Nanofillers In Polymer Nanocomposites Research Articles

One-Component Nanocomposites Made from Diblock Copolymer Grafted Cellulose Nanocrystals.

Cellulose nanocrystals (CNCs) are bio-based, rod-like, high-aspect-ratio nanoparticles with high stiffness and strength and are widely used as a reinforcing nanofiller in polymer nanocomposites. However, due to hydrogen-bond formation between the large number of hydroxyl groups on their surface, CNCs are prone to aggregate, especially in nonpolar polymer matrices. One possibility to overcome this problem is to graft polymers from the CNCs' surfaces and to process the resulting "hairy nanoparticles" (HNPs) into one-component nanocomposites (OCNs) in which the polymer matrix and CNC filler are covalently connected. Here, we report OCNs based on HNPs that were synthesized by grafting gradient diblock copolymers onto CNCs via surface-initiated atom transfer radical polymerization. The inner block (toward the CNCs) is composed of poly(methyl acrylate) (PMA), and the outer block comprises a gradient copolymer rich in poly(methyl methacrylate) (PMMA). The OCNs based on such HNPs microphase separate into a rubbery poly(methyl acrylate) phase that dissipates mechanical energy and imparts toughness, a glassy PMMA phase that provides strength and stiffness, and well-dispersed CNCs that further reinforce the materials. This design afforded OCNs that display a considerably higher stiffness and strength than reference diblock copolymers without the CNCs. At the same time, the extensibility remains high and the toughness is increased up to 5-fold relative to the reference materials.

Direct measurement of charge trap depth in polymer nanocomposites

Polymer nanocomposites (PNCs) exhibit excellent electrical properties owing to charge trapping provided by nanofillers. However, the role of nanofillers in trap formation at the microscopic level is poorly understood. In this study, we propose a method to determine the charge trap depth of nanofillers in PNCs using x-ray photoelectron spectroscopy (XPS) measurements and first-principles calculations. The low-density polyethylene (PE)/TiO2 nanocomposite is selected as the measurement target as it was previously reported the charges are trapped by TiO2 loading to PE. We observe TiO2 can serve as a trap for holes, and the trap depth is determined to be 0.9 eV. Furthermore, the computed charge trap depth calculated by G 0 W 0 calculation, which reproduce the experimental band gap, is comparable to the XPS result, which strongly supports the validity of our method. In addition, owing to the quantitative evaluation of the electronic structure, it was shown that the charge trap depth of the nanofiller can be controlled by tuning the surface dipole with surface modification of the nanofiller. The approach proposed in this study to determine the charge trap depth of nanofillers provides the prospect of designing PNCs with desirable properties from the atomic or molecular level.

Dispersion and Diffusion Mechanism of Nanofillers with Different Geometries in Bottlebrush Polymers: Insights from Molecular Dynamics Simulation.

The dispersion and diffusion mechanism of nanofillers in polymer nanocomposites (PNCs) are crucial for understanding the properties of PNCs, which is of great significance for the design of novel materials. Herein, we investigate the dispersion and diffusion behavior of two geometries of nanofillers, namely, spherical nanoparticles (SNPs) and nanorods (NRs), in bottlebrush polymers by utilizing coarse-grained molecular dynamics simulations. With the increase of the interaction strength between the nanofiller and polymer (εnp), both the SNPs and NRs experience a typical "aggregated phase-dispersed phase-bridged phase" state transition in the bottlebrush polymer matrix. We evaluate the validity of the Stokes-Einstein (SE) equation for predicting the diffusion coefficient of nanofillers in bottlebrush polymers. The results demonstrate that the SE predictions are slightly larger than the simulated values for small SNP sizes because the local viscosity that is felt by small SNPs in the densely grafted bottlebrush polymer does not differ much from the macroscopic viscosity. The relative size of the length of the NRs (L) and the radius of gyration (Rg) of the bottlebrush polymer play a key role in the diffusion of NRs. In addition, we characterize the anisotropic diffusion of NRs to analyze their translational and rotational diffusion. The motion of NRs in the direction perpendicular to the end-to-end vector is more hindered, indicating that there is a strong coupling between the rotation of NRs and the motion of the polymer. The NR motion shows stronger anisotropic diffusion at short time scales because of the steric effects generated by side chains of the bottlebrush polymer. In general, our results provide a fundamental understanding of the dispersion of nanofillers and the microscopic mechanism of nanofiller diffusion in bottlebrush polymers.

The effect of branched carbon nanotubes as reinforcing nano-filler in polymer nanocomposites

This work discusses the mechanical and dissipative properties of nanocomposite materials made of a high-performance thermoplastic polymer (polybutylene terephthalate, PBT) integrated with branched carbon nanotubes (bCNTs) as nanofiller. The storage and loss moduli as well as the loss factor/damping ratio of the nanocomposites are experimentally characterized for increasing bCNT weight fractions (wt% bCNT) upon variations of the input cyclic strain amplitude and of the input frequency, respectively. The trends obtained for the nanocomposites mechanical properties indicate improvements both in storage and loss modulus by increasing the bCNT weight fraction from 0.5% to 2%. The striking differences between the damping capacities exhibited by CNT/polymer and bCNT/polymer nanocomposites are discussed to shed light onto the different underlined mechanics of the nanocomposites. Due to the stick–slip relative sliding motion of the polymer chains with respect to the straight CNTs, CNT/PBT nanocomposites are known to exhibit a peak in the damping vs. strain amplitude curves, past which, the damping capacity shows a monotonically increasing trend due to the conjectured sliding of the polymer crystals. On the other hand, we show for the first time that bCNT/PBT nanocomposites do not exhibit a peak in the damping capacity but rather a plateau after an initial drop at low strains. This behavior is attributed to the much reduced mobility of the branched CNTs and the lack of formation of crystalline structures around the bCNTs.

The interconnection of efficiency and the degree of aggregation of nanofiller in polymer nanocomposites

The rule of mixtures was the first theoretical model, used for a description of the elastic modulus of multicomponent systems, including those of polymer nanocomposites. However, the use of nominal magnitudes of the characteristics of system components in such an approach led to overestimated values of their elastic modulus. Therefore, various modified versions of the rule of mixtures are currently used for this purpose, which significantly complicate its application and do not indicate the physical factors leading to overestimated theoretical results. In this study, a modified rule of mixtures was proposed, taking into account the decrease in the effective (actual) elastic modulus of the nanofiller in a polymer matrix of the nanocomposite compared to the nominal value determined only by the aggregation of the nanofiller. It is known that the aggregation process is the main negative factor reducing the final properties of nanomaterials, while other factors (for example, the interfacial adhesion level, nanofiller orientation, etc.) depend on the degree of aggregation. The physical sence of the aggregation process is a decrease in the relative proportion of nanofiller-polymer matrix interfacial regions, i.e., the effectiveness of a nanofiller as a reinforcing element of a nanocomposite is determined by its ability to generate high-modulus interfacial regions. The rule of mixtures modified in this way correctly describes the dependence of the elastic modulus of the nanocomposite on the content of the nanofiller, regardless of the type of the latter (carbon nanotubes, graphene, etc.). Therefore, the nanofiller efficiency indicator can serve as a complex parameter that is characteristic of the nanocomposite quality.

Quantifying the 3D multiscale dispersion structure of nanofillers in polymer nanocomposites by combining 3D-STEM and Synchrotron Radiation X-ray CT

In this study, a method for quantifying the 3D multiscale dispersion structure of nanofillers including nano-sized primary filler nanoparticles, nano-to sub-micron-sized agglomerates, and micron-sized filler networks in rubber nanocomposites was established for the first time by combining 3D-Scanning Transmission Electron Microscopy (3D-STEM) in a High-angle Annular Dark Field mode and Synchrotron Radiation X-ray CT. By using this method, a model of multiscale dispersion structure of silica (SiO2) in hydrogenated nitrile butadiene rubber (HNBR) nanocomposites with different SiO2-HNBR interactions (If-r) was established. Interestingly, when the content of SiO2 is near the percolation threshold, as the If-r increases, the homogeneity of SiO2 increases, the compactness of SiO2 agglomerates decreases, and the branching degree of SiO2 agglomerates increases, resulting in higher branching degree and connectivity of filler networks. Furthermore, it was firstly revealed that the stronger Payne effect directly correlate with the higher connectivity of filler networks, rather than the higher homogeneity of nanofillers.

Atomistic simulations of functionalization of aramid fiber‐epoxy nanocomposite

AbstractOwing to its high degree of crystallinity and orientation, the surface of aramid fiber is smooth, causing its low bonding strength with polymer matrix. This has restricted the application of aramid fiber in reinforced polymer materials. Effective methods are by introducing functional groups through surface modification and by increasing its surface roughness thereby greatly improving its bonding strength with the polymer. In this work, molecular dynamics (MD) simulation study fiber functionalized with hydroxyl (OH), carboxyl (COOH), and the silane coupling agent as nanofillers for polymer nanocomposites. The interfacial characteristics and the mechanical behavior of polymer nanocomposites are investigated. The results show that the functionalization can enhance the interfacial shear stress and tensile strength. The functional group not only provides a stronger interface, but also provides additional mechanical interlocking effect, which effectively improves load‐bearing transmission capacity. The analysis of the micro‐mechanism from the energy level also provides new insights for the functionalized design of nanocomposites.

Novel Fluorescence Method for Determination of Spatial Interparticle Distance in Polymer Nanocomposites.

Interparticle distance (ID) is generally used for spatial evaluation on the dispersion of nanofillers in polymer nanocomposites (PNCs) in order to gain in-depth insight into fundamental understanding of reinforcement and structure-property correlation. However, currently available methods mainly rely on two-dimensional observation technologies or simulation methods. Herein, using layered double hydroxides (LDHs) in low-density polyethylene (LDPE) as a model matrix, we developed a novel spatial ID determination method through a post labeling fluorescent imaging technique. The spatial ID of LDH nanofillers was achieved by a MATLAB program based on the 3D coordinates of LDH nanofillers in PNCs. The spatial ID data indicated the varied dispersion states of LDH nanofillers from "random", "even", to "clustered" in PNCs. More importantly, the so-called exceptional performances of PNCs at high loading of LDH nanofillers can be reasonably explained in combination with the mechanical studies. This proposed approach could undoubtedly provide valuable information in elucidating the structure-property correlation in PNCs. We believe that this work would be a guide to design advanced PNC materials.

Quantification of Dispersion for Weakly and Strongly Correlated Nanofillers in Polymer Nanocomposites

The dispersion of nanoparticles in viscous polymers is dictated by kinetics, interaction potentials between particles, and interfacial compatibility between the matrix and dispersed phases. It was ...

Graphene Oxide-Silver Nanoparticle Nanohybrids: Synthesis, Characterization, and Antimicrobial Properties.

Drug resistance of pathogenic microorganisms has become a global public health problem, which has prompted the development of new materials with antimicrobial properties. In this context, antimicrobial nanohybrids are an alternative due to their synergistic properties. In this study, we used an environmentally friendly one-step approach to synthesize graphene oxide (GO) decorated with silver nanoparticles (GO–AgNPs). By this process, spherical AgNPs of average size less than 4 nm homogeneously distributed on the surface of the partially reduced GO can be generated in the absence of any stabilizing agent, only with ascorbic acid (L-AA) as a reducing agent and AgNO3 as a metal precursor. The size of the AgNPs can be controlled by the AgNO3 concentration and temperature. Smaller AgNPs are obtained at lower concentrations of the silver precursor and lower temperatures. The antimicrobial properties of nanohybrids against Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa, Gram-positive Staphylococcus aureus, and the yeast Candida albicans were found to be concentration- and time-dependent. C. albicans and S. aureus showed the highest susceptibility to GO–AgNPs. These nanohybrids can be used as nanofillers in polymer nanocomposites to develop materials with antimicrobial activity for applications in different areas, and another potential application could be cancer therapeutic agents.

Determining the Orientation and Interfacial Stress Transfer of Boron Nitride Nanotube Composite Fibers for Reinforced Polymeric Materials

Boron nitride nanotubes (BNNTs) are promising nanofillers in polymer nanocomposites due to their high strength and high modulus as well as thermal and chemical stability. In BNNTs nanocomposites, t...

Rheological and electrical properties of polystyrene nanocomposites via incorporation of polymer-wrapped carbon nanotubes

Carbon nanotubes (CNTs) are used as nanofillers in polymer nanocomposites to improve the properties of a matrix polymer because of their excellent properties. However, CNTs tend to aggregate due to the strong van der Waals force between CNTs. To solve the problem, surface-modified CNTs with hydrophilic polymers, such as polyvinyl pyrrolidone (PVP) and polystyrene sulfonate (PSS), were employed. Polystyrene (PS)/CNT nanocomposites were fabricated by latex technology, which is a suitable method for dispersing nanofillers in aqueous particle suspension. The effect of the incorporation of the modified CNT was significant, thereby resulting in increased modulus at lower frequencies when compared to that of neat PS. Electrical percolation thresholds of PS/PSS-wrapped CNT and PS/PVP-wrapped CNT nanocomposites corresponded to 0.39 and 0.52 wt.%, respectively. The PS/PSS-CNT nanocomposites exhibited higher rheological and electrical properties than the PS/PVP-CNT counterparts due to the hydrophilic nature of PSS with strong negative charge groups.

Large specific surface area and rigid network of nanocellulose govern the thermal stability of polymers: Mechanisms of enhanced thermomechanical properties for nanocellulose/PMMA nanocomposite

Cellulose nanofibrils (CNFs) are an ideal candidate for green nanofillers in polymer nanocomposites. Benefiting from the unique structural features of CNFs, mechanical and thermal properties of polymers are efficiently improved. To tailor the material properties, we must first understand how the features of CNFs lead to their function. Here, thermomechanical properties of CNF/poly(methylmethacrylate) (PMMA) nanocomposite were investigated through several approaches with a focus on understanding how the nanosize of CNFs influences the properties. Results confirmed that the nanocomposite film showed efficient improvements in thermal dimensional stability and storage modulus by achieving homogeneous and individual dispersion of CNF in the matrix. Moreover, the ultrathin width of the CNF could maintain high optical transparency of PMMA.

Intercalation and Characterization of Kaolinite Amazon to Production Polymer Nanocomposites

Polymer nanocomposites using natural clays such as nanofiller have mechanical properties, flame-retardant, the gas barrier improvement compared to polymers without nanoclay. The aim of this work is intercalated molecules between the clay layers and characterize it with a view to its use in polymer nanocomposites. The kaolinite neat and modified used was characterized by fourier transform spectroscopy (FTIR), X-ray diffraction (XDR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry (TGA). The results showed that kaolinite can be used as a nanofiller in polymer nanocomposites.

Role of organic/inorganic salts and nanofillers in polymer nanocomposites: enhanced conduction, rheological, and thermal properties

Electromagnetic interference shield materials which are multicomponent polymer nanocomposites consisting of insulating polymer matrix of poly (vinylidene fluoride-hexafluoropropylene) (PVdF-HFP), organic/inorganic salts, electron-conducting nanofillers (MWCNTs), and insulating superparamagnetic nanoparticles (Fe3O4), have been studied. It has been found that the introduction of the salts and nanofillers in PVdF-HFP not only improves the conducting nature and skin depth of the polymer nanocomposites but also keeps the composite films thermally stable up to ~ 200 °C. Changes in the surface morphology on addition of each individual constituent have been evidenced by scanning electron microscopy. The rheological study shows the plasticization effect of organic/inorganic salts as well as provides a good estimation of the polymer–particle interaction in the polymer nanocomposites. Furthermore, effect of organic/inorganic salts and interaction between the polymer and the fillers (MWCNTs and Fe3O4) has also been observed in differential scanning calorimetry in terms of lowering of glass transition temperature (leading to enhanced flexibility). The stress versus strain behavior has shown specific interactions among different constituents of the shield material.

Heterogeneities in Polymer Structural and Dynamic Properties in Graphene and Graphene Oxide Nanocomposites: Molecular Dynamics Simulations

The effect of graphene (G) and graphene oxide (GO), used as the nanofiller in polymer nanocomposites (NC), on the structural and dynamic properties of polymer chains, has been studied by means of molecular dynamics (MD) simulations. Two polymers, i.e., poly(propylene) and poly(vinyl alcohol), are employed as matrices to cover a wider range of polymer–filler interactions. The local structural properties, e.g., density profile, average Rg, and end‐to‐end distance as well as dynamic properties, e.g., estimated translational and orientational relaxation times, of polymer chains are studied. In addition, the interaction energies are estimated between polymers and nanofillers for different hybrid systems using MD pullout simulations. Strong heterogeneities in polymer structural and dynamic properties have been observed such that chains are more oriented and exhibit slower dynamics in the vicinity of the nanofillers (G and GO) as compared to bulk. It is also found that the orientation of polymer chains at the interface is more influenced by the nanofiller in such a way that the more oriented polymer chains are observed in G‐based NC for both polymers. However, the immobilization of polymer chains at the interface proves to be very much dependent on the polymer–filler interactions. image

Preparation and physical properties of polypropylene nanocomposites with dodecylated graphene nanoplatelets

The most important practical application of graphene nanoplatelets (GNPs) would be as nanofillers for polymer nanocomposites. However, the modification of GNPs is needed to improve the interfacial adhesion between GNPs and a polymer matrix. Therefore, in this study, the alkylation of GNPs by dodecylamine was carried out via chemical reactions between the amine groups of the alkyl amine and the carboxyl and epoxy groups of the oxidized GNPs’ surfaces. The dodecylation of the GNPs was confirmed by FTIR and TGA. The TGA data showed that the dodecyl-GNPs comprised alkyl groups 2.4%. Polypropylene nanocomposites with the dodecyl-GNPs were prepared in a platy shape by melt-blending followed by compression molding. The mechanical and thermal properties of the nanocomposites were measured by UTM, izod impact tester, DSC and DMA. Compared to the neat PP sample, the flexural modulus, flexural strength and impact strength of the PP nanocomposite with the dodecyl-GNPs 0.5 phr were increased by 38, 4 and 34% respectively. The fracture surfaces’ images of the nanocomposites taken by SEM showed that the dodecylation of the GNPs improved the interfacial adhesion between the GNPs and the PP matrix.

Microwave synthesis of ultrathin, non-agglomerated CuO nanosheets and their evaluation as nanofillers for polymer nanocomposites

In this work, ultrathin, non agglomerated and defect free CuO nanosheets (NS) were produced by the microwave assisted route and evaluated as nanofillers for a high-performance epoxy resin. They were used in various weight fractions ranging from 0.1 to 2 wt%. The synthesized CuO-NS were found to have a thickness of around 10 nm and length/width in the micro/submicro size range. These NS are highly crystalline mainly in the (11-1) and (111) directions and have the regular Ag and Bg Raman vibration modes. The mechanical tensile properties of the CuO-NS/epoxy nanocomposites, including their Young’s modulus, stiffness, and load at fracture, were investigated. Moreover, the effect of degassing (voids removal) on the mechanical properties of these nanocomposites was studied. The obtained results showed a significant improvement in the stiffness by around 63% upon the addition of 0.5 wt% CuO-NS to the epoxy matrix. The load and stress at fracture were also improved. The test results show that degassing the initial solutions is essential and has a significant role in the mechanical properties of this nanocomposite. These results show that the microwave synthesized CuO-NS could overcome the agglomeration problem associated with other nanomaterials and might be quite useful as a reinforcement material for high-stiffness products.

Grafting PMMA Brushes from α-Alumina Nanoparticles via SI-ATRP.

Alumina nanoparticles are widely used as nanofillers for polymer nanocomposites. Among several different polymorphs of alumina, α-alumina has the most desirable combination of physical properties. Hence, the attachment of polymer chains to α-alumina to enhance compatibility in polymeric matrixes is an important goal. However, the chemical inertness and low concentration of surface hydroxyl groups have rendered polymer modification of α-alumina a long-standing challenge. Herein, we report that activation of α-alumina in concentrated or molten NaOH as well as in molten K2S2O7 increased polymer graft density up to 50%, thereby facilitating the synthesis of α-alumina brush particles with uniform grafting density of 0.05 nm(-2) that are readily miscible or dispersible in organic solvents or in chemically compatible polymeric hosts.

Uniform distribution of low content BaTiO3 nanoparticles in poly(vinylidene fluoride) nanocomposite: toward high dielectric breakdown strength and energy storage density

The uniform distribution of low content nanofillers in polymer nanocomposites was achieved to maximize energy storage with improved breakdown strength and simultaneously increased the relative dielectric constant.