Hydrophobic microchannel

D. C. Tretheway and C. D. Meinhart, Apparent fluid slip at hydrophobic microchannel walls, Phys. Fluids 14, L9-L12 (2002) Chang-Hwan Choi, J. A. Westin, and K. S. Breuer, Apparent slip flows in hydrophilic and hydrophobic microchannels, Phys. Fluids 15, 2897-902 (2003). 

Choi et al. [1] presented the slip velocity and slip length of hydrophilic and hydrophobic microchannels (1 and 2 pm depth) based oti the flow rate and pressure drop measurements. Sample results from their study are compiled in Fig. 2. The flow rate for hydrophobic surface is higher than that compared to the hydrophiUc surface. The corresponding slip velocity and sUp length for hydrophobic surface is also higher than that of the hydrophilic surface. The slip velocity and sUp length increases with strain rate. 

Barrat and Bocquet [6] reported slip in Couette and Poiseuille flows using molecular dynamics simulation (Fig. 7). Tretheway and Meinhart [4] reported micron-resolution velocity profile in hydrophilic and hydrophobic microchannels of cross section 30 x 300 pm using the p-PIV technique (Fig. 5a). Their results showed significant fluid velocity near a hydrophobic (octadecyltrichlorosilane or... 

Tretheway D, Meinhart C (2002) Apparent fluid slip at hydrophobic microchannel walls. Phys Fluids 14 L9-L12... 

Choi CH, Westin JA, Brener KS (2003) Apparent slip flows in hydrophilic and hydrophobic microchannels. Phys Fluids 15(10) 2897-2902... 

D.C. Trethway, C.D. Meinhart, A generating mechanism for apparent fluid slip in hydrophobic microchannels, Phys. Fluids, 2004, 36, 1509-1515. 

J. Harting, C. Kunert, and H. Herrmann, Lattice Boltzmann simulations of apparent slip in hydrophobic microchannels, Europhys. Lett, 75, 328-334 [2006]. 

Davies J, Maynes D, Webb BW, Woolford B (2006) Laminar flow in a microchannel with super hydrophobic walls exhibiting transverse ribs. Phys Fluids 18 087110... 

Stretched Polymers MF membranes may be made by stretching (Fig. 20-68). Semicrystalline polymers, if stretched perpendicular to the axis of crystallite orientation, may fracture in such a way as to make reproducible microchannels. Best known are Goretex produced from Teflon , and Celgard produced from polyolefin. Stretched polymers have unusually large fractions of open space, giving them very high fluxes in the microfiltration of gases, for example. Most such materials are very hydrophobic. 

Handique K, Burke DT, Mastrangelo CH, Burns MA (2000) Nanoliter liquid metering in microchannels using hydrophobic patterns. Anal Chem 72 4100-4109... 

T. Kawakatsu, G. Tragardh, C. Tragardh, M. Nakajima, N. Oda, and T. Yonemoto The Effect of Hydrophobicity of Microchannels and Components in Water and Oil Phases on Droplet Formation in MicroChannel Water-in-Oil Emulsification. Colloid and Surfaces A Physicochem. Eng. Aspects 179, 29 (2001). 

Efforts toward integrating SPE onto a lab-on-a-chip device are currently being investigated by the Collins group. Two complementary approaches are being pursued. One approach is to use small-diameter, Cl8 functionalized silica beads that are packed into a microchannel to form an extraction bed [46], A sample solution containing trace levels of explosives is electrokinetically directed across the microcolumn bed, causing the hydrophobic explosive molecules to adsorb onto the stationary phase with nearly 100% efficiency. Subsequently,... 

Example 7.10. Prins et al. [306] used electrowetting to control fluid motion in microchannels. To do so, they coated aluminum electrodes first with a 12 pm thick layer of parylene and then with a 10 nm thick fluoropolymer film. The channels were 0.35 mm wide. Due to the hydrophobic polymer water does not flow into the capillaries. Only after applying voltages of typically 200 V did the capillaries fill with water. When switching the voltage off, the water flowed out of the capillaries again. 

Reversible bonding of PDMS to PMMA was also achieved [177,178,364]. A PDMS replica containing microchannels (< 100 pm deep) was sealed against a PMMA plate (or a PDMS replica of it) that had deep (300-900 pm) solution reservoirs machined in it [1042]. PDMS was also sealed against a patterned hydrophobic fluorocarbon film [179]. 

Liquid evaporation was employed for liquid pumping in Si-glass microchannels. With hydrophobic patterning at the outlet reservoir, the evaporation rate at the liquid meniscus was controlled to produce a flow rate of 5 nL/min. The hydro-phobic region was patterned by an A1 mask using a silane solution (FDTS) [146]. 

Affinity chromatography of streptavidin was performed on a PET chip. The microchannel was first filled with the dual-modified latex beads (as shown in Figure 6.3). The biotinylated beads were surface-modified with a temperature-sensitive polymer, poly(N-isopropylacrylamide (PNIPAAm, 11 kDa). When the temperature was raised above the lower critical solution temperature (LCST) of PNIPAAm, the beads aggregated and adhered to the channel wall, because of a hydrophilic-to-hydrophobic phase transition. Then streptavidin from a sample solution was captured by these adhered biotinylated beads. Thereafter, when the temperature was reduced below the LCST, the beads dissociated and eluted from the channel wall together with the captured streptavidin [203],... 

Wang,Y.X., Cooper, J.W., Lee, C.S., DeVoe, D.L., Efficient electrospray ionization from polymer microchannels using integrated hydrophobic membranes. Labchip 2004, 4, 363-367. 

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