Gravity in the segregation phenomenon observed near the gelation threshold

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Abstract
We investigate the phase diagram of sols and gels formed by copolymerization of acrylamide and bisacrylamide. In the vicinity of the sol-gel transition, we observe segregated samples with a viscous zone lying above an elastic part. A detailed rheological study has been done in the different domains of concentrations. The interpretation of the data in terms of critical behavior demonstrates that the samples where segregation occurs are gel phases. We also report calculations of the deformation and of the sedimentation kinetics of a tenuous polymer network under its own weight and experimental measurements in the segregated samples of the variations with height of the total monomer concentration and of the mobility of Brownian probes. This set of results shows that the gravitational field is at the origin of this segregation phenomenon.