Particle drift in temperature gradients — the Soret coefficient in action
Thermophoresis is the motion of particles in response to a temperature gradient. The Soret coefficient S_T = D_T / D determines the steady-state concentration ratio: ln(c₂/c₁) = −S_T ΔT. Positive S_T drives particles toward cold regions (thermophobic); negative S_T drives them toward hot regions (thermophilic). This effect governs colloidal separation, DNA trapping in temperature gradients, and origin-of-life concentration mechanisms.