Abstract: A concept for improving the impact resistance of carbon fibre reinforced plastic (CFRP) laminates by using a carbon nanotube (CNT)/epoxy surface coating is presented. An initial parametric numerical study shows the effects of interphase properties on the macroscopic stress-strain behaviour of carbon nanotube/epoxy nanocomposites. Finite element (FE) simulations carried out for fully aligned single-walled CNTs (SWCNTs) and double-walled CNTs (DWCNTs) investigated the influence of properties of the polymer/CNT interphase and the interwall phase of DWCNTs. They reveal that a high shear stiffness of the CNT/polymer interphase is essential to take the full advantage of the load-bearing ability of the inner wall of the DWCNT, and thus enhance the mechanical performance of the nanocomposite. Furthermore the interphase shear stress distributions in interwall and CNT/polymer interphase of a DWCNT point out the relationship between CNT/epoxy interphase damage propagation and shear stress in the interwall phase.
Abstract: A micromechanics-based approach using a self-consistent scheme based on the double-inclusion model is adopted to develop a pertinent model for describing the viscoelastic response of polymer/clay nanocomposites. The relationship between the intercalated nanostructure and the effective nanocomposite stiffness is constructed using an equivalent stiffness method in which the clay stacks are replaced by homogeneous nanoparticles with predetermined equivalent anisotropic stiffness. The capabilities of the proposed micromechanics-based model are checked by comparing with the experimental viscoelastic (glassy to rubbery) response of two polyamide-6-based nanocomposite systems reinforced with a modified montmorillonite clay (Cloisite 30B) and an unmodified sodium montmorillonite clay (Cloisite Na+), favoring, respectively, exfoliation and intercalation states.
Abstract: The context of this work is the enhancement of the thermal conductivity of polymer by adding conductive particles. It will be shown how we can use effective thermal conductivity models to investigate effect of various factors such as the volume fraction of filler, matrix thermal conductivity, thermal contact resistance, and inner diameter for hollow particles. Analytical models for lower bounds and finite element models will be discussed. It is shown that one can get some insights from effective thermal conductivity models for the tailoring of conductive composite, therefore reducing the amount of experimental work.
Abstract: A multiscale finite element (FE) methodology is applied to study failure behaviour of an intercalated epoxy-clay nanocomposite. A 2D FE model of the nanocomposite is built to capture nanocomposite morphology and gallery failure mechanism. Intercalated morphology is reconstructed using a random dispersion of clay tactoids within the epoxy matrix, while the galleries are modeled using cohesive zone elements. The nanocomposite response is predicted by numerical homogenization technique. The effects of cohesive law parameters (particularly the fracture energy) and clay volume fraction on the macroscopic behavior of the nanocomposite are investigated. The analysis shows that gallery failure is the main cause of strength reduction of the nanocomposite. Moreover, the strength reduction is found to increase with the clay content, which is in a qualitative agreement with available experimental results.
Abstract: The carbon nanotube (CNT) structure is a promising building block for future nanocomposite structures. Mechanical properties of the electrospun butadiene elastomer reinforced with CNT are analyzed by multiscale method. Effective properties of the fiber at microscale determined by homogenization procedure using modified shear-lag model, while on the macro scale effective properties for the point-bonded stochastic fibrous network determined by volume homogenization procedure using multilevel finite element. Random fibrous network was generated according experimentally determined stochastic quantificators. Influence of CNT reinforcement on elastic modulus of electrospun sheet on macroscopic level is determined.
Abstract: In this work, different types of nanostructured systems containing azobenzene groups were studied. With that aim, firstly, novel azo-functionalised block copolymers (BCP) were synthesized from epoxidized poly (styrene-b-butadiene-b-styrene) (SBS) modified with azobenzene units by one-step facile reaction between the epoxy groups and an azo-amine. The epoxy/amine reaction was verified by Fourier transform infrared spectroscopy. In addition, the effect of covalent attachment of the azobenzene moieties was investigated by analyzing the morphology and the optical anisotropic response of the resulting azo-containing BCP, with respect to solution mixing of the azobenzene as a guest in the BCP host without chemical bonding. On the other hand, epoxidized SBS was also used as template for the generation of nanostructured thermosetting epoxy matrices with azobenzene groups covalently linked. This BCP can self-assemble in the epoxy matrix to produce microphase-separated domains, thanks to the selective segregation of polystyrene blocks due to reaction induced microphase separation. In this case, the influence of the azobenzene content and the amount of epoxidized SBS on the generated morphologies and the photo-induced anisotropy was studied.
Abstract: Solid-state nuclear magnetic resonance (NMR) spectroscopy has emerged as a relatively facile technique for the characterization of multi-component polymer systems. In particular, it has emerged to be a useful technique for probing the molecular structure, conformation and dynamics of polymer chains at interfaces between phases in various types of multi-component polymer systems including nanomaterials. The usefulness of solid-state NMR stems from its ability to non-destructively probe not only the bulk of the polymer, but moreover its ability to selectively probe the interface or interphase. As such, the technique has been extensively exploited in the study of multi-component polymer systems. To achieve 13C spectral resolution in the solid-state magic angle spinning (MAS), dipolar decoupling and cross-polarization are applied which enables the study of individual carbon atoms directly with excellent resolution and sensitivity. Some examples of applications of this technique to the study of multiphase aliphatic polyesters are reviewed herein.
Abstract: The effects of orientation on the segmental dynamics of vulcanized natural rubber have been studied by dielectric relaxation spectroscopy. Morphological changes during the stretching process were also investigated by wide-angle X-ray scattering using a synchrotron radiation. Results reveal that segmental dynamics of NR is affected by uniaxial stretching since a slowing down of the segmental relaxation is achieved. Also, there is evidence of an amorphous/semi-crystalline transition around 300% strain; below this extension, molecular chains show orientation, but no crystallization takes place; while above such strain, the crystalline structure formed limits the segmental dynamics of NR.
Abstract: In this work we have performed a systematic study of blends of [6,-phenyl C61 butyric acid methyl ester (PCBM) with the following amorphous and semi-crystalline polymers: atactic polystyrene (PS), syndiotactic polystyrene (syn-PS), poly (2-vinyl-naphthalene) (P2VN), poly (9-vinyl-phenanthrene) (P9VPh), poly (vinylidene-fluoride) (PVdF) and poly (3-hexyl-thiophene) (P3HT). Experimental measurements using DSC, x-ray and neutron scattering coupled with molecular modeling (MD and DFT) have been utilized to determine the solubility and phase morphology of these model polymer-fullerene blends.