【作者】 钟敏成；

【导师】 郭光灿； 李银妹；

【作者基本信息】 中国科学技术大学 ， 光学， 2010， 博士

【摘要】 分散体系是自然界中广泛存在的一种物质体系,对分散体系性质的研究一直具有重要的科学意义和应用价值。分散体系的宏观性质归根结底是由体系中的微粒的性质特别是微粒的动力学行为所决定,所以涉及特征尺度为微米量级的微粒、液滴或者气泡的运动的问题,是流体力学在分散体系应用研究的一个主要领域。然而长期以来,因为缺乏有效的实验手段,对单个微粒动力学行为的实验研究非常困难。光与物质相互作用的过程中传递动量,也能够传递角动量,基于此原理的光镊技术可以非机械接触的方式三维操控水溶液中的O.1μm-10μm的微粒。另外,光镊可以精确测量光阱对微粒施加的光阱力,使得在光镊出现之后,很快就被成功地应用于对分散体系中微粒的动力学行为进行研究。本文的工作主要是利用光镊研究分散体系中微粒的运动。对分散体系中微粒的扩散运动、旋转运动以及光镊操控界面中的微粒等进行了深入的研究和详细的讨论。对这些研究过程中所需要的实验设备、实验方法和涉及的相关问题也进行了实验研究和模拟计算。分散体系中微粒运动的一个主要特征是布朗运动,可以使用微粒的扩散系数参数描述其运动。利用光镊操控微粒的特点,非常适合于测量微粒的扩散系数。根据不同的研究对象,人们已经发展了多种利用光镊测量扩散系数的方法。论文根据纳米光镊系统,研究了溶液中微粒扩散系数的测量方法,测量不同浓度的溶液中微粒的扩散系数,并发展了结合高低频功率谱测量扩散系数的方法。微粒在光阱中不仅会平面运动,而且会做旋转运动。论文研究了双折射小球旋转速度随光阱的各种条件的变化。发现随着捕获高度的增加,微粒的旋转速度逐渐下降,并指出该下降是由于折射率不匹配引起的球差导致的。在无穷远显微系统上使用有限远物镜对球差进行补偿,将小球最大的旋转速度的位置平移至捕获高度约等于50μm的位置。光镊可以测量微区和界面中微粒的力学行为是其他研究手段无法比拟的。将光镊应用于界面体系研究的基础是光镊能够操控界面上的微粒。操控界面微粒与液体中操控微粒不一样,当微粒处于界面时,纵向方向主要受表面张力影响,而激光的辐射压力是次要的,所以光镊只能够二维操控界面上的微粒。论文使用几何光学模型,计算微粒处于界面时的光阱捕获力,指出如何才能最大限度的增加光阱力,以更好的操控界面微粒。计算结果指出低数值孔径的物镜更适合于操控界面微粒,在实验中使用了数值孔径为0.75的物镜对空气-水界面上的微粒进行了操控和移动,为光镊研究空气-水界面的性质做了初步的实验基础。论文利用光镊捕获粘附于Hela细胞的小球,测量小球与Hela细胞的非特异性结合力,研究了该结合力的强度和断裂过程,并分析该结合力的来源,认为该结合力是空间相互作用和静电力共同作用的结果。实验设备是实验研究工作的基础。论文前期还对光镊系统的参数进行了研究,测量了系统的光阱刚度包括横向刚度和纵向刚度,纵向刚度测量中小球的纵向位移采用信息熵进行标定。明确光阱中的微粒个数,是光镊在微观层次开展实验研究的前提。论文根据光散射原理,提出通过测量光阱内微粒的背散光强度来区分光阱中的微粒个数的方法,实验中成功地分辨了光阱中直径分别为1μm、0.5μm、0.2μm、100nm和73 nm的微粒个数。论文还对光阱中微粒布朗运动引起的背散光光强度变化进行分析,研究光阱中存在两个微粒时微粒的排列状态和光阱的物理参数。更多还原

【Abstract】 Since the dispersion system widely exists in nature, it is important to do research in this field. The properties of dispersion rely on the properties of small particles especially their dynamics behaviors, so the research on the motion behavior of micro-sized particles is a large application field of hydrodynamics in the research of dispersion system. However, it is difficult to investigate the dynamics of single particle experimentally for a long time due to the lack of appropriate instruments.Light carries both linear and angular momentum and can thus exert force and torques on matter. Optical tweezers exploit this fundamental property to trap objects in a potential well formed by tightly focused light. This technique allows the manipulation of microscopic objects without mechanical contact. Moreover, the optical forces on a micro-particle trapped in an optical trap can be accurately measured. Such optical tweezers have been used in the study of dynamics behaviors of colloidal particles.In this thesis, we use optical tweezers to study the motion of the particles in the dispersion system. The main subjects of this thesis are the diffusion and rotation of particles in the trap, manipulation of particles at the interfaces. The contents are also investigated related to the main subjects such as experimental setup and methods by experiment or simulation.One of the main features of particles in the dispersion system is Brownian motion which can be described by the diffusion coefficient. Optical tweezers is suitable for measuring the diffusion coefficient of particles due to its manipulation contactless. The researchers have developed several measurement methods for different research objects. In this thesis, the diffusion coefficients of micro-sized particles were investigated with several methods based on the nanometer optical tweezers system, and a new method with combination of high-low frequency power spectrum has been developed to measure the diffusion coefficient.Birefringent particles rotate when trapped in elliptically polarized light. The rotation rates of the particles have been investigated with the condition of the optical trap. When an infinity corrected oil-immersion objective is used for trapping, the maximum rotation rate of birefringent particles occurs close to the coverslip, and the rotation rate decreases dramatically as the trapped depth increases. The descease is due to the spherical aberration at the glass-water interface. In the thesis the spherical aberration is compensated by using a finite-distance-corrected objective to trap and rotate the birefringent particles, and the result shows that the trapped depth corresponding to the maximum rotation rate is moved to 50μm.One of the characteristic of optical tweezers is applicable to non-conventional geometries:thin films, interior of biological cell, membranes etc. Manipulation of the particles at the interfaces is the basis of optical tweezers applied to the interface system. However, it’s different to manipulate the particles at the interfaces from manipulation of the particles in the solutions. We numerically investigated the transverse trapping forces on a dielectric sphere located at an oil/air-water interfaces with ray-optics model, and manipulated the micron-sized particles at an air-water interface. The results establish the base for the applications of optical tweezers to measure the interaction of colloidal particles at the interfaces.The polystyrene particle adhered to Hela cell was trapped by the optical tweezers to measure the rupture force between the particle and the cell. The process of bond rupture was observed with the help of detection photodiode. The result showed that the adhesion is a nonspecific adhesion due to a combination of electrostatic and steric effects.Experimental equipment is the basis for experimental research. This thesis is based on optical tweezers technology, so the optical stiffness the nanometer optical tweezers system is studied in the second chapter first. We measured the optical stiffness including the lateral stiffness and axial stiffness, and the axial displacement of the particles calibration with information entropy during the measurement process.Optical tweezers can trap multiple particles in single trap, and how to distinguish the number of particles in single optical trap was the key work in the experiment. A novel method based on laser scattering method to distinguish the numbers of nanometer-particles in single trap was presented in Chapter Seven. The number of particles in single trap was distinguished by measure the intensity of backscattering light with corresponding situation. In the thesis, the number of particles with diameters of 1μm,0.5μm,0.2μm,100 nm,73 nm was distinguished successfully. The method presented may find applications of optical tweezers in the nanometer dimension.更多还原