Microchannels surface modification

MicroChannel glow discharge MicroChannel surface modification MicroChannel surface sterilization Plasma bonding... 

An understanding of multiphase microflows is critical for the development and application of microstructured chemical systems in the chemical industry. As one of the most important meso-scientific issues, interfacial science could be a bridge connecting microscopic molecular components and macroscopic fluid behaviors in these systems. Working together with viscous and inertial forces, the interfacial force also dominates complicated multiphase flow patterns and well-controlled droplets and bubbles. In this review, the generation mechanisms of different flow patterns and the break-up rules for droplets and bubbles in microchannels are introduced first. The effects of the adjustable fluid/solid interfaces, or so-called wetting properties, of microchannels on multiphase flow patterns, as well as microchannel surface modification methods, are then discussed. The dynamic fluid/fluid interfaces in multiphase microflows with variable... 

As in the case of normal chromatography both stationary and mobile phases are also required in NLC. On the other hand, in NCE hydrophilic channel walls with improved control over electroosmotic flow are required for better separation of biological samples. Briefly, the separation efficiencies and selec-tivities in NLC and NCE depend on the properties of the microchannels, and, therefore, surface modification of the microchannel is usually necessary to achieve good separation of a variety of analytes. Recently, Muck and Svatos... 

In some applications, an alteration in the microchannel surface charge is needed in order to modify EOF, i.e., to increase, suppress, or stabilize EOF. This charge alteration can be achieved by surface modification. 

Kirby, B.J., Wheeler, A.R., Shepodd, T.J., Fruetel, J.A., Hasselbrink, E.F., Zare, R.N., A laser-polymerized thin film silica surface modification for suppression of cell adhesion and electroosmotic flow in microchannels. Micro Total Analysis Systems, Proceedings 5th pTAS Symposium, Monterey, CA, Oct. 21-25, 2001, 605-606. 

Kitamori s group has proposed selective chemical surface modification utilizing capillarity (called the capillarity restricted modification or CARM method) (Hibara et al., 2005). In the CARM method, a microchannel structure combining shallow and deep microchannels and the principle of capillarity are utilized. The procedures are shown in Figure 19. A portion of an ODS/toluene solution (lwt%) is dropped onto the inlet hole of the shallow channel, and the solution is spontaneously drawn into this channel by capillary action. The solution is stopped at the boundary between the shallow and deep channels by the balance between the solid-liquid and gas-liquid interfacial energies. Therefore, the solution does not enter the deep channel. It remains at the boundary for several minutes and is then pushed from the deep channel side by air pressure. 

Phase separation improvements are based on either surface modification, fluid property control, or physical separation. Studies have shown that organic liquid membranes can be developed in a microchannel device using surface modification [207,208]. An organic liquid membrane consists of an organic phase with aqueous phases on either side. An analyte can be extracted from the aqueous phase, into the organic phase and then back-extracted into the second aqueous phase. These three phases can flow stably within a single microchannel, but better separation of the three phases is possible with surface modification of the organic phase channel (Fig. 7.16). 

The development and application of chip-based solvent extraction is gradually expanding as shown in this chapter. With methods for surface modification, the liquid-liquid interface in a microchannel can be stabilized, and so special techniques for solvent extraction are not required. Therefore, since solvent extraction is one of the basic chemical processes, it is expected that it will be used more often in the future. 

Hibara, A., Iwayama, S., Matsuoka, S., Ueno, M., Kikutani, Y, Tokeshi, M. and Kitamori, T., Surface modification method of microchannels for gas-liquid two phase flow in microchips. Anal Chem, 11, 943, 2005. 

The feasibility of synthesizing monolithic material in PDMS, glass, and polymeric substrates has been shown. However, PDMS is not so suited for the analysis of nonpolar analytes. The analytes are absorbed onto and into the PDMS, which results in poor recovery and low enrichment. Without surface modification, PDMS is only suited for polar samples such as genomic DNA. In Figure 50.27, a SEM image of monolithic material inside a Zeonor polymer microchannel is shown... 

Surface modification for microchannels in microfluidic and nanofluidic devices. 

Chang et al. [5] utilized microtubes to generate micro-segmented flow. Upon surface modification, the prepared nanoparticles were mixed with a monomer and emulsified into uniform droplets in a capillary-based microfluidic device. The microchannel-based reactor offered reliable control over the nanocomposite products by precisely adjusting the interfacial tension. 

Microchannels that range in diameter from tens to hundreds of microns have emerged as potentially powerful tools for a variety of biomedical applications. They can be used to minimize sample volume and reduce costs, as well as to increase throughput and analysis sensitivity. Since microfluidic devices operate at small length scales, their functionality is greatly dependent on their surface properties, which vary depending on the type of material that is used to fabricate the channel and the subsequent surface modifications. 

Plasma treatment of microchannels can be useful for improving the functionality of microdevices. For example, previous studies have shown that PDMS microchannels can be made hydrophilic by the addition of silane molecules with polar head groups [6]. In this process (3-mercaptopropyl)trimethoxysilane (3-MPS) was absorbed to PDMS to increase the hydrophilic properties of microchannels. Additionally, plasma polymerization has been used to induce in the long-term hydrophilic surface modification by covalently bonding a polymer layer to the surface. Barbier et al. [7] describe a method based on plasma polymerization modification with acrylic acid coatings. First, argon plasma pretreatment was used to activate trace oxygen molecules in the chamber, which partially oxidize the top layer of the substrate. This step cross-linked the surface to reduce ablation of silicon... 

Makamba H et al (2003) Surface modification of poly (dimethylsiloxane) microchannels. Electrophoresis 24(21) 3607-3619... 

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