Forced Soft Lithography

In 2008, Fernandez et al. [46] have introduced a technique, called forced soft lithography, by which solution-processable polymers can be patterned without relying on capillary forces. In this process, the mold is placed inside a chamber with the stmctured surface upward. Then, a liquid pre-polymer (chitosan or PDMS) is poured into the chamber and the pressure is increased by a plunger at a determined rate. After pressure release, the chamber is opened to let the solvent evaporation and the curing of the pre-polymer. The pressure applied acts in the same direction as the capillary forces to displace the air inside the mold cavities. Researchers have used this method to successfully stmcture chitosan polymers with features in the nanometer range (400 nm) [46, 47]. 

The financial support of the ISCIII through the FIS project PI071162 is gratefully acknowledged. E. Martinez also acknowledges the financial support of the Spanish Ministry of Science an Education through 13 program. 

and Whitesides, G.M. (1993) Features of gold having micrometer to centimeter dimensions can be formed through a combination of stamping with an elastomeric stamp and an alkanethiol ink followed by chemical etching. Appl. Phys. Lett, 63 (14), 2002-2004. 

Abbott, N.L., Kim, E Biebwck, H.A., and Whitesides, G.M. (1995) Patterned self-assembled monolayers and meso-scale phenomena. Acc. Chem. Res., 28, 219-226. 

6 Mrksich, M. and Whitesides, G.M. (1995) Patterning self-assembled monolayers using microcontact printing - a new technology for biosensors. Trends Biotechnol., 13, 228-235. 

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Fernandez, J.G., Mills, C.A., Pla-Roca, M., and Samitier, (. (2008) Forced Soft lithography (FSL) production of micro-and nanostructures in thin freestanding sheets ofchitosan biopolymer. Adv. Mater, 19, 3696-3701. 

Multiple valves have been constructed on a PDMS valve control layer (see Figure 3.27) [167]. Multilayer soft lithography has been used to generate the valve control layer (4 mm thick for strength) plus a fluid layer (40 pm thick) on PDMS. The small Young modulus ( 750 kPa) of PDMS allows a large deflection (1 mm) to be produced using a small actuation force ( lOOkPa on a 100- x 100-pm valve area). The response time is on the order of 1 ms. Round channels were... 

Fig. 2 Atomic force microscopy (AFM) friction images and schematic illustrations of the patterning processes of a microcontact printed SAMs (mercaptoethanol dots in oc-tadecanethiol matrix, scale bar 10 xm) b patterned molecular printboards fabricated by supramolecular dip-pen nanolithography (DPN) (reprinted with permission from [92] Copyright 2004. WUey VCH) e locally hydrolyzed tert-butyl acrylate-terminated polymer film on oxidized silicon (soft lithography scale bar 3 xm) (Feng CL, Vancso GJ, SchOn-herr H, manuscript submitted to Langmuir) d photopatterned bilayer of diacetylene lipid (scale bar 10 xm). Reprinted in part with permission from [93], copyright (1999), American Chemical Society...

Local reactions take place, for instance, in unconventional lithography approaches. Here, the surface of a polystyrene-Woc -poly(ter/-butyl acrylate) (PS69o-fr-PtBA12io) block copolymer film comprising reactive ter/-butyl ester moieties at the film surface (skin layer of 8 nm thickness) is locally hydrolyzed by a reactant (trifluoro acetic acid) that is delivered by a soft elastomeric stamp, as shown in Fig. 4.38. Thus, the surface is locally modified to yield poly(acrylic acid), which possess higher friction forces than the unreacted tert-butylester region. 

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