Driven Pattern Formation in Organic Thin Film Materials: Complex Mesoscopic Organization in Microcontact Printing on Si/SiO2 via the Spontaneous Dewetting of a Functionalized Perfluoropolyether Ink

Abstract

Polyfluoropolyether (PFPE) films have long been used as lubricant coatings for magnetic recording media. In this paper, we demonstrate that the unique wetting properties of PFPEsmore specifically, the dynamical organizations that result from spontaneous dewettingcan be harnessed to generate mesoscopically patterned features of these materials on SiO2. In this work, a functionalized PFPE amphiphile with the formula CF3CF2CF2O(CF(CF3)CF2O)nCF(CF3)CONHCH2CH2CH2Si(OCH3)3 (Krytox SA, DuPont) was deposited on a SiO2 surface by both spin-casting and contact printing. Both methods produce complex surface structures comprised of beaded domains and depletion regions (and in the case of spin-casting, also thin films) that result from dewetting processes. Spontaneous dewetting was used to generate self-organizing PFPE bead patterns by microcontact printing. The wetting transitions in this latter case occur directly on the printing tool and, via the bias provide by the topography of the stamp, provide a means for generating and transferring complex organizations of adsorbate domains to the substrate. The combination of contact printing with spontaneous dewetting of the PFPE enabled us to produce high-fidelity patterns of discrete, micron-scale beads from printing tools with continuous line shapes without any alteration to the original mask pattern. The patterned beads typically had radii and characteristic separation lengths on the micron-scale, and heights on the nanoscale. These length scales appear to be governed by the combined influences of solvent-mediated nucleation processes and coarsening. Characterization was performed by optical microscopy, atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (XPS). These data suggest general design strategies that can be exploited to control the contours and structural profiles that result from the dewetting of the PFPE ink on a stamp used for contact printing.