Molecular effects Mean free path of the fluid molecules V.S.size Knudsen number Kn=λ/2R -A factor to Stokes drag (1+2AKn) 。Brownian motion -Diffusivity D=KT/6TucR Displacement Temperature gradient-thermophoresis -Radiation gradient-photophoresis Sound field-sonophoresisMolecular effects • Mean free path of the fluid molecules V.S. size – Knudsen number – A factor to Stokes drag • Brownian motion – Diffusivity – Displacement • Temperature gradient- thermophoresis – Radiation gradient – photophoresis – Sound field- sonophoresis