細菌地毯微流道中的次擴散動力學; Sub-diffusive Dynamics in Bacterial Carpet Microfluidic Channel

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題名:	細菌地毯微流道中的次擴散動力學;Sub-diffusive Dynamics in Bacterial Carpet Microfluidic Channel
作者:	蕭翌登;Hsiao,Yi-Teng
貢獻者:	物理學系
關鍵詞:	次擴散動力學;細菌地毯;Sub-diffusive Dynamics;Bacterial Carpet
日期:	2013-06-25
上傳時間:	2013-07-10 12:00:01 (UTC+8)
出版者:	國立中央大學
摘要:	我們研究在低雷諾數環境下的集體動力學及流體力學。我們將大量的細菌鋪在玻璃基板上形成「細菌地毯」，並利用一些追蹤小粒子觀察流場變化。以上議題為一個有趣的非平衡動力問題。細菌擁有高效率的分子馬達鞭毛，可以在低雷諾數環境下有效運作。我們利用單鞭毛的溶藻弧菌(VIO5或NMB136)，其特性是鞭毛的轉速可以利用溶液中納離子的濃度來調控。VIO5的鞭毛可以順時鐘及逆時鐘旋轉，並利用大角度的揮動互相切換。反之，NMB136的鞭毛只能逆時鐘旋轉。從實驗中，我們觀察到在VIO5的地毯中，鞭毛轉速較高及溶液黏滯係數較低時，追蹤粒子表現出有次擴散的動力學(Sub-diffusive dynamics)。反之，在NMB136的地毯中，並沒有觀察到上述現象。為了更進一步了解上述次擴散動力學的原因，我們利用螢光技術來標記鞭毛，並觀察相鄰近的鞭毛運動方式，以及利用光學攝子來量測細菌地毯所產生的流場大小。從這些實驗中，我們推測流場變化的原因是由鞭毛集體運動所造成的。相鄰近的鞭毛運動會隨著轉速變高而有互相越來越相似的情況。由光學攝子所量測到的流場的大小，也有隨著轉速變高而有類似相變的趨勢變化。同時由於所量測到的流場的方向大都是垂直方向，我們參考Saffman所提出在低雷諾數環境下粒子受到水平剪切流場時會受到一個Saffman上升力(Saffman lift force)來解釋所觀察到的次擴散動力學。在細菌地毯產生的不均勻垂直流場下，Saffman上升力有可能讓追蹤粒子被吸引至高垂直流場的位置，造成粒子具有回到前一刻位置的傾向，而形成次擴散的動力學。 We investigate the collective dynamics in array formed by self-propelling particle (SPP) under low Reynolds number (Re) condition. This system is an interesting non-equilibrium issue to be explored. In microfluidic devices, Re is low due to small characteristic length scale and low inertial effect. The above constraints lead to non-rotational flow in microfluidics devices. Bacteria, as a kind of self-propelling particles, possess molecular motors that are able to perform highly efficient flagellum rotation even under low Re condition. In this work, we form self-propelling particle array by depositing bacteria on treated surface in a microfluidic device. The formed high density bacterial carpet renders high density ensemble of freely rotating flagella that are able to exert thrust in the surrounding fluid. The micro?uidic channel is composed of single polarly-?agellated Vibrio alginolyticus (VIO5 or NMB136) deposited glass substrates. The individual ?agellum swimming speed is tuned by varying buffer sodium concentration. Hydrodynamic coupling strength is tuned by varying buffer viscosity. Particle tracking statistics shows high ?agellum rotational rate and strong hydrodynamic coupling strength lead to collective sub-diffusive dynamics in VIO5 case, while not the case for NMB136. The flick motions of the VIO5 could generate a thrust that propagates back to the original bacteria and exert a counteraction in the flow in between. In bacterial carpet condition, the suspended particle could experience an effectively confining action by the counteractions from all directions through hydrodynamic coupling. The NMB136 counterpart, however, could not generate strong thrust by rotational motion that could lead to strong anti-persistent motions in particle, thus no sub-diffusive dynamics. According to the experiment observation, we find out a vertical force generated by bacterial carpet. It can be measured by optical tweezers. Interactions between neighboring ?agella and force measurement show the forces may come from the collective ?agella motion. At the low Reynolds number system, Saffman force pushes the tracer particles to the region of higher ?uid velocity in the non-uniform flow. This is a physically probable mechanism to explain the sub-diffusive behavior.
顯示於類別:	[物理研究所] 博碩士論文

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