Stability of Molded Microstructures in Polydimethylsiloxane

Micron-sized lines molded in poly(dimethylsiloxane) are susceptible to collapse under the stresses of gravity, adhesion, and hydrodynamics exerted on the elastomer. The stability of these lines and their utility as parts of stamps to form defect-free structures by microcontact printing depend on the aspect ratio of the line, how the elastomeric stamp is prepared and handled, and its exposure to solvent. Cleaning the stamp with sodium dodecyl sulfate (5%) in water, rinsing it with heptane, and drying it with supercritical CO(2) provided the best method for reversing the effects of mechanical and fluid-derived pressures on the surface of the stamp. No treatment provided useful stamps having lines with aspect ratios of less than 0.2 or larger than 2. Combined, these data suggest a series of qualitative constraints on the design of elastomeric stamps that include their geometry, material of construction, and the target of their application.