Remarks on the depletion interaction between nanoparticles and flexible polymers

The depletion interaction between nanoparticles and flexible polymers is discussed when the suspensions are nondilute. It is argued that a mean-field approximation is often useful. It is shown that the capacitance is a variable of interest for a nanoparticle immersed in a semidilute polymer solution. We also investigate the contraction of a polymer chain in a fixed array of nanosized obstacles. The contraction of a chain in a semidilute suspension of proteins is viewed as a problem of osmotic equilibrium.