Structure of laponite-styrene precursor dispersions for production of advanced polymer-clay nanocomposites

One method for production of polymer-clay nanocomposites involves dispersal of surface-modified clay in a polymerisable monomeric solvent, followed by fast in situ polymerisation. In order to tailor the properties of the final material we aim to control the dispersion state of the clay in the precursor solvent. Here, we study dispersions of surface-modified Laponite, a synthetic clay, in styrene via large-scale Monte-Carlo simulations and experimentally, using small angle X-ray and static light scattering. By tuning the effective interaction between simulated laponite particles we are able to reproduce the experimental scattering intensity patterns for this system, with good accuracy over a wide range of length scales. However, this agreement could only be obtained by introducing a permanent electrostatic dipole moment into the plane of each Laponite particle, which we explain in terms of the distribution of substituted metal atoms within each Laponite particle. This suggests that Laponite dispersions, and perhaps other clay suspensions, should display some of the structural characteristics of dipolar fluids. Our simulated structures show aggregation regimes ranging from networks of long chains to dense clusters of Laponite particles, and we also obtain some intriguing ‘globular’ clusters, similar to capsids. We see no indication of any ‘house-of-cards’ structures. The simulation that most closely matches experimental results indicates that gel-like networks are obtained in Laponite dispersions, which however appear optically clear and non-sedimenting over extended periods of time. This suggests it could be difficult to obtain truly isotropic equilibrium dispersion as a starting point for synthesis of advanced polymer-clay nanocomposites with controlled structures

Interface-tuned epoxy/clay nanocomposites

Though interface has been known for a critical role in determining the properties of conventional composites, its role in polymer nanocomposites is still fragmented and in its infancy. This study synthesized a series of epoxy/clay nanocomposites with different interface strength by using three types of modifiers: ethanolamine (denoted ETH), Jeffamine� M2070 (M27) and Jeffamine� XTJ502 (XTJ). XTJ created a strong interface between clay layers and matrix because it bridged the layers with matrix by a chemical reaction as proved by Fourier transform infrared spectroscopy; M27 produced an interme-diate interface strength due to the molecular entanglement between grafted M27 chains and matrix molecules; the interface made by ETH was weak because neither chemical bridging nor molecular entanglement was involved. The studies of mechanical and thermal properties and morphology at a wide range of magnification show that the strong interface promoted the highest level of exfoliation and dispersion of clay layers, and achieved the most increment in Young’s modulus, fracture toughness and glass transition temperature (Tg) of matrix. With w1.3 wt% clay, the critical strain energy release rate G1c of neat epoxy improved from 179.0 to 384.7 J/m, 115% improvement and Tg enhanced from 93.7 to 99.

Modeling of Polymer Clay Nanocomposite for a Multiscale Approach

The mechanical property enhancement of polymer reinforced with nano-thin clay platelets (of high aspect ratio) is associated with a high polymer-filler interfacial area per unit volume. The ideal case of fully separated (exfoliated) platelets is generally difficult to achieve in practice: a typical nanocomposite also contains multilayer stacks of intercalated platelets. Here we use numerical modelling to investigate how the platelet properties affect the overall mechanical properties. The configuration of platelets is modelled using a statistical interpretation of the Representative Volume Element (RVE) approach, in which an ensemble of "sample" heterogeneous material is generated (with periodic boundary conditions). A simple Monte Carlo algorithm is used to place non-intersecting platelets in the RVE according to a specified set of statistical distributions. The effective stiffness of the platelet-matrix system is determined by measuring the stress (using standard Finite Element analysis) produced as a result of applying a small deformation to the boundaries, and averaging over the entire statistical ensemble. In this work we determine the way in which the platelet properties (curvature, filling fraction, stiffness, aspect ratio) and the number of layers in the stack affect the overall stiffness enhancement of the nanocomposite. Thus, we bridge the gap between behaviour on the macroscopic scale with that on the scale of the nano-reinforcement, forming part of a multi-scale modelling framework.Comment: 39 pages, 19 figure

Fabrication, structure and properties of epoxy/metal nanocomposites

Gd2O3 nanoparticles surface-modified with IPDI were compounded with epoxy. IPDI provided an anchor into the porous Gd2O3 surface and a bridge into the matrix, thus creating strong bonds between matrix and Gd2O3. 1.7 vol.-% Gd2O3 increased the Young’s modulus of epoxy by 16–19%; the surface-modified Gd2O3 nanoparticles improved the critical strain energy release rate by 64.3% as compared to 26.4% produced by the unmodified nanoparticles. The X-ray shielding efficiency of neat epoxy was enhanced by 300–360%, independent of the interface modification. Interface debonding consumes energy and leads to crack pinning and matrix shear banding; most fracture energy is consumed by matrix shear banding as shown by the large number of ridges on the fracture surface

RÄCKVIDDENS ROLL I REKLAMENS VÄRLD

Denna studie har haft som avsikt att undersöka begreppet räckvidds roll i en reklamkampanjprocess, samt i vilken utsträckning relationen till begreppen effekt och påverkan är relevanta för att nå denna förståelse. Det har tillämpats en begreppshistorisk analys för att kartlägga räckvidds historiska betydelser parallellt med effekt och påverkan. Därefter har kvalitativ empiri från intervjuer med aktörer från branschen studerats i ett sammanhang med syfte att nå en djupare förståelse för hur deras olika tolkningar av räckvidd har resulterat i dagens olika betydelser. Resultatet visar på begreppet räckvidds skilda innebörder som är beroende på situation och att det som aktör finns en viktig poäng i att vara medveten om dess skilda innebörder i olika sammanhang.The purpose of the following study is to investigate and analyze the significance of the concept of reach in advertising. Furthermore whether its relationship with effect and influence can contribute to further understanding of the concept. Firstly the concept of reach has been analyzed in a historical context. Together with the concepts of effect and influence, its historical meaning has been investigated and presented. Secondly, several interviews with actors in advertising have been conducted. The main purpose of the interviews has been to hear from those in the trade to understand what their views are of reach, and how they interpret its importance. The information gathered in the interviews shed light on how the advertising community has shaped the discourse of the subject. Additionally, the interviews have enabled an analysis of the evolution of today’s different meanings of the concept of reach. The results indicate that the different meanings of the concept of reach are dependent on the surrounding circumstances of advertisement. Furthermore, as a result it becomes evident that as an actor in the world of advertisement one can benefit from understanding its different interpretations

RÄCKVIDDENS ROLL I REKLAMENS VÄRLD

Denna studie har haft som avsikt att undersöka begreppet räckvidds roll i en reklamkampanjprocess, samt i vilken utsträckning relationen till begreppen effekt och påverkan är relevanta för att nå denna förståelse. Det har tillämpats en begreppshistorisk analys för att kartlägga räckvidds historiska betydelser parallellt med effekt och påverkan. Därefter har kvalitativ empiri från intervjuer med aktörer från branschen studerats i ett sammanhang med syfte att nå en djupare förståelse för hur deras olika tolkningar av räckvidd har resulterat i dagens olika betydelser. Resultatet visar på begreppet räckvidds skilda innebörder som är beroende på situation och att det som aktör finns en viktig poäng i att vara medveten om dess skilda innebörder i olika sammanhang.The purpose of the following study is to investigate and analyze the significance of the concept of reach in advertising. Furthermore whether its relationship with effect and influence can contribute to further understanding of the concept. Firstly the concept of reach has been analyzed in a historical context. Together with the concepts of effect and influence, its historical meaning has been investigated and presented. Secondly, several interviews with actors in advertising have been conducted. The main purpose of the interviews has been to hear from those in the trade to understand what their views are of reach, and how they interpret its importance. The information gathered in the interviews shed light on how the advertising community has shaped the discourse of the subject. Additionally, the interviews have enabled an analysis of the evolution of today’s different meanings of the concept of reach. The results indicate that the different meanings of the concept of reach are dependent on the surrounding circumstances of advertisement. Furthermore, as a result it becomes evident that as an actor in the world of advertisement one can benefit from understanding its different interpretations

Thermal Stability of Polymer based Nanocomposites

International audienc

Elaboration et caractérisation d'un alliage thermoplastique conducteur

International audienc