低介電係數溶液於微管道中之電動力學行為; Electro-kinetic phenomena in a Microchannel with Low-permittivity Media

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题名:	低介電係數溶液於微管道中之電動力學行為;Electro-kinetic phenomena in a Microchannel with Low-permittivity Media
作者:	張怡雯;Yi-wen Chang
贡献者:	化學工程與材料工程研究所
关键词:	毛細管徑;毛細管電泳;低介電係數溶劑;capillary electrophoresis;low dielectric constant solvent;capillary diameter
日期:	2011-06-23
上传时间:	2012-01-05 11:16:39 (UTC+8)
摘要:	由目前市面上主要的電子紙顯示技術中以E-ink與Sipix電泳式電子紙為主流，兩者皆是將粒子存在於低介電係數溶液中，在由外加電場來驅動，帶動粒子電泳來作為文字或圖像的顯示。一般來說，當粒子處於低介電係數溶劑中，因較強烈的庫倫作用力將導致其反離子不易解離而難以帶電。本論文主要利用毛細管電泳，研究在高、低介電係數salt-fee溶液與額外添加離子於salt-free中，改變毛細管的zeta potential，造成不同電滲流及電泳行為並配合理論推算，進而分析其解離原因、泳動速度及改善方法。利用熔融矽(二氧化矽)材質之毛細管，針對去離子水、NMF、THF及dioxane於不同管徑中的電滲流速率々可知高介電係數溶劑於不同管徑毛細管中，其電滲流速率不隨管徑大小而更所改變，與管徑為size-independent々而在低介電係數溶劑中，電滲流速率則與管徑為size-dependent關係。而在salt-free中添加額外離子(NaCl)，對於高、低介電係數溶液皆存在screening effect，隨著鹽濃度上升mobility下降，但在低介電係數中，在未達到鹽濃度飽和狀態下，還是存在mobility與管徑為size-dependent關係。由實驗結果，可知在低介電係數溶劑中，除了可避免交耳熱的產生外，亦可使mobility受鹽離子的下降程度較不劇烈々且要使mobility上升除了增加表面電荷量，亦可藉由改變粒子大小來增快電子紙中畫面的反應時間的下降。 The commercially dominant e-paper technologies today are E Ink and SiPix. In an electrophoretic technology, charged particles are suspended in a low dielectric fluid. When an electric field is applied, the ink particles will move towards the electrode with the opposite charge to display words and photos. In general, the dissociation of counterion from charged particle is difficult in a medium with low dielectric constant due to strong Coulomb attraction. In this work, the electrophoretic mobility and the origin of counterion dissociation from charged particle are investigated by using capillary electrophoresis system through electro-osmosis in high and low dielectric constant salt-free medium, and addition of salt. We consider DI water and organic solvents including, tetrahydrofuran, n-methylformamide and dioxane and their mixtures with water in fused silica capillary of different sizes to measure the electro-osmotic flow (EOF). The EOF mobility of high dielectric constant solvents are essentially independent of the microchannel size. However, in low-permittivity solvents, the mobility is found to grow with the capillary radius. With ions add to the salt-free medium, the screening effect is present and the mobility is inversely proportional to salt concentration, and decays exponentially with high free ionic concentration. In low-permittivity solvents, the mobility also is found to grow with the capillary radius until the solution is an saturated solution. In conclusion, using nonaqueous solutions, especially low dielectric constant, not only can reduce joule heat effect but also lessen the reduction of EOF mobility by the addition of salt. Consequently, in order to increase the response time in e-paper applications, the electrophoretic mobility can be increased by tuning the surface charge density or particle size.
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