We report in this work the grafting of laponite clay particles with monofunctional c-methacryloxy... more We report in this work the grafting of laponite clay particles with monofunctional c-methacryloxypropyl dimethyl methoxy silane (c-MPTDES) and trifunctional c-methacryloxypropyl trimethoxy silane (c-MPTMS) coupling agents. The evolution of the grafted amount and of the grafting yield was monitored as a function of the reaction time and of the initial silane concentration. We showed that the grafted amount increased with time and with the silane content up to a plateau value. The amount of chemisorbed silane at saturation varied from 0.56 to 1.9 mmol g 21 depending on the nature of the coupling agent, the reaction time and the grafting conditions. While the trifunctional silane was capable of both reaction with the clay edges and formation of complex polysiloxane oligomers in the bulk which were further deposited on the particulate surface, the monofunctional silane formed a monolayer coverage on the border of the clay plates with the carbonyl groups being directed toward the surface as attested by Fourier transform infrared (FTIR) spectroscopy. The properties of the organosilane-modified laponite were examined by various analytical techniques such as wide-angle X-ray diffraction (WAXD), nitrogen adsorption and thermogravimetric analysis (TGA). The monofunctional silane exhibited nearly no effect on the physicochemical properties of the clay whereas grafting of the trifunctional silane resulted in decreased porosity, increased interlamellar distance and higher hydrophobicity.
Polystyrene-based nanocomposite films containing up to 20 wt% laponite clay have been prepared by... more Polystyrene-based nanocomposite films containing up to 20 wt% laponite clay have been prepared by emulsion polymerization. Significant increases in the storage and tensile moduli were observed in both the glassy and rubbery state on laponite addition. However, whereas in the glassy state these increases were correlated with the extent of exfoliation of the laponite, in the rubbery state they were more dependent on the overall laponite content. These results are discussed in terms of the observed morphologies and micromechanical models for the reinforcing effect of rigid nano-sized filler particles.
Nanocomposite films containing up to 50 wt. % laponite have been prepared from emulsion polymeriz... more Nanocomposite films containing up to 50 wt. % laponite have been prepared from emulsion polymerized polystyrene (PS)/laponite latexes with the laponite attached to the PS particle surfaces. Below T g , the observed stiffness increases are accounted for by classical models for mechanical reinforcement, but these severely underestimate the stiffness above T g . An alternative model has therefore been proposed, in which the laponite and PS with reduced mobility form a cellular network, consistent with TEM observations. This cellular network is also argued to play an important role in the decrease in fracture resistance at high laponite contents, through decreases in matrix ductility and breakdown of the laponite stacks.
Summary: Polymer latex particles were synthesized in the presence of inorganic particles, which h... more Summary: Polymer latex particles were synthesized in the presence of inorganic particles, which had been organically-modified to promote favorable interactions with growing macromolecules. The organic modification was performed using three different routes: (1) surface covalent grafting of vinyl trialkoxysilanes, (2) surface adsorption of polyethylene glycol-based macromonomers, and (3) bulk modification through ion exchange with cationic monomers or cationic initiators. Two types of mineral particles were studied: commercial and self-prepared silica particles (with diameters from 80 nm to 1 µm), and commercial laponite clay particles with a cation exchange capacity of 0.75 meq · g−1. Emulsion polymerization was performed in the presence of styrene or butyl acrylate monomers. The morphologies of the nanocomposite particles were observed by (cryogenic) transmission electron microscopy and correlated to the organic modification procedure.
Polymer/silica and polymer/Laponite nanocomposite colloids with various morphologies have been el... more Polymer/silica and polymer/Laponite nanocomposite colloids with various morphologies have been elaborated through emulsion polymerization using a polymerizable organosilane (route I) and a methyl methacrylate-terminated macromonomer (route II) as coupling agents. Depending on the synthetic strategy and on the nature of the mineral particles, either core-shell, raspberry-like, multipod-like, currant bun or inverted core-shell morphologies (the mineral forming the shell) were achieved. Beyond the control of particle shape, we have demonstrated that some of the polymerizations exhibited particular kinetics behaviors which could be correlated to the mechanism of formation of the composite particles. Interestingly, conversion versus time curves of a series of soap free polymerizations performed in the presence of the macromonomer showed a significant increase in the polymerization rate with increasing the inorganic particles concentration. Characterization of the composite latexes by transmission electron microscopy showed that the mineral was located at the surface of the latex spheres and participated therefore to their stabilization. The higher the amount of inorganic particles, the lower the particles size and the higher the polymerization rate.
We report in this work the grafting of laponite clay particles with monofunctional c-methacryloxy... more We report in this work the grafting of laponite clay particles with monofunctional c-methacryloxypropyl dimethyl methoxy silane (c-MPTDES) and trifunctional c-methacryloxypropyl trimethoxy silane (c-MPTMS) coupling agents. The evolution of the grafted amount and of the grafting yield was monitored as a function of the reaction time and of the initial silane concentration. We showed that the grafted amount increased with time and with the silane content up to a plateau value. The amount of chemisorbed silane at saturation varied from 0.56 to 1.9 mmol g 21 depending on the nature of the coupling agent, the reaction time and the grafting conditions. While the trifunctional silane was capable of both reaction with the clay edges and formation of complex polysiloxane oligomers in the bulk which were further deposited on the particulate surface, the monofunctional silane formed a monolayer coverage on the border of the clay plates with the carbonyl groups being directed toward the surface as attested by Fourier transform infrared (FTIR) spectroscopy. The properties of the organosilane-modified laponite were examined by various analytical techniques such as wide-angle X-ray diffraction (WAXD), nitrogen adsorption and thermogravimetric analysis (TGA). The monofunctional silane exhibited nearly no effect on the physicochemical properties of the clay whereas grafting of the trifunctional silane resulted in decreased porosity, increased interlamellar distance and higher hydrophobicity.
Polystyrene-based nanocomposite films containing up to 20 wt% laponite clay have been prepared by... more Polystyrene-based nanocomposite films containing up to 20 wt% laponite clay have been prepared by emulsion polymerization. Significant increases in the storage and tensile moduli were observed in both the glassy and rubbery state on laponite addition. However, whereas in the glassy state these increases were correlated with the extent of exfoliation of the laponite, in the rubbery state they were more dependent on the overall laponite content. These results are discussed in terms of the observed morphologies and micromechanical models for the reinforcing effect of rigid nano-sized filler particles.
Nanocomposite films containing up to 50 wt. % laponite have been prepared from emulsion polymeriz... more Nanocomposite films containing up to 50 wt. % laponite have been prepared from emulsion polymerized polystyrene (PS)/laponite latexes with the laponite attached to the PS particle surfaces. Below T g , the observed stiffness increases are accounted for by classical models for mechanical reinforcement, but these severely underestimate the stiffness above T g . An alternative model has therefore been proposed, in which the laponite and PS with reduced mobility form a cellular network, consistent with TEM observations. This cellular network is also argued to play an important role in the decrease in fracture resistance at high laponite contents, through decreases in matrix ductility and breakdown of the laponite stacks.
Summary: Polymer latex particles were synthesized in the presence of inorganic particles, which h... more Summary: Polymer latex particles were synthesized in the presence of inorganic particles, which had been organically-modified to promote favorable interactions with growing macromolecules. The organic modification was performed using three different routes: (1) surface covalent grafting of vinyl trialkoxysilanes, (2) surface adsorption of polyethylene glycol-based macromonomers, and (3) bulk modification through ion exchange with cationic monomers or cationic initiators. Two types of mineral particles were studied: commercial and self-prepared silica particles (with diameters from 80 nm to 1 µm), and commercial laponite clay particles with a cation exchange capacity of 0.75 meq · g−1. Emulsion polymerization was performed in the presence of styrene or butyl acrylate monomers. The morphologies of the nanocomposite particles were observed by (cryogenic) transmission electron microscopy and correlated to the organic modification procedure.
Polymer/silica and polymer/Laponite nanocomposite colloids with various morphologies have been el... more Polymer/silica and polymer/Laponite nanocomposite colloids with various morphologies have been elaborated through emulsion polymerization using a polymerizable organosilane (route I) and a methyl methacrylate-terminated macromonomer (route II) as coupling agents. Depending on the synthetic strategy and on the nature of the mineral particles, either core-shell, raspberry-like, multipod-like, currant bun or inverted core-shell morphologies (the mineral forming the shell) were achieved. Beyond the control of particle shape, we have demonstrated that some of the polymerizations exhibited particular kinetics behaviors which could be correlated to the mechanism of formation of the composite particles. Interestingly, conversion versus time curves of a series of soap free polymerizations performed in the presence of the macromonomer showed a significant increase in the polymerization rate with increasing the inorganic particles concentration. Characterization of the composite latexes by transmission electron microscopy showed that the mineral was located at the surface of the latex spheres and participated therefore to their stabilization. The higher the amount of inorganic particles, the lower the particles size and the higher the polymerization rate.
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Papers by Norma Herrera