Numerical demonstration of negative thermophoresis of nanoparticles in the free molecular regime

Thermophoresis is a transport phenomenon of small particles caused by temperature gradients. It has essential influences on various areas, such as aerosol industry, biology, and nanofabrication. Traditionally, it is well known that particles transport from high temperature to low temperature region. However, Wang and Li analytically showed the existence of negative thermophoresis, where particles move from low temperature to high temperature in gas media, especially when the particle size is of nanometer. Due to the complexity of the interactions between particles and gas molecules, it is difficult to capture the real picture of the mechanism analytically. In this work, we use molecular dynamics simulations to study negative thermophoresis for nanoparticles. It is shown that negative thermophoresis can take place for nanoparticles and it depends on both the particle size and the molecular interactions between nanoparticles and gas molecules.