EQUILIBRIUM SWELLING OF RUBBER NETWORKS LOADED WITH MODIFIED SILICA -AN INTERESTING VERSION OF LANGMUIR ADSORPTION

Equilibrium swelling of silica-loaded natural rubber networks in prese nce of surface active adsorbents is studied. ''Reinforcement'' is syst ematically reduced when parts of the silica surface are occupied by th e adsorbent (silanes or glycol). Extending the description of the swel ling of networks loaded with carbon black or silica within the framewo rk of the van der Waals network model, this observation can be describ ed as adsorption equilibrium. Langmuir adsorption turns out to be a go od approach. This elucidates the dynamics in the filler surfaces. Inte resting is the finding that the phenomenological Einstein-Smallwood mo dification of the modulus can be reformulated so as to account for the reduction of ''network-active'' adsorption sites. The description of the experimental data reveals different adsorption behavior of silanes and of glycol. The physical consequences are discussed.