Nanoscale Channels and Tunnels in Surface-Modified Poly(dimethylsiloxane).

Thin Films;Plasma-oxidized PDMS;Atomic Force Microscopy;Nanochannels and Nanotunnels;Adhesion;Mechanical Engineering;Engineering;Mechanical Engineering

Mills, Kristen L.Pollock, Tresa ;

University of Michigan

关键词: Thin Films;    Plasma-oxidized PDMS;    Atomic Force Microscopy;    Nanochannels and Nanotunnels;    Adhesion;    Mechanical Engineering;    Engineering;    Mechanical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/61680/klmills_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

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 μm 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.