Vahid Hossein, Scacchi Alberto, Sammalkorpi Maria, Ala-Nissila Tapio
Department of Applied Physics, Aalto University, P.O. Box 15600, FI-00076 Aalto, Finland.
Department of Chemistry and Materials Science, Aalto University, P.O. Box 16100, FI-00076 Aalto, Finland.
J Chem Phys. 2024 Oct 7;161(13). doi: 10.1063/5.0223124.
We examine the interactions between polyelectrolytes (PEs) and uncharged substrates under conditions corresponding to a dielectric discontinuity between the aqueous solution and the substrate. To this end, we vary the relevant system characteristics, in particular the substrate dielectric constant ɛs under different salt conditions. We employ coarse-grained molecular dynamics simulations with rodlike PEs in salt solutions with explicit ions and implicit water solvent with dielectric constant ɛw = 80. As expected, at low salt concentrations, PEs are repelled from the substrates with ɛs < ɛw but are attracted to substrates with a high dielectric constant due to image charges. This attraction considerably weakens for high salt and multivalent counterions due to enhanced screening. Furthermore, for monovalent salt, screening enhances adsorption for weakly charged PEs, but weakens it for strongly charged ones. Meanwhile, multivalent counterions have little effect on weakly charged PEs, but prevent adsorption of highly charged PEs, even at low salt concentrations. We also find that correlation-induced charge inversion of a PE is enhanced close to the low dielectric constant substrates, but suppressed when the dielectric constant is high. To explore the possibility of a PE monolayer formation, we examine the interaction of a pair of like-charged PEs aligned parallel to a high dielectric constant substrate with ɛs = 8000. Our main conclusion is that monolayer formation is possible only for weakly charged PEs at high salt concentrations of both monovalent and multivalent counterions. Finally, we also consider the energetics of a PE approaching the substrate perpendicular to it, in analogy to polymer translocation. Our results highlight the complex interplay between electrostatic and steric interactions and contribute to a deeper understanding of PE-substrate interactions and adsorption at substrate interfaces with varying dielectric discontinuities from solution, ubiquitous in biointerfaces, PE coating applications, and designing adsorption setups.
我们研究了在水溶液与底物之间存在介电不连续性的条件下，聚电解质（PEs）与不带电底物之间的相互作用。为此，我们改变相关系统特性，特别是在不同盐条件下的底物介电常数ɛs。我们采用粗粒度分子动力学模拟，在含有明确离子和介电常数ɛw = 80的隐式水溶剂的盐溶液中使用棒状PEs。正如预期的那样，在低盐浓度下，ɛs < ɛw时PEs会从底物上被排斥，但由于镜像电荷会被吸引到高介电常数的底物上。由于增强的屏蔽作用，这种吸引力在高盐和多价抗衡离子存在时会大大减弱。此外，对于单价盐，屏蔽作用增强了弱电荷PEs的吸附，但减弱了强电荷PEs的吸附。同时，多价抗衡离子对弱电荷PEs影响很小，但即使在低盐浓度下也会阻止高电荷PEs的吸附。我们还发现，靠近低介电常数底物时，PE的相关诱导电荷反转会增强，但当介电常数高时会受到抑制。为了探索形成PE单层的可能性，我们研究了一对平行于介电常数ɛs = 8000的高介电常数底物排列的同电荷PEs之间的相互作用。我们的主要结论是，只有在单价和多价抗衡离子的高盐浓度下，弱电荷PEs才有可能形成单层。最后，类似于聚合物易位，我们还考虑了PE垂直于底物接近时的能量学。我们的结果突出了静电和空间相互作用之间的复杂相互作用，并有助于更深入地理解PE - 底物相互作用以及在生物界面、PE涂层应用和设计吸附装置中普遍存在的、具有不同溶液介电不连续性的底物界面处的吸附。
