Polydimethylsiloxane channels

After activation by heating, the catalyst was dusted over the surface of a thin polydimethylsiloxane (PDMS) layer, being coated on the PDMS top plate of the micro reactor [19]. Such a modified plate was baked for 1 h at 100 °C. A high surface area and firm immobilization of the catalyst resulted. Then, the micro reactor was assembled from the top and another bottom plate, having at one micro-channel wall the catalyst layer. Stable operation with the PDMS micro reactor up to 175 °C could be confirmed. 

Abstract We review various methods for the photochemical grafting of organic polymers to various substrates including, organic films, membranes, planar gold, silicon wafers, glass, silica gel, silica nanoparticles, and polydimethylsiloxane micro-channels. An emphasis is placed on photoinitiated synthesis of polymer brushes from planar gold and silicon. 

Recently Allbritton and Li coated polydimethylsiloxane (PDMS) microfluidic channels with BP [36]. Upon irradiation in the presence of a monomer solution, they were able to graft poly(acrylic acid) and poly(ethylene glycol) monomethoxyl acrylate to the interior walls of the channels. This is a significant achievement since the device did not require disassembly in order to modify the channel walls. The electrophoretic separation of the modified channels was different from the native channels. This technique holds particular promise for the microfluidic separations commimity. 

The microfluidic devices, often called Christmas tree owing to the pattern of the channels, were fabricated from polydimethylsiloxane (PMDS) using common micro technologies (see Figure 1.69). A mask is formed by using a high-resolution 3300 dpi printer to transfer the CAD pattern to a transparent mask substrate. 

The micro channel structure of the device is fabricated in a glass wafer by common procedures (Figure 4.14). To allow sealing of the channels, the whole surface is coated with CYTOP, a Teflon -like polymer. On the one hand it forms a bondable layer and on the other it makes the micro channel surface strongly hydrophopic. Bonding with a CYTOP-coated cover glass plate occurs under moderate pressure at 180 °C. Because sometimes the CYTOP layer peels off and disturbs the fluid flow behavior, the whole device is fabricated in polydimethylsiloxane (PDMS) [71]. 

Mata, A., Boehm, C., Fleischman, A.J., Muschler, G., Roy, S., Analysis of connective tissue progenitor cell behavior on polydimethylsiloxane smooth and channel micro-textures. Biomed. Microdevices 2002, 4(4), 267-275. 

Jo, B.-H.,VanLerberghe, L.M., Motsegood, K.M., Beebe, D.J., Three-dimensional micro-channel fabrication in polydimethylsiloxane (PDMS) elastomer /. Micro-electromech. Syst. 2000, 9, 76-81. 

Recently Sok et simulated the transport of He and of CH4 through a polydimethylsiloxane (PDMS) membrane. The polymer was selected because of the almost invariably amorphous condition of its samples. Thus the interpretation of experimental diffusion data is uncomplicated by the presence of crystallites. The PDMS chains were represented by oligomers consisting of 30 monomer units, and the MD simulation was based on a fine-grained representation of polymer and diffusant, i.e., all atoms were included explicitly. Like the mechanism described by Takeuchi " " here, too, transport occurred by a jump mechanism. Facilitated by fluctuations in the polymer chains, the hole surrounding the diffusant was observed to expand just prior to the jump, and a transient channel was opened, thus enabling the transition to occur. Diffusion coefficients derived for He and CH4 (respectively, 18 X 10" and 2.1 x 1(T cm s ) are consistent with at least the magnitudes of experimental measurement (10 x 1(T and 2.0 x 10" cm ... 

A number of creative ways have been developed to create nonuniformities in an electric field using insulators. Initial efforts simply used prefabricated posts embedded in the channels [6] or rectangular [8], triangular [3], oil menisci [9], and other protrusions into the channels. The most common insulator materials are polymers utilized for photolithography or hot press microfahrication including polydimethylsiloxane PDMS and polymethyl methacrylate PMMA, or glass or silicone, which can be chemically etched or ablated [2]. A key attribute of direct current dielectrophoresis is that the electrodes supplying the electric field can be located more remotely on the lab-on-a-chip device. Electrodes can be immersed in fluid in chambers at either end of the test channel to avoid detrimental electrolysis reaction products [31]. Please see Pig. 1. 

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