A nano-mechanical instability as primary contribution to rolling resistance

Area of Science:

• Materials Science
• Nanotechnology
• Polymer Chemistry

Background:

• Rolling resistance is a major factor in automobile fuel efficiency and emissions.
• The underlying mechanisms of energy dissipation in tire tread materials are complex and difficult to observe experimentally.
• Silica-filled elastomers are key components in modern tire technology.

Purpose of the Study:

• To identify and characterize novel nano-mechanical mechanisms responsible for energy dissipation in silica-filled elastomers under dynamic strain.
• To understand the role of filler particle interactions in energy loss.
• To explore the temperature dependence of these dissipative mechanisms.

Main Methods:

• Atomistic molecular modeling was employed to simulate silica particle interactions within a polyisoprene rubber matrix.
• Cyclic forces were applied to open and close silica particle-to-particle contacts to generate force-vs-separation curves.
• Analysis focused on identifying particle displacements and energy dissipation pathways.

Main Results:

• A novel energy dissipation mechanism, termed 'jolts,' involving spontaneous relative displacements of silica filler particles, was identified.
• These particle 'jolts' contribute to energy dissipation beyond conventional viscous losses in the polymer matrix.
• The contribution of this new loss mechanism becomes dominant as temperature increases.

Conclusions:

• The study reveals a previously unrecognized nano-mechanical origin of energy dissipation in silica-filled elastomers.
• This discovery has significant implications for controlling and reducing tire rolling resistance.
• The findings are also relevant to other elastomer composite applications subjected to dynamic loading.