脈動式電滲透流對質傳與溶質分離之提升

Abstract

本文以數學解析之模式探討二維微流道中，由脈動式電滲透流所誘發的物質傳輸以及溶質分離之現象。在流道上下板電雙層互不影響、線性化之電場、不可壓縮且流線方向完全發展之流場，以及電中性物質之稀薄溶液的假設下，電雙層線性化電場、電滲流速度場，以及被傳輸物質濃度場為非偶合之統馭方程式所描述，並得以由格林函數所解出。結果顯示，微流道中的速度與濃度分布(場)會因為無因次震盪頻率(Womersley數)數值之提升，而愈趨非均勻分布。計算結果亦透露，流場在固定的震盪幅度(固定流率)之下，物質平均傳輸率會因為無因次頻率提升所增強的對流與物質分散效應(Dispersion Effects)而提高。在放大流場振幅的同時，平均質傳率也會因為對流效應之強化而增加。不同物種之間平均質傳率的越跨現象(Cross-Over Phenomenon)會因為德拜厚度(Debye Length)之增厚與震盪頻率的提升而愈趨明顯。當此越跨現象能有效提升質傳擴散係數較高物質之平均質傳率時，此一脈動式電滲流動即可成為生物晶片中，對溶質進行初步分離之基礎設計。

Mass transport induced by pulsatile electroosmotic flows in a two-dimensional microchannel is studied theoretically herein. With the assumptions of non-overlapping electrical double layers, linearized electrical potentials, streamwise fully-developed incompressible flows, and an infinitely dilute solution of neutral species, the governing equations for the electrical potential, the velocity field, and the species concentration distribution are solved analytically. The results indicate that the velocity and concentration distributions across the channel become more and more non-uniform as the Womersley number , or the oscillation frequency, increases. Results also reveal that, with a constant tidal displacement, the averaged mass transport rate increases with the Womersley number due to both the stronger convective and transverse dispersion effects. The averaged mass transport rate also increases with an increasing tidal displacement because of the associated stronger convective effects. The cross-over phenomenon of the mass transport rates for different species becomes possible with sufficiently large Debye lengths and at sufficiently high values of . As a result, with proper choices of the Debye length, oscillation frequency, and tidal displacement, pulsatile electroosmotic flow may become a good candidate for the first-step separation of the mass species.