We extend the model proposed by Merabia et al. [2008] regarding reinforcement mechanisms of filled elastomers. This model is based on the presence of glassy layers around filler particles which may bridge neighboring particles. The model was solved by Merabia et al. for spherical particles only and for a single dispersion state. However, experiments show that mechanical properties depend crucially on the complex shape of fillers as well as on their spatial distribution. We consider extensively both aspects in this article. We show that the distribution state of the fillers is key for controlling the reinforcement at high temperature. For a given distribution state, we show a strong effect of filler morphology on reinforcement. Distances between fillers are smaller with fractal aggregates, which leads to stronger reinforcement. Our model opens the path for the development of systems with tailored properties by tuning the filler distribution state and morphology.

Gelation kinetics and rheological properties of poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-co-HFP)] solutions in methyl-ethyl-ketone and in 2-heptanone are investigated. Small-angle X-ray scattering measurements indicate that the systems undergo phase separation by a nucleation process. For concentrations between 6 and 10 wt% of copolymer, strain-hardening appears when gels are sheared in the nonlinear regime, around 50% of deformation. At some critical shear amplitude, the rheological response changes abruptly, but reversibly, from hyperelastic towards viscous liquid. This indicates that the system undergo fracture or shear banding, in bulk or at walls. In other words the continuous network formed by the elastic, polymer-rich phase is locally broken under high amplitude oscillatory shear, thus breaking down the overall elastic response of the material. More interestingly, when the strain amplitude is progressively decreased back to zero, the initial nonlinear viscoelastic behavior is quantitatively recovered. In addition, when the strain is removed, the solution turns back to gel state very fast as compared with thermal gelation kinetics. These observations indicate that the initial structure can heal within a short time. It is proposed that strain-hardening depends on the intrinsic hyperelastic behavior of the polymer-rich phase, which should have a high density of effective crosslinks and/or entanglements.

Thermoreversible poly(vinylidene fluoride‐co‐hexafluoropropylene) (P(VDF‐co‐HFP)) gels are formed in an aliphatic ketone − methyl ethyl ketone (MEK) − at high concentrations (above 11 wt%). This gelation phenomenon is first investigated in terms of gelation kinetics which is found to depend strongly on both copolymer concentration and temperature. Melting temperatures Tm of P(VDF‐co‐HFP)‐based gels prepared at different concentrations, in MEK are measured by DSC. Combination of 19F Nuclear Magnetic Resonance (NMR), Small‐Angle X‐ray Scattering (SAXS), and Wide‐Angle X‐ray Scattering (WAXS) on undried/nonlyophilized gels is used to probe both the gelation mechanisms and the structure of these systems. 19F NMR experiments allow studying selectively the fluorinated copolymer. The occurrence of a polymer network‐like structure with rigid zones acting as cross‐links has been highlighted. Such a behavior is only observed in the gel state: no polymer network or rigid zones exist when the polymer–solvent system is in the liquid state. Moreover, the fraction of rigid zones as well as the fraction of elastically active chain portions increases with the copolymer concentration. The nature, of the rigid zones present within the gels are investigated by X‐ray diffraction. Rigid regions are found to display a crystalline order.