Phys. Rev. Lett. 2024
Transport mechanisms (of gas, ions, sound, thermal phonons) in polymer-grafted nanoparticle (GNP) melts are radically different if interpenetrated chain segments can be “pushed out of the way” or not. This provides a facile new means for manipulating the properties of these materials.
MPIP researchers, in collaboration with Bohai Liu and Xiangfan Xu
of
, Tongji University, Shanghai , China M. Jhalaria and S. K. Kumar (Columbia University, New York, USA) and E. Ruzicka, B. Benicewicz (University of South Carolina, Columbia, USA), investigated the thermal conduction in GNP melts. In contrast to normal diffusion processes, thermal conduction in one-dimensional systems is anomalous. The thermal conductivity
κ is found to vary with the length as
κ ~
Lα (
α > 0), but there is a long-standing debate on the value
α. Here, we present a canonical example of this behavior in GNP melts with different degree of polymerization, N, at fixed grafting density (0.47 chains/nm
2) and silica radius (8nm). For long chains (
N ≥ 945), the experimental
κ(
N) of GNP melts expectedly decreases with
N, i.e., polymer composition. For
N < 945, however,
κ(
N) unexpectedly increases with
N attaining a maximum at
N ~ 945 at which the extensional free energy per PMA chain is predicted to attain its maximum. The crossover from extended at short
Ndry to Gaussian-like chain conformation for longer
N> N
dry. In the former regime, the thermal conductivity of extended polymer chains increases with
N and follows
κp ~
Ndry0.46 ± 0.02 that provides experimental evidence of a novel class of superdiffusive thermal transport with
α = 1/2 . PHYSICAL REVIEW LETTERS 133, 248101 (2024)
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