Nanofilled Composites Research Articles

Polymer Nanocomposites-A Comparison between Carbon Nanotubes, Graphene, and Clay as Nanofillers.

Nanofilled polymeric matrices have demonstrated remarkable mechanical, electrical, and thermal properties. In this article we review the processing of carbon nanotube, graphene, and clay montmorillonite platelet as potential nanofillers to form nanocomposites. The various functionalization techniques of modifying the nanofillers to enable interaction with polymers are summarized. The importance of filler dispersion in the polymeric matrix is highlighted. Finally, the challenges and future outlook for nanofilled polymeric composites are presented.

Clay/Polyaniline Hybrid through Diazonium Chemistry: Conductive Nanofiller with Unusual Effects on Interfacial Properties of Epoxy Nanocomposites.

The concept of conductive network structure in thermoset matrix without sacrificing the inherent mechanical properties of thermoset polymer (e.g., epoxy) is investigated here using "hairy" bentonite fillers. The latter were prepared through the in situ polymerization of aniline in the presence of 4-diphenylamine diazonium (DPA)-modified bentonite (B-DPA) resulting in a highly exfoliated bentonite-DPA/polyaniline (B-DPA/PANI). The nanocomposite filler was mixed with diglycidyl ether of bisphenol A (DGEBA), and the curing agent (4,4'-diaminodiphenylsulfone) (DDS) at high temperature in order to obtain nanocomposites through the conventional melt mixing technique. The role of B-DPA in the modification of the interface between epoxy and B-DPA/polyaniline (B-DPA/PANI) is investigated and compared with the filler B/PANI prepared without any diazonium modification of the bentonite. Synergistic improvement in dielectric properties and mechanical properties points to the fact that the DPA aryl groups from the diazonium precursor significantly modify the interface by acting as an efficient stress transfer medium. In DPA-containing nanocomposites, unique fibril formation was observed on the fracture surface. Moreover, dramatic improvement (210-220%) in fracture toughness of epoxy composite was obtained with B-DPA/PANI filler as compared to the weak improvement of 20-30% noted in the case of the B/PANI filler. This work shows that the DPA diazonium salt has an important effect on the improvement of the interfacial properties and adhesion of DGEBA and clay/PANI nanofillers.

Fabrication and properties of ZrO2/AZ31 nanocomposite fillers of gas tungsten arc welding by accumulative roll bonding

In the present study, a new method for fabricating ZrO2/AZ31 nanocomposite fillers of gas tungsten arc (GTA) welding was developed by applying accumulative roll bonding (ARB) to the magnesium sheets coated with ZrO2 nanoparticles. The purpose of ARB was to create a uniform dispersion of ZrO2 nanoparticles in the fillers and to form a good interfacial bonding between the magnesium matrix and ZrO2 nanoparticles. After welding, the effect of ZrO2 nanoparticles on the microstructure and mechanical properties of weld was evaluated. The test results showed that the yield strength of weld was greatly increased when using the nanocomposite fillers. The improvement in the yield strength was attributed to the grain refinement, coefficient of thermal expansion mismatch and Orowan strengthening mechanisms.

Extrinsic Wrinkling and Single Exfoliated Sheets of Graphene Oxide in Polymer Composites

We study the conformation of graphene oxide as the filler in nanocomposites of polystyrene and poly(methyl methacrylate) using inverse-space scattering techniques and atomic force microscopy. By subtracting the polymer scattering to estimate the scattering contribution from the graphene oxide, we discover surface fractal scattering that spans a range of more than two decades in reciprocal space, indicating that the graphene oxide within these materials is rough on a very wide range of length scales and implying extensive extrinsic wrinkling and folding. We discover that well-exfoliated, locally flat sheets of graphene oxide produce a crossover in the scattering at a length scale of 16 nm, which becomes dominated by the signature of mass fractal scattering from thin disks or sheets. We show that the local graphene oxide structure in these polymer–graphene oxide nanocomposites is identical to that of graphene oxide in a water solution studied on the same length scale. Our results confirm the presence of wel...

Effects of shape and flexibility of conductive fillers in nanocomposites on percolating network formation and electrical conductivity.

Nanocomposites consist of nanofillers and matrices, thus allowing one to design novel materials with desirable properties of both nanofillers and matrices. The percolating network formation of nanofillers in matrices is critical to such desired properties. Some nanofillers such as carbon nanotubes and graphene nanosheets are so flexible that they become either wavy or crumpled. Such a variability in the nanofiller conformation may affect the percolating network formation but has been often (but not always) ignored in the theoretical and computational investigation. In this work, we investigate how the flexibility of different kinds of nanofillers influences the formation of the percolating network by performing extensive Langevin dynamics simulations. We consider three kinds of nanofillers of different shape: nanospheres, nanorods, and nanoplates. When the sizes of nanofillers (or the radius of gyration, R(g)) are comparable, nanorods form a percolating network at a lower volume fraction than nanoplates while nanofillers require the highest volume fraction to form the percolating network, which is consistent with previous experiments. The percolation threshold concentration (ϕ(c)) of nanospheres increases with an increase in their R(g), while ϕ(c) of nanorods and nanoplates decrease with R(g). However, the effect of flexibility on the percolation threshold volume fraction is much more significant for nanoplates than nanorods. We also estimate the electric conductivity and find that the electric conductivity follows a scaling relation faithfully but with different critical exponents depending on the shape and flexibility.

Multi-functional polyhedral oligomeric silsesquioxane-functionalized carbon nanotubes for photo-oxidative stable Ultra-High Molecular Weight Polyethylene-based nanocomposites

Nanohybrid (phPOSS-f-CNTs) based on Carbon Nanotubes (CNTs) and Phenyl Polyhedral Olygomenric Silsesquioxane (phPOSS) have been synthesized to be used as multifunctional filler for polymer nanocomposites. The success of the functionalization procedure has been demonstrated via accurate spectroscopic, spectrometric and thermo-gravimetric analyses. The results reveal that a large portion of phPOSS is covalently linked to CNTs, while a small amount of phPOSS remains physically adsorbed due to the strong interactions coming from π electron coupling between the CNTs and phenyl rings in phPOSS. Small amounts (1wt.%) of phPOSS-f-CNTs have been dispersed in Ultra High Molecular Weight Polyethylene (UHMWPE), aiming at improving the photo-stability of the resulting nanocomposite. The rheological and thermo-mechanical behavior of UHMWPE/phPOSS-f-CNTs nanocomposite reflects two different opposite contributions, namely the reinforcement effect of CNTs and the plasticizing action of phPOSS molecules. Concerning the photo-oxidative behavior, phPOSS-f-CNTs show a remarkable protective ability, which is absolutely much higher than those exerted by CNTs and phPOSS molecules when added one by one. Such unexpected results could be explained considering (i) a synergic effect between phPOSS and CNTs, (ii) the possibility of phPOSS to act at the polymer–nanoparticles interface, which is a critical region for the degradation processes, and (iii) the formation of a phPOSS-rich layer that may hinder the oxygen diffusion within the polymeric matrix.

Enhancing the mechanical and thermal properties of boron nitride nanoplatelets/elastomer nanocomposites by latex mixing

Hexagonal boron nitride nanoplatelets (BNNPs) can serve as two-dimensional (2D) fillers for elastomer nanocomposites due to their excellent and intriguing mechanical and thermal properties.

Enhanced tribological properties in core–shell structured SiO2@GO hybrid fillers for epoxy nanocomposites

SiO2 coated with graphene oxide (GO) hybrids (SiO2@GO) were fabricated by electrostatic self-assembly and introduced into an epoxy polymer (EP) matrix to prepare epoxy composites by a solvent-free curing process.

Optical properties of supra-nano spherical filled resin composites compared to nanofilled, nano-hybrid and micro-hybrid composites.

This study aimed to evaluate and compare the optical properties of supra-nano spherical filled resin composites and the nanofilled, nano-hybrid and microhybrid composites using the Kubelka-Munk Theory. Diffuse reflectance of samples (Shade A2) was measured against white and black backgrounds, using a spectroradiometer, using a viewing booth with D65 illuminant and d/0º geometry. S and K coefficients and T were calculated using Kubelka-Munk's equations. The spectral behavior of S, K and T was similar for all dental resin composites analyzed (VAF close to 100%), even though they were, generally, statistically different (p≤0.05). The K-M T values overestimate the real value of Transmittance of the resin composites. Supra-nano spherical filled resin composites show the highest scattering and Transmittance when compared with the others materials, probably due to the shape and size of the filler. Such difference should be taken into consideration in a clinical situation to reproduce natural esthetic restorations.

EFFECT OF LIGHT EMITTING DIODE (LED) VERSUS HALOGEN PHOTO- POLYMERIZATION ON SHEAR BOND STRENGTHOF THREE TYPES OF RESIN COMPOSITES

Objective: This study investigated the effect of light emitting diode (LED) and halogen (QTH) photopolymerization on shear bond strength of three types of resin composites. Materials and methods: Sixty molars were selected and randomly assigned into 6 groups. The materials used were: Hybrid resin composite, nano-filled resin composite and silorane based resin composite. The analyzed resin composites were polymerized either by LED or halogen curing sys- tems. After 24 hours storage in distilled water the specimen was submitted to push-out shear bond strength testing using a universal testing machine at cross head speed of 0.5mm/min. one debonded representative specimen of each tested group was examined using an environmental scanning elec- tron microscope to determine the mode of failure. Results: All the specimens cured by LED demonstrated higher shear bond strength than those cured by QTH. There was no statistically significant difference between the two light curing units (LCUs) except for nano-filled resin composite that showed a significant difference. Silorane based resin composite groups were statistically significant higher than nano-filled and hybrid resin com- posites groups. While nano-filled resin composites was statistically non-significant higher than hy- brid resin composite groups. Conclusions: (1) The light emitting diode is effective as halogen curing light to obtain resin- composite with shear bond strength of no significant difference. (2) The silorane-based resin-com- posite restorative material is promising material regarding bonding efficiency to dentin. Recommendation: It is advised to cure nano-filled resin composite with light emitting diode (LED) to obtain higher shear bond strength to dentin

Surface roughness and erosion of nanohybrid and nanofilled resin composites after immersion in red and white wine

Aims:This study aimed to investigate the effects of red and white wine on the surface roughness and erosion of nanohybrid and nanofilled resin composites.Materials and Methods:Sixty specimens of each resin-based composite (RBC) were prepared. Before immersion, baseline data roughness values were recorded using a profilometer. Three groups of discs (n = 20) were then alternately immersed in red wine, white wine, and deionized water (as a control) for 25 min and artificial saliva for 5 min over four cycles. The specimens were then stored in artificial saliva for 22 h. This process was repeated for 5 days following immersion in artificial saliva for 2 days. Subsequently, the process was repeated. After immersion, the specimens were evaluated and data were analyzed by two-way repeated analysis of variance (ANOVA) and Tukey's honestly significant difference (HSD) (α = 0.05).Results:Red wine caused significantly greater roughness and erosion than did white wine and deionized water (P < 0.05). Nanohybrid resin composites were significantly rougher than nanofilled resin composites (P < 0.05).Conclusion:The effects of red and white wine on the surface roughness and erosion of resin composite restorative materials depended upon the physical and chemical composition of the restorative materials and the types of wine.

Revealing nanocomposite filler structures by swelling and small-angle X-ray scattering.

Polymer nanocomposites are used widely, mainly for the industrial application of car tyres. The rheological behavior of such nanocomposites depends in a crucial way on the dispersion of the hard filler particles - typically silica nanoparticles embedded in a soft polymer matrix. It is thus important to assess the filler structure, which may be quite difficult for aggregates of nanoparticles of high polydispersity, and with strong interactions at high loading. This has been achieved recently using a coupled TEM/SAXS structural model describing the filler microstructure of simplified industrial nanocomposites with grafted or ungrafted silica of high structural disorder. Here, we present an original method capable of reducing inter-aggregate interactions by swelling of nanocomposites, diluting the filler to low-volume fractions. Note that this is impossible to reach by solid mixing due to the large differences in viscoelasticity between the composite and the pure polymer. By combining matrix crosslinking, swelling in a good monomer solvent, and post-polymerization of these monomers, it is shown that it is possible to separate the filler into small aggregates. The latter have then been characterized by electron microscopy and small-angle X-ray scattering, confirming the conclusions of the above mentioned TEM-SAXS structural model applied directly to the highly loaded cases.

Influence of micro- and nanofiller contents on friction and wear behavior of epoxy composites

AbstractIn this study, the influence of micro- and nanofiller contents on the tribological performance of epoxy composites was studied. The fillers are micro-Al2O3, micro-TiO2, and micro-fly ash and nano-Al2O3, nano-TiO2, and nanoclay fillers. The microfillers were added to the epoxy by 10%, 20%, and 30% by weight. The nanofillers were added to the epoxy by 2.5%, 5%, and 10%. Friction and wear tests were conducted using the pin-on-disc arrangement. Tribo elements consisted of polymer pin and DIN 1.2344 steel counterface disc. A load value of 15 N, a sliding speed of 0.4 m/s, a sliding distance of 2000 m, and dry atmospheric conditions were applied to test conditions. The results show that the friction coefficients and the specific wear rates of the nanofilled composites increase as the filler content increases. For microfiller-filled epoxy composites, these values decrease as filler content increases. The tribological performance of epoxy composites is enhanced by the addition of microfillers, and the higher enhancement is reached with the addition of 30% fly ash filler. Finally, the pin and disc worn surface images show the presence of adhesive and some abrasive wear mechanisms.

Effect of the orientation of graphene-based nanoplatelets upon the Young's modulus of nanocomposites

The spatial orientation of the reinforcing elements in polymer-based composites plays a vital role in controlling mechanical properties but there is no generally-accepted way of quantifying the spatial orientation at the nanoscale of plate-like fillers in nanocomposites. A previous study found that the intensity of scattering of the Raman band is dependent on the axis of laser polarization when the laser beam is parallel to the surface of the graphene plane and demonstrated that this could be used to quantify the spatial orientation of the graphene. Based on this approach, polarized Raman spectroscopy is used here to quantify, as an example, the level of spatial orientation of graphene oxide (GO) flakes in different nanocomposites. Furthermore, the spatial orientation of nanoplatelets is quantitatively linked to the stress transfer to the reinforcement in nanocomposites and, in particular, a method for determining the Krenchel orientation factor for these plate-like fillers directly from the Raman data is demonstrated. This approach is employed to estimate the effective Young's modulus of the reinforcement in graphene-based nanocomposites.

Preparation and characterization of polystyrene-MgAl layered double hydroxide nanocomposites using bulk polymerization

Abstract Polymer/mineral filler nanocomposites are more and more used for diverse applications. As mineral fillers, layered double hydroxides (LDHs) present a great advantage as flame retardants from an environmental point a view (reduction of smoke and toxic gases). This article deals with the use of LDH as flame retardants as compared to montmorillonite (MMT). In situ bulk polymerization of styrene was carried out in the presence of MgAl LDH modified with dodecyl sulfate (DDS) and dodecylbenzene sulfonate (DBS) surfactants. LDH concentrations used were lower than 10 wt.%. X-ray diffraction analysis of the LDH-styrene suspensions revealed the monomer intercalation into the DDS-LDH galleries and a slight decrease in the DBS-LDH basal spacing. Transmission electron microscopy analysis showed that the polymerization occurred outside the DBS-LDH galleries, leading to exfoliation of the layers on the outer surface of LDH platelets. DDS-LDH particles were trapped in the PS polymer. The thermal stability effect was observed for all LDH nanocomposites by thermogravimetric analysis. Cone calorimetry measurements revealed that only the DBS-LDH nanofiller resulted in a reduction of the peak heat released rate (PHHR) and a decrease of smoke released. DBS-LDH/PS exhibited fire properties close to those of clay-PS nanocomposite at 7 wt.% montmorillonite. The PHRR reduction remained small and the total heat release rate constant at 7 wt.% DBS-LDH loading.

Experimental and analytical model for the electrical conductivity of polymer-based nanocomposites

In this research, an analytical formula has been developed to predict electrical conductivity of composites reinforced by conductive fillers such as polymer-based carbon composites. In this model, the percolation threshold phenomenon in the curve of electrical conductivity versus the filler volume fraction is represented by a sigmoidal equation. Moreover, four variables, consist of the filler electrical conductivity, filler aspect ratio, filler roundness, and wettability are included in the sigmoidal equation in specific sites. in this research in order to validation of model, some composites are provided by graphite, expanded graphite, and carbon fiber as reinforcement and phenolic resin as polymer. The manufacturing method is hot compaction. These composites plus several other composites derived from the literature are used to validate the model. The curve fitting is performed by MATLAB software. The composites are divided into two main categories: the first, nanofiller composites including graphene, carbon nanotube, expanded graphite, and carbon black; the second, microfiller composites including graphite and carbon fiber. In the paper, the effective factors on composite conductivity including the mixing methods, filler conductivity, filler aspect ratio, filler alignment, surface energy between filler and matrix, and matrix conductivity are comprehensively discussed. In addition, the filler volume fractions ascribed to percolation threshold in all samples is calculated and is compared together. The results show there is good agreement between the model and experimental data on both nanofiller and microfiber composites. In addition, it was specified that the aspect ratio and nanosizing of fillers are the most important factors effective on percolation threshold and jumping rate of sigmoidal curve.

Inorganic/organic nanocomposites: Reaching a high filler content without increasing viscosity using core-shell structured nanoparticles

Extensive research is being conducted on the development of inorganic/organic nanocomposites for a wide variety of applications in microelectronics, biotechnologies, photonics, adhesives, or optical coatings. High filler contents are usually required to fully optimize the nanocomposites properties. However, numerous studies demonstrated that traditional composite viscosity increases with increasing the filler concentration reducing therefore significantly the material processability. In this work, we synthesized inorganic/organic core-shell nanocomposites with different shell thicknesses. By reducing the shell thickness while maintaining a constant core size, the nanoparticle molecular mass decreases but the nanocomposite filler fraction is correlatively increased. We performed viscosity measurements, which clearly highlighted that intrinsic viscosity of hybrid nanoparticles decreases as the molecular mass decreases, and thus, as the filler fraction increases, as opposed to Einstein predictions about the viscosity of traditional inorganic/polymer two-phase mixtures. This exceptional behavior, modeled by Mark-Houwink-Sakurada equation, proves to be a significant breakthrough for the development of industrializable nanocomposites with high filler contents.

Decomposition and particle release of a carbon nanotube/epoxy nanocomposite at elevated temperatures

Carbon nanotubes (CNTs) as fillers in nanocomposites have attracted significant attention, and one of the applications is to use the CNTs as flame retardants. For such nanocomposites, possible release of CNTs at elevated temperatures after decomposition of the polymer matrix poses potential health threats. We investigated the airborne particle release from a decomposing multi-walled carbon nanotube (MWCNT)/epoxy nanocomposite in order to measure a possible release of MWCNTs. An experimental set-up was established that allows decomposing the samples in a furnace by exposure to increasing temperatures at a constant heating rate and under ambient air or nitrogen atmosphere. The particle analysis was performed by aerosol measurement devices and by transmission electron microscopy (TEM) of collected particles. Further, by the application of a thermal denuder, it was also possible to measure non-volatile particles only. Characterization of the tested samples and the decomposition kinetics were determined by the usage of thermogravimetric analysis (TGA). The particle release of different samples was investigated, of a neat epoxy, nanocomposites with 0.1 and 1 wt% MWCNTs, and nanocomposites with functionalized MWCNTs. The results showed that the added MWCNTs had little effect on the decomposition kinetics of the investigated samples, but the weight of the remaining residues after decomposition was influenced significantly. The measurements with decomposition in different atmospheres showed a release of a higher number of particles at temperatures below 300 °C when air was used. Analysis of collected particles by TEM revealed that no detectable amount of MWCNTs was released, but micrometer-sized fibrous particles were collected.

1,2,3-Triazole/MWCNT conjugates as filler for gelcoat nanocomposites: new active antibiofouling coatings for marine application

A polyester-based gelcoat nanocomposite was synthesized by using as nanofiller multi-walled carbon nanotubes (MWCNTs) conjugated with a biocidal 1,2,3-triazole to be used as a new eco-friendly antibiofouling coating. 1,2,3-Triazole/MWCNT conjugates containing differently substituted 1,2,3-triazoles have been synthesized and characterized by physical, chemical, and morphological analyses. Ecotoxicological studies, performed on marine organisms belonging to different evolutive classes, provided information about the choice of the more interesting nanofiller. The synthesized gelcoat nanocomposite showed a significant improvement in the wet ability with respect to the Gelcoat alone. Preliminary biological tests performed on the nanocomposite revealed great biocidal properties, thus providing new opportunities to develop an effective antibiofouling coating.

Modification of mechanical properties in polymer nanocomposites by the incorporation of specific self-complementary hydrogen bonding interactions

The dispersion, aggregate morphology, and interfacial strength of fillers in polymer nanocomposites are crucial in determining their physical properties. Here, we utilize the quadruple hydrogen bonding group ureidopyrimidinone (UPy) to investigate enthalpic effects on the dispersion of silica nanoparticles in a poly(butyl acrylate) copolymer matrix and to correlate dispersion with mechanical properties. Butyl acrylate was copolymerized with an UPy side chain functional methacrylate monomer and blended with silica nanoparticles containing various degrees of UPy, hexyl, or silanol surface functionality. The tensile and dynamic mechanical responses of these nanocomposites were measured, and the effects of varying surface functionality on mechanical properties are discussed and correlated to dispersion by TEM. The competing effects of filler–filler, matrix–filler, and matrix–matrix hydrogen bonding lead to a system where both the type and amount of filler surface functionality are of critical importance to the material's final strength.