Understanding Unusual Thermal Transport Behavior in Soft Materials Under Mechanical Strain and Confinement – a Molecular Dynamics Study

Experiments have shown a dependence of the thermal conductivity of soft polymer materials on shear stress, which is common to several applications, such as film processing, fiber spinning, blow molding, and vacuum forming. Experiments reveal that the conductivity initially decreases with shear, but then increases as additional shear rate is applied. Based on molecular principles, we hypothesize that when molecules are initially placed under tension and extended, they disentangle, which reduces the number of points of interaction and diminishes the heat flux. Further molecular stretching increases this flux because the molecules are now better axially aligned with the direction of heat transfer. Molecular dynamics simulations confirm this competition and reproduce the inflection in the flux-strain relationship, which has not been previously explained. We have also examined interfacial thermal resistance when such soft materials interact with hydrophobic and hydrophilic surfaces