Chain-length-dependent correlated molecular motion in polymers
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866912725311946752 |
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| author | Reynolds, Matthew Baker, Daniel L. Olmsted, Peter D. Mattsson, Johan |
| author_facet | Reynolds, Matthew Baker, Daniel L. Olmsted, Peter D. Mattsson, Johan |
| contents | We show how dynamic heterogeneities (DH), a hallmark of glass-forming materials, depend on chain flexibility and chain length in polymers. For highly flexible polymers, a relatively large number of monomers ($N_c\sim500$) undergo correlated motion at the glass transition temperature $T_g$, independent of molecular weight ($M$). In contrast, less flexible polymers show a complex $N_c(M)$ behaviour divided into three regimes, consistent with observation in both $T_g(M)$ and chain conformational structure. For short oligomers ($\lesssim$ 2 Kuhn steps), a transition from mainly $\it{inter}$molecular correlations and $N_c\sim 200$, to strongly $\it{intra}$molecular correlations and $N_c< 50$ (roughly the molecular size) is observed; for longer chains, $N_c$ increases weakly, before saturating. For poly(methyl methacrylate), a remarkable similarity is found between $N_c(M)$ and the $M$-dependent ratio of the activation barriers of the structural ($α$) and secondary ($β$) relaxations. Our results suggest a link between the DH length-scale and the number of $β$ relaxation events jointly-activated to facilitate the $α$ relaxation. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2405_02733 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Chain-length-dependent correlated molecular motion in polymers Reynolds, Matthew Baker, Daniel L. Olmsted, Peter D. Mattsson, Johan Soft Condensed Matter Materials Science We show how dynamic heterogeneities (DH), a hallmark of glass-forming materials, depend on chain flexibility and chain length in polymers. For highly flexible polymers, a relatively large number of monomers ($N_c\sim500$) undergo correlated motion at the glass transition temperature $T_g$, independent of molecular weight ($M$). In contrast, less flexible polymers show a complex $N_c(M)$ behaviour divided into three regimes, consistent with observation in both $T_g(M)$ and chain conformational structure. For short oligomers ($\lesssim$ 2 Kuhn steps), a transition from mainly $\it{inter}$molecular correlations and $N_c\sim 200$, to strongly $\it{intra}$molecular correlations and $N_c< 50$ (roughly the molecular size) is observed; for longer chains, $N_c$ increases weakly, before saturating. For poly(methyl methacrylate), a remarkable similarity is found between $N_c(M)$ and the $M$-dependent ratio of the activation barriers of the structural ($α$) and secondary ($β$) relaxations. Our results suggest a link between the DH length-scale and the number of $β$ relaxation events jointly-activated to facilitate the $α$ relaxation. |
| title | Chain-length-dependent correlated molecular motion in polymers |
| topic | Soft Condensed Matter Materials Science |
| url | https://arxiv.org/abs/2405.02733 |