基于分子动力学模拟的α-SiO2纳米颗粒油-水界面吸附行为研究

Adsorption Behavior of α-SiO2 Nanoparticles at Oil-Water Interface Based on Molecular Dynamics Simulation

摘要:

纳米颗粒相界面吸附与自组装被广泛应用于石油采收、泡沫浮选、药物输送及新型功能材料等研究领域。然而，由于溶剂化力、静电斥力等多种相互作用所导致的吸附势垒，纳米颗粒自发吸附至界面的过程受到阻碍。基于分子动力学方法研究了α-SiO₂纳米颗粒相界面吸附动力学特征，深入分析了水化层结构及离子浓度对颗粒吸附行为的影响。首先，通过修饰表面基团获取了不同亲疏水性α-SiO₂纳米颗粒的吸附特征：纳米颗粒自发扩散至亚界面后会经历弛豫吸附至界面、快速吸附以及在界面区域经历一段弛豫后达到动态平衡三个过程。随后，从径向分布函数、角度分布、氢键密度分布等对纳米颗粒水化层结构以及氢键结构和进行了量化和比较，通过水化层内水分子驻留自相关函数以及氢键寿命分析了水化层结构及氢键结构的动力学特性。结果表明：水化层结构依赖于所作用颗粒的表面特性，与亲水表面相比，水分子在疏水表面具有明显的择优取向和更强的流动性；表面-水间氢键相互作用和水化层内特殊氢键结构是影响颗粒吸附的重要原因；不同离子效应可以通过共同作用干扰氢键结构以促进纳米颗粒相界面吸附。本研究为理解纳米颗粒相界面吸附动力学特性以及吸附壁垒形成机制提供参考，对于纳米颗粒相界面可控吸附在石油采收、新型功能材料等应用领域具有指导意义。

Abstract:

The adsorption and self-assembly of nanoparticles at fluid interfaces are widely applied in various fields such as oil recovery， foam flotation， drug delivery， and novel functional materials. However， nanoparticles may not spontaneously adsorb to oil-water interfaces due to various interactions， such as solvation forces and electrostatic repulsion， which create an adsorption barrier. In this study， the dynamic characteristics of the adsorption of α-SiO₂ nanoparticles at the oil-water interface are investigated， including an in-depth analysis of the effect of both hydration layer structure and ionic concentration on the adsorption behavior of nanoparticles using the molecular dynamics simulation method. Surface modification using hydrophilic/hydrophobic groups has been utilized to achieve diverse adsorption characteristics of α-SiO₂ nanoparticles. The nanoparticles undergo three distinct processes upon spontaneous diffusion to the sub-interface： relaxation adsorption to the interface， rapid adsorption， and a period of relaxation in the interfacial region before reaching dynamic equilibrium. The analysis aims to quantify and compare the structure of the hydrated layer and hydrogen bond network near the surface of the nanoparticles. This was achieved by using radial distribution functions， angular distribution functions， as well as hydrogen bonds density distribution. The dynamic properties of the hydrated layer and hydrogen bond structure were analyzed using the residence autocorrelation function of water molecules and hydrogen bond lifetime. The study reveals that the structure of the hydration layer is influenced by the surface properties of the interacting particles. Water molecules exhibit greater orientation and mobility on hydrophobic surfaces compared to hydrophilic surfaces. Surface-water hydrogen-bond interactions and special hydrogen-bond structures within the hydration layer play a crucial role in particle adsorption. Different ionic effects can also interfere with the hydrogen-bonding structure， promoting adsorption at the phase interface of the nanoparticles. This study provides a reference for understanding the kinetic properties of nanoparticle phase-interface adsorption and the formation mechanism of adsorption barriers. It can be of significant guidance for the controllable adsorption of nanoparticles at phase-interfaces in the fields of petroleum recovery and new functional materials.