Equilibrium swelling of rubber networks loaded with modified silica: an interesting version of Langmuir adsorption

Abstract

Equilibrium swelling of silica-loaded natural rubber networks in presence of surface active adsorbents is studied. “Reinforcement” is systematically reduced when parts of the silica surface are occupied by the adsorbent (silanes or glycol). Extending the description of the swelling of networks loaded with carbon black or silica within the framework of the van der Waals network model, this observation can be described as adsorption equilibrium. Langmuir adsorption turns out to be a good approach. This elucidates the dynamics in the filler surfaces. Interesting is the finding that the phenomenological Einstein-Smallwood modification 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.