Polymers, substrate-based fabrication

A vapor phase grafting process based on the ozonization of polymer films and fabrics followed by a treatment with vapors, such as acrylonitrile, dichloroethylene, and vinyl acetate, has been patented by Polyplastic (66). Also cotton fabrics can be used as substrates. 

Following these CNT electronic gas sensor studies, many other methods have been explored focusing on the reduction of fabrication cost. Snow et al. demonstrated that a low-density random network of SWCNTs can be fabricated into p-type thin-fllm transistors [Figure 14.7(c)] with a fleld-effect mobility of about 10 cm / Vs and an on-to-off ratio of about 10 [65]. They demonstrated that such thin-fllm transistors can detect dimethyl methylphosphonate (DMMP), a simulant for the nerve agent sarin, at sub-ppb levels [45]. SWCNT network transistors have also been transferred to polymer substrates to form flexible electronic gas sensors [66]. Other resistive sensors based on random SWCNT network [47] or MWCNT films [41] have also been reported. Besides the cost, CNT network and thin-film sensors increase the statistical reliability by averaging out the response at many adsorption sites. This is particularly important when gas concentration is extremely small. 

The substrate for the microfluidic device should be selected with consideration of the end application. Substrates used to fabricate the microchip device should not interact with target analytes, and must be compatible with the detection method employed (i.e., should not exhibit background fluorescence, BGF.). For the analysis of nonpolar compounds, it should be kept in mind that substrates such as poly(dimethyl)siloxane (PDMS) can adsorb hydrophobic analytes such as peptides and proteins. Plasma oxidation or treatment of the surface can sometimes be useful to minimize these interactions [34,35]. For perfusates containing organic solvents, compatibility with polymer substrates can also be an issue. Substrates to be used for the fabrication of electrophoresis-based separation devices should be capable of supporting a stable electroomostic flow (EOF). The use of a low cost material and standard processing procedures can permit mass fabrication of devices. 

FIGURE 9.1 Flexible solar cells based on different kinds of polymer substrates. (A) Photograph of a flexible DSSC based on ITO-coated PET substrate wrapped on a pen. (B) Schematic illustration of the layer structure of a solid-state DSSC based on PEDOT on Goretex film as a counter electrode. (C) Schematic illustration (left) and photograph (right) of the PSC based on ITO-coated PET substrate. (D) Comparison of PSCs fabricated on conventional FTO/glass and flexible PEDOT PSS/PET substrate. (E) Schematic illustration of the flexible solar cell based on Ag-grid/PET substrate. 

Coating and laminating are very exciting technologies with a myriad of possibilities [15]. The aim of coating or laminating a textile substrate with a polymer layer is to significantly influence its external characteristics and physical properties. Textiles coated with, or laminated, bonded with a continuous polymer layer acquire new properties that cannot be achieved by the base fabric alone. 

Figure 5.33a shows the electrowetting-based tunable liquid lens on a flexible substrate. The fabrication of such a lens takes advantage of the transfer technique discussed in Chapter 3. The lens structure was first formed as an island housing the lens on a thin polymer substrate. Both the housing island and the substrate could be made of PDMS. The whole structure could then be wrapped conformally onto a curvilinear surface. 

Yoon et al. [48] proposed a liquid junction free polymer membrane-based reference electrode system for blood analysis under flowing conditions. They used silicmi wafers as well as ceramic substrate to fabricate ion selective sensors with an integrated reference electrode. The silver chloride layer was coated with a membrane based on aromatic polyurethane (PU 40 membrane) with equimolar amounts of both cathodic and anodic lipophilic additives (TDMACl and KTpCIPB) to reduce the electrical resistance (see Chaps. 12 and 13). The ceramic-based sensors were fabricated by screen-printing methods. Both reference electrodes showed a rather stable potential in various electrolyte solutions with different pH values and different concentrations of clinically relevant ions, providing that the ionic strength of the solution is over 0.01 M. The integrated ISE cartridge based on the ceramic chip could be used continuously for a week. 

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