where μ i is a chemical potential of the i-th constituent, having a charge z i e, which is located in an electrostatic field of a potential φ. If the electroneutrality condition inside the effective volume of the polymer is assumed, the electrostatic part of the potential does not have to be considered, as no net charge is exchanged between the polymer spherical region and the reservoir. Thus we will use only the chemical potentials μ i of the constituents.