光镊中的Janus粒子运动研究
发布时间：2018-11-11 10:52
【摘要】：自光镊技术问世以来,人们已经熟练使用各种激光光束对微纳米介电粒子及纳米尺度的金属粒子进行三维捕获和操控,并利用被捕获的粒子作为手柄,探索生物体内单细胞、单分子的未解之谜。在光镊早期发展历史上,其通常捕获的对象为纯介电微球和纯金属纳米球。由于其各向同性的光学性质,通常被牢牢地捕获在光阱中,因此很难观测到其在微观世界中丰富多彩的运动形态。而对于介电和金属性质结合为一体的非对称颗粒,比如半裹金面的Janus粒子,由于其结合了介电和金属双重光学性质,打破了粒子的结构对称性,在光场中受力变得十分复杂,难以直接估测在光阱中的运动形态。目前对于捕获这一类特殊构造小球的研究基本处于空白状态。本文主要针对这类介电-金属材料Janus粒子在多种光场中的运动形态展开研究。本文内容主要包括五个方面:第一,基于几何光学方法,提出了一套计算半裹金面的Janus粒子在光场中受力和受力矩的方法。该方法结合金属膜理论和动量守恒定律,通过计算光线在Janus粒子的金面和非金面上折射、反射和吸收,从而计算出Janus粒子在光阱中的受力和受力矩。第二,从实验上观察到聚苯乙烯小球在线聚焦光阱中自组装结晶过程。其中,光致结晶过程分为两种增长模式,外延式增长和嵌入式增长。此外,我们还观察到胶体从一维到二维结晶的转变过程。这些观察有助于深入认识胶体的结晶过程。第三,通过调节聚苯乙烯小球的浓度,控制自组装后成膜的聚苯乙烯小球阵列的间隙,利用磁控溅射技术实现“半月状”和普通半裹金面的Janus粒子的制备。在实验中,我们发现“半月状”Janus粒子更容易在点聚焦光阱中旋转,而普通Janus粒子在点聚焦光阱中趋于稳定;Janus粒子的旋转方向和旋转速度可分别通过粒子进入光阱的方向以及激光功率来控制。经数值计算,“半月状”Janus粒子的稳定旋转是主要由粒子的自发对称性的破缺而引起的。第四,首次报道了Janus粒子在线聚焦光阱中进行着罕见的自驱动式循环往复运动。考虑到点聚焦光阱中单位面积上激光强度很强,导致金属膜强吸收而产生热效应,从而对Janus粒子的运动有一定影响。为了降低金属热效应带来的影响,我们利用柱透镜生成线聚焦光阱,减少光阱一个方向上的束缚,降低了单位面积的光场强度。线聚集光阱在聚焦线平面呈现中心强、两端弱的光强分布,因此沿着聚焦线方向自然产生了一个指向聚焦线中心的横向梯度力,并且该梯度力随着位置的变化而变化。产生循环往复运动的主要原因有两点,一是Janus粒子材料结构的不对称性而产生的推动力和线聚焦光阱的不对称性而提供的横向梯度力共同作用和相互竞争;二是由于Janus粒子的自发对称性破缺,粒子在受力为零时所受光力矩不为零,改变了Janus粒子的取向。这两个因素给循环往复运动提供了必要条件。第五,我们观察到Janus粒子围绕着环形光阱做同步转动。当意识到Janus粒子在平动和转动两个方面具有强大的耦合能力之后,我们利用锥形透镜生成环形光镊,构建在光的环形路径上完全一致的光强分布,一是降低光的聚焦强度,从而降低热效应;二是提供曲率一致的环形路径。如此一来,便可以减少外在因素的影响,专注研究Janus粒子在光场中平动和转动的耦合。实验表明Janus粒子围绕着环形光阱做同步转动,如同太空中月亮围绕着地球运动,自转周期等于公转周期。这意味着Janus粒子在环形光阱中不仅围绕光阱中心沿着环形聚焦光阱公转,即平动;同时围绕自己的中心轴自转,即自转。并且在实验中观测到的Janus粒子公转周期和自转周期基本一致。总的来说,Janus粒子在点聚焦、线聚焦、环聚焦光阱中丰富多彩的运动形态展示着它们强大的平动和转动的耦合能力。此外,Janus粒子的取向随着光场分布的变化进行自动的调整,具有很强的光学自适应性,在未来智能操控微纳米颗粒中具有极强的潜力。
[Abstract]:Since the technology of optical tweezers, various laser beams have been used for three-dimensional capture and manipulation of the micro-nano-dielectric particles and the nano-scale metal particles, and the trapped particles are used as a handle to explore the unsolved mysteries of single-cell and single-molecule in the living body. In the history of the early development of the optical tweezers, the commonly captured object is a pure dielectric microsphere and a pure metal nanosphere. Because of its isotropic optical properties, it is usually firmly trapped in the light trap, and it is difficult to observe its rich and colorful motion form in the microworld. and the structure symmetry of the particles is broken due to the combination of the dielectric and the metal dual optical properties, the stress in the optical field becomes very complex, it is difficult to directly estimate the motion morphology in the light trap. At present, the research on the capture of this kind of special construction ball is in the blank state. In this paper, the movement of Janus particles of this kind of dielectric-metallic material in a variety of optical fields is studied. This paper mainly includes five aspects: first, based on the geometric optics method, a set of methods for calculating the force and moment of Janus particles in a half-covered gold surface in the optical field is proposed. The method combines the theory of metal film and the law of momentum conservation, and calculates the force and moment of Janus particles in the light trap by calculating the refraction, reflection and absorption of light on the gold surface and the non-gold surface of the Janus particle. Secondly, the self-assembly and crystallization process of polystyrene beads on-line focused optical trap was observed. The photo-induced crystallization process is divided into two growth modes, epitaxial growth and embedded growth. In addition, we also observed the transformation of the colloid from one-dimensional to two-dimensional. These observations contribute to the in-depth understanding of the crystallization process of the colloid. and thirdly, by adjusting the concentration of the polystyrene beads, controlling the gap of the film-forming polystyrene ball array after assembly, and utilizing the magnetron sputtering technology to realize the preparation of the Janus particles of the 鈥渟emilunar鈥，
本文编号：2324616
[Abstract]:Since the technology of optical tweezers, various laser beams have been used for three-dimensional capture and manipulation of the micro-nano-dielectric particles and the nano-scale metal particles, and the trapped particles are used as a handle to explore the unsolved mysteries of single-cell and single-molecule in the living body. In the history of the early development of the optical tweezers, the commonly captured object is a pure dielectric microsphere and a pure metal nanosphere. Because of its isotropic optical properties, it is usually firmly trapped in the light trap, and it is difficult to observe its rich and colorful motion form in the microworld. and the structure symmetry of the particles is broken due to the combination of the dielectric and the metal dual optical properties, the stress in the optical field becomes very complex, it is difficult to directly estimate the motion morphology in the light trap. At present, the research on the capture of this kind of special construction ball is in the blank state. In this paper, the movement of Janus particles of this kind of dielectric-metallic material in a variety of optical fields is studied. This paper mainly includes five aspects: first, based on the geometric optics method, a set of methods for calculating the force and moment of Janus particles in a half-covered gold surface in the optical field is proposed. The method combines the theory of metal film and the law of momentum conservation, and calculates the force and moment of Janus particles in the light trap by calculating the refraction, reflection and absorption of light on the gold surface and the non-gold surface of the Janus particle. Secondly, the self-assembly and crystallization process of polystyrene beads on-line focused optical trap was observed. The photo-induced crystallization process is divided into two growth modes, epitaxial growth and embedded growth. In addition, we also observed the transformation of the colloid from one-dimensional to two-dimensional. These observations contribute to the in-depth understanding of the crystallization process of the colloid. and thirdly, by adjusting the concentration of the polystyrene beads, controlling the gap of the film-forming polystyrene ball array after assembly, and utilizing the magnetron sputtering technology to realize the preparation of the Janus particles of the 鈥渟emilunar鈥，
本文编号：2324616
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