Linking Electrostatic-Induced Chain Stiffening to Heat Flow in Amorphous Polymers

Amorphous polymers are soft materials whose thermal properties are dominated by weak, nonbonded interactions that strongly suppress heat flow, limiting the thermal transport coefficient, κ, to below 0.40 W m^-1 K^-1. Recent experiments, however, show that electrostatic modification of poly(acrylic acid) (PAA) can increase κ beyond 1.00 W m^-1 K^-1 in highly ionized systems, compared to κ ≃ 0.33 W m^-1 K^-1 for uncharged PAA. Using molecular-dynamics simulations of a bead-spring polymer model, we study the effect of ionization on κ in amorphous polymers. In agreement with experiment, we observe a more than 2.5-fold enhancement in κ, driven by electrostatically induced, local chain stiffening that increases the bonded contribution to κ. These results identify a generic mechanism for tuning κ across a broad class of charged polymers.