Superdiffusive Thermal Transport in Polymer-Grafted Nanoparticle Melts.

Area of Science:

• Condensed Matter Physics
• Polymer Science
• Materials Science

Background:

• One-dimensional systems exhibit anomalous thermal conduction, deviating from normal diffusion.
• The exponent α in thermal conductivity scaling (κ∼L^α) has been a subject of long-standing debate.

Purpose of the Study:

• To investigate anomalous thermal transport in polymer-grafted nanoparticle (GNP) melts.
• To experimentally determine the exponent α in thermal conductivity scaling for GNP melts.
• To explore the relationship between polymer chain conformation and thermal conductivity.

Main Methods:

• Experimental measurement of thermal conductivity (κ) in GNP melts as a function of polymer chain length (N).
• Analysis of thermal conductivity scaling with chain length (κ(N)).
• Theoretical prediction of extensional free energy per polymer chain to correlate with conformation.

Main Results:

• Thermal conductivity κ(N) decreases with N for long chains (N≥945) but unexpectedly increases for shorter chains (N<945), peaking near N∼945.
• A maximum in extensional free energy per chain near N≈940 suggests a transition from extended to Gaussian-like polymer conformations.
• For extended polymer chains (short N), thermal conductivity follows κ_p∼N_dry^(0.46±0.02), providing evidence for superdiffusive transport with α=1/2.

Conclusions:

• Polymer-grafted nanoparticle melts serve as a model system for anomalous thermal transport.
• The study provides experimental evidence for a novel class of superdiffusive thermal transport (α=1/2) in one-dimensional systems.
• Polymer chain conformation significantly influences thermal conductivity in these nanomaterials.