Polydimethylsiloxane etching

S. Ndonl, M. E. Vigild, and R. H. Berg, "Nanoporous Materials with Spherical and Gyroid Cavities Created by Quantitative Etching of Polydlmethylsiloxane in Polystyrene-Polydimethylsiloxane Block Copolymers,"/Am. Chem.Soc. 125,13366-13367 [2006]. 

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. 

Microchannels created using dry etching techniques on silicon-based substrates often have a cross section that is close to a rectangle. This geometry is also common in polymer-based microchips, e.g., created using PDMS (polydimethylsiloxane) material, which are popularly used in the research commxmity due to their simpler fabrication procedure. The effect of the rectangular geometry on the hydrodynamic... 

There are a number of materials used for the fabrication of pTAS devices. Perhaps the most common is glass due to its low cost, ease of machining, and suitability for electrophoresis and electroosmotic flow (EOF) applications without requiring surface modifications. It is also chemically inert to most reagents (apart from hydrofluoric acid and concentrated alkali). Silicon is also a valuable material that has similar chemical inermess and can easily be machined by chemical etching. While it is more expensive, it can be easily chemically etched to yield far higher aspect ratios than are possible with glass. Silicon is not suitable for electrophoresis or EOF applications without surface pretreatment. Devices fabricated from polymers such as polymethylmethacrylate (PMMA) and polydimethylsiloxane (PDMS) are also frequently used due to the low cost of the material (especially important for disposable devices) and the ease of fabrication. Perhaps one drawback with polymers is their incompatibility with solvents. They are suited to electrophoretic applications but frequently require surface modification to support EOF. Occasionally, metals are used however, these are far more frequently encountered in chemical microreactors. 

Plastic mold is fabricated by polydimethylsiloxane (PDMS). The chemical structure of PDMS is shown in Figure 4.20. A monolayer of DPE (4,4-diami-nodiphenylether) is coated on the plastic mold. The monolayer is transferred to the base plate. After stripping of the plastic mold, a multilayer of terephthaloyl chloride (TPC) and DPE is self-assembled on a monolayer by vapor deposition, as shown in Figure 4.21. The multilayer is then hardened by condensation polymerization. The reaction scheme of condensation polymerization is shown in Figure 4.22. The final pattern on the base plate is obtained after etching and resist removal. 

Ahn, H., Lee, K.J., Childs, W.R., Rogers, J.A., Nuzzo, R.G., and Shim, A. (2006) Micron and submicron patterning of polydimethylsiloxane resists on electronic materials by decal transfer lithography and reactive ion-beam etching Application to the fabrication of high-mobility, thin-film transistors. 

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