Klushin Leonid I, Skvortsov Alexander M, Polotsky Alexey A, Ivanova Anna S, Schmid Friederike
Department of Physics, American University of Beirut, P. O. Box 11-0236, Beirut 1107 2020, Lebanon and Institute of Macromolecular Compounds, Russian Academy of Sciences, 31 Bolshoy Pr, 199004 Saint Petersburg, Russia.
Chemical-Pharmaceutical University, Professora Popova 14, 197022 St. Petersburg, Russia.
J Chem Phys. 2021 Feb 21;154(7):074904. doi: 10.1063/5.0038202.
We propose a novel class of responsive polymer brushes, where the effective grafting density can be controlled by external stimuli. This is achieved by using end-grafted polymer chains that have an affinity to the substrate. For sufficiently strong surface interactions, a fraction of chains condenses into a near-surface layer, while the remaining ones form the outer brush. The dense layer and the more tenuous outer brush can be seen as coexisting microphases. The effective grafting density of the outer brush is controlled by the adsorption strength and can be changed reversibly and in a controlled way as a response to changes in environmental parameters. The effect is demonstrated by numerical self-consistent field calculations and analyzed by scaling arguments. Since the thickness of the denser layer is about a few monomer sizes, its capacity to form a microphase is limited by the product of the brush chain length and the grafting density. We explore the range of chain lengths and grafting densities where the effect is most pronounced. In this range, the SCF studies suggest that individual chains inside the brush show large rapid fluctuations between two states that are separated by only a small free energy barrier. The behavior of the brush as a whole, however, does not reflect these large fluctuations, and the effective grafting density varies smoothly as a function of the control parameters.
我们提出了一类新型的响应性聚合物刷，其有效接枝密度可通过外部刺激来控制。这是通过使用对基底具有亲和力的端接枝聚合物链来实现的。对于足够强的表面相互作用，一部分链凝聚成近表面层，而其余的链形成外层刷。致密层和较稀疏的外层刷可视为共存的微相。外层刷的有效接枝密度由吸附强度控制，并且可以作为对环境参数变化的响应以可控方式可逆地改变。通过数值自洽场计算证明了该效应，并通过标度论证进行了分析。由于较致密层的厚度约为几个单体尺寸，其形成微相的能力受到刷链长度和接枝密度乘积的限制。我们探索了该效应最显著的链长和接枝密度范围。在此范围内，自洽场研究表明，刷内部的单个链在仅由小自由能垒分隔的两种状态之间表现出大的快速波动。然而，整个刷的行为并未反映出这些大的波动，并且有效接枝密度随控制参数平滑变化。
