The effects of mechanical mixing and filler-filler (F-F) and polymer-filler (P-F) interactions on the normalized state of a filler microdispersion [d(x)] and the viscoelastic properties of silica-filled rubbers were studied. The rubbers were prepared with or without the addition of n-octyl-triethoxysilane (OTES) to modify F-F interactions or coupling agents such as 3-mercaptopropyl-trimethoxysilane and 3-mercaptopropyl-triethoxysilane (MPTES) to increase P-F interactions. Increased mixing improved d(x) and enhanced the hysteresis temperature dependence (HTD) by giving a higher tan 8 value near the compound glass-transition temperature (T-g) but lowered tan 6 at elevated temperatures for stocks containing a coupling agent. The changes in P-F and F-F interactions in rubbers with mixing and subsequent thermal treatment were shown to be responsible for the property differences observed among stocks containing different silanes. Attempts were made to quantify the efficiency for improving d(x) with various silanes. The increased P-F interactions in compounds containing MPTES showed better efficiency for improving d(x) and enhancing HTD in comparison with OTES. It was also demonstrated that the change in hysteresis near T-g was mainly governed by the degree of filler networking, whereas elevated-temperature hysteresis was strongly influenced by the P-F interactions in compounds. (c) 2008 Wiley Periodicals, Inc.