Eijkel, Jan C.T.

Shui, Lingling

van den Berg, Albert

English

We developed a novel method to control two-phase flow in nanochannels using regulating microchannels connected to the nanochannels. The flow rate inside a nanochannel can be regulated based on the pressure drops along the channel network. Stable flows with flow rates as low as 10-5 �?�L.min-1 (&lt; pL.s-1) can be obtained for both oil and water phases using a conventional syringe pump. We also demonstrate two-phase nanofluidics by confluence of two immiscible liquid flows in nanochannel

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A DEVICE FOR TWO-PHASE FLOW CONTROL IN NANOCHANNELS  Lingling Shui, Albert van den Berg and Jan C. T. Eijkel MESA+ institute for nanotechnology, University of Twente, The Netherlands  ABSTRACT We developed a novel method to control two-phase flow in nanochannels using regulating microchannels connected to the nanochannels. The flow rate inside a nanochannel can be regulated based on the pressure drops along the channel net-work. Stable flows with flow rates as low as 10-5 μL.min-1 (< pL.s-1) can be obtained for both oil and water phases using a conventional syringe pump. We also demon-strate two-phase nanofluidics by confluence of two immiscible liquid flows in nano-channels.  KEYWORDS: Flow-control, Nanofluidics, Two-phase, Nanochannel  INTRODUCTION Precise understanding of biological or chemical functions requires tools compa-rable in size to the basic components[1]. A nanofluidic device is ideal for manipulat-ing small volumes of liquid. Nanochannels can currently be easily fabricated by the standard photolithography process. However, the specific interfacial area of a nano-channel is very high, leading to a high hydrodynamic flow resistance so that high pumping pressures are needed. Furthermore, when two immiscible fluids (oil and water) are applied into the same nanofluidic device, an additional experimental diffi-culty is introduced, since one of the phases typically is non-wetting, necessitating higher applied pressures for this phase due to capillarity. Moreover, typically one of the phases is non-conductive (gas or oil), making electro-osmotic-flow unavail-able[2]. Pressure-driven flow by a syringe pump is therefore preferred for a two-phase nanofluidic system, even though it is experimentally difficult due to the high backpressure, the low flow rates needed (less than μL.min-1) and the very long time it takes to replace the liquid due to the dead volume of e.g. the connecting capillar-ies. In this report, we solved these complications by designing a flow control system using microchannels connected to nanochannels to regulate the flow rate in the nanochannels. Our system is similar to the pressure-controlled system of Hibara et al.[4].   EXPERIMENTAL The chip design is shown in Fig. 1. We used the same fabrication process and setup as reported in μTAS2008[3]. Liquids used were an 0.01M SDS aqueous solu-tion, made fluorescent by dissolving fluorescein sodium salt (0.01M), and hexadec-ane as the oil phase.   RESULTS AND DISCUSSION Liquids were introduced to the nanochannels by microchannels connecting an inlet and an outlet. The total flow was divided between the nanochannel and a flow Thirteenth International Conference on Miniaturized Systems for Chemistry and Life SciencesNovember 1 - 5, 2009, Jeju, Korea978-0-9798064-2-1/µTAS2009/$20ⓒ2009CBMSThirteenth International Conference on Miniaturized Systems for Chemistry and Life SciencesNovember 1 - 5, 2009, Jeju, Korea978-0-9798064-2-1/µTAS2009/$20ⓒ2009CBMSregulating microchannel. The hydrophobic oil phase did not enter the nanochannel until the applied pressure in the oil phase was larger than the negative capillary pres-sure, which leads to the minimum applied oil flow rate: Qmin=2σWmHm3/(CηLmHn), see Fig. 2. The liquid from the inlet split to the nanochannel and regulation micro-channel at the junction; the split ratio was determined by the nanochannel and regu-lating microchannel geometry: Qn/ Qm=Lmwnhn3/(lnWmHm3).Since most of the liquid that was pumped by the syringe pump flowed through the regulating microchannel, nanochannel volume flow rates lower than pL.s-1 could be obtained and the flow in nanochannel remained stable. Using this method, we could study for the first time the behavior of an oil-water immiscible two-phase flow in nanochannels (Fig. 3), showing non-oil flow, dripping and threading flow regimes.   Figure 1. Sketch of the chip design. Except for the regulating microchannels the nanofluidic channel section consists of two identical inlets and a constriction chan-nel (the leg of the ‘T’). Two identical microchannel sections run from the inlet to an outlet via a flow regulating channel, and also connect to both of the nanochannel inlets. The nanochannel dimensions are of height (h) = 150 ~ 900 nm, width (w) = 10 μm and length (l) = 1000 μm; the microchannel dimensions (height(H), length(L) and width(W)) are varied to regulate the flow in the nanochannels (the split ratio).   200 400 600 800 10000,00,10,20,30,4Qmin.m / μL.min-1h / nm Experimental Calculation Figure 2.  Plot of Qmin (the minimum applicable oil flow rate when oil starts to enter the nanochannel) vs. h (nanochannel depth). This flow rate is determined by the capillary pressure. Here, H = 10 μm, W = 100 μm, L = 5 mm, σ = 30 mN.m-1 and ηο = 3 mPa.s.  inlet inlet nanochannelsregulating regulating Thirteenth International Conference on Miniaturized Systems for Chemistry and Life SciencesNovember 1 - 5, 2009, Jeju, Korea978-0-9798064-2-1/µTAS2009/$20ⓒ2009CBMS Figure 3. Flow diagram of water-oil two-phase flow in nanochannels (h = 500 nm). The micrographs were taking in fluorescent mode. Qw and Qo indicate water and oil phase flow rates in nanochannels, respectively.  CONCLUSIONS We investigate the flow control in a nanochannel by using a regulating micro-channel. Stable flows with flow rates as low as 10-5 μL.min-1 (< pL.s-1) in nanochan-nels can be obtained. Confluence of immiscible two-phase flow in nanochannels has been demonstrated using this flow control method.   ACKNOWLEDGEMENTS We appreciate Nanoned and TheraEDGE for financial support.  REFERENCES [1] Y. Rondelez, G. Tresset, K. V. Tabata, et al., Nat. Biotechnol., 23, pp. 361- 365, (2005). [2] L. Shui, J. C. T. Eijkel, A. van den Berg, Sensor Actuat. B-Chem., 121, pp.  263-276, (2007). [3] L. Shui., S. Kooij, J. C. T. Eijkel, et al., μTAS2008, San Diego, USA, pp.  125-127, (2008). [4] A.Hibara, T.Tsukahara, T. Kitamori, J.Chromatography A, 1216, pp. 673-683 (2009).  0,1 10,11  Qo / 10-4  (μL.min-1)Qw / 10-4 (μL.min-1)non-oildrippingthreadingThirteenth International Conference on Miniaturized Systems for Chemistry and Life SciencesNovember 1 - 5, 2009, Jeju, Korea978-0-9798064-2-1/µTAS2009/$20ⓒ2009CBMS

A device for two-phase flow control in nanochannels

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A device for two-phase flow control in nanochannels

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