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

Nouvelles formulations thermoplastiques ou réactives de revêtements nanocomposite à base de silicates lamellaires

Cette thèse consiste à formuler de nouveaux revêtements nanocomposite à partir de polymères ou d\u27une polymérisation in-situ de monomères, en solution. La caractérisation des interactions développées dans les suspensions argile/solvant montre que le gonflement macroscopique s\u27effectue par percolation de 3-4 nanofeuillets et qu\u27une tension superficielle élevée du solvant est nécessaire pour obtenir un gonflement interfoliaire remarquable. Des liaisons chimiques ou physiques avec le monomère peuvent influencer la cinétique de réaction. La morphologie finale, analysée par RX, TEM et AFM, montre que la dispersion des feuillets dépend de l\u27argile, des interactions et de la diffusion dans le système. L\u27étude des propriétés thermomécaniques met en évidence une barrière aux solvants créée par les feuillets. Un renforcement via la formation d\u27un réseau argile/polymère est observé, toutefois la dispersion à l\u27échelle microscopique semble également déterminer les propriétés du nanocomposite

Nouvelles formulations thermoplastiques ou réactives de revêtements nanocomposite à base de silicates lamellaires

Cette thèse consiste à formuler de nouveaux revêtements nanocomposite à partir de polymères ou d'une polymérisation in-situ de monomères, en solution. La caractérisation des intéractions développées dans les suspensions argile/solvant montre que le gonflement macroscopique s'effectue par percolation de 3-4 nanofeuillets et qu'une tension superficielle élevée du solvant est nécessaire pour obtenir un gonflement interfoliaire remarquable. Des liaisons chimiques ou physiques avec le monomère peuvent influencer la cinétique de réaction. La morphologie finale, analysée par RX, TEM et AFM, montre que la dispersion des feuillets dépend de l'argile, des interactions et de la diffusion dans le système.L'étude des propriétés thermomécaniques met en évidence une barrière aux solvants créée par les feuillets. Un renforcement via la formation d'un réseau argile/polymère est observé, toutefois la dispersion à l'échelle microscopique semble également déterminer les propriétés du nanocomposite.In this study, new nanocomposite coatings were formulated from a polymer solution or from in-situ polymerisation between monomers. The characterization of the interactions between solvent molecules and organophilic clay has demonstrated that the macroscopic swelling results from the percolation of small tactoids. Furthermore, high surface tension solvents are necessary to obtain an efficient interlamellar swelling. Some preferential interactions with the monomer lead to chemical or physical bonds, which may have an influence on the reaction kinetic. The final dispersion states analyzed by X-ray diffraction, TEM and AFM, confirm the clay dispersion depends on the clay, the interactions and diffusion in the system. The study of thermomecanical properties has demonstrated that clays act as solvents barrier. A thermoplastic matrix reinforcement is observed thanks to the clay/polymer network formation, but the microscopic state of dispersion seems to determinate the nanocomposite properties.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF

Effect of selected non-ionic surfactants on the flow behavior of aqueous veegum suspensions

The aim of this work was to investigate the influence of some non-ionic surfactants, Tween 80 and Brij 98, on the viscosity and flow behavior of a commercial montmorillonite clay, Veegum Granules. The effect of different concentrations of the surfactants on the shear stress-shear rate rheograms of hydrated concentrated clay suspensions was determined by shear viscometry. The addition of either surfactant increased the plastic viscosity and the yield stress of the suspensions. Furthermore both surfactants altered the thixotropy of the suspensions to an extent that depended on both the surfactant concentration and the time of equilibration of the surfactant and Veegum. Brij 98 had a greater and more rapid effect. It is proposed that the surfactant polar head-groups anchor at the tetrahedral sheet surface, leaving the alkyl chains extending away from the edges and faces. Consequently, the alkyl chains undergo hydrophobic interactions that facilitate the association between the platelets and increase the physical structure within the suspension. Stereochemical differences between the polar groups may lead to differences in the way the surfactants associate with the tetrahedral sheet and hence their ultimate effect on the rheological behavior. There is a significant interaction between these surfactants and montmorillonite clays, and the rheological changes that occur could have a major impact on any pharmaceutical formulation that uses these ingredients