de Carvalho Sidney J, Metzler Ralf, Cherstvy Andrey G
Institute of Biosciences, Letters and Exact Sciences, Sao Paulo State University, 15054-000 Sao Jose do Rio Preto, Brazil.
Soft Matter. 2015 Jun 14;11(22):4430-43. doi: 10.1039/c5sm00635j.
What are the fundamental laws for the adsorption of charged polymers onto oppositely charged surfaces, for convex, planar, and concave geometries? This question is at the heart of surface coating applications, various complex formation phenomena, as well as in the context of cellular and viral biophysics. It has been a long-standing challenge in theoretical polymer physics; for realistic systems the quantitative understanding is however often achievable only by computer simulations. In this study, we present the findings of such extensive Monte-Carlo in silico experiments for polymer-surface adsorption in confined domains. We study the inverted critical adsorption of finite-length polyelectrolytes in three fundamental geometries: planar slit, cylindrical pore, and spherical cavity. The scaling relations extracted from simulations for the critical surface charge density σc-defining the adsorption-desorption transition-are in excellent agreement with our analytical calculations based on the ground-state analysis of the Edwards equation. In particular, we confirm the magnitude and scaling of σc for the concave interfaces versus the Debye screening length 1/κ and the extent of confinement a for these three interfaces for small κa values. For large κa the critical adsorption condition approaches the known planar limit. The transition between the two regimes takes place when the radius of surface curvature or half of the slit thickness a is of the order of 1/κ. We also rationalize how σc(κ) dependence gets modified for semi-flexible versus flexible chains under external confinement. We examine the implications of the chain length for critical adsorption-the effect often hard to tackle theoretically-putting an emphasis on polymers inside attractive spherical cavities. The applications of our findings to some biological systems are discussed, for instance the adsorption of nucleic acids onto the inner surfaces of cylindrical and spherical viral capsids.
对于带相反电荷的聚合物吸附到带相反电荷的凸面、平面和凹面表面上，其基本规律是什么？这个问题是表面涂层应用、各种复杂形成现象以及细胞和病毒生物物理学背景的核心。这一直是理论聚合物物理学中一个长期存在的挑战；然而，对于实际系统，通常只有通过计算机模拟才能实现定量理解。在这项研究中，我们展示了针对受限域中聚合物 - 表面吸附的此类广泛的蒙特卡罗计算机模拟实验的结果。我们研究了有限长度聚电解质在三种基本几何形状中的反转临界吸附：平面狭缝、圆柱形孔和球形腔。从模拟中提取的定义吸附 - 解吸转变的临界表面电荷密度σc的标度关系，与我们基于爱德华兹方程基态分析的解析计算结果非常吻合。特别是，对于小κa值，我们证实了凹面界面的σc的大小和标度与德拜屏蔽长度1/κ以及这三种界面的受限程度a的关系。对于大κa，临界吸附条件接近已知的平面极限。当表面曲率半径或狭缝厚度a的一半约为1/κ时，两种状态之间发生转变。我们还阐述了在外部限制下，半柔性链与柔性链相比，σc(κ)的依赖性是如何改变的。我们研究了链长对临界吸附的影响——这一效应在理论上通常难以处理——重点关注吸引性球形腔内的聚合物。我们讨论了我们的发现对一些生物系统的应用，例如核酸吸附到圆柱形和球形病毒衣壳的内表面。
