Behavior Of Polymer Nanocomposites Research Articles

Dynamic mechanical analysis of graphene and nano silica reinforced hybrid epoxy composites under dual cantilever mode

This paper presents Dynamic mechanical behaviour of polymer Nano composites reinforced with various weight percentages of polymer and Nano particles and effect of Nano particles with polymer. The Graphene and Nano silica were used as fillers with epoxy resin. The Nano composite plates were prepared using cold compression moulding technique. Finally, the prepared composite plates were sized in laser cutting according to ASTM standards and subjected to DMA test. A series of dynamic mechanical tests were performed for prepared composites over a range of testing temperatures. Test frequency was kept constant. The dynamic mechanical properties of prepared Nano composites were studied by recording storage modulus, loss modulus, tan δ and glass transition temperature (Tg). It was found that the storage modulus (E’) recorded was decreasing with increasing temperature. The loss modulus (E”) and damping peaks (Tan δ) values were found to be increased with increasing in temperature up to certain value and beyond certain temperature it was found to be decreased. Also, the loss modulus (E”) and damping peaks (Tan δ) values were found to be reduced with increasing reinforcements whereas Tg decreases as reinforcements increase.

Modeling the Effect of Polymer Chain Stiffness on the Behavior of Polymer Nanocomposites.

Due to their central role in industrial formulations spanning from food packaging to smart coatings, polymer nanocomposites have been the object of remarkable attention over the last two decades. Incorporating nanoparticles (NPs) into a polymer matrix modifies the conformation and mobility of the polymer chains at the NP-polymer interface and can potentially provide materials with enhanced properties as compared to pristine polymers. To this end, it is crucial to predict and control the ability of NPs to diffuse and achieve a good dispersion in the polymer matrix. Understanding how to control the NPs' dispersion is a challenging task controlled by the delicate balance between enthalpic and entropic contributions, such as NP-polymer interaction, NP size and shape, and polymer chain conformation. By performing molecular dynamics (MD) simulations, we investigate the effect of polymer chains' stiffness on the mobility of spherical NPs that establish weak or strong interactions with the polymer. Our results show a sound dependence of the NPs' diffusivity on the long-range order of the polymer melt, which undergoes an isotropic-to-nematic phase transition upon increasing chain stiffness. This phase transition induces a dynamical anisotropy in the nematic phase, with the NPs preferentially diffusing along the nematic director rather than in the directions perpendicular to it. Not only does this tendency determine the NPs' mobility and degree of dispersion in the polymer matrix, but it also influences the resistance to flow of the polymer nanocomposite when a shear is applied. In particular, to assess the role of the chains' conformation on the macroscopic response of our model PNC, we employ reverse nonequilibrium MD to calculate the zero-shear viscosity in both the isotropic and nematic phases, and unveil a plasticizing effect at increasing chain stiffness when the shear is applied along the nematic axis.

Unveiling the impact of nanoparticle size dispersity on the behavior of polymer nanocomposites

Polymer nanocomposites (PNCs), a class of polymer materials incorporating nano-sized particles (NPs), have tremendous potential in industrial formulations and technological applications, such as protective coatings and food packaging. In this work, we perform Molecular Dynamics simulations to unveil the impact of NP size dispersity on a variety of properties that characterize the response of PNCs at the nano and macro scales. In particular, at the nano scale, we investigate the space distribution of small and large polydisperse NPs and their ability to diffuse through a dense isotropic distribution of unentangled polymer chains. We find very interesting scaling laws relating the average size and polydispersity index of NPs with their diffusion coefficients, generally underestimated by existing theoretical models. These theories are here adapted to include the effect of NP size dispersity and their predictions, confirming the relevance of incorporating such contributions, are validated against our simulation results. We also analyze the diffusivity of the polymer chains as a function of the interparticle distance for a spectrum of NP diameters and confirmed the existence of a single master curve as recently observed experimentally (S. Gam et al., Soft Matter, 2012, 8, 6512). To assess the effect of NP size dispersity on the macroscopic response of our model PNC, we evaluate two key transport properties, shear viscosity and thermal conductivity, which are found to display an intriguing universal behavior when plotted against the polymer/NP specific interface area and the inverse of the NP's mass, respectively.

Ordering of block copolymer/nanoparticle composite thin films

The ordering behavior of polymer nanocomposites composed of gold nanoparticles confined in the polystyrene (PS) domains of PS based block copolymers was investigated. The results reveal that the self-assembly of nanoparticles in the PS domains improved the ordering of microdomains. This is attributed to the presence of nanoparticles that reduced the degree of segregation of the system, causing slow phase separation. This facilitates the packing of the cylindrical microdomains, leading to a well-ordered structure of the composite. When particles were incorporated into the major domains of cylindrically ordered block copolymer, the connectivity of the domains allowed particles to move to the top of the film to gain additional entropy of the system. In contrast, when particles were organized in parallel cylinders in the block copolymer, they were confined in the cylinders which prevented them from diffusing in the depth direction. The aggregation of nanoparticles was amplified when the composite was annealed in air. We believe that the results from this study will enable more understanding of the effects of nanoparticles on the ordering of block copolymer/nanoparticle composite thin films and will provide a tool in the fabrication of composite thin films. Copyright © 2012 Society of Chemical Industry

Effect of Nanoscale Species on the Behavior of Polymer Nanocomposites Subjected to Laser Pulse Heating

ABSTRACTPolymers and polymer nanocomposites have been studied under conditions of extremely high heating rates. Traditionally, these materials have been examined by the flammability research community using methods which have heating rates on the order of 10 degrees C/min. In this study, we have examined how polypropylene-nanoclay (montmorillonite) and polypropylene-carbon nanotube nanocomposites behave subjected to heating rates on the order of one million degrees C/min when irradiated with a 1064 nm Nd-YAG variable pulse millisecond laser. Time-resolved temperature data and mass loss data was collected for each sample as well as post-mortem surface characterization using spectroscopy and electron microscopy. The analysis shows that the nanospecies are effective in providing a protective barrier that decreases the amount of degradation and mass loss to the underlying polymer material. The effect is clearly seen after irradiating with a single pulse and multiple pulses. A comparison between the performance of the nanoclay and carbon nanotube composites is given.

Thermomechanical and rheological behaviour of polymer nanocomposites based on ethylene–methyl acrylate (EMA) and multiwalled carbon nanotube (MWNT)

Ethylene–methyl acrylate copolymer and multiwalled carbon nanotubes (MWNTs) were melt processed in order to determine the structure–property relationship of the resulting nanocomposites. The effect of MWNT loading on the thermomechanical and rheological properties of the nanocomposites is systematically investigated. Morphological characteristics these reinforced were investigated using field emission scanning electron microscopy and high resolution transmission electron microscopy. X-ray diffraction and differential scanning calorimetry studies showed that the MWNTs affect the crystallisation process. Dynamic mechanical analysis revealed that the storage modulus of the composites was significantly increased particularly at high temperatures. Thermogravimetric analysis showed that the MWNTs stabilise the ethylene–methyl acrylate matrix. The influence of concentration of filler was also realised by a frequency sweep experiment. Storage modulus (in dynamic shear) value increases especially at higher frequency levels due to increased polymer–filler interactions. Both the unfilled and filled composites exhibit rheological behaviour of non-Newtonian fluids. The dynamic and steady shear rheological properties register a good correlation in regard to the viscous versus elastic response of such systems.

Thermal and Mechanical Behavior of Polymer Nano-composite

This paper presents the results on thermal transport and mechanical properties of CdS/ PMMA nano-composites prepared by solution casting method at different concentrations of nano-particles in the composites. Thermal conductivity was determined using Transient Plane Source (TPS) method at room as well as elevated temperatures. The measurement of thermal conductivity of CdS/PMMA nano-composites at room as well as elevated temperatures shows an increasing trend upto glass transition temperature, beyond which it shows a constant value. This peculiarity in the increase of thermal conductivity of CdS/PMMA nanocomposites is explained through the presence of CdS in PMMA matrix. Mechanical properties of these nano-composites have been studied using Dynamic Mechanical Analyzer (DMA). The increase in elastic properties in the CdS nano-particles embedded PMMA as compared to pure PMMA is explained on the basis of interaction between CdS and polymer and decrease in free volume of PMMA in the composite. The results on these measurements show that 6 wt. % of CdS nano-particles in PMMA matrix provides higher values of thermal conductivity and elastic properties, which is a critical composition.

Designed Interfaces in Polymer Nanocomposites: A Fundamental Viewpoint

AbstractUsing nanocomposites in design-critical applications requires an understanding of their structure–property–function relationships. Despite many reports of highly favorable properties, the behavior of polymer nanocomposites is not generally predictable. The ability to tailor the filler/matrix interaction and an understanding of the impact of the inter face on macroscopic properties are key to designing their properties. Tailoring can be achieved by grafting short mole cules or polymer chains from the surface with precise control over their chain length (1–1000 mers), graft density (0.01–1 chains/nm2), and chemical architecture. The challenge is understanding the impact of the modified surfaces on the properties of the interfacial polymer, which can be more than 50% of the volume of the polymer matrix and, hence, can exert significant control over the macroscopic behavior of the nanocomposite. This ar ticle highlights the fundamental technical challenges that need to be overcome before spherical nanopar ticle or nanotube composites can be designed. In particular, we discuss results from the recent literature that have significantly advanced our ability to predict and control nanocomposite properties through the use of designed interfaces.

Application of reptation models to modeling of rheological behavior of polymer nanocomposites

Characteristic rheological behaviors of polymer nanocomposites were studied in shear flow and uniaxial elongational flow. Solid-like plateau storage modulus, strong shear thinning at low frequency regions, and strain hardening at elongational flow were observed. Especially, strain hardening was clearly observed for polymers without long chain branches if nanoparticles were homogeneously dispersed in the polymer matrix and interactions between nanoparticles and surrounding polymer molecules were sufficiently strong. Reptation models were used to model the nanoscale dynamics of nanoparticles and macromolecular chains, and the characteristic rheological behavior of nanocomposites could be explained. Brownian dynamics simulation of Doi-Edwards reptation model was applied and two particle constraint coefficients were introduced to express the influence of nanoparticles on molecular orientation and reptational diffusion of polymer chains. In the simulation, stress tensor including link tension coefficient which characterizes anisotropic friction coefficient of the molecular chain was used to obtain material functions by assuming that the anisotropy of friction was altered by the presence of nanoparticles. Additional frictional force between polymer chains and nanoparticles was considered and the suitable relaxation process and chain stretch were incorporated by considering the full chain geometry of polymer molecular chains. All the reptation models considering the effect of nanoparticles were verified by comparing the theoretical results with experimental data for polymer nanocomposites in shear and elongational flows.

Fracture behaviour of nanoplatelet reinforced polymer nanocomposites

The authors present a review of the recent research effort towards developing a fundamental understanding of fracture behaviour of polymer nanocomposites that contain nanoplatelet fillers. Various toughening mechanisms reported in the literature are summarized and discussed. Within this review, an emphasis is placed on the up to date understanding of how the nanofiller aspect ratio affects the fracture behaviour of polymer nanocomposites. Besides, the effect of nanoplatelet dispersion and exfoliation on the fracture behaviour of polymer nanocomposites will be addressed.

Nanoscale Strain Measurements in Polymer Nanocomposites

AbstractThe paper describes a multiscale experimental investigation of the mechanical behavior of polymer nanocomposites with nanoscale fused silica inclusions with the objective to shed light into the effect of the hard nanoparticles on the quasistatic mechanical behavior of epoxy matrix and the implications of the latter to the effective composite properties. The main variable in this study was the nanofiller volume fraction while the particle size was either 15 nm or 100 nm. Local strain measurements indicated strain field localization in the vicinity of the nanofillers at strains that macroscopically fall in the linearly elastic regime. The matrix strains were as high as three times the applied far field strain at applied effective strains of ∼ 1%. At larger stresses the local strain fields evolved to maxima that were considerably higher than the applied strain, and they were affected by local particle density and distribution. In composites with the largest particle volume fraction, 5 vol.%, 100 nm fillers, neighboring particles located in small proximities behaved as single large particles and often resulted in matrix strain shielding thus decreasing the benefit of the large surface-to-volume ratio and the associated efficiency in load transfer. On the other hand the 15 nm fillers resulted in more uniformly distributed deformation compared to composites with 100 nm particles.

A Hybrid Numerical-Analytical Method for Modeling the Viscoelastic Properties of Polymer Nanocomposites

In this paper, we present a novel hybrid numerical-analytical modeling method that is capable of predicting viscoelastic behavior of multiphase polymer nanocomposites, in which the nanoscopic fillers can assume complex configurations. By combining the finite element technique and a micromechanical approach (particularly, the Mori-Tanaka method) with local phase properties, this method operates at low computational cost and effectively accounts for the influence of the interphase as well as in situ nanoparticle morphology. A few examples using this approach to model the viscoelastic response of nanotube and nanoplatelet polymer nanocomposite are presented. This method can also be adapted for modeling other behaviors of polymer nanocomposites, including thermal and electrical properties. It is potentially useful in the prediction of behaviors of other types of nanocomposites, such as metal and ceramic matrix nanocomposites.

Mechanical Behavior of Polymer Nanocomposites: a discrete simulation approach

ABSTRACTThis work reports the dynamic mechanical characterization of nanocomposites based on a poly(butyl acrylate) matrix filled with spherical particles of either polystyrene or silica both of diameter around 100 nm. A discrete numerical simulation, taking into account the microstructure and the nature of contact between reinforcing particles has been developed. This simulation enables to quantify the effect of interactions between filler particles on the elastic modulus, and in a more general sense, to clarify the concept of mechanical percolation. It gives results in very good agreement with experimental data.