Exposing the elastomer polydimethylsiloxane (PDMS) to oxygen plasma creates a very thin, stiff, and brittle surface-modified layer. Nano-scale crack patterns can be introduced to this layer with tensile stress. To optimize the pattern formation for a specific nano- or bio-technology research application, the surface-modified layer must be fully characterized. A characterization method was developed, using a combination of experiments and finite-element modeling. Phase imaging and nanoindentation with the atomic force microscope showed that the surface-modified layer was graded over approximately 200 nm, with an elastic modulus at the surface approximately ten-times that of the unmodified PDMS. Finite-element analyses indicated that the toughness of the surface-modified layer is extremely low (0.1--0.3 J/m2) and that the embrittlement extends 100--400 nm below that of the measured layer thickness, signifying that the cracks may extend deeper than the apparent layer thickness.;Variations of the nanocrack-patterning method were used to produce functional nanoscale patterns. First, surface-modified PDMS cubes and microspheres were uniaxially compressed causing their surfaces to be decorated with nanocrack patterns. Pattern formation, due to the distribution of tensile stresses in the surface-modified layer, on the cube surfaces was associated with friction at the contacts with the platens; whereas, for the microspheres it could exclusively be attributed to the changing cross-sectional area along the axis of compression. Second, an array of parallel tunnel cracks was produced in the surface-modified layer, when sandwiched between PDMS substrates, with an applied uniaxial tensile strain. The tunnel cracks functioned as tunable nanochannels when they connected pre-patterned microchannel reservoirs. Modulated fluidic transport of single particles between the reservoirs was demonstrated and electrical resistance measurements confirmed the nanochannel adjustability (from approximately 1 mum wide to completely closed).;Due to the compliance of PDMS, surface forces were able to cause the channel and tunnel cracks to close, or heal, upon removal of applied tensile strain. The self-adhesion of the nanochannel walls due to surface forces was studied and the conditions for collapse were determined. A method for determining and applying a non-uniform traction on the surface of bodies that are interacting due to surface forces was developed.
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