Li Bing, Zhang Pei-Lei, Sun Zhao-Yan
State Key Laboratory of Polymer Physics and Chemistry & Key Laboratory of Polymer Science and Technology, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 130022 Changchun, China.
University of Science and Technology of China, Hefei 230026, China.
J Chem Phys. 2024 Sep 7;161(9). doi: 10.1063/5.0230107.
The adsorption of polymer-grafted nanoparticles at interfaces is a problem of fundamental interest in physics and soft materials. This adsorption behavior is governed by the interplay between interaction potentials and entropic effects. Here, we use molecular dynamics simulations and umbrella sampling methods to study the adsorption behavior of a Janus-like homopolymer-grafted nanoparticle at fluid-fluid interfaces. By calculating the potential of the mean force as the particle moves from fluid A to the interface, the adsorption energy Ea can be obtained. When two homopolymer chains with types A and B are grafted to the opposite poles of the particle, Ea shows a scaling behavior with respect to chain length N: Ea ∝ N0.598. This is determined by the interactions between polymers and fluids. The enthalpy dominates, and the entropy effects mainly come from the rotational entropy loss of the polymer-grafted nanoparticle at interfaces, which disfavors the stabilization of particles at interfaces. When the grafted polymer number m is large, the adsorption energy exhibits a linear dependence on m. While the enthalpy dominates the behavior, the entropy becomes significant at a larger chain length of N = 15, where the configurational entropy of the polymer chains dominates the entropy of the system. The globule-coil transition occurs when polymers move from poor solvents to good solvents, increasing the configurational entropy and favoring the stabilization of particles at interfaces. Our study provides novel insights into the stabilization mechanism of polymer-grafted nanoparticles at interfaces and reveals the stabilization mechanism favored by the configurational entropy of grafted polymer chains.
聚合物接枝纳米粒子在界面处的吸附是物理学和软材料领域中一个具有根本重要性的问题。这种吸附行为由相互作用势和熵效应之间的相互作用所支配。在此，我们使用分子动力学模拟和伞形抽样方法来研究类Janus均聚物接枝纳米粒子在流体-流体界面处的吸附行为。通过计算粒子从流体A移动到界面时的平均力势，可以获得吸附能Ea。当具有A和B类型的两条均聚物链接枝到粒子的相对两极时，Ea相对于链长N呈现标度行为：Ea ∝ N0.598。这是由聚合物与流体之间的相互作用决定的。焓起主导作用，熵效应主要来自聚合物接枝纳米粒子在界面处的旋转熵损失，这不利于粒子在界面处的稳定。当接枝聚合物数量m较大时，吸附能对m呈现线性依赖关系。虽然焓主导了该行为，但在较大的链长N = 15时熵变得显著，此时聚合物链的构象熵主导了系统的熵。当聚合物从不良溶剂转移到良溶剂时会发生球-线团转变，增加了构象熵并有利于粒子在界面处的稳定。我们的研究为聚合物接枝纳米粒子在界面处的稳定机制提供了新的见解，并揭示了由接枝聚合物链的构象熵所青睐的稳定机制。
