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<p>The thermal-mechanical properties of vulcanized styrene-butadiene rubber (SBR) are fundamentally determined by its cross-linked network structure. However, a systematic understanding of how cross-linking degree influences molecular dynamics and thermal transport remains limited. In this work, we investigate the dual micro-mechanisms through which cross-linking degree (<i>D</i>c) governs both viscoelastic and thermal properties: namely, the restriction of chain segment mobility and modulation of low-frequency phonon density. The molecular dynamics (MD) simulations coupled with experimental validation are employed to investigate the effect of <i>D</i>c on shear viscosity(<i>η</i>), bulk viscosity(<i>η</i><sub>b</sub>), specific heat capacity (<i>C</i><sub>p</sub>, <i>C</i><sub>v</sub>), and thermal conductivity(<i>κ</i>). Results demonstrate that increasing <i>D</i>c enhances intermolecular constraints, leading to a rise in <i>η</i> by 65.5–23.3% and an increase in <i>η</i><sub>b</sub> by 6.6–11.1% under fixed shear conditions. In contrast, increasing shear rate (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\dot {\gamma }\)</EquationSource> </InlineEquation>) promotes molecular chain orientation, thereby decreasing <i>η</i> by 83.4–93.2%, while simultaneously strengthening intermolecular forces and constraining chain movement, which increases <i>η</i><sub>b</sub> by 88.6–100.9%. Thermally, <i>κ</i> increases by 48.4% at <i>D</i>c = 8.0 compared to <i>D</i>c = 1.0, due to enhanced low-frequency phonon excitation within the tightened network. Furthermore, suppressed chain mobility reduces specific heat capacity by 8.9% (<i>C</i><sub>p</sub>) and 8.6% (<i>C</i><sub>v</sub>) over the temperature range of 300–330&#xa0;K. These findings establish a clear microstructure–property relationship that elucidates the competing roles of chain dynamics and phonon transport in cross-linking elastomers, providing a theoretical basis for the rational design of vulcanized rubber with tailored multifunctional performance.</p>

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Effect of cross-linking degree on thermal-mechanical properties of vulcanized SBR

  • 期刊论文

  • 发表日期：

    2026年1月6日

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  • Tian Yan,
  • Kejian Wang,
  • Xiuying Zhao

摘要

The thermal-mechanical properties of vulcanized styrene-butadiene rubber (SBR) are fundamentally determined by its cross-linked network structure. However, a systematic understanding of how cross-linking degree influences molecular dynamics and thermal transport remains limited. In this work, we investigate the dual micro-mechanisms through which cross-linking degree (Dc) governs both viscoelastic and thermal properties: namely, the restriction of chain segment mobility and modulation of low-frequency phonon density. The molecular dynamics (MD) simulations coupled with experimental validation are employed to investigate the effect of Dc on shear viscosity(η), bulk viscosity(ηb), specific heat capacity (Cp, Cv), and thermal conductivity(κ). Results demonstrate that increasing Dc enhances intermolecular constraints, leading to a rise in η by 65.5–23.3% and an increase in ηb by 6.6–11.1% under fixed shear conditions. In contrast, increasing shear rate ( \(\dot {\gamma }\) ) promotes molecular chain orientation, thereby decreasing η by 83.4–93.2%, while simultaneously strengthening intermolecular forces and constraining chain movement, which increases ηb by 88.6–100.9%. Thermally, κ increases by 48.4% at Dc = 8.0 compared to Dc = 1.0, due to enhanced low-frequency phonon excitation within the tightened network. Furthermore, suppressed chain mobility reduces specific heat capacity by 8.9% (Cp) and 8.6% (Cv) over the temperature range of 300–330 K. These findings establish a clear microstructure–property relationship that elucidates the competing roles of chain dynamics and phonon transport in cross-linking elastomers, providing a theoretical basis for the rational design of vulcanized rubber with tailored multifunctional performance.