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界面胶体体系聚集机制及剪切形变的微观结构研究
Alternative TitleMicrostructural Study of Aggregation Process and Shear Deformation in The Interfacial Colloidal System
谢天
Thesis Advisor郑中玉
2019-11-25
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype硕士
Degree Discipline一般力学与力学基础
Keyword水油界面 胶体聚集 二元 剪切流动 相互作用 微观结构
Abstract

胶体悬浮液广泛应用于工业生产和日常生活中,如墨水、染料及乳液等。胶体体系的聚集行为一直以来是研究关注的热点问题,关系到胶体系统的稳定性和流变性,在石油化工、生物医药及环境治理等方面具有广泛应用。因此研究胶体聚集行为既有深刻的理论意义又有较强的实用价值。

近年来,两种不相溶液体形成的界面体系常被用来研究胶体聚集行为,主要原因有以下两点:(1)胶体粒子由于界面张力被限制在二维平面内,与三维悬浮液相比,微观结构的所有信息都包含在一个平面内,可以使用简单的光学显微镜对粒子运动、聚集过程及界面胶体结构进行高时间分辨率和空间分辨率的研究,而且适用于范围广泛的表面覆盖率。(2)已有大量研究表明可以通过多种手段调控胶粒间的相互作用,胶体粒子在界面上可以形成各种丰富的结构,如泡沫结构和形态不同的聚集结构等。

目前,对界面胶体粒子的研究主要集中在两个方面。一方面是胶体粒子间各种类型相互作用力起源和作用机理的研究,通过改变两相流体中电解质浓度和表面活性剂等条件,对不同体系中粒间作用力进行测量并绘制势能曲线。另一方面是通过调控粒间作用力改变胶体粒子在界面上的聚集结构。对于不同条件下界面上胶体粒子聚集的动态过程和微观聚集行为分析较少。而且界面胶体体系的研究中大多是一元体系,对不同尺寸或带电量的胶体粒子混合的二元系统关注较少。而二元体系在自然界中更为常见,不均质粒子混合单层膜的性能更为丰富,为控制结构开辟了新的途径。

本文通过水或盐溶液与癸烷形成的液-液界面,研究了不同面积分数带电胶体球在不同浓度盐溶液-癸烷界面上的汇聚过程,对粒子或聚集体的动态行为及结构演化进行了量化表征。并对不同盐溶液浓度和不同表面覆盖度的带电胶体粒子形成的微观结构尺度和形态进行了对比分析。发现水相中加入盐可以降低粒子间排斥作用,加快聚集速度。初始界面上团簇体的形状影响聚集过程。聚集结构的分形维度随着盐溶液浓度或表面覆盖率增高而减小,聚集形式逐渐由RLCADLCA转变。

本文还研究了硬球与带电粒子掺杂的比例对界面结构的影响。为制备不同面积分数比的二元胶体体系,我们按所需体积比混合两种胶体粒子悬浮液,分别在纯水-油界面和盐溶液-油界面上扩散,跟踪胶体粒子聚集,对其聚集结构进行分析, 旨在发现掺杂程度和聚集程度的关联。实验结果和分析数据表明引入硬球可以引发带电球在纯水-油界面上产生聚集,改变具有不同作用势的粒子混合比例可以改变凝聚的路径、速率和状态。

本文还对界面凝胶结构在剪切作用下的行为进行了初步研究。以往研究多关注其力学行为,如屈服、弹性应变,和加载下宏观形状的变化,如团簇的大小和致密度,缺乏对形变的微观机理的研究。本文利用自行设计的界面剪切装置对界面上的静态凝胶施加剪切,关注剪切作用下界面凝胶微观结构的形变,对不同形态微观结构对应的几种变形方式进行了总结,希望对以后更复杂的多尺度微观结构有一定参考性。

Other Abstract

Colloidal suspensions are widely used in industrial production and daily life, such as cosmetics, ink, paints and so on. The aggregation behavior of colloidal systems has always been a hot issue of research, which is related to the stability and rheology of colloidal systems, and has been widely used in petrochemical, biomedical and environmental management. Therefore, studying colloidal aggregation behavior has both profound theoretical significance and strong practical value.

In recent years, interface systems formed by two kinds of insoluble liquids have often been used to study colloidal aggregation behavior. The main reasons are as follows:

(1) Colloidal particles are confined in a two-dimensional plane due to interfacial tension, and all information of the microstructure can be contained in one plane so that the microscopic structures and aggregation processes in 2D suspensions are much more easily and clearly observed compared to the three-dimensional suspensions.

(2) A large number of studies have shown that the interaction between colloids can be tailored by various means. Colloidal particles can form a variety of rich structures at the interface, like soap forths, particle loop and aggregates with different morphology.

At present, the research of colloidal particles at the inteface mainly focuses on two aspects. On the one hand, the origin and mechanism of various types of interaction forces between colloidal particles at the interface were widely studied. By changing the electrolyte concentration and surfactant in the liquids, the interaction force between colloidal particles in different systems can be measured and the potential energy curve plotted. On the other hand, many researches were about how to change the microstructure of aggregates or gel network formed by the colloidal particles at the interface. There are few analyses of the dynamic process and microscopic aggregation behavior of colloidal particles on the interface under different conditions. However, previous studies mainly focused on simply one-component systems with mono-charged and mono-sized particles. Little is known about the mixed systems composed of particles with different interactions, which are more generally existed in nature and industry. And the performance of the heterogeneous particle-mixed monolayer membrane is more abundant, which opens up a new way for controling structures.

In this paper, the liquid-liquid interface formed by water (or salt solution) and decane was used to study the aggregation process of charged colloidal spheres at different electrolyte concentrations and surface coverage, and the dynamic behavior of particles or aggregates and structural evolution were quantitatively characterized. Besides, the microstructure scale and morphology of charged colloidal particles with different salt solution concentrations and different surface coverages were compared and analyzed. It is found that the addition of salt in the aqueous phase can reduce the interparticle repulsion and accelerate the aggregation speed. The shape of the cluster on the initial interface affects the aggregation process. The fractal dimension of the aggregated network decreases with increasing concentration of salt solution. And the regimes of aggregating change from RLCA to DLCA.

The influence of the doping ratio of hard spheres and charged particles on the interfacial collidal structures was also studied. In order to prepare binary colloidal systems with different area fraction ratios, we mixed two kinds of colloidal particle suspensions according to the required volume ratio, and then respectively diffused at the pure water-oil interface and the salt solution-oil interface, tracked the colloidal particles and accumulating the aggregate structure. The analysis was conducted to find the correlation between the degree of doping and the degree of aggregation. The experimental results and analysis show that the introduction of hard spheres can induce the aggregation of charged spheres at the pure water-oil interface. Changing the mixing ratio of particles with different potentials can change the path, rate and state of particle aggregation.

In this paper, the deformation of the interfacial gel network under shear was also studied. Previous studies have focused on their mechanical behavior, such as yield, elastic strain, and changes in macroscopic shape under load, such as the size and density of clusters. These studies lack the study of the microscopic mechanism of deformation. In this paper, a self-designed interface shearing device is used to apply shear to the static gel on the interface. We pay attention to the deformation of the interfacial gel microstructure under shearing, and summarize the several deformation modes corresponding to different morphological microstructures. It is hoped that there will be some reference for more complex multi-scale microstructures.

Call NumberMas2019-032
Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/80723
Collection国家微重力实验室
Recommended Citation
GB/T 7714
谢天. 界面胶体体系聚集机制及剪切形变的微观结构研究[D]. 北京. 中国科学院大学,2019.
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