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.     

The elastic modulus of filled polymer composites

The elastic modulus of polyepichlorohydrin (PECH) filled with glass beads and wollastonite was studied. It was found that the elastic modulus of the composites depends not only on the volume fraction of the fillers but also on their size. Percolation theory was used to explain the experimental results. © 1993 John Wiley & Sons, Inc.     

Young's modulus of effective clay clusters in polymer nanocomposites

In polymer nanocomposites, the interfacial region plays a key role in the reinforcement of materials properties. Traditional two-phase micromechanical models usually ignore the contribution of such interfacial region to the overall materials properties. In this study, we use molecular dynamics simulation to determine the effective size and the Young's modulus of effective clay clusters which are regarded as basic building blocks in clay-based polymer nanocomposites. Two types of clay clusters are considered: one is fully exfoliated clay and another is partially exfoliated clay. The calculated Young's modulus of effective clay clusters can be used to predict the overall mechanical properties of clay-based polymer nanocomposites.     

A comparative study to predict the interphase modulus in polymer nanocomposites

In this study, the interphase modulus (E_i) in polymer nanocomposites is calculated by two methods and the calculated results are compared at different conditions. In the first method, the experimental moduli of samples are applied to Ji model and suitable “E_i” is calculated. In the second method, a multilayered interphase is considered, in which the Young's moduli of layers (E_k) depend to the distance between the nanoparticle surface and the polymer matrix by power function of “Y” parameter. The “E_i” is calculated for multilayered interphase assuming the same and different layer thicknesses (t_k) by Parallel and Series models. Finally, the “E_i” values calculated by the explained methods are compared for two reported samples. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44076.     

Tensile modulus of polymer/CNT nanocomposites containing networked and dispersed nanoparticles

The properties of three‐dimensional networks of nanoparticles in polymer/carbon nanotubes (CNT) nanocomposites (PCNT) are particularly interesting from fundamental and application views. In this article, a new model is suggested for predicting the tensile modulus of PCNT using the Ouali and Paul models. The Ouali model considers the network of CNT in a polymer matrix, while the Paul model predicts the tensile modulus of samples containing dispersed nanoparticles. The predictions of the suggested approach are compared with experimental data from several samples. Also, the roles of the main parameters in the tensile modulus of PCNT are evaluated. The predictions agree with the experimental results at different filler concentrations. The roles of these parameters on the tensile modulus of PCNT are discussed based on the properties of CNT networks. © 2017 American Institute of Chemical Engineers AIChE J, 63: 220–225, 2018     

Processability studies of silica‐thermoset polymer matrix nanocomposites

The aim of this study is to investigate the processability of silica‐thermoset polymer matrix nanocomposites in terms of dispersion of silica nanoparticles and their effect on curing. Two thermosetting resins were considered, an epoxy and a polyester resin, with 5% silica, although 1% silica was also used in preliminary studies in the polyester system. Various combinations of mechanical mixing and sonication were investigated for the dispersion of silica nanoparticles under different processing conditions and times in solvent‐free and solvent‐containing systems. It was found that the best dispersion route involved a solvent‐aided dispersion technique. Consequently, different procedures for the solvent removal were investigated. Optical microscopy and SEM were used to characterize the resulting nanocomposites. DSC and rheological DMTA tests demonstrated that the silica nanoparticles shorten the gel time and promote curing in these thermosetting systems. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

Exfoliated polymer nanocomposites by in situ coprecipitation of layered double hydroxides in a polymer matrix

Polyvinylalcohol (PVA) nanocomposites were prepared by a “one step” method based on the coprecipitation of layered double hydroxide (LDH) platelets in the polymer aqueous solution. The PVA/LDH nanocomposites displayed an exfoliated morphology and the concentration of LDH in the nanocomposite was evaluated by IR analysis. Moreover, it was shown that the PVA/LDH nanocomposites had an improved photostability over PVA, which makes this material a good candidate for coating applications. Further optimization will be considered to tune the polymer/LDH properties. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of polymer matrix and nanofiller on non-bonding interfacial properties of nanocomposites

To investigate the effect of polymer matrix and nanofiller on interfacial mechanical properties of their resulting nanoreinforced composites, pull-out tests of different nanofillers, such as graphene (GE), graphane (GA) and carbon nanotube (CNT), from various polymer matrix including polyethylene (PE), poly(methyl methacrylate) (PMMA), polytetrafluoroethylene (PTFE) and poly(vinylidene chloride) (PVDC), are simulated using molecular dynamics method (MD). The velocity-load model is applied in MD simulations, and the variation of non-bonding energy (van der Waals interaction), pull force and the average interfacial shear strength (ISS) in the pull-out process are obtained and presented graphically. Under the same mass density, when PE is used as polymer matrix for GE and CNT nanofillers, the resulting nanoreinforced composite possesses the highest non-bonding interfacial energy and the strongest ISS, and the pull force required for pulling out the nanofiller is the largest. For GA nanofiller, the GA-PMMA produces the highest non-bonding interfacial energy and the ISS. With the increase of diameter of CNT, the effect of its reinforcement becomes weak gradually. The chirality of GE does not influence the interfacial mechanical property of GE-reinforced nanocomposite. The (3, 3) CNT nanofiller produces the almost identical interfacial characteristic compared with GE nanofiller. However, when the GA nanofiller is used, the non-bonding energy, pull force and the average ISS of nanocomposite increases by nearly 100%.     

The elastic modulus of nylons

The energy balance method previously described gives values for the elastic modulus of single crystals of nylons that are reasonably close to experimental data, where these are available, apart from nylon-6. Force constants were derived from Urey Bradley (UBFF) and valence (VFF) force fields. Modulus values, in GN/m², are as follows:

Consideration of the cross-sectional area and repeat distance of the polymer chain indicates that the modulus will decrease in the order given. The extensibility (f value) of each polymer was within the expected range (0.4 to 0.5nN). The method is applicable to similar polymers, e.g. poly(tetramethylene hexamethylene sulphone) has a modulus of 176.7 GN/m² and an f value of 0.403nN.     

The effect of porosity on the compressive strength and elastic modulus of polymer impregnated concrete

Three concretes of widely differing water/cement ratios were impregnated with varying amounts of methyl methacrylate monomer. The monomer was polymerised thermally, using a free radical initiator. The compressive strength and elastic modulus of the polymer-impregnated concrete are shown to be a function of the total porosity of the concrete after polymer impregnation. The elastic modulus of the composite system can be explained on the basis of a two phase material: an aggregate phase and a polymer impregnated cement paste phase. A possible explanation of the role of the polymer is suggested.     

Graphene-based polymer nanocomposites

Graphene-based materials are single- or few-layer platelets that can be produced in bulk quantities by chemical methods. Herein, we present a survey of the literature on polymer nanocomposites with graphene-based fillers including recent work using graphite nanoplatelet fillers. A variety of routes used to produce graphene-based materials are reviewed, along with methods for dispersing these materials in various polymer matrices. We also review the rheological, electrical, mechanical, thermal, and barrier properties of these composites, and how each of these composite properties is dependent upon the intrinsic properties of graphene-based materials and their state of dispersion in the matrix. An overview of potential applications for these composites and current challenges in the field are provided for perspective and to potentially guide future progress on the development of these promising materials.     

Peculiar dynamics and elastic properties of hybrid semi-interpenetrating polymer network-3-D diamond nanocomposites

Polyurethane-poly(2-hydroxyethyl methacrylate)-3-D nanodiamond (PU-PHEMA-ND) composites were studied using combined CRS/DSC/AFM approach. The peculiar behavior and the pronounced heterogeneity of their glass transition dynamics were revealed. Two opposite tendencies for changing dynamics by 3-D NDs, with prevailing sharp suppression of motions, and three-fold increasing elastic properties were shown. Maximal effects were found at minimal ND content of 0.25 wt%. This was associated, besides the improved dispersion/spatial distribution of NDs, with formation of thoroughly cross-linked nanocomposite network, due to the double hybridization resulting in a low rheological percolation threshold and the synergistic effect in dynamics.     

Akaganeite polymer nanocomposites

An “in situ” method for the production of akaganeite polymer nanocomposites is described. A controlled precipitation is achieved by using a polymer matrix, polyvinylpyridine, containing N-base functional groups that form coordination bonds with iron ions. The resulting materials have permitted the observation of two sources of magnetic moment in akaganeite nanoparticles: (1) finite size effects with a characteristic blocking temperature below 2 K; and (2) a deficient Cl⁻ occupancy, with a characteristic blocking temperature around 18 K. Moreover, the nanocomposites can be dissolved in slightly acidic media to obtain stable aqueous nanoparticle dispersions that could be useful in biomedical applications.     

A new approach to the preparation of nanocomposites based on a polymer matrix

A new approach to the preparation of nanocomposites is advanced. This approach includes preliminary formation of a nanoporous matrix and subsequent loading of the formed pores by the second component. These advantageous opportunities are provided by one of the most fundamental phenomena of the physical chemistry of polymers: solvent crazing of polymers in the presence of the liquid media. Several examples illustrate that solvent crazing not only provides a universal means of self-induced dispersion of a polymer material into nanoscale aggregates but also offers a universal route for the delivery of diverse low-molecular-mass compounds to the nanoporous structure of the solvent-crazed polymer. The results on the preparation of new types of nanomaterials, such as porous polymeric sorbents, polymeric separation membranes, new types of polymer-polymer nanoblends, fireproof and conducting polymer nanocomposites, and metal-containing polymers, are reviewed. Some aspects of the practical application and technological design of solvent crazing of polymers as a means for the preparation of diverse nanocomposites are discussed.     

Analysis of the modulus of polyamide-6 silicate nanocomposites using moisture controlled variation of the matrix properties

The stiffness of PA6 silicate nanocomposites has been measured for a number of silicate fractions and moisture levels. The matrix modulus was varied experimentally by moisture conditioning, resulting in three different moisture levels. The moduli have been analysed with a Halpin-Tsai composite model. This model was used to calculate the matrix modulus in the nanocomposites based on the crystallinity, the amount of surfactant and the moisture content. The measured modulus of the nanocomposites with different moisture content was used to calculate the effective aspect ratios of the reinforcing particles with the Halpin-Tsai model. The calculated aspect ratio for each nanocomposite is independent on the moisture concentration. This indicates the validity of this composite model to describe nanocomposites, despite the small particle size. The results suggest that changes on the molecular level due to the presence of the silicate layers only have a small influence on the modulus, because the modulus can be explained with a composite model. The reduced efficiency of reinforcement at increasing filler levels can be partially explained by the reduction of the matrix modulus due to surfactant and reduced crystallinity, and partially by the occurrence of small stacks of platelets.     

Multiscale modeling of size-dependent elastic properties of carbon nanotube/polymer nanocomposites with interfacial imperfections

We developed an efficient and extensible multiscale analysis to consider the carbon nanotube (CNT) size effect and weakened bonding effect at the interface on the effective elastic stiffness of CNT/polymer nanocomposites using molecular dynamics (MD) simulations and continuum micromechanics. Under the assumption that the CNT molecular structure is an equivalent solid cylinder, molecular mechanics calculation results for transversely isotropic elastic stiffness were found to decrease as the radius of the CNT increased. Similarly, the transversely isotropic elastic moduli of aligned pristine CNT-reinforced polypropylene composites obtained from molecular dynamics simulations exhibited the same CNT size dependency. However, a weakened interface effect was observed from the transverse Young’s modulus and two shear moduli. To account for the size effect and the weakened interface in the micromechanics-based multiscale model, a modified multi-inclusion model is derived with an effective particle scheme. Also, an effective matrix concept is suggested to account for the formation of an interphase near the surface of the CNT, and the elastic stiffness of the CNT and the effective matrix is defined as a function of the CNT radius to describe size-dependent elastic stiffness in the micromechanics regime.