Explaining the Sensitivity of Polymer Segmental Relaxation to Additive Size Based on the Localization Model

TQ McKenzie-Smith and JF Douglas and FW Starr, PHYSICAL REVIEW LETTERS, 127, 277802 (2021).

DOI: 10.1103/PhysRevLett.127.277802

We use molecular simulations to examine how the dynamics of a coarse- grained polymer melt are altered by additives of variable size and interaction strength with the polymer matrix. The effect of diluent size sigma on polymer dynamics changes significantly when its size is comparable to the polymer segment size. For each sigma, we show that the localization model (LM) quantitatively describes the dependence of the segmental relaxation time tau on temperature T in terms of dynamic free volume, quantified by the Debye-Waller factor < u(2)>. Within this model, we show that the additive size alone controls the functional form of the T dependence. The LM parameters reach asymptotic values when the diluent size exceeds the monomer size, converging to a limit applicable to macroscopic interfaces.

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