where J is the heat flux at the steady state and dT /dz is the temperature gradient. An example of the system configuration and temperature profile in the steady state is shown in Figure . The NEMD simulations are performed at a constant volume (NVT) using the box dimension averaged over the last half period from the equilibration step. Three replicas of NEMD production runs starting from different equilibrium configurations are performed to compute the standard deviations that are taken as error bars. In experiments, the thermal conductivity of PDMS (M w ≈ 3700 g/mol with PDI ≈ 1.1) is measured using the transient hot-wire method, with the equipment model DRL-III thermal conductivity tester from Xiangtan Xiangyi Instrument Co. Ltd. The transient hot-wire method involves using a thin wire as a heat source to apply heat to the material for a specific duration. As the wire heats up, it raises the temperature of the surrounding material. By monitoring the temperature change of the wire, the thermal conductivity of the material can be calculated. We employ Green-Kubo method 27 to calculate the viscosity of PDMS materials from the equilibrium MD simulations of Type III production run. This approach utilizes the time correlation function of the off-diagonal elements of the stress tensor, which is related to the viscosity of the system. The viscosity η is then computed from the Green-Kubo relation given by: