Biesheuvel P Maarten, van der Veen Marijn, Norde Willem
Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6703 HB Wageningen, The Netherlands.
J Phys Chem B. 2005 Mar 10;109(9):4172-80. doi: 10.1021/jp0463823.
The equilibrium adsorption of polyelectrolytes with multiple types of ionizable groups is described using a modified Poisson-Boltzmann equation including charge regulation of both the polymer and the interface. A one-dimensional mean-field model is used in which the electrostatic potential is assumed constant in the lateral direction parallel to the surface. The electrostatic potential and ionization degrees of the different ionizable groups are calculated as function of the distance from the surface after which the electric and chemical contributions to the free energy are obtained. The various interactions between small ions, surface and polyelectrolyte are self-consistently considered in the model, such as the increase in charge of polyelectrolyte and surface upon adsorption as well as the displacement of small ions and the decrease of permittivity. These interactions may lead to complex dependencies of the adsorbed amount of polyelectrolyte on pH, ionic strength, and properties of the polymer (volume, permittivity, number, and type of ionizable groups) and of the surface (number of ionizable groups, pK, Stern capacity). For the adsorption of lysozyme on silica, the model qualitatively describes the gradual increase of adsorbed amount with pH up to a maximum value at pHc, which is below the iso-electric point, as well as the sharp decrease of adsorbed amount beyond pHc. With increasing ionic strength the adsorbed amount decreases (for pH > pHc), and pHc shifts to lower values.
使用一个修正的泊松-玻尔兹曼方程来描述具有多种可电离基团的聚电解质的平衡吸附，该方程包括聚合物和界面的电荷调节。采用一维平均场模型，其中假设在平行于表面的横向方向上静电势恒定。计算不同可电离基团的静电势和电离度作为距表面距离的函数，之后获得对自由能的电学和化学贡献。模型自洽地考虑了小离子、表面和聚电解质之间的各种相互作用，例如吸附时聚电解质和表面电荷的增加以及小离子的位移和介电常数的降低。这些相互作用可能导致聚电解质吸附量对pH、离子强度以及聚合物性质（体积、介电常数、可电离基团的数量和类型）和表面性质（可电离基团的数量、pK、斯特恩容量）产生复杂的依赖关系。对于溶菌酶在二氧化硅上的吸附，该模型定性地描述了吸附量随pH逐渐增加直至在低于等电点的pHc处达到最大值，以及在pHc之后吸附量的急剧下降。随着离子强度增加，吸附量降低（对于pH > pHc），并且pHc向更低的值移动。
