| 초록 |
The elastic moduli of linear viscoelastic materials at a wide range of temperatures can be estimated by superimposing the elastic moduli of different time scales at a reference temperature. This is known as the time-temperature superposition (TTS) principle and has been applied through decades. The TTS principle breaks down, however, especially close to the glass transition (Tg), of which origin remains a matter of debate. We perform all-atom molecular dynamics simulations for poly(ethylene) oxide melts and aim to elucidate the origin of the TTS failure. We calculate the dynamic structure factor Fi(k, t) for segmental modes of different segment sizes of PEOs and estimate the friction coefficient ζi of the ith segmental mode. We find that as temperature decreases down to the Tg, the ratios of ζi's decouple to one another, otherwise known as the TTS failure. We demonstrate the translational-rotational decoupling along with the dynamic heterogeneity can be the reason of the TTS failure. |
