Mikhailov Ivan V, Darinskii Anatoly A
NRC «Kurchatov Institute»-PNPI-IMC, St. Petersburg 199004, Russia.
Int J Mol Sci. 2024 Dec 7;25(23):13175. doi: 10.3390/ijms252313175.
Using the self-consistent field approach, we studied the salt-controlled vertical segregation of mixed polymer brushes immersed into a selective solvent. We considered brushes containing two types of chains: polyelectrolyte (charged) chains and neutral chains. The hydrophobicity of both types of chains is characterized by the Flory-Huggins parameters χC and χN, respectively. It was assumed that the hydrophobicity is varied only for the polyelectrolyte chains (χC), while other polymer chains in the brush remain hydrophilic (χN=0) and neutral. Thus, in our model, the solvent selectivity (χ=χC-χN) was varied, which can be controlled in a real experiment, for example, by changing the temperature. At low salt concentrations, the polyelectrolyte chains swell and occupy the surface of the mixed brush. At high salt concentrations, the hydrophobic polyelectrolyte chains collapse and give place to neutral chains on the surface. By changing the selectivity of the solvent and the ionic strength of the solution, the surface properties of such mixed brushes can be controlled. Based on the numerical simulations results, it is shown how the critical selectivity corresponding to the segregation transition in polyelectrolyte/neutral brushes depends on the ionic strength of the solution. It is shown that at the same ionic strength, the critical selectivity increases with an increasing degree of dissociation of charged groups, as well as with an increasing fraction of polyelectrolyte chains in the mixed brush. It has also been shown that at low ionic strengths, the critical selectivity of the solvent decreases with increasing grafting density, while at high ionic strengths, on the contrary, it increases. Within the framework of the mean field theory, a two-parameter model has been constructed that quantitatively describes these dependencies.
采用自洽场方法，我们研究了浸入选择性溶剂中的混合聚合物刷的盐控垂直分离。我们考虑了包含两种链的刷：聚电解质（带电）链和中性链。两种链的疏水性分别由弗洛里-哈金斯参数χC和χN表征。假设仅聚电解质链的疏水性发生变化（χC），而刷中的其他聚合物链保持亲水性（χN = 0）且呈中性。因此，在我们的模型中，溶剂选择性（χ = χC - χN）是变化的，这在实际实验中可以通过改变温度等方式来控制。在低盐浓度下，聚电解质链膨胀并占据混合刷的表面。在高盐浓度下，疏水性聚电解质链塌陷，表面被中性链取代。通过改变溶剂的选择性和溶液的离子强度，可以控制这种混合刷的表面性质。基于数值模拟结果，展示了聚电解质/中性刷中对应于分离转变的临界选择性如何取决于溶液的离子强度。结果表明，在相同离子强度下，临界选择性随着带电基团解离度的增加以及混合刷中聚电解质链比例的增加而增加。还表明，在低离子强度下，溶剂的临界选择性随着接枝密度的增加而降低，而在高离子强度下则相反。在平均场理论框架内，构建了一个双参数模型来定量描述这些依赖性。
