Influence of Preparation Method and Molecular parameters on the Rheology of Model PEO/ Laponite Nanocomposites
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Influence of Preparation Method and Molecular parameters on the Rheology of Model PEO/ Laponite Nanocomposites Jesmy Jose1, Abakar Adam Omar1, Guillaume Brotons2, Jean-François Tassin1 1
Polymères, Colloïdes, Interfaces, UMR CNRS 6120, Université du Maine Avenue Olivier Messiaen, 72085 Le Mans Cedex, France
2 Laboratoire de Physique de l’Etat Condensé, UMR CNRS 6087, Université du Maine Avenue Olivier Messiaen, 72085 Le Mans Cedex, France
ABSTRACT Model polymer nanocomposites based on geometrically well defined and protected Laponite particles dispersed in Poly(ethylene oxide) were investigated in order to improve the understanding of the filler dispersion effects on rheology by varying two experimental factors, namely preparation method and PEO matrix molecular weight. Preparation methods are divided into a solution dispersion and a melt dispersion by twin screw extrusion. The linear viscoelastic properties of the samples prepared by solution method revealed an elastic solid like behaviour at Laponite weight fractions as low as 0.1%, dramatically lower than the percolation threshold so far reported for such kind of systems. The sample preparation by melt dispersion, although leading to dispersed particles, does not achieve the same levels of modulus as compared to solution prepared mixtures. We propose a qualitative interpretation of this phenomenon, based on the mixture between a liquid and a dispersed phase of rather solid character. Further experiments using small angle X-ray scattering techniques (SAXS) show that the modulus level is not necessarily related to the height of the correlation peak characteristic of the Laponite stacks. However, for samples prepared with varying PEO matrix molecular weight the fraction of Laponite stacks decreases with increasing PEO molecular weight. The rheology master curve analyses show that confinements of polymer chains arising from high concentrations of particles and high molecular weight matrix chains do not impact the level of the low frequency modulus. However, a slower polymer dynamics, as observed for higher molecular weights, leads to an increase of the modulus at low particle loadings. INTRODUCTION Dispersions of nanoparticles, especially anisotropic ones, in polymers offer significant potential for providing a wealth of attractive material properties [1-4]. The interest in these materials stems from the ability to impart huge changes in properties (rheological, mechanical, barrier, thermal etc.) at “fairy dust levels”. A prerequisite being the nanofiller dispersion, the dispersal of nanoparticles, which have a very high specific surface, into polymeric matrices remains an outstanding challenge. Dynamic rheology in the linear regime is sensitive to filler dispersion in polymers. At filler concentrations above the percolation value, a sample spanning percolated filler network dominates the viscoelastic behavior in polymer/clay nanocomposites. We chose to work on a model system consisting of a water soluble polymer, poly (ethylene oxide - PEO), available with differ
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