- 學位論文
親溶劑奈米粒子於高分子溶液中的自組裝現象
Self-assembly of Solvophilic Nanoparticles in Polymer Solution: Depletion Attraction
摘要
從許多實驗結果我們可以得知，當奈米粒子懸浮液中加入適量的高分子後，整個系統的相平衡行為和結構都會產生很大的改變。其中的一個重要現象，如果添加物為非吸附性高分子，則溶液中的奈米粒子會自組裝而聚集在一起。這種粒子間的相互作用力被稱為空乏力(Depletion force)。特別的是空乏力的產生受到系統亂度所主導，而非常見的焓的影響。 本實驗透過耗散粒子動力學的電腦模擬方式，來模擬空乏力對溶液中奈米粒子型態的影響。實驗結果可知，不論是片狀或立方體的奈米粒子一開始均能均勻懸浮在溶液中，在加入高分子超過一定濃度後皆會開始靠近而形成聚集。我們進一步分析其聚集的大小和排列方式，發現其聚集大小會有一平均值，這代表著我們可以藉由調整高分子濃度或是奈米粒子濃度來控制奈米粒子在高分子溶液中自組裝的大小，同時藉由計算沒有產生聚集的自由奈米粒子數量，推測其自組裝機制類似於界面活性劑形成臨界微胞濃度的過程。 除此之外，我們改變高分子和溶劑間的相互關係，探討疏溶劑高分子和親溶劑高分子對系統中奈米粒子自組裝程度的影響。當高分子為疏溶劑時，系統中不會產生空乏力，奈米粒子皆均勻懸浮於溶液中。相反地當高分子為親溶劑時，系統中的奈米粒子間所受到的吸引力變強，而造成較大聚集體的同時，奈米粒子間吸引力的作用距離也會隨著變遠，造成其聚集體結構上的變化。
並列摘要
The mixtures of colloidal particles and polymers are used extensively in a wide range of applications including paints, coatings as well as cosmetics. In general, when colloidal particles suspend in the solution, those particles tend to aggregate due to van der Waals forces while they disperse through steric or electrostatic stabilization. However, some of applications require those dispersed particles to cluster together for separation or assembly to well-ordered structures. In order to achieve this goal, one approach is to add smaller depletants like non-adsorbing polymers or surfactant micelles into system. As a result, the depletion attraction is induced due to the entropy origin and the aggregation of colloidal particles is found. In this study, we perform dissipative particle dynamics ( DPD ) simulation to investigate the self-assembly behavior of colloidal nanoparticles in a polymer solution. The degree of aggregation in terms of the mean aggregation number is evaluated to determine the size of aggregates. The influence of the polymer concentration, overlapped depletion zone and solvent quality of polymer on the aggregation behavior is studied as well. It is found that the aggregation of nanodiscs can be controlled by tuning concentration of both polymer and nanoparticles. In addition, the mechanism of self-assembly of nanodiscs is similar to that of the micellization process of surfactants. Depending on the solvent quality of the polymer, the self-assembled structures are changed from string structure to spherical structure.
參考文獻
延伸閱讀
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