Deposition of charge-regulated biocolloids on a charged surface

A theoretical investigation on the rate of deposition of biocolloids onto a rigid, charged surface is presented. Here, a biocolloid is modeled by a hard core covered by an ion-penetrable charge membrane, which contains dissociable functional groups. We show that, for a constant amount of fixed groups, the thicker the membrane the faster the rate of deposition grows. Also, a lower concentration of fixed groups, lower surface potential of the rigid surface, smaller equilibrium constant for the dissociation of functional groups K-a, and lower bulk pH all lead to a faster rate of deposition. The rate of deposition for various valence of cations follows the order (3: 1) > (1: 1) > (2: 1). The variation of the characteristic time of the deposition process (time required to reach roughly the saturation of surface coverage), t(c), as a function of the pK(a) (from 4 to 6) reveals that the behavior of the rate of deposition is influenced significantly by pH ranged from 4 to 7. As pH increases, t(c) approaches a constant value for the values of pK(a) examined.