二甲基甲醯胺之特殊潤濕行為: 擴散、收縮、移動;Peculiar wetting behavior of N,N-dimethylformamide: expansion, contraction, and running

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题名:	二甲基甲醯胺之特殊潤濕行為: 擴散、收縮、移動;Peculiar wetting behavior of N,N-dimethylformamide: expansion, contraction, and running
作者:	王承洋;Wang, Cheng-Yang
贡献者:	化學工程與材料工程學系
关键词:	二甲基甲醯胺;潤濕現象;接觸角;親水性;自體移動;N,N-dimethylformamide;wetting behavior;contact angle;hydrophilic;self-propulsion
日期:	2019-06-17
上传时间:	2019-09-03 12:27:25 (UTC+8)
出版者:	國立中央大學
摘要:	二甲基甲醯胺為非揮發性溶液，其液滴在某些表面可表現非典型潤濕行為，如: poly(methyl methacrylate)、經燃燒處理過的黃銅和藍寶石基材。類似於水液滴擴散於完全潤濕性質基材，二甲基甲醯胺液滴展現一自發性擴散，其擴散係數大於Tanner’s law。液滴在擴散時，液滴的外圍厚度高於其中心。與典型擴散不同，液滴在擴張到一定程度後會停止並開始向內收縮。最終，液滴在五分鐘內會縮成球帽形狀並有著相當低的接觸角角度。有趣的是，若在二甲基甲醯胺中添加界面活性劑，液滴會在擴張並收縮後表現一自發性移動。其移動軌跡為隨機路線，擴散係數為0.005~0.01 mm2/s。有別於大多數自發移動為反應性移動，二甲基甲醯胺液滴可重複跨越其經過的軌跡。這種自發性移動可以被歸功於無接觸角遲滯的基材和Marangoni stress。基於這些結果，我們提出了一種有關液滴的擴散、收縮和移動機制。;The nonvolatile N,N-dimethylformamide (DMF) droplet can display peculiar wetting behavior on some substrates such as poly(methyl methacrylate), flametreated brass, and sapphire. Similar to the expansion of a water drop on a total wetting surface, the DMF droplet shows a spontaneous spreading initially but its spreading dynamics is beyond Tanner’s law. The spreading droplet exhibits a ridge near the rim whose height is greater than that of the center. Contrary to typical spreading, the DMF droplet stops its outward expansion at some point and begins inward contraction. Eventually, the droplet shrinks to a spherical cap with a low contact angle within 5 min. It is interesting to find that upon addition of surface-active agents, the droplet performs the self-propelled motion after spreading-contraction. The trajectory is random and can be described as the diffusive motion with the diffusivity ~0.005- ~0.01 mm2/s. Unlike self-propulsion driven by reactive wetting, the DMF droplet can cross the trail left by itself. This self-propulsion can be attributed to the effects of the hysteresis-free surface and Marangoni stress. Based on those results, a mechanism explaining the contraction and self-propelled droplet motion is proposed.
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