Hydrophobically recovered and contact printed siloxane oligomers for general-purpose surface patterning

Hydrophobic recovery of elastomeric polydimethylsiloxane (PDMS) has been well-known in various fields, such as microcontact printing (μCP), microfluidics, and electric insulation, etc., which has been believed to be due to the transfer of out-diffused siloxane oligomers in PDMS. The recovery phenomenon has been used to control surface energy of a substrate, due partly to its nanoscale thickness. In this work, we extend the use of recovered oligomers to a general-purpose surface patterning process, in combination with both dry and wet pattern transfer processes. The out-diffused and transfer-printed oligomers play exactly the same role of "ink" in the conventional μCP; thus, the present method can be termed as "inkless" microcontact printing (IμCP). Also, the detailed nature of recovered oligomers has been investigated, and they are found to have a molecular weight ∼10 times larger than that of pristine, uncured PDMS oligomers. And the molecular weight distribution is very broad with a polydispersity index of ∼15. Then, we present and discuss various aspects of the IμCP process, such as pattern transfer onto substrate via wet or dry etching, effect of process variables on printing results, minimum feature size achieved by the technique, repeated printing with the same stamp, and the generation of more complex patterns from simpler ones by applying multiple IμCP.