Dynamic Shaping of Femtoliter Dew Droplets

Abstract

Herein, we show that wetting properties such as giant wetting anisotropy and dynamic shaping can be observed when femtoliter (submicron scale) dew droplets are condensed on nanopatterned mildly hydrophilic surfaces. Large-scale, optically transparent, nanopatterned TiO surfaces were fabricated by direct nanoimprinting lithography of sol-gel-derived films. Square, infinitely elongated, or circular droplets were obtained with square, line, or concentric patterns, respectively, and were visualized in situ during formation and recession using optical microscopy and environmental scanning electronic microscopy. We first describe how extremely elongated droplets could form on mildly hydrophilic surfaces, naturally contaminated in real environmental conditions. In this configuration, the dew droplet shape can be dynamically and reversibly varied by controlling the out-of-equilibrium conditions associated with condensation/evaporation kinetics. As an example of the application, we propose a "morphological" sensor that exploits the shape of the dew droplets as a transduction mode for detecting organic vapors in the outer atmosphere. Importantly, this study is underlining that environmentally stable, purely hydrophilic surfaces can be smartly engineered to induce wetting phenomena at very small scale never observed so far for hydrophobic or heterogeneous surfaces. Our versatile approach based on nanoimprinted, transparent sol-gel films could open great perspectives for the implementation of environmentally stable, mildly hydrophilic materials for "dew engineering" applications such as open microfluidics, fuming for fingerprints, vapor sensing, or water harvesting on glass windows, for instance.

Tailored Nanopatterning by Controlled Continuous Nanoinscribing with Tunable Shape, Depth, and Dimension

“…Beyond simple micro- and nanograting with homogeneous depths, nanopatterns having variable depths and dimensions within a single substrate zone may be capitalized in many applications requiring tunable optical, mechanical, and/or physicochemical characteristics, such as holograms, color filters, − microfluidic platforms, , biosensors, − photonic structures, , and electrochemical devices. − Typical fabrication methods involving simple lithography and/or normal NIL, however, cannot easily produce such structures without resorting to time-consuming and costly procedures. By controlling the mold–substrate alignment angle and inscribing stroke direction, DNI enables tailored nanopatterning with gradient depth profiles and multidimensional structures in a continuous and very practical fashion.…”

“…Tailored Nanopatterning with Gradient Profiles and Multidimensions by Controlling the Mold Alignment Angle and Inscribing Stroke Direction. Beyond simple micro-and nanograting with homogeneous depths, nanopatterns having variable depths and dimensions within a single substrate zone may be capitalized in many applications requiring tunable optical, mechanical, and/or physicochemical characteristics, such as holograms, 37 color filters, 38−40 microfluidic platforms, 41,42 biosensors, 43−45 photonic structures, 46,47 and electrochemical devices. 48−50 Typical fabrication methods involving simple lithography and/or normal NIL, however, cannot easily produce such structures without resorting to time-consuming and costly procedures.…”

Nanoimprint Lithography Processing of Inorganic-Based Materials

“…55 The deposition of a too-thick initial layer led to the presence of a 200 nm-thick residual layer. The same authors reproduced this method to elaborate patterned surfaces for controlled wetting 56 and 250 nm TiO 2 dielectric Mie resonator pillar arrays (aspect ratio 1) 57 with a residual layer as thin as 10 nm by applying a thinner initial sol−gel layer (see Figure 13). Chen et al 58 reported the fabrication of ultrathin GaAs solar cells with a TiO 2 /Ag nanostructured back mirror using the same procedure.…”

Replacing Metals with Oxides in Metal-Assisted Chemical Etching Enables Direct Fabrication of Silicon Nanowires by Solution Processing

“…The imprinting process is pressure-less, does not require any imprinting equipment and can be realized on large scale. [35][36][37] Figure S1 in Supplementary Material displays the photo of a patterned sample of 4 cm 2 exhibiting areas with different iridescent colors characteristic of diffractive gratings with periodicities ranging from 400 to 1000 nm. These two effects have been investigated by in-situ spectroscopic ellipsometry on a plane film during the thermal treatment.…”