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 PFPEsmore specifically, the dynamical organizations that result from spontaneous dewettingcan 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) n CF(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.

Ordered to Isotropic Morphology Transition in Pattern-Directed Dewetting of Polymer Thin Films on Substrates with Different Feature Heights

“…The instability mediated structures are generally isotropic and the lack of order severely limits their practical utility. In order to utilize dewetting mediated structure formation as a viable patterning technique, it becomes necessary to impose certain degree of order to the dewetted features, a problem that has received significant research attention, both theoretically − and experimentally. − While prepatterning a film by rubbing in a specific direction was used to demonstrate the concept for the first time, dewetting on chemically ,− ,− and topographically patterned substrates ,,− are preferred routes to create aligned patterns in a reproducible manner over large areas. Vertically confining the film under a mold during dewetting has also been utilized to obtain ordered structures. − …”

“…On a chemically patterned substrate comprising of alternating zones of different wettability, dewetting is engendered by the in-plane wettability gradient between the less- and more-wettable areas on the substrate. − This is in contrast to spinodal dewetting of a film on a homogeneous nonwettable substrate, where dewetting is engendered due to amplification of thermally excited capillary wave spectrum on the film surface, as a result of attractive interfacial van der Waals interaction. Theoretical − as well as experimental studies − have identified conditions under which variety of ordered structures can be obtained on a chemically patterned substrate. ,,,,− Sehgal et al have shown that a variety of ordered and partially ordered structures are possible, depending on the commensuration between the pattern dimensions ( λ P ) and the characteristic length scale of the dewetted features on a flat substrate ( λ D ) . They have also shown that the ordering tends to get distorted in overconfined systems, where λ P < λ D as the final droplets become anisotropic and coarsen to a scale comparable to the stripe width, eventually transforming into circular droplets leading to quantization droplet size, spanning across multiple stripes .…”

Tailored Covalent Grafting of Hexafluoropropylene Oxide Oligomers onto Silica Nanoparticles: Toward Thermally Stable, Hydrophobic, and Oleophobic Nanocomposites

“…Recently, new nanohybrids covered with oligomers of hexafluoropropylene oxide (HFPO), a model PFPE, , have been described. For instance, Erhardt and Nuzzo deposited a functional amphiphilic PFPE on a silica surface by spin casting and contact printing. The former method produced a thin film, whereas the latter method led to complex surface structures composed of beaded domains and depleted regions that result from dewetting processes.…”

Engineering the Microstructure of Organic Energetic Materials

“…In the case of subsequent deposition of a material on a surface, the fabrication of patterns is governed by growth phenomena that are typically nonequilibrium processes − . Growth is ultimately governed by the competition between the kinetics of deposition and the thermodynamics of the interaction between the substrate and the deposited molecule . For example, if the surface diffusion rate of the deposited molecules is slower compared to the pattern formation rate, the pattern growth is essentially determined by the kinetics and leads to stable structures .…”