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Title: | 各種膠體粒子於微/奈米流體通道中之電泳運動現象 Electrophoretic Motion of Colloidal Particles in a Micro/Nanochannel |
Authors: | Cheng-Hsuan Huang 黃政瑄 |
Advisor: | 李克強 |
Keyword: | 電泳,電滲透,軟球複合型粒子,多孔性球體粒子,液滴,微/奈米流體通道, Electrophoresis,Electroosmotic Flow,Soft Composited Particle,Porous Particle,Liquid Droplet,Micro-/Nanofluidic Channel, |
Publication Year : | 2012 |
Degree: | 博士 |
Abstract: | 本研究計畫探討非硬性膠體粒子於微/奈米流體通道中之電動力學現象,包括軟球複合型粒子、多孔性球體粒子以及液滴暨微乳液等系統。而在電動力學討論則包含電泳運動(electrophoresis)以及電滲透現象(electroosmosis)。為了清楚描述非硬性球膠體粒子在通道中的電動力學情形,吾人突破幾何系統的座標限制,採取球座標與圓柱座標描述此物理系統;並以Chebyshev多項式為基底之假性光譜法及牛頓-拉福森疊代(Newton-Raphson iteration scheme)等數值方法求解相互耦合之電動力學方程組。
以往非硬性球體粒子研究都針對粒子本身特性做探討,例如粒子表面電位(surface potential),高分子層固定電荷密度(fixed charged density),高分子層勻相摩擦阻力(frictional force),液滴內外黏度比(viscosity ratio)等等。然而隨著科技進步,諸多研究與設備皆逐漸往奈米尺度發展,傳統上僅研究粒子特性之文獻已不敷解釋,必須更進一步瞭解微小化實體邊界與粒子交互作用之影響。因此本研究以現今最具廣泛應用之微奈米流體通道為基底,深入探討非硬球膠體粒子在此通道中交互作用之電動力學現象。文中先針對電動力學以及各種膠體粒子特性及應用作一系列文獻回顧,並說明本次研究目的;而在第二章做進一步的理論分析。第三章則介紹相關數值方法。其後三章(四、五、六章)則依序針對軟球複合型粒子、多孔性球體粒子以及液滴在微奈米流體通道之電動力學現象做深入研究分析。 研究結果發現,當粒子表面電位越高,亦或是高分子層固定電荷密度越高時,粒子泳動速度將隨之提升;然而相對的受外加電場作用,其粒子周圍的離子雲扭曲也越嚴重,進而產生一誘發電場與原外加電場競爭而降低電泳動度,並隨電雙層變化而造成粒子速度產生極值;有趣的是流體通道的的出現,將大幅增加此效應!另一方面高分子層勻相摩擦阻力會有效降低電泳動度,而針對液滴其黏度大小也大幅決定了其速度快慢。此外,當電雙層厚度較厚時由於受通道邊界的影響,此時電雙層會受到擠壓而變形,故使粒子泳動速度因邊界效應而變慢;反之電雙層較薄時較不受限於邊界。且不論電雙層厚度大小,在流體通道半徑達一定值時則可忽略邊界效應。有趣的是在某些高分子層勻相摩擦阻力低的情況,越狹窄的流體通道反而有較快的粒子電泳動度;此外也有機會觀察到帶電量較低之液滴泳動度快過較高電量之液滴!最後,因管壁帶電性質所造成的電滲透流將大幅改變粒子的運動狀態,若其電性與粒子相反則有助於粒子傳輸,反之則會降低粒子泳動度,甚至造成反向移動的可能性。 General microfluidic and nanofluidic electrokinetics in a cylindrical channel is investigated in this project, which emphases the electrophoresis and electroosmosis of a spherical non-rigid colloidal particle, including soft composited particles, porous particles, and droplets. Both spherical and cylindrical coordinates are adopted to describe the physical systems. General electrokinetic equations are employed and solved with a pseudo-spectral method based on Chebyshev polynomials and Newton-Raphson schemes. Traditional studies of electrophoresis have been focused on characteristics of the particle, such as the surface potential of particles, the fixed charge density and homogeneous frictional force on polymer layers, and the viscosity ratio of microemulsions, and so on. Thanks to the advances of the micro-/nanofabrication technology, microdevices with even smaller features can be produced now and the electrokinetic technique can be further downscaled to tens or hundreds of nanometers, allowing manipulation of even smaller colloidal particles. Therefore, it is essential to consider aforementioned electrokinetic phenomena to develop a comprehensive transport model of molecules in micro-/nanofluidic channels. We found, among other things, that the higher the particle surface potential or the fixed charge density of the polymer layer, the more serious distortion of the ion clouds, which generates an induced electric field opposite to the particle motion, thus reducing the electrophoretic velocity. This phenomenon can be enhanced by the presence of a nearby channel. The particle mobility is found to decrease as the permeability of the porous layer decreases and exhibit an extreme value in the profile with varying double-layer thickness. Furthermore, the confinement effect of the fluidic channel can be so drastic when double-layer thickness is thick, however vanishing when the thickness is thin. In particular, an intriguing phenomenon is observed for the highly permeable particle: The narrower the channel is, the faster the particle moves! The reason behind it is thoroughly explained here. Moreover, as the fluidic channel is quite narrow, that the lowly charged droplet may move faster than the highly one! Finally, charged channels can exert electroosmosis flow so dominant that sometimes it may even reverse the direction of the particle motion. This has direct impact in practical applications of nanofluidics when a weak electric field is applied. Conducting operations near these critical double-layer thicknesses should be avoided in practice |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/65676 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 化學工程學系 |
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