Interaction potential trick
Experimentally, the probability P(r) of finding two colloidal particles with separation r can be measured via optical microscope. Such probability is related to the free energy U(r) of the system through the Boltzman relation: P(r) ~ Exp[-U(r)/K_BT].
Based upon these, the interaction free energy can be measured by taking the natural logarithm of the equilibrium probability distribution of the two colloidal particles.
Reference: Ritu Verma, J. C. Crocker, T. C. Lubensky, and A. G. Yodh, Phys.Rev.Lett., Vol.81, Pg.4004, 1998.
Based upon these, the interaction free energy can be measured by taking the natural logarithm of the equilibrium probability distribution of the two colloidal particles.
Reference: Ritu Verma, J. C. Crocker, T. C. Lubensky, and A. G. Yodh, Phys.Rev.Lett., Vol.81, Pg.4004, 1998.