Capillary valve

Figure 4.18 Photographs of the sequence of laminar flow formation with the assistance of capillary valves. (A) (a) Red and blue aqueous solutions (1.7 10"3 Pa s) are introduced into the channels and stopped at the valves ...

Figure 3.4. Differential gas adsorption manometry with capillaries (valves for initial evacuation of equipment or filling of reservoir not represented) (after Schlosser, 1959).

Soiled mobile phase (and, as a consequence, also soiled frits, capillaries, valve and/or column) ... 

Figure 11. Passive centrifugal microfluidic valves, (a) Positioning of valves relative to center of rotation and centrifugal force, (b) geometric capillary valve [191], (c) hydrophobic valve [197], (d) centrifugo-pneumatic valve [201]and (e) hydrophihc siphon valve [188].

Madou et al. from the University of California, Irvine showed a series of capillary valves to perform enzyme-linked immunosorbent assays (ELISAs) on the centrifugal platform [222], The different assay liquids are held back in reservoirs coimected to the reaction chamber via valves of different burst frequency. The capillary valves are opened subsequently by increasing the frequency of rotation. It was shown that in terms of detection range the centrifugally conducted assay has the same performance as the conventional method on a 96-well plate, but with less reagent consumption and shorter assay time. 

Liu V, Song YA, Han JY (2010) Capillary-valve-based fabrication of ion-selective membrane junction for electrokinetic sample preconcentration in PDMS chip. Lab Chip 10(11) 1485-1490... 

Capillary Force Valves, Fig. 4 Schematics of a capillary valve using a hydrophobic patch. The pressure required to move the liquid (Af i) is higher when the liquid-air interface reaches the region of increased hydro-phobicity (Af 2)... 

Capillary Force Valves, Fig. 6 Schematics of capillary valves using changes in the diameter of the capillary. Rapid enlargement of a capillary changes the physical angle between the liquid interface and the solid surface and can form a temporary barrier for the advancing liquid... 

Capillary valves are burst valves, i.e., once the liquid passes through them, they no longer function as valves. Resetting a capillary valve requires the formation of the liquid-liquid or liquid-gas interface at the location of hydrophobic interaction. This can be achieved by the... 

Centrifugal Flow Control, Fig. 3 Schematic of flow control using the siphon and in-line capillary valves (a, b) centrifugo-pneumatic siphon at high and low spin rates (c-f) and the centrifugo-pneumatic cascade on... 

Capillary valves have no moving parts, are simple and easy to implement and thus are very attractive for low-cost microfluidic devices. At the same time, several areas of improvement are under scrutiny, to increase the performance of the valve, to improve the integration and to... 

Keywords— microfluidic compact disc, capillary valve, flap valve, point-of-care, BioMEMS. 

A siphon valve operates on the principle of the capillary effect. Unlike the capillary valves, a siphon valve prevents fluid flow at high rotational speeds. Figure 3 shows the operation of a typical U-shaped siphon valve. The hydrophilic U-shape channel between the two chambers primes the liquid from the source to the destination chamber. At high rotational speed, the centrifugal force pushes the liquid outward away from the center of the CD, trapping it at the bottom of the U shape channel. [9] [10]. 

For the microfluidic CD, the capillary valves are designed and implemented accordingly to ensure proper flow sequencing of the intended processes. The capillary-flap valves are introduced in series after the capillary valves. Hgure 9 shows the positioning of the capillary valve and the capillary-flap valve between the source and destination chambers. 

Hence, by introducing a modified flap valve in series after the capillary valve, flow sequencing is still controlled by the capillary valve, while the flap valve then prevents mixing of vaporized reagents/chemicals in the channels. 

The design of a hybrid capillary-flap valve is presented for vapor control in point-of-care microfluidic CDs. The design of the capillary-flap valve is developed after consideration of a wide range of available valves such as membrane valves, flap valves, diaphragm valves, manual valves, and sacrificial valves. The capillary-flap valve is derived from a flap valve for its simplicity in design and low in cost to fabricate, and it complements the existing capillary valves used in microfluidic CDs. 

Chen J M, Huang P, Lin M (2008) Analysis and experiment of capillary valves fa- microfluidics on a rotating disk. Microfluidics and Na-noHuidics 427-437... 

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