Complex micropatterning of periodic structures on elastomeric surfaces

We report a simple methodology to fabricate complex sub-micrometre periodic structures in poly(dimethylsiloxane) over large surface areas (several cm 2). Single-frequency, uni- and multi-axial sinusoidal surface modulations, with tunable amplitude and wavelength, in the nano- to micrometre range, are readily demonstrated. The technique builds upon a buckling instability of a stiff layer supported by an elastomeric membrane (reported earlier), induced by surface oxidation of a pre-stretched elastomer coupon followed by removal of the applied mechanical strain. Plasma oxidation yields model surfaces with single wavelengths, sub-micrometre periodicity, achieving a dynamic range from sub-200 nm to 10s of mm, which UV ozonolysis extends to 100s of mu m. We find that a single 'dose' parameter (exposure time X power) characterizes the surface conversion. The strain control provides unprecedented tunability of surface pattern amplitude and morphology, ranging from lines to complex periodic topologies induced under multi-axial deformation. We introduce a novel multiple strain-exposure and replication approach that extends surface topologies beyond lines, chevron and spinodal patterns (isotropic structures with a dominant wavelength). The resulting structures exhibit a glass-like surface, which is easily grafted with self-assembled monolayers to enhance functionality. Applications of this inexpensive and fast methodology include stamps for soft lithography, micromolding, templating and surface patterning.