International audienceThe visco elastic behavior of graphite oxide-loaded PDMS suspensions showed, at low frequencies, a dominant elastic behavior with the appearance of a secondary plateau above 1.5 wt %. Within the investigated concentrations, such behavior was not observed for the graphite and functionalized graphite oxide/PDMS suspensions. This low percolation threshold of GO sheets was attributed to a macroscale aggregation. Furthermore, the critical strain (transition between the linear and nonlinear regime) was observed to slightly s. depend on the particle concentration (gamma(c) proportional to phi(-1 +/- 0.2)) Consequently, the exponent x (x = 0.4), related to the filler volume fraction and the aggregate structure, is lower than 1. This result means that a fractal structure cannot be associated with the aggregation of GO sheets. Actually, GO sheets aggregate into agglomerates that span through the gap between the plates of the rheometer. Agglomeration of GO sheets without any fractal structure explains this particular behavior. Furthermore, recovery tests consisting of subsequent strain sweep tests proved that the initial equilibrium network can be totally and rapidly restored. This particular behavior originates from the low viscosity of the PDMS suspension allowing Brownian motion of graphene oxide sheets to occur within only a few seconds
International audiencePolyethylenes and azide-terminated polyethylenes can be converted to macroradicals and nitrenes, respectively followed by addition reactions onto the unsaturated system of graphite oxide sheets. For the first time, the addition of these macroradicals to graphite oxide sheets was compared by performing grafting reactions at 190 degrees C in 1,2,4-trichlorobenzene as a solvent and at 100 degrees C followed by a solvothermal reduction at 150 degrees C in a solvent mixture of 1,4-dioxane and 1,2-dichlorobenzene. Dispersion of PE coated graphite oxide in a DMF-heptane mixture was utilised to follow the introduction of polyethylene onto the GO sheet surface while the thermogravimetric analysis indicated the extent of this grafting. The grafting ratio was found to be in the 1.5 wt% range and despite this low grafting content, the amount of grafted PE was high enough to dramatically improve the affinity of GO with the heptane phase in the DMF-heptane (50/50 v/v) mixture. Polyethylene functionalised GO was imaged by scanning electron microscopy showing a significant difference in morphology between the two grafting paths. It was found that a higher level of grafting was obtained using a radical grafting reaction in the presence of benzoyl peroxide rather than the thermal cleavage of PE-N-3 onto GO while a similar grafting content was obtained with the thermal cleavage of PE-N-3 onto GO grafted trimethoxy(7-octen-1-yl)silane
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