Polymer Brushes for Molecular Transport - Paul Braun Research ...

straightforward, the actual implementation can be very expensive and time consuming, due to the
high demands on resolution, placement accuracy, throughput, and defect density.[24]
1.3.2 Microcontact printing on silica
With the microcontact printing technique developed in the Whitesides group,[25, 26]
microscale patterning of end-grafted polymer brushes on gold and silica surfaces has been
achieved.[9, 27-34] In general, microcontact printing is a cost-efficient method to create two-
dimensional patterns of organic materials on both hard and flexible surfaces with spatial
resolutions approaching 250 nm (and better in specific cases).[35] Recently there have been
multiple publications reporting the synthesis and properties of patterned polymer brushes on gold
substrates,[9, 29-32] but very few publications on patterned polymer brushes on silica
surfaces.[27, 33, 34] This may be because the reproducible formation of organosilane
monolayers on silica can be difficult, and the film quality is sensitive to the details of the reaction
conditions including temperature, solvent, water content of the solvent, and deposition time.[36-
38] But recent publications have demonstrated that by controlling the reaction conditions
carefully, highly ordered alkyltrichlorosilane based SAMs can be reproducibly patterned.[27, 37,
39] Inherently, patterned polymer brushes on silica have many advantages over similar brushes
on gold. The silane/silica interface is much stronger than the thiol/gold interface. The S-Au
bond energy is 30-40 kcal/mol[30] while the Si-O bond dissociation energy is 96-133 kcal mol -1
and the Si-C bond dissociation energy is 90-95 kcal/mol.[40] The stability of polymer brushes
formed on silica surfaces can be further increased with the crosslinked polysiloxane structure
formed on the substrate surface when multifunctional silanes are used as end grafting agents.[37]
Silica substrates are low in cost, stable (high tolerance to UV, heat, sonication and oxidation),
smooth, and easy to prepare, whereas gold films are prone to delamination (at least in our
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