【摘要】：自光鑷技術問世以來,人們已經(jīng)熟練使用各種激光光束對微納米介電粒子及納米尺度的金屬粒子進行三維捕獲和操控,并利用被捕獲的粒子作為手柄,探索生物體內(nèi)單細胞、單分子的未解之謎。在光鑷早期發(fā)展歷史上,其通常捕獲的對象為純介電微球和純金屬納米球。由于其各向同性的光學性質(zhì),通常被牢牢地捕獲在光阱中,因此很難觀測到其在微觀世界中豐富多彩的運動形態(tài)。而對于介電和金屬性質(zhì)結合為一體的非對稱顆粒,比如半裹金面的Janus粒子,由于其結合了介電和金屬雙重光學性質(zhì),打破了粒子的結構對稱性,在光場中受力變得十分復雜,難以直接估測在光阱中的運動形態(tài)。目前對于捕獲這一類特殊構造小球的研究基本處于空白狀態(tài)。本文主要針對這類介電-金屬材料Janus粒子在多種光場中的運動形態(tài)展開研究。本文內(nèi)容主要包括五個方面:第一,基于幾何光學方法,提出了一套計算半裹金面的Janus粒子在光場中受力和受力矩的方法。該方法結合金屬膜理論和動量守恒定律,通過計算光線在Janus粒子的金面和非金面上折射、反射和吸收,從而計算出Janus粒子在光阱中的受力和受力矩。第二,從實驗上觀察到聚苯乙烯小球在線聚焦光阱中自組裝結晶過程。其中,光致結晶過程分為兩種增長模式,外延式增長和嵌入式增長。此外,我們還觀察到膠體從一維到二維結晶的轉變過程。這些觀察有助于深入認識膠體的結晶過程。第三,通過調(diào)節(jié)聚苯乙烯小球的濃度,控制自組裝后成膜的聚苯乙烯小球陣列的間隙,利用磁控濺射技術實現(xiàn)“半月狀”和普通半裹金面的Janus粒子的制備。在實驗中,我們發(fā)現(xiàn)“半月狀”Janus粒子更容易在點聚焦光阱中旋轉,而普通Janus粒子在點聚焦光阱中趨于穩(wěn)定;Janus粒子的旋轉方向和旋轉速度可分別通過粒子進入光阱的方向以及激光功率來控制。經(jīng)數(shù)值計算,“半月狀”Janus粒子的穩(wěn)定旋轉是主要由粒子的自發(fā)對稱性的破缺而引起的。第四,首次報道了Janus粒子在線聚焦光阱中進行著罕見的自驅(qū)動式循環(huán)往復運動�？紤]到點聚焦光阱中單位面積上激光強度很強,導致金屬膜強吸收而產(chǎn)生熱效應,從而對Janus粒子的運動有一定影響。為了降低金屬熱效應帶來的影響,我們利用柱透鏡生成線聚焦光阱,減少光阱一個方向上的束縛,降低了單位面積的光場強度。線聚集光阱在聚焦線平面呈現(xiàn)中心強、兩端弱的光強分布,因此沿著聚焦線方向自然產(chǎn)生了一個指向聚焦線中心的橫向梯度力,并且該梯度力隨著位置的變化而變化。產(chǎn)生循環(huán)往復運動的主要原因有兩點,一是Janus粒子材料結構的不對稱性而產(chǎn)生的推動力和線聚焦光阱的不對稱性而提供的橫向梯度力共同作用和相互競爭;二是由于Janus粒子的自發(fā)對稱性破缺,粒子在受力為零時所受光力矩不為零,改變了Janus粒子的取向。這兩個因素給循環(huán)往復運動提供了必要條件。第五,我們觀察到Janus粒子圍繞著環(huán)形光阱做同步轉動。當意識到Janus粒子在平動和轉動兩個方面具有強大的耦合能力之后,我們利用錐形透鏡生成環(huán)形光鑷,構建在光的環(huán)形路徑上完全一致的光強分布,一是降低光的聚焦強度,從而降低熱效應;二是提供曲率一致的環(huán)形路徑。如此一來,便可以減少外在因素的影響,專注研究Janus粒子在光場中平動和轉動的耦合。實驗表明Janus粒子圍繞著環(huán)形光阱做同步轉動,如同太空中月亮圍繞著地球運動,自轉周期等于公轉周期。這意味著Janus粒子在環(huán)形光阱中不僅圍繞光阱中心沿著環(huán)形聚焦光阱公轉,即平動;同時圍繞自己的中心軸自轉,即自轉。并且在實驗中觀測到的Janus粒子公轉周期和自轉周期基本一致。總的來說,Janus粒子在點聚焦、線聚焦、環(huán)聚焦光阱中豐富多彩的運動形態(tài)展示著它們強大的平動和轉動的耦合能力。此外,Janus粒子的取向隨著光場分布的變化進行自動的調(diào)整,具有很強的光學自適應性,在未來智能操控微納米顆粒中具有極強的潛力。
[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，

本文編號：2324616