Strain-Induced Accelerated Chain Dynamics in Cross-Linked Natural Rubber under Active Deformation: An In Situ Nuclear...

Area of Science:

• Materials Science
• Polymer Science
• Physical Chemistry

Background:

• Understanding the molecular-level network evolution in polymers during deformation is crucial for material design.
• Sulfur-cured natural rubber is a widely used elastomer whose mechanical properties are governed by its cross-linked network structure.

Purpose of the Study:

• To elucidate the molecular-level chain network evolution in sulfur-cured natural rubber under tensile deformation.
• To investigate the relationship between microscopic chain dynamics and macroscopic mechanical responses.

Main Methods:

• Simultaneous in situ tensile testing and time-domain (TD) nuclear magnetic resonance (NMR) measurements.
• Proton T₂ relaxation time measurements to probe microscopic chain dynamics.
• Variable-temperature tensile NMR to assess temperature independence of observed phenomena.

Main Results:

• Observed both restricted chain dynamics and an abnormal accelerated semi-restricted chain dynamics within a specific stretching ratio range (2.1 < λ_mac < 3.5).
• This abnormal dynamics correlated with an invariant tensile modulus (0.42 MPa) in the same range.
• The turning points of these phenomena were largely independent of temperature (35-85 °C).

Conclusions:

• Proposed a strain-induced heterogeneous network deformation model for sulfur-cured natural rubber.
• This model suggests differential relaxation of network chains in low and high cross-linking regions during deformation.
• The findings provide insights into the complex deformation mechanisms of elastomers.