Alignment Of Nanofillers Research Articles

Structure–Property Correlation in Natural Rubber Nanocomposite Foams: A Comparison between Nanoclay and Cellulose Nanofiber Used as Nanofillers

Nanocomposite foams of natural rubber (NR) with 5 phr of two kinds of nanofillers, nanoclay (NC) and cellulose nanofiber (CNF), were produced using the latex mixing method and foaming with azodicarbonamide. The effect of the nanofiller on the structure and mechanical properties of NR foams was investigated through SEM, TEM, tensile tests, WAXD, and compression set measurements. Smaller cells with a narrower distribution were attained in the NC/NR foam when compared to the NR and CNF/NR foams, and the expansion ratio was larger due to the suppression of the shrinkage in the NC/NR foam. The foaming of the NR nanocomposites reduced the size of the filler aggregates and improved the dispersion and alignment of nanofillers in the cell walls. The addition of NC and CNF enhanced the tensile strength of the NR foam by 139% and 62%, respectively, without sacrificing the excellent strain of the NR, due to the acceleration of the strain-induced crystallization and small size of the filler aggregates. The compression set of the NR foam could also be reduced in the NC/NR foam compared with the NR and CNF/NR foams.

Magnetic-field-assisted DLP stereolithography for controlled production of highly aligned 3D printed polymer-Fe3O4@graphene nanocomposites

Layer-based 3D printing of digital light processing offer good control over the orientation of long reinforcing fibers but still lacks superior mechanical properties. In this paper, nanocomposites with polymer and magnetic Fe3O4@graphene fillers were printed by the DLP method where the magnetic Fe3O4@graphene inside the polymer was aligned with a magnetic field. The alignment of nanofillers significantly enhanced the mechanical properties. By varying the angle of the magnetic field, Fe3O4@graphene reinforced composites produced different mechanical properties. Aligned structure-mechanical property relation revealed that 0⁰ alignment enhanced mechanical property more compared to 90⁰ alignment of filler materials at the concentrations of 0.4, 0.8, and 1.6 wt.%. This is attributed to the dispersion and orientation of the nanofillers and the photopolymerization of the monomer. The Young's modulus for the aligned 0.8 wt.% of Fe3O4@graphene(1/3) filler showed a significant improvement when a magnetic field was applied at a 0⁰ angle.

Modelling the effect of nanofiller’s shape and alignment on the dielectric strength and permittivity of polyethylene nanocomposite insulation

Solid insulation defects are a major cause of power failures. Incorporation of micro and nanoparticles in the solid insulation materials has proven its advantage. It has been reported that nanocomposites are far superior in terms of insulation to microcomposites because of larger interphase area between nanofillers and polymer in nanocomposites. In addition to that nature, size, shape, concentration and alignment of nanofillers affect the properties of resulting nanocomposite insulation. A lot of work has reported the effect of nanofiller’s nature, size and concentration but very little is reported on the effect of filler’s shape and alignment on the insulation and dielectric properties. In this paper nanocomposite dielectrics with nanofillers of various shapes and alignment are modelled by varying their permittivity using finite element method. To characterize the effect of various shapes and orientation electric field intensity and energy density models are computed. Simulations are performed using AC/DC module of COMSOL Multiphysics. The results revealed that shape and alignment of nanofillers are the two key factors in tuning the breakdown strength and permittivity of nanocomposite dielectrics for their applications in insulation as well as high voltage capacitors.

In-Plane Oriented Linear Assembly of Te Nanowires in Polydimethylsiloxane-Based Composite Film for the Enhancement of Piezoelectric Property

Flexible piezoelectric materials are attractive as empowering devices in the field of sensors, actuators and energy harvesting. Herein, we fabricate a polymer-based nanocomposite with piezoelectric property by incorporation of tellurium (Te) nanowires. Firstly, large-scale selective synthesis of uniform single crystalline tellurium nanowires with a diameter of 150 nm av. and 10 μm av. in length, can be realized by a hydrothermal process. The Te nanowires with random distribution in pre-polymer of polydimethylsiloxane (PDMS) is relocated forming linearly aligned assembly controlled by application of external AC electric field. The aligned Te-PDMS at 0.5 wt% Te content gives a maximum output voltage of 13.9 V, which is 2.4-fold comparing corresponding film with random distribution. This work provides an effective alignment of nanofillers in a viscous polymer matrix and noble method to fabricate enhance piezoelectric composite film materials.

Improving the efficiency of Nafion-based proton exchange membranes embedded with magnetically aligned silica-coated Co3O4 nanoparticles

In this study, Nafion proton exchange membranes with incorporated silica-coated Co3O4 nanoparticles (Nafion/CT) were prepared. The nanoparticles were synthesized and characterized using FT-IR spectroscopy, XRD, magnetic measurements, TEM, SEM, and EDX spectroscopy. Thereafter, the nanoparticles were employed as an effective additive so as to improve the Nafion/CT properties. To do so, the spherical core-shell nanoparticles (Co3O4 diameter 12 nm; SiO2 layer thickness 20 nm) were aligned by a magnetic field in the Nafion matrix during solution casting and solvent evaporation. The thus obtained nanocomposite membranes, including control samples without particles or with particles but without alignment, were investigated with respect to their structure by SEM, EDX, and XPS analyses, and also with regard to their water uptake, proton conductivity, and methanol permeability. Overall, the aligned nanocomposite membranes showed much better performance than that of randomly dispersed nanocomposite membranes. The data indicate that regarding aligned structure, the proton transfer channels in the membrane matrix become less tortuous so that proton transfer through the membrane occurs faster while at the same time methanol transfer is partially blocked. The Nafion/CT nanocomposite membrane containing 1 wt% of CT exhibited a proton/methanol selectivity at 25 °C of 6.04 × 104 S s−1 cm−3, whereas the pristine Nafion membrane showed a selectivity of 4.2 × 104 S s−1 cm−3. The nanofiller alignment by magnetic field improved the proton conductivity at 90 °C from 0.14 S cm−1 (no field) to 0.18 S cm−1.

A computational exploration of the effect of alignment and aspect ratio on alternating current conductivity in carbon nanofiber–modified epoxy

Carbon nanofiller–modified polymers have been the subject of intense study for years due to their potential use in diverse and far-reaching applications. The effect of nanofiller network parameters on macroscale direct current electrical transport has been thoroughly elucidated by extensive nano-to-microscale modeling. As a result, we now have great insight into how the conductive and piezoresistive properties of nanocomposites can be tailored through judicious control of the underlying nanofiller network. It is also well-known that carbon nanofiller–modified polymers possess frequency-dependent alternating current electrical properties. Even though work has been done to understand the alternating current properties of nanocomposites via experimental characterization and through the development of macroscale equivalent circuit models, much less has been done to understand how macroscale alternating current conductivity depends on microscale effects such as nanofiller alignment and aspect ratio. This is an important knowledge gap because, like direct current conductivity, the underlying nanofiller network ultimately gives rise to macroscale alternating current transport in these materials. To this end, we herein present an alternating current microscale percolation model for carbon filler–based polymer nanocomposites. After calibration against experimental complex impedance data from randomly ordered carbon nanofiber–modified epoxy, this model is used to explore the effect of carbon nanofiber alignment and aspect ratio on alternating current conductivity. These simulations show that alternating current conductivity generally increases with increasing alignment and with aspect ratio; however, the competing effects of alternating current and direct current percolation give rise to substantial variation in alternating current conductivity at low frequencies and with poor percolation. The methodology presented in this article provides a modeling tool by which nanocomposites with highly optimized alternating current properties can be developed through careful control and tailoring of nanofiller network properties for the realization of exotic, next-generation material functionality.

Effect of crystal orientation and nanofiller alignment on dielectric breakdown of polyethylene/montmorillonite nanocomposites

Extrusion blown polyethylene and polyethylene/montmorillonite nanocomposite films were cold stretched to various ratios to quantify the influence of the crystal orientation and the nanofiller alignment on their dielectric breakdown performance. It was found that the crystal orientation could increase the breakdown strength (EBD) in the stretched blown films. The aligned pseudo-2D inorganic nanoclays provided additional strong improvements in EBD that can be superimposed to any EBD enhancement due to the polymer crystal orientation. At high filler loadings and high stretching ratios, the onset of percolation was observed through a substantial improvement in the dielectric breakdown strength.

Structured Polyethylene Nanocomposites: Effects of Crystal Orientation and Nanofiller Alignment on High Field Dielectric Properties

ABSTRACTIn previous work we have shown that aligned high aspect-ratio (pseudo-2D) nanofillers can yield large dielectric breakdown strength (EBD) improvements for a nanocomposite with a low-crystallinity polyethylene matrix. Here, we report a systematic study which delineates the contributions of the aligned inorganic fillers and of the aligned polymer crystallites in the overall EBD improvement achieved in the nanocomposites. Specifically, extrusion blown-molded polyethylene/montmorillonite nanocomposite films were cold-stretched to various strains, to further align the nanoparticles parallel to the film surface; this filler alignment is accompanied by a commensurate alignment of the polymer crystallites, especially those heterogeneously nucleated by the fillers. A systematic series of films are studied, with increased extent of alignment of the fillers and of the crystalline lamellae (quantified through Hermans orientation order parameters from 2D X-ray diffraction studies) and the aligned structure is correlated to the electric field breakdown strength (quantified through Weibull failure studies). It is shown that aligned pseudo-2D inorganic nanofillers provide additional strong improvements in EBD, improvements that are beyond, and added in excess of, any EBD increases due to polymer-crystal orientation.

Processing and characterization of amorphous polyethylene terephthalate fibers for the alignment of carbon nanofillers in thermosetting resins

The engineering aspects, which are associated with the development of nanocomposites, involve in either final properties or processability of nanocomposites. Both are affected by the distribution of nanofiller in the matrix and by the aspect ratio of the nanofiller. A nanofilled thermosetting resin can be exploited as a matrix for continuous fibers when the alignment of a high aspect ratio nanofiller is achieved, and in this case, a hierarchical composite is obtained. In this study, a new procedure for the alignment of nanofillers in a thermosetting matrix is proposed. The two‐step approach is based on (i) the alignment of nanofillers (carbon nanotubes, graphene, etc.) in thermoplastic fibers by a fiber spinning process and (ii) the use of these nanocomposite fibers as a carrier to bring aligned nanofillers into a reactive thermosetting resin. These fibers, soluble in the thermosetting resin, release the nanofillers orientated according to the direction in which fibers are positioned, even after the curing of the matrix. The proof of concept is demonstrated by producing melt spun polyethylene terephtalate (PETg) fibers filled with graphene nanoplatelets (GNP) and multiwall carbon nanotubes (MWCNT) with a very high filler content (up to 10 wt%) in view of producing a hierarchical composite. POLYM. COMPOS., 36:1096–1103, 2015. © 2015 Society of Plastics Engineers

Where micro- and nano-worlds meet: multiscale polymer composites

data has been published on the preparation and characterization of polymer nanocomposites. Despite the very intense research efforts, the mechanical properties reported so far for nanocomposites are quite disappointing, particularly when compared to that of structural composites reinforced with highperformance continuous fibers (DOI: 10.1126/science.1151434). Among the main causes invoked to explain the obtained results one could mention i) poor dispersion and alignment of nanofillers, ii) difficulties in achieving an elevated volume fraction of nanofillers and iii) scarce bond and load transfer ability at the nanofiller/matrix interface. Intensive research is currently ongoing to tackle and possibly solve the above mentioned problems. Recently, new strategies emerged for the preparation of structural materials in which both microand nano-reinforcements coexist in multiscale composites (DOI: 10.1177/0731684412456612). Nanoscale reinforcements have been included within fiber reinforced composites in several ways, such as i) grafting or electrophoretic deposition (mostly of carbon nanomaterials) onto the fiber surface (DOI: 10.1016/j.compscitech.2014.06.019), ii) localization in sizing/coatings for fiber treatment (DOI: 10.1016/j.compositesa.2012.08.027) iii) homogeneous dispersion in the whole polymer matrix (DOI: 10.1177/0731684414542668). The presence of nanoreinforcements in traditional microcomposites has been proven to play beneficial effects on several properties, including delamination resistance, fiber/ matrix shear strength (DOI: 10.1016/j.compscitech. 2012.12.016), electrical and thermal conductivities. The possibility to improve the electrical conductivity of typically insulating materials such as glass/ epoxy laminates, is opening new possibilities for the monitoring of deformation and damage in composite structures under service. For example, it has been proven that an integrated system of carbon nanotubes and piezoelectric sensors can be used to detect both microcracks and localized damage/ delamination in composite structures (DOI: 10.1016/ j.carbon.2012.04.008). Therefore, nanomodified matrices can be used for a continuous monitoring of deformational levels and damage of structural composites under various loading conditions such as fatigue, impact and creep (DOI: 10.1016/j.compositesa.2012.03.019). Can we dream of polymer composites in which microand nano-structures synergistically operate to provide both structural and functional features, including self-repairing and adaptive responses?

The influence of nanofiller alignment on transverse percolation and conductivity

Nanocomposites have unprecedented potential for conductivity-based damage identification when used as matrices in structural composites. Recent research has investigated nanofiller alignment in structural composites, but because damage identification often requires in-plane measurements, percolation and conductivity transverse to the alignment direction become crucial considerations. We herein contribute indispensable guidance to the development of nanocomposites with aligned nanofiller networks and insights into percolation trends transverse to the alignment direction by studying the influence of alignment on transverse critical volume fraction, conductivity, and rate of transition from non-percolating to percolating in three-dimensional carbon nanotube composite systems.

Nanocomposite fibres: a strategy for stronger materials?

The scientific literature is full of claims for the exceptional potentialities of nanoscale reinforcing materials, such as nanoparticles, nanofibres, nanotubes and nanoplatelets, to improve the mechanical properties of polymer matrices. However, most of the reliable data on the effective properties of polymer nanocomposites are somewhat disappointing, particularly when compared to structural composites reinforced with high-performance continuous fibers. The main reasons advocated to explain the discrepancies with theoretical predictions include poor dispersion, inadequate alignment of nanofillers, and bad stress-transfer ability at the interface (i.e. poor adhesion with polymer matrix). A possible route for introducing nanofillers into polymer matrices, and retaining a certain control on orientation and improving the dispersion level, can be offered by polymer fibres technology. In fact, the elevated draw ratios and elongational flow involved in typical fibre production processes can concurrently promote a disruption of the aggregates and a strong orientation of the nanofillers along the fibre axis. A variety of processing techniques can be adopted for the production of nanocomposite fibres, including spinning from polymer melts or solutions, gel-spinning, melt-blowing and electrospinning. This approach has been proven to be extremely efficient when nanofillers with an elevated aspect ratio, such as nanofibres or nanotubes, are concerned. In fact, in the last decade several papers have been published documenting the extraordinary reinforcing efficiency of single- or multiwalled carbon nanotubes in highly oriented polymer fibres or tapes. More recently, some successful attempts have been made to extend this approach to nanoplatelets, in particular layered silicates and graphene. Among the drawback to overcome, one can list the marked viscosity increments generally induced by nanofillers in polymer matrices, and the consequent necessity to identify proper processing conditions for the fibre production. Moreover, the decrease of elongation at break (which is also reflected in the molten state) typically induced by some nanofillers may also limit fibre preparation possibilities. The outstanding properties of nanocomposite fibres could improve traditional textile products, or be exploited in some advanced processing technologies, such as single- or all-polymer composites and commingled yarns composites.

Effect of external electric field on the microstructures and properties of carbon nanotubes/thermosets nanocomposites

AbstractThe alignment of multiwalled carbon nanotubes (MWCNTs) and thermosetting resins in nanocomposites based on field‐aided micro‐tailoring (FAiMTa) technology was studied by means of scanning electric microscopy (SEM), Raman spectroscopy, and atomic force microscopy (AFM), and the effect of the different values of electric field intensity on the changes of the microstructures and properties of nanocomposites were presented. The experimental results implied that the electric field encouraged the molecular alignment of polymers and MWCNTs orientation within the polymeric matrices along the field direction during their curing stages. It was found that the extents of their orientation and alignment were closely dependent on the external electric field intensity by means of Raman spectroscopy and AFM measurements. The thermal and dielectric properties of nanocomposites were examined by thermogravimetric analysis (TGA) and dielectric analysis (DEA), respectively. The TGA and DEA measurements revealed substantial differences in the thermal and dielectric behaviors for the thermoelectrically processed nanocomposites. These differences could be ascribed to the microstructural changes of matrix at the molecular level and the alignment of nanofillers. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

A comparative study of melt spun polyamide-12 fibres reinforced with carbon nanotubes and nanofibres

A range of multi-wall carbon nanotubes and carbon nanofibres were mixed with a polyamide-12 matrix using a twin-screw microextruder, and the resulting blends spun to produce a series of reinforced polymer fibres. The aim was to compare the dispersion and resulting mechanical properties achieved for nanotubes produced by the electric arc and a variety of chemical vapour deposition techniques. A high quality of dispersion was achieved for all the catalytically-grown materials and the greatest improvements in stiffness were observed using aligned, substrate-grown, carbon nanotubes. The use of entangled multi-wall carbon nanotubes led to the most pronounced increase in yield stress, most likely as result of increased constraint of the polymer matrix due to their relatively high surface area. The degrees of polymer and nanofiller alignment and the morphology of the polymer matrix were assessed using X-ray diffraction and differential scanning calorimetry. The carbon nanotubes were found to act as nucleation sites under slow cooling conditions, the effect scaling with effective surface area. Nevertheless, no significant variations in polymer morphology as a function of nanoscale filler type and loading fraction were observed under the melt spinning conditions applied. A simple rule-of-mixture evaluation of the nanocomposite stiffness revealed a higher effective modulus for the multi-wall carbon nanotubes compared to the carbon nanofibres, as a result of improved graphitic crystallinity. In addition, this approach allowed a general comparison of the effective nanotube modulus with those of nanoclays as well as common short glass and carbon fibre fillers in melt-blended polyamide composites. The experimental results further highlight the fact that the intrinsic crystalline quality, as well as the straightness of the embedded nanotubes, are significant factors influencing the reinforcement capability.

Carbon Nanotube and Nanofibre Reinforced Polyamide-12 Fibres

ABSTRACTA range of multi-wall carbon nanotubes and carbon nanofibres were mixed with a polyamide-12 matrix using a twin-screw microextruder, and the resulting blends used to produce a series of reinforced polymer fibres. The aim was to compare the dispersion and mechanical properties achieved for nanofillers produced by different techniques. A high quality of dispersion was achieved for all the catalytically-grown materials and the greatest improvements in stiffness were observed using aligned, substrate-grown, carbon nanotubes. The use of entangled multi-wall carbon nanotubes led to the most pronounced increase in yield stress. The degrees of polymer and nanofiller alignment and the morphology of the polymer matrix were assessed using X-ray diffraction and calorimetry.