| 摘要: | 當液體被降溫至冰點附近，此時的冷液體在微觀尺度下的行為並非完全無序的。經由強的粒子間交互作用以及弱的熱擾動之間的競爭，冷液體在時空中都存在著異質性。空間上，冷液體具有整齊的結晶區塊以及包圍在這些區塊周圍的缺陷團簇。時間上，粒子的運動具有小振幅的熱顫抖以及集體躍遷換位。也就是說，冷液體可以被視為由整齊的結晶區塊形成的補丁結構，並且帶有一部分的固體的特性，但是結構卻仍然可以被熱擾動或是外力改變。
在這論文中，利用微粒電漿冷液體的實驗以及冷湯川液體的數值模擬，我們探討了下述之議題。(1) 到底有哪些集體運動模式存在於冷液體之中，(2)冷液體的結構是如何被集體運動改變與重組，(3)結晶區塊的成長在結晶化的過程中是否與在冷液體中具有相似的表現，(4)當冷液體受到不同大小的外力時，最基本的流動反應為何，(5)在受到輕微的外力時，冷液體中的崩潰式結晶區塊的破裂動力學為何？
利用我發明的鍵動力學分析法，我們很有效的突破了許多問題背後的核心。例如，我們可以將集體運動分門別類，並找出在冷液體中最代表的運動模式，並解釋冷液體的結構變化與運動的關係。除此之外，利用這個鍵動力學分析法，我們更解決了懸念於二維結晶化的百年議題：晶格區域如何透過晶塊旋轉而長大？我們更發現，，冷液體在受到不同外力大小時所表現的行為迥異。我們更發現裂痕是如何藉由斷層的碰撞機制導致晶格區塊破碎不已。
;Microscopically, unlike intuitive expectation, the cold liquid around freezing is not completely disordered. The competition between the strong particle interaction and weak thermal agitation leads to the heterogeneous structure with coexisting crystalline ordered domains and surrounding defect clusters, and heterogeneous dynamics with alternating particle rattling in the caging wells of nearest neighbor particles and cooperative particle hopping which induces structural rearrangements. Namely, the cold liquid can be viewed as a patchwork of crystalline ordered domains, which partially possesses solid like behavior but can still be rearranged under thermal agitation or external stress. In this work, through direct experimental microscopic visualization of cold dusty plasma liquid and numerical simulation of cold Yukawa liquids, we address the following important unexplored fundamental issues. (1) What is the cooperative motion existing in cold liquids, (2) How is structure rearranged through the cooperative motion, (3) whether the growth of crystalline ordered domains in crystallization and cold liquids are similar, (4) what is the generic flow behavior of cold liquids under various applied stresses, and (5) what is the avalanche dynamics of cracking of crystalline ordered domains in the weakly stressed cold liquid?
It is found, using a novel bond-dynamics analysis, the cooperative motion in cold liquids can be categorized into static patches, rotating patches, drifting patches, and shear strips located at the interface of co-rotating patches, beyond the earlier findings of the cooperative hopping strings and bands. The structural evolution is thereby accomplished by the drifting, rotation, rupture, and healing of crystalline ordered domains. In addition, the similar domain rotation, regarded as the kinetic origins of grain coalescence, is found in the crystallization of quenched two dimensional Yukawa liquids. Furthermore, suffering to the external stress which provides local force and torque, the above cooperative processes are enhanced persistently. Strong applied stress can cause the formation of the shear band with a higher averaged forward displacement and coherent vortical excitations. However, under weak stress, crystalline ordered domains either crack and heal in the loading zone, or temporally sustain and propagate stress to remote regions for avalanche cracking. The spatiotemporal behaviors of the avalanche cracking are discussed through the collision of dislocations with mismatched Burgers vectors, which is the key to generate the large crack clusters inside a crystalline ordered domain. |
