Revealing Microdynamics that Underlie Tire Tread Performance*

Filled elastomers are used in many applications, including tire tread. Functionalized chain additives and coupling agents have been used to enhance interactions between filler and polymer matrix in silica-filled styrene butadiene rubber (SBR). These interactions create bound polymer layers around the filler that alter the dynamic performance by changing aggregate size and connections among particles, forming strong “force chains”.

We have synthesized well-defined functionalized polymeric chain additives and nonfunctional analogs to probe how changing the filler/polymer interface chemistry changes the filler microscopic response and thus the macrodynamics. This study spans length scales from that of the networked agglomerates to that of filler/polymer interfaces. We probe the filler network’s microscopic response using X-ray Photon Correlation Spectroscopy (XPCS) while the sample is under oscillatory strain. The rate of change in the intensity-intensity time autocorrelation during the measurement provides information on the filler network microdynamics. The microscopic responses of samples containing functionalized chain additives differ from those of samples containing nonfunctional additives.