非對稱粒子在雙氧水水溶液中運動研究

Abstract

近十年來，微奈米主動材料的研究開始蓬勃發展，人們研究其運動機制與發展控制運動的手段，也設下了許多實用願景，諸如感光材料、生物材料、藥物載體等，而探求微奈米主動材料的製備方式、載物裝填、運動設計等等是現階段的努力目標。在過去的報導中，半球面鍍上鉑金屬的Janus粒子放入雙氧水水溶液中有自泳動的現象，其運動方向為遠離催化端。科學家試圖找出一個力學模型來描述此自泳動，而我們發現，在含有雙十二烷基二甲基溴化銨（DDAB）的雙氧水水溶液中Janus粒子自泳動方向反轉，此現象與許多過去的假設不符合，而也給了我們一把解開自泳動力學機制謎團的鑰匙。 過去的觀點，Janus粒子在催化端進行異相催化反應，反應產生新溶質與氧氣氣泡，而這些被視為自泳動的主因。在加入雙十二烷基二甲基溴化銨後運動方向反轉，不只將前述可能推翻，也由於雙十二烷基二甲基溴化銨為陽離子界面活性劑，對帶負電的粒子表面有特定性，引導我們猜測自泳動的來源可能與表面的帶電荷轉變有關。我們也觀察到陽離子界面活性劑加入溶液中，對帶負電荷的膠體粒子進行吸附，在超過一臨界濃度時，帶負電荷的膠體粒子出現電荷正負反轉，此電荷反轉的濃度我們將之命名為臨界電轉濃度。Janus粒子的自泳動方向反轉濃度與此臨界電轉濃度呈現吻合，使我們可以大膽猜測Janus粒子在雙氧水中的自泳動可符合自電泳模型。

In recent years, the research of active material has been widely developed, including motion mechanics, motion control, and application ranging from optical materials and biomaterials to medicine delivery. At the present stage, scientists focus on topics of active material preparation, material carrying and packing, and motion design. It has been reported that Janus particles made by coating platinum on the hemisphere in hydrogen peroxide solution convert chemical energy to kinetic energy and cause self-propulsion, and the direction of self-propulsion is away the catalytic side. Scientists attempted to find out the mechanism of this kind of self-propulsion. We discovered that after a small amount of surfactant, DDAB (Didodecyldimethylammonium bromide) has been added to the hydrogen peroxide solution, the direction of self-propulsion reversed. This phenomenon contradicts many suggested propulsion model. However, it also provides us a clue to self-propulsion mechanism. In general opinion, heterogeneous catalytic reaction occurs on the coated side and generates excess solute and oxygen bubbles, which were regarded as the major cause of self-propulsion. Those propulsion models failed because small amount of DDAB in the solution causes self-propulsion to reverse. DDAB is cationic surfactant, may be adsorbed specifically on the negatively charged surface of Janus particle. We also observed that when added DDAB concentration was higher than a critical point, the particle surface charge reversed. We named this point isoelectric concentration. The concentration causing self-propulsion direction reverse matches with isoelectric concentration, so we suggest a self-electrophoretic model to the self-propulsion of Janus particles in hydrogen peroxide solution.