藉由表面雷射捕陷形成單一巨大拓展之聚苯乙烯奈米粒子之聚集體

Abstract

在這個研究當中， 藉由連續波近紅外雷射光照射在溶液表面， 我們示範了雷射捕陷 形成巨大的微米及奈米粒子之聚集體。 在章節三當中， 直徑 100 奈米之聚苯乙烯粒子被 用作是雷射捕陷的目標。在雷射捕陷的初始階段，粒子被聚集在雷射焦點，小的粒子聚 集體其大小與雷射焦點相同且被形成在溶液表面。 由於粒子持續不斷地被散射力吸引及 介面性質壓抑， 粒子的高濃度區域出現導致穿透式影像之穿透率下降。 在建立粒子的高 濃度區域之後，粒子聚集體開始擴張。 巨大的粒子聚集體伴隨著針狀結構形成在溶液表 面，並且暗示著光學位能變廣。為了檢驗粒子的高濃度區域扮演之角色，粒子濃度有關 於粒子聚合體形成時間。經過長時間雷射照射，歸因於雷射熱能致使粒子熔在一起，導 致不可逆粒子聚合體的形成。此不可逆粒子聚合體被定義為” 即便停止雷射照射，此粒 子聚合體還是聚在一起而非散開” 。 在章節四， 我們檢驗不可逆粒子聚合體對巨大聚合 體形成扮演之角色，於是以 10 微米之聚苯乙烯粒子取代了 不可逆粒子聚合體。有趣的 是， 單一 10 微米之聚苯乙烯粒子加上 100 奈米之聚苯乙烯粒子之雷射捕陷聚合行為與 100 奈米之聚苯乙烯粒子之雷射捕陷聚合行為相當類似。然而，在相同實驗條件下，以 雷射直接照射單一 10 微米之聚苯乙烯粒子並無不可逆粒子聚合體之形成。我們採用了 玻璃轉換溫度來詮釋為何粒子無法熔合在一起。在章節五， 我們示範以不同雷射焦點位 置之雷射捕陷聚合之微米粒子。六方最密堆積結構之粒子聚合體粒子聚合體僅在溶液表 面形成。在此溶液表面，粒子的遷移速度以粒子追蹤方法量測。相反的，在其他雷射焦 點位置，只有單一 10 微米之聚苯乙烯粒子可以被抓在焦點位置。 總結來說， 透過上述三個章節光學位能寬廣化可以被檢驗，而且可行之機制應該與 雷射捕陷誘導之長距離作用有關。

In this study, we have so far demonstrated the formation of large assembly of micron and nanometer-sized polystyrene particle by shinning a continuous-wave near-infrared laser beam at solution surface. In chapter 3, the pure 100 nm polystyrene particles are treated as trapping targets. At the initial stage of trapping experiment, the particles are gathered at the focal spot upon laser irradiation, and a small particle assembly is formed whose size is equal to focal spot. When particles are continuously attracted to the solution surface which is due to not only scattering force but the suppression of particle motion by interface characteristic, the highly concentrated domain of particles emerges, resulting in transmittance decrease of transmission images. After the establishing of concentrated domain of particles, the particle assembly proceeds to expand. After then, the large assembly with needle structures is acquired at the solution surface which implies that the optical potential broadening. To check how the role of concentrated domain of 100 nm particles play, the particle concentration dependent of assembling time is examined. Upon long term laser irradiation, the particles fused together which is risen from laser heating, leading to the formation of irreversible assembly. The irreversible assembly is defined as “the particles assembly remains its components instead of dispersing away even if stopping laser trapping”. We have examined the role of irreversible assembly acts for the formation of large assembly by replacing it with 10 μm polystyrene particle. Interestingly, the similar assembling behavior of a single 10 μm polystyrene particle plus 100 nm particles is repeated with pure 100 nm PS particles case. However, with the same III experimental condition, by irradiating the 10 μm polystyrene particle directly, there is no irreversible assembly can be formed. We employ the glass transition temperature to interpret why particles are not able to fuse together. In chapter 5, the laser trapping of micro particles is demonstrated at different focal position. The hexagonal close packing structure of particle assembly is merely formed at solution surface. Here, the speed of directional diffusion of particles are measured by particle tracking method. On the contrary, at another focal position, there is only single 10 μm polystyrene particle can be trapped at the focal spot. To summarize, the broadening of optical potential is checked through these three chapters, and the possible dynamics should be related with long-range interaction induced by laser trapping.