler into clusters (involving both conducting and nonconducting particles) and rearrangement of these clusters with the growth of volume fraction of filler (which leads to a reduction in tunneling resistivity and an increase in the number of bridging contacts between conducting particles). The governing equations involve five material constants with transparent physical meaning: the depolarization factor of clusters, volume fraction of polymer in clusters of filler, effective conductivity of an individual filler particle, and two coefficients characterizing an increase in the effective electrical conductivity of filler driven by the growth of bridging contacts between neighboring particles in clusters. Good agreement is demonstrated between results of simulation and experimental data on the electrical conductivity of epoxy resin reinforced with carbon black and graphite particles, poly(vinyl chloride) reinforced with copper and nickel particles, polypropylene loaded with spherical and spheroidal tin particles, poly(butylene terephthalate) reinforced with graphene nanosheets, and polypropylene loaded with multiwalled carbon nanotubes.     

Influence of silicon filler size and concentration on thermal stability and erosion wear resistance of polymer composite

Silicon - Infusion of silicon filler introduces a strong interaction with the polymer matrix used to develop a hybrid composite with improved structural qualities. This research work investigates...     

Antimicrobial resistance of clay polymer nanocomposites

Antimicrobial-resistant polymeric Na⁺–bentonite nanocomposites were prepared by treating Na⁺–bentonite (Na⁺–Bent) with polymeric ultra-thin films of poly(diallyldimethyl ammonium chloride) (PDADMAC), poly(methylmethacrylate) (PMMA) and poly(vinylidene chloride) (PVDC) by admicellar polymerization technique. The clay polymer nanocomposites (CPNs) were characterized by several techniques including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), BET surface analysis, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). In additional, the antimicrobial resistance was studied by measuring the diameter of inhibition zone of growths of Escherichia coli and Salmonella typhimurium. The results showed an inhibitory effect of these CPN against microbial growth in inoculated samples. The CPN exhibited efficacy in the inhibition of bacterial growth.     

Enhanced mechanical properties of graphene/natural rubber nanocomposites at low content

Graphene/natural rubber (GE/NR) nanocomposites were prepared by a modified latex mixing method combined with in situ chemical reduction. It was found that the GE nanosheets are well dispersed and have strong interfacial interaction with NR. Thus, adding a low content of GE can remarkably increase the tensile strength and the initial tensile modulus of NR. With incorporation of as low as 0.5 phr of GE, a 48% increase in the tensile strength and an 80% increase in the initial tensile modulus are achieved without sacrificing the ultimate strain. But further increasing the GE loading degrades the tensile strength and the ultimate strain. Dynamic mechanical measurement indicates that the storage modulus of the nanocomposites is greatly enhanced with addition of GE, while the loss tangent peak is depressed due to the reduced mobility of the rubber molecules. The reinforcement effect of GE on NR is interpreted as a change in the strain induced crystallization and network structure of the nanocomposites, based on the analysis of Mooney ? Rivlin plots and the tube model.© 2013 Society of Chemical Industry     

Enhanced mechanical properties of nanocomposites at low graphene content based on in situ ball milling

In this study, epoxy‐based nanocomposites with low content mechanically exfoliated graphene were successfully prepared via one‐step in situ ball milling method. The effect of graphene on mechanical properties of the nanocomposites was investigated. The results showed that samples with loadings less than 0.1% weight of mechanically exfoliated graphene increased by 160% in tensile strength and 65% in Young's modulus. The experimental value of Young's modulus was also compared with the predictions of the well‐established Halpin‐Tsai model. In addition, the adding of graphene did not decrease the impact strength of epoxy. The microstructural results showed that the as‐prepared graphenes were single‐ and few‐layer graphene sheets and preserved perfect structure. Thus enhancements of mechanical properties in the nanocomposites could be ascribed to the strong interfacial interaction between the stiff graphene nanosheets and the epoxy matrix. POLYM. COMPOS. 37:1190–1197, 2016. © 2014 Society of Plastics Engineers     

The wear resistance of Ni alumina and NiAl2O4 alumina nanocomposites

The influence of metallic Ni or NiAl₂O₄ as a reinforcing particle on grain growth and wear resistance in alumina matrix composites was evaluated. Alumina composites with various Ni or NiAl₂O₄ concentrations were prepared by multiple-infiltrations of Ni-nitrate into bisque-fired (necked) alumina green bodies followed by heat treatment and sintering at 1600 °C for 2 h. Sintering in a reducing environment resulted in composites with metallic Ni nanoparticles, while NiAl₂O₄ alumina composites were formed when sintering in air. The addition of Ni or NiAl₂O₄ resulted in a reduction in alumina grain size after sintering. The material response to abrasive wear was estimated by measuring the time to section samples of a defined area using a diamond wafering saw and was compared to the wear resistance of undoped alumina. In both cases, reinforcing alumina with Ni or NiAl₂O₄ particles resulted in a significant increase in wear resistance, correlated to the reduced grain size.     

Mechanism of filler action in reducing the wear of PTFE polymer by differential scanning calorimetry

Two types of representative nanometer materials, i.e., fibroid nanometer attapulgite and approximate spherical ultrafine diamond, were selected as fillers of polytetrafluoroethylene (PTFE) to study the mechanism of the wear‐reducing actions of the fillers in PTFE composites. The friction and wear tests were performed on a block‐on‐ring wear tester under dry sliding conditions. Differential scanning calorimetry (DSC) was used to investigate material microstructure and to examine modes of failure. No significant change in coefficient of friction was found, but the wear rate of PTFE composites was orders of magnitude less than that of pure PTFE. DSC analysis revealed that nanometer attapulgite and ultrafine diamond played a heterogeneous nucleation role in PTFE matrix and consequently resulted in increasing the crystallinity of PTFE composites. Moreover, the PTFE composite with higher heat absorption capacity and crystallinity exhibited improved wear resistance. A propositional “sea‐frusta” frictional model explained the wear mechanism of filler action in reducing the wear of PTFE polymer, i.e., fillers in the PTFE matrix effectively reduced the size of frictional broken units for PTFE composites and restrained the flowability of the units, as well as supporting the applied load. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

BIIR/OMMT纳米复合材料的阻透性能和耐寒性能

采用机械混炼法制备了溴化丁基橡胶/有机蒙脱土(BIIR/OMMT)纳米复合材料,采用SEM和XRD对其亚微观结构进行了表征,并对其耐寒性能和阻透性能进行了研究。实验结果表明:OMMT片层以剥离状态分散于BIIR基体中;添加OMMT之后,BIIR的交联密度明显提高;OMMT能够略微降低BIIR的耐寒性能;OMMT片层具有优异的阻透效应,能够明显提高BIIR的热稳定性能和耐油性能。     

Impact of ultrasonication on carbon nanotube demixing and damage in polymer nanocomposites

While ultrasonication is universally employed for dispersion and distribution of carbon nanotubes (CNTs) in a solvent or polymer solution, the current work focuses on the underlying mechanisms of CNT demixing and CNT damage that can occur during processing. Here, multi-walled CNTs were dispersed in a polycaprolactone polymer matrix using an established solution processing technique. Electrical, rheological, and mechanical characterization results suggest that once nanocomposite property enhancements reach an optimal level, further sonication leads to a decrease in the corresponding properties due to a combination of CNT damage and demixing mechanisms. Evidence of CNT damage from transmission electron microscopy, poor CNT distribution from optical image analysis and shear-induced crystallization results, and reagglomeration observed from ultraviolet–visible results, taken together, suggest that mechanisms of demixing and damage of the CNTs coexist for excessive sonication times.     

Extraordinarily high plastic deformation in polyurethane/silica nanoparticle nanocomposites with low filler concentrations

We have synthesized segmented polyurethane (SPU)/silica nanoparticle (SiNP) nanocomposites with extraordinarily high tensile strength and strain-at-break using an in-situ polymerization method with low SiNP concentrations. A 20-fold increase in strain-at-break compared with the pristine polymer has been achieved for the 0.5 wt% SiNP nanocomposites. A suite of characterization tools including transmission electron microscopy, ultra-small angle X-ray scattering, X-ray diffraction, differential scanning calorimetry and thermogravimetric analysis has been used to correlate the phase morphology, crystallization, and mechanical properties. The location of SiNP in the phase separated SPU is believed to be the main reason for the mechanical property enhancement.     

Multifunctional nanocomposites integrate electromagnetic shielding,thermal, mechanical,and wear resistance properties

The SiC_nws/SiC nanocomposites were in situ synthesized by using nickel carbon foam as catalyst and skeleton. This technique has a series of advantages including simple operation, low cost, and high efficiency. Due to the excellent microwave absorption and thermal properties of SiC_nws, SiC_nws/SiC nanocomposites possess excellent electromagnetic shielding performance with a high SE_T value of 38.3 dB and good thermal properties with thermal conductivity of 13.77 ± 0.098 wm⁻¹k⁻¹ at room temperature. Meanwhile, the bending strength of the nanocomposites is 110.9 ± 7.7 MPa. The friction coefficient of nanocomposites is about 0.26 with a wear speed of about 67 um³/s. Therefore, the nanocomposites integrate many advantages including lightweight (2.0 g/cm³), excellent electromagnetic shielding, good heat conduction, high strength, and wear resistance.     

Mechanical reinforcement and wear resistance of aligned carbon nanotube/epoxy nanocomposites from nanoscale investigation

The anisotropic mechanical reinforcement compression and scratch resistance of epoxy nanocomposites filled with well-aligned carbon nanotubes (ACNTs) sliding in different orientations were investigated by nanoindentation techniques. It was found the addition of ACNTs to epoxy very effectively improved the microscopic hardness, elastic modulus, and nanoscratch resistance of pure epoxy, and the nanocomposites in antiparallel orientation of ACNTs showed the highest enhancement. However, macroscopic compression test showed the normal orientation of ACNTs enhanced the compression strength the most. Based on nanoscale observations, new ACNTs related reinforcing and scratch resistance mechanisms were further proposed and discussed. This study will enhance the understanding of the anisotropic reinforcement effect of ACNTs with new characteristics, and will be helpful for the design and application of ACNT nanocomposite materials into precision instruments and related anisotropic nanomaterials.     

Elucidation of polymer wear resistance via nanoscale healing and fracture of sintered polystyrene particles

Polymer wear resistance evolution was studied based on nanoscale healing and fracture of a model polyinterface system: sintered film of uniform submicron polystyrene particles. The observed phenomenon was divided into three regimes namely interdiffusion, trough, and recovery, respectively. Film annealing up to 10 min in interdiffusion regime enhanced wear resistance with a 3.8 power dependence on interpenetration depth. Further annealing led to a severe wear resistance decrease, trough regime. Wear resistance then showed a sharp increase followed by a gradual rise to a plateau, recovery regime. Surfactants preservation during film formation shifted whole wear resistance‐annealing time curve to shorter times, decreased differentiations among observed regimes and reduced wear resistance power dependence on interpenetration depth to 2.3. Aforementioned regimes were also discernible in impact strength‐annealing time curves but without the steep rise of the recovery regime. Wear resistance scaled impact strength with a 0.67 power by omitting trough regimes data points. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Enhancement of mechanical and wear resistance performance in hexagonal boron nitride‐reinforced epoxy nanocomposites

Hexagonal boron nitride (hBN), a two‐dimensional nanofiller with good mechanical properties, high thermal conductivity and excellent lubrication properties, has the potential to substantially reinforce polymers to form nanocomposites with advanced properties. In this study, we successfully prepared hBN nanosheets with a thickness of a few atoms by using amine‐capped aniline trimer (AT) as dispersant. Epoxy/hBN nanocomposites were prepared by curing reaction of epoxy E51, Jeffamine D230 and AT‐modified hBN nanosheets, where the hBN contents were 0.5, 1, 2 and 4 wt%. An increase in contact angle of the epoxy/hBN nanocomposites was evident in the presence of hBN nanosheets, implying an increase in the hydrophobic nature of the composites. The as‐prepared composites exhibited enhanced mechanical and tribological performance compared to pure epoxy resin. This effectiveness in improving the mechanical, friction and wear behavior of the epoxy composites could be attributed to the complementary action of excellent mechanical properties, lubrication and thermal conductivity of hBN nanofillers. © 2016 Society of Chemical Industry     

Impact of filler geometry and surface chemistry on the degree of reinforcement and thermal stability of nitrile rubber nanocomposites

The morphological, mechanical, and thermal stability of Nitrile rubber nanocomposites reinforced with fillers such as layered silicate (LS), calcium phosphate (CP) and titanium dioxide (TO) having different particle size and chemical nature were analyzed. The results revealed that the filler geometry played an important role on the mechanical and thermal stability of the composites. Calcium phosphate and titanium dioxide filled systems showed comparatively better mechanical and thermal stability compared to neat rubber. The activation energy needed for the thermal degradation was found to be higher for layered silicate filled system. DSC (Differential Scanning Calorimetry) analysis revealed a change in the T_g values as a result of the addition of fillers. This was more prominent with the case of layered silicate filler addition in comparison with calcium phosphate and titanium dioxide. The heat capacity values of the nanocomposites were carefully evaluated. The (∆Cp) with values obtained for different nanocomposites were correlated with the degree of reinforcement. It can be assumed that more polymer chains are attached on to the surface of the filler and there exists an immobilized layer around the filler surface and the layers do not take part in the relaxation process. The FTIR spectrum of the different samples highlighted the possible filler matrix interaction. The filler dispersion and aggregation in the polymer matrix were analyzed using X-ray diffraction studies (XRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM).     

聚合物基纳米复合材料的制备与应用

简述了聚合物基纳米复合材料的特性,介绍了聚合物基纳米复合材料的制备方法,包括纳米颗粒填充法、纳米微粒原位合成法、聚合物基体原位聚合法、两相同步原位合成法的合成工艺和特点,并对聚合物基纳米复合材料的应用进行了概括。     

Morphological,thermal, and mechanical characteristics of polymer/layered silicate nanocomposites: The role of filler modification level

Composite materials consisting of poly(L ‐lactic acid) and montmorillonite modified to a different extent, using various contents of hexadecylammonium cation, were prepared by the solution intercalation method. Investigation of the composites' morphology revealed that a surfactant quantity higher than the mineral's cation exchange capacity (CEC) was necessary for the organomodified clay to be dispersed at nanoscale level into the polymer matrix. The surfactant content in organoclay was found to play a major role in controlling the composite's mechanical properties. Thus, although increase of the alkylammonium concentration initially enhanced these properties, even higher concentrations corresponding to higher modification levels had a negative impact to them causing their dramatic deterioration. Observation of the deformed surfaces showed that the deformation process mechanism of the material is directly related to the degree of clay modification. Thermal degradation studies revealed that the intermediate surfactant excess reinforces the thermal stability of the nanocomposite by increasing the onset decomposition temperature. Additionally, the alkylammonium concentration was found to affect the crystallization temperature and the glass transition temperature of the polymer. In conclusion, an ideal balance between thermal and mechanical properties can be obtained at surfactant quantity equivalent to 1.5 times the clay CEC. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Design and fabrication of electro‐conductive polymer nanocomposites with mechanical and thermal resistance

The commencement of the industrial revolution paved the way for the fabrication of flexible polymers with high‐strength metalloceramics as novel materials of all kinds. Fabricating metal–ceramic/polymer conductive composites is one such dimension followed for the present research work making use of the properties of the three components. Electroless deposition, for permanent metallic coating, was performed to coat Al₂O₃ with metallic Cu followed by the inclusion of the Cu–Al₂O₃ filler into a poly(vinyl chloride) (PVC) matrix. X‐ray diffraction and energy‐dispersive X‐ray studies predicted a prominent growth of metallic Cu crystallites onto Al₂O₃ with an increased average size and variation in elemental composition, respectively, when compared to pristine Al₂O₃. Morphological behaviour via scanning electron microscopy also envisioned uniform Cu coating onto Al₂O₃ and a homogeneous dispersion throughout the polymer matrix. When incorporated into PVC, electrical conductivity analysis highlighted a distinct variation in composite phases from insulating (7.14 × 10^?16 S cm^?1) to semiconducting behaviour (8.33 × 10^?5 S cm^?1) as a function of Cu–Al₂O₃ filler. Mechanical behaviour (tensile strength, Young's modulus and elongation at break) and thermal properties of the prepared composites also indicated a substantial improvement in material strength with Cu–Al₂O₃ incorporation. The enhanced electrical conductivity along with improved thermomechanical status with significant filler–matrix interaction permits the potential usage of such novel composites in a range of state‐of‐the‐art semiconducting electronic devices. © 2018 Society of Chemical Industry     

Tensile modulus of polymer nanocomposites

Based on Takayanagi's two‐phase model, a three‐phase model including the matrix, interfacial region, and fillers is proposed to calculate the tensile modulus of polymer nanocomposites (E_c). In this model, fillers (sphere‐, cylinder‐ or plateshape) are randomly distributed in a matrix. If the particulate size is in the range of nanometers, the interfacial region will play an important role in the modulus of the composites. Important system parameters include the dispersed particle size (t), shape, thickness of the interfacial region (τ), particulate‐to‐matrix modulus ratio (E_d/E_m), and a parameter (k) describing a linear gradient change in modulus between the matrix and the surface of particle on the modulus of nanocomposites (E_c). The effects of these parameters are discussed using theoretical calculation and nylon 6/montmorillonite nanocomposite experiments. The former three factors exhibit dominant influence on E_c. At a fixed volume fraction of the dispersed phase, smaller particles provide an increasing modulus for the resulting composite, as compared to the larger one because the interfacial region greatly affects E_c. Moreover, since the size of fillers is in the scale of micrometers, the influence of interfacial region is neglected and the deduced equation is reduced to Takayanagi's model. The curves predicted by the three‐phase model are in good agreement with experimental results. The percolation concept and theory are also applied to analyze and interpret the experimental results.