Interface effects in elastomers reinforced by modified precipitated silica

The contributions of the so-called "interface effects" on the overall visco elastic. behavior of SBR reinforced by precipitated silica modified by mode l sizing agents are evaluated by using micromechanical models in a reverse mode. According to the nature of the coupling agent, two kinds of "interfac e effects" can be distinguished: (i) an overall change in the viscoelastic behavior of the polymer matrix, when the sizing agent is a chemical promoto r acting as additional ties of the SBR network, and (ii) the formation of a n actual mesophase, when direct interactions between SBR chains and silica could occur, as for example, when the coating agent of silica is an organos ilane based on short aliphatic chains. With increasing the length of the al iphatic chains of the coating agent (LOS agent), some a plasticisizing effe ct of the polymer is detected by DSC. It can affect either the entire polym er matric, or a confined region at the close vicinity of silica aggregates. According to this assumption, the bimodal viscoelastic behavior of the LOS -mesophase revealed by the modeling indicates that in addition to a local p lasticisizing effect induced by this agent, some direct interactions could occur between silica surface and SBR constraining the mobility of rubber mo lecules.