  We use the dynamic length and time scale separation in suspensions to
formulate a general description of colloidal thermophoresis. Our approach
allows an unambiguous definition of separate contributions to the colloidal
flux and clarifies the physical mechanisms behind non-equilibrium motion of
colloids. In particular, we derive an expression for the interfacial force
density that drives single-particle thermophoresis in non-ideal fluids. The
issuing relations for the transport coefficients explicitly show that
interfacial thermophoresis has a hydrodynamic character that cannot be
explained by a purely thermodynamic consideration. Our treatment generalises
the results from other existing approaches, giving them a clear interpretation
within the framework of non-equilibrium thermodynamics.
