Directing the Formation of Nanostructured Rings via Local Oxidation

Abstract

We provide compelling evidence that ring formation in solutions of thiol-passivated Au nanoparticles is driven by breath figure dynamics. A method for the controlled placement of rings of nanoparticles on a solid substrate, which exploits variations in substrate wettability to fix the positions of the submicrometer water droplets formed in the breath figure process, has been developed. This is achieved by heterogeneously patterning hydrogen-terminated silicon substrates with oxide regions that act as adsorption sites for the droplets. The droplets in turn template the formation of thiol-passivated Au nanoparticle rings during spin-casting from volatile solvents.

Dewetting-mediated pattern formation in nanoparticle assemblies

“…Nanofluid dewetting offers a significant number of alternative pathways towards the generation of rings of nanoparticles and nanorods on solid substrates. Many groups have reported the formation of nanoparticle rings, with diameters ranging from a few hundred nm to a few micrometres, composed of, for example, Ag [14], Au [13,16], Ni [51], FePt [52], and polypyrrole [53] nanoparticles. Due to the complex physical and chemical processes involved in nanofluid dewetting, a wide variety of mechanisms have been put forward to explain the formation of rings of nanoparticles following solvent evaporation.…”

“…The small droplets of water that condense on the substrate, due to evaporative cooling, template the formation of nanorings. This highly versatile technique has been employed on a range of solutes such as nanoparticles [16], polymers [62], hybrid nanoparticle-polymer systems [63], and single-molecule magnets [64].…”

“…Dewetting of volatile nanofluids gives rise to various morphologies as the positions of nanoparticles indicate the history of solvent dewetting moments prior to complete solvent evaporation, which is assumed to arrest the motion of nanoparticles on moderate timescales. A plethora of nonequilibrium self-organized morphologies of nanoparticle arrays have been reported, including isolated islands [6][7][8], worm-like domains [6,7], continuous labyrinthine structures and interconnected cellular networks [6,7,[9][10][11][12][13], rings [9,[13][14][15][16], and viscous-fingeringlike fractal structures [13,17]. Figure 1 shows a selection of self-organized nanoparticle arrays, including most of the aforementioned, on silicon substrates.…”

Nanomaterial Patterning in 3D Printing

“…Hence, patterning methodologies that can achieve a more scalable patterning of nanomaterials in micro or mesoscale is highly desirable. For example, evaporative assembly40,45,46,78 has been demonstrated to be capable of creating a highly controlled pattern of microstructures at that span from the nanoscale to the centimeter scale 254–264. Nevertheless, evaporative colloidal assembly remains a complex and dynamic phenomenon that is extremely sensitive to a wide range of properties.…”

“…This can mitigate the coffee‐ring phenomenon, which Song and co‐workers demonstrated by assembling polystyrene nanoparticles to form a range of microstructures from flat disks to dome structures with an increasing height to diameter ratio 231. In addition to counter‐acting the coffee‐ring effect, nonequilibrium dewetting processes can be leveraged to produce a plethora of patterns through the modification of factors such as nanoparticle concentration in the ink, the solvent used to form printable ink, method of deposition, and the free surface energy of the substrate237 For example, isolated islands,254–256 worm‐like domains,257 interconnected cellular networks with continuous labyrinthine structures,258–261 and ring structures262–264 have been reported with gold, latex, and silver nanoparticles.…”