how does modification of interface by a long chain silane alter gas transport in nbr/silica composites?

As impermeability of elastomers has a technological importance in design of rubber parts such as tires, inflatable structures and seals. in the case of filled elastomers, gas transport is dictated by the tortuosity factor, the interface effects and the existence of layers with restricted mobility. here, for a number of nbr compounds, the surface of silica has been systematically treated at various degrees by a monofunctional long chain silane, and the change in the nitrogen gas permeability of the composites was probed and related to the change of the bound rubber, the interface strength and the dispersion quality. results indicated that by increasing the grafting density of silane, the gas permeability first follows an increasing trend and then it gradually decreases. by scrutinizing the various mechanisms being responsible for the observed gas transport behavior, it was finally concluded that the long chain of silane creates new inter-silane channels for gas transport at low level of grafting density which leads to high nitrogen permeability. however, further increase in silane grafting density causes a blockage for silica pores which would translate into a lower gas permeability.