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受限空间中非球形胶体的粒子扩散行为研究
Alternative TitleDiffusion behavior of non-spherical colloidal particles in confined space
李瀚海
Thesis Advisor王育人 ; 郑中玉
2019-05-31
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype博士
Degree Discipline一般力学与力学基础
Keyword胶体粒子 受限空间 非球形 扩散行为 流体动力学相互作用
Abstract

胶体是软物质研究领域一个很重要的组成部分,由于其具有独特的物理、力学、化学、生物学等特性,近年来对于胶体系统的研究得到了越来越多的关注。

受限空间中非球形胶体粒子的扩散行为在自然界、工业生产和基础科学研究中大量存在。不同于在无约束空间中各向同性粒子的简单布朗扩散,非球形胶体粒子本身形状的各向异性会导致其扩散行为的各向异性,同时它的扩散行为还会受到空间约束作用,胶体粒子间相互作用的影响,这三个因素之间的耦合作用更会增加这一研究的难度。在过去的几十年中,研究者对这三个因素如何影响了胶体粒子的扩散行为进行了大量研究。但截止目前,非球形胶体粒子在准一维空间约束中扩散行为的理论研究尚不充分,更缺乏相应的实验研究,而这一研究对于血管中的流动、微流道芯片设计、药物输运等实际应用问题有着重要指导作用,并且对拓展和完善各向异性胶体粒子在受限空间中扩散行为的研究领域有着重要意义。

本文结合显微实验观测、力学模型理论推导和计算机数值模拟,对这一系列问题进行了系统的研究。

我们利用控制形变法制作了长径比可控的聚苯乙烯(PS)椭球胶体粒子,使用光刻掩模法制作硅片基片并利用模塑法得到了聚二甲基硅氧烷(PDMS)管道模型。采用荧光显微观测技术,分别观测并记录了不同实验体系下椭球胶体粒子的运动录像。利用图像粒子追踪技术,得到各种实验体系中椭球胶体粒子的运动轨迹数据,并通过Matlab编写程序,计算出椭球粒子的自扩散系数,互扩散系数,均方位移,径向分布函数等关键特征参数。

在实验观测中,我们发现了许多新奇的实验现象:

1、对于在准一维管道中做布朗运动的孤立椭球胶体粒子,椭球在管道中出现了横向分层现象并保持稳定,并且其长轴与管道方向保持近乎平行;

2、在准一维管道中临近的两个布朗椭球粒子,出现了以管道中心对称分布的位置特征,其短时自扩散系数会随着胶体粒子间距的改变出现明显变化,并且在它们长时自扩散中出现了一段扩散系数随时间增大的过渡区域;

3、在准一维管道中做布朗运动的两个椭球粒子,其平动-平动互扩散随着椭球间沿管道横向间距的增加,出现了从正相关到反常负相关的变化。

这些新奇的实验现象在之前的研究中都很少被报道,为了深入研究它们的物理本质,我们通过合理的假设,建立了相应的矩形管道模型、圆管-哑铃点力模型,并通过理论推导计算得到了与实验数据相对应的特征参数理论解。同时利用商业有限元分析软件,对相关问题进行了有限元数值模拟,得到了直观的流场图像及相应特征参数的数值模拟结果。

通过定量比较实验观测,理论推导及有限元数值模拟所得到的各种特征参数,验证了我们建立的理论模型的合理性,解释了非球形粒子形状、空间几何约束及粒子间流体动力学相互作用对其扩散行为的影响,揭示了上述新奇实验现象的物理本质。

这些研究将加深和拓展我们对胶体形状、空间约束如何影响胶体粒子自扩散、胶体粒子间流体动力学相互作用等问题的认识和理解,同时为药物输运、微流控芯片设计等实际应用提供理论指导。

Other Abstract

Colloids is an important research area of soft matter. Recent years, more and more attention has been paid to the study of colloidal systems, due to their unique physical, mechanical, chemical and biological characteristics.

The diffusion behaviors of non-spherical colloidal particles in confined space are widely encountered in nature, industrial production and basic scientific research. Different from the simple Brownian diffusion of isotropic particles in unconstrained space, the shape of non-spherical colloidal particles will lead to the anisotropy of the diffusion behavior, and the diffusion behaviors are also affected by the spatial constraint and the interactions between colloidal particles, thus increasing the difficulty of this research. Over the past decades, researchers have conducted extensive research on how these three factors affect the diffusion behavior of colloidal particles. However, the theoretical research on the diffusion behavior of non-spherical colloidal particles in quasi-one-dimensional confinement is insufficient, and there is no relevant experimental research. This research plays an important role in guiding the practical problems, such as blood vessel flow, microchannel chip design, and drug delivery and so on. It also plays an important role in expanding and improving the research field of the diffusion behavior of anisotropic colloidal particles in confined space.

In this paper, experimental observation, theoretical analysis and computer numerical simulation are considered to study these problems systematically.

Polystyrene (PS) ellipsoidal particles with controllable aspect ratios are fabricated by controlled deformation method. Silicon wafer substrates are fabricated by photolithographic mask method and polydimethylsiloxane (PDMS) channel models are obtained by molding method. Using fluorescence microscopy, we observed and recorded the Brownian motion of ellipsoidal particles in various experimental systems. The trajectory data of ellipsoidal colloidal particles are obtained by image particle tracking technique, and characteristic parameters such as diffusion coefficients, mean squared displacement (MSD) and radial distribution function of ellipsoidal particles are calculated by MATLAB.

In the experimental observation, we obtained some novel experimental observations:

(1) The isolated ellipsoid particles Brownian diffusing in a quasi-one-dimensional (q1D) channel shows stable stratification, and its long axis nearly parallel to the direction of channel.

(2) Two adjacent Brownian ellipsoidal particles in a q1D channel are located symmetrically in the centre of the channel. Their short-term self-diffusion coefficients change obviously with the change of their separation distance, and the self-diffusion appears a crossover region, in which the diffusion coefficient increase with the increasing time, in the intermediate time regime.

(3) The translation-translation coupling diffusion of two adjacent ellipsoidal particles diffusing in a q1D channel changes from positive to anomalous negative correlation with the increase of their transverse separation.

These novel experimental phenomena have rarely been reported in previous studies. With reasonable assumptions, we proposed the corresponding rectangular channel model and cylinder-dumbbell point force model to different experimental systems. Thus the theoretical solutions of characteristic parameters which correspond to experimental data in various experimental systems are obtained through theoretical derivation. By using finite element analysis software, the finite element numerical simulations of the relevant problems are carried out, and the flow field and numerical simulation results of characteristic parameters are obtained.

The rationality of the theoretical model is verified by comparing various characteristic parameters obtained by experimental observation, theoretical derivation and finite element numerical simulation. We can explain how particle shapes, spatial constraints, and hydrodynamic interaction affect particles self-diffusion behaviors. As a result, the physical nature of these novel experimental phenomena is revealed.

These studies will deepen and expand our understanding on how colloidal particle shapes, spatial constraints affect their self-diffusion, the hydrodynamic interaction between them and other issues. It also provides theoretical guidance for drug delivery, microfluidic chip design and other practical applications.

Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/79104
Collection国家微重力实验室
中国科学院力学研究所
Recommended Citation
GB/T 7714
李瀚海. 受限空间中非球形胶体的粒子扩散行为研究[D]. 北京. 中国科学院大学,2019.
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