Many-body depletion interactions among protein spheres in a semidilute polymer solution

The polymer segment distribution is shown to obey the Laplace equation for a suspension of small protein spheres and semidilute polymer. The depletion interaction is computed at all protein concentrations by introducing void distributions. Within a linear response Ansatz for the solution to the Laplace equation, the average depletion energy depends on two- and three-point void (-surface) correlation functions. It is concluded that depletion correlations of long range do not appear at high protein concentrations.