高分子胶体颗粒在水油界面上的异常动力学行为研究

Colloidal particles can be adsorbed onto water/oil interfaces. The diffusion of adsorbed particles regulates the particle arrangement, giving rise to the self-assembly into a two-dimensional ordered structure having emergent properties. The adsorption switches from an anomalous diffusion-controlled to an interaction-controlled steric process as the particle interfacial concentration is increased. In order to establish a design principle for the preparation of the self-assembled two-dimensional ordered structure, it is vital to understand the effect of the surface structure of particles on the interaction-controlled steric process. The aim of this project is to investigate the interfacial dynamics, particle collision and time-resolved structural arrangement of polymeric colloidal particles having distinct surface structures (i.e., symmetric particles and Janus particles whose surfaces have two or more distinct physical properties) at water/oil interfaces by employing the single-molecule fluorescence method complemented with the tensiometer and small-angle X-ray scattering. We focus on how the diffusion and structural arrangement evolve as a function of the particle concentration. We hope to understand the relation between the microscopic dynamics and the macroscopic structural arrangement by studying the effect of the surface structure, morphology, size and concentration of the adsorbed particle. We hope to reveal the general rationale of particle interfacial dynamics and the unique feature of Janus particles at water/oil interfaces. It is desirable that the experimental results supported by this grant can stimulate the new theory that is able to interpret the microscopic dynamics of colloid particles at liquid interfaces.

胶体颗粒能够吸附到水油界面，通过界面扩散调整构象，形成具有各种特殊性质的二维有序材料。吸附过程在低浓度区由异常扩散控制，高浓度区由界面颗粒相互作用、受限扩散和空间位阻效应控制。认识胶体颗粒在二维界面异常动力学行为的微观机制是设计调控二维有序材料的关键所在。本项目计划通过运用具有不同时空分辨率的单分子荧光技术，辅以宏观力学测试和结构表征技术，研究表面均匀胶体和一端亲水一端亲油的Janus胶体水油界面动力学、相互作用机制和结构特征。研究随着浓度增加，界面动力学从自由扩散到受限扩散再到空间位阻效应的微观机制和结构从无序到有序的转变过程，对比分析Janus胶体和均匀胶体动力学行为和结构特征的共性与特性，揭示颗粒动力学和微观相互作用与宏观界面张力、结构特征之间的关系，为建立新的理论模型提供实验依据。

本项目通过运用单分子荧光技术，辅以宏观力学测试，系统研究表面均匀胶体和一端亲水一端亲油的Janus颗粒在水油界面动力学和相互作用机制。重点研究不同浓度范围内，Janus胶体和均匀胶体动力学从自由扩散到受限扩散再到空间位阻效应的微观机制。研究发现， Janus纳米颗粒在水油界面扩散明显慢于同样大小的表面均匀纳米颗粒，其原因在于表面接枝聚合物构象发生形变，致使界面处Janus纳米粒子流体力学半径比溶液中测量得到的流体力学半径大，导致其在界面的扩散速率低于预测值；发现表面活性剂浓度增加诱发纳米粒子界面扩散出现短程布朗、长程异常现象，其机制为：在短程范围内，由于纳米粒子与表面活性剂之间相互排斥，相对于纳米粒子形成一个由表面活性剂构成的瞬时“笼”，粒子在笼中展现布朗运动，不受水油界面吸附表面活性剂分子浓度影响；发现纳米颗粒在高浓度时，扩散展现出“老化”现象，即扩散系数随着时间发生改变，其机制在于颗粒存在近程吸引、远程排斥，随着时间的延长，由于随机运动的发生，导致距离较近的颗粒发生了碰撞和聚集，使得颗粒逐步聚集。在本项目的支持下，以上述科学发现为主体，共以第一或通讯作者在Phys. Rev. Lett.、ACS nano等杂志发表研究论文9篇，培养博士生硕士生2人。