Droplet Memory on Liquid-Infused Surfaces

The knowledge of droplet friction on liquid-infused surfaces (LIS) is of paramount importance for applications involving liquid manipulation. While the possible dissipation mechanisms are well-understood, the effect of surface texture has thus far been mainly investigated on LIS with highly regular solid topographies. In this work, we aim to address this experimental gap by studying the friction experienced by water droplets on LIS based on both random and regular polysilsesquioxane nanostructures. We show that the available models apply to the tested surfaces, but we observe a previously unreported droplet memory effect: as consecutive droplets travel along the same path, their velocity increases up to a plateau value before returning to the original state after a sufficiently long time. We study the features of this phenomenon by evaluating the motion of droplets when they cross the path of a previous sequence of droplets, discovering that moving droplets create a low-friction trace in their wake, whose size matches their base diameter. Finally, we attribute this to the temporary smoothing out of an initially conformal lubricant layer by means of a Landau–Levich–Derjaguin liquid film deposition behind the moving droplet. The proposed mechanism might apply to any LIS with a conformal lubricant layer

Measurement of sub-4 nm particle emission from FFF-3D printing with the TSI Nano Enhancer and the Airmodus Particle Size Magnifier

The emission of ultrafine particles from small desktop Fused Filament Fabrication (FFF) 3D printers has been frequently investigated in the past years. However, the vast majority of FFF emission and exposure studies have not considered the possible occurrence of particles below the typical detection limit of Condensation Particle Counters and could have systematically underestimated the total particle emission as well as the related exposure risks. Therefore, we comparatively measured particle number concentrations and size distributions of sub-4 nm particles with two commercially available diethylene glycol-based instruments – the TSI 3757 Nano Enhancer and the Airmodus A10 Particle Size Magnifier. Both instruments were evaluated for their suitability of measuring FFF-3D printing emissions in the sub-4 nm size range while operated as a particle counter or as a particle size spectrometer. For particle counting, both instruments match best when the Airmodus system was adjusted to a cut-off of 1.5 nm. For size spectroscopy, both instruments show limitations due to either the fast dynamics or rather low levels of particle emissions from FFF-3D printing in this range. The effects are discussed in detail in this article. The findings could be used to implement sub-4 nm particle measurement in future emission or exposure studies, but also for the development of standard test protocols for FFF-3D printing emissions.</p

Three-Dimensional Organization of Surface-Bound Silicone Nanofilaments Revealed by Focused Ion Beam Nanotomography

One-dimensional (1D) nanostructures have been identified as key technology for future devices and integrated into surface-bound materials. The roughness of surface-bound 1D silicone nanofilaments (SNFs) has been used extensively to create surfaces with extreme wetting properties and as carrier material. Electron microscopy has shown that this material is made of individual filaments with diameters spanning tens of nanometers and a length of several micrometers which arrange into a highly entangled quasi-porous network. However, a comprehensive analysis of the three-dimensional (3D) superstructure has remained elusive so far. In this study, focused ion beam nanotomography (FIB-nt) is used to quantify the otherwise hardly accessible structural parameters roughness (12.68) and volume fraction (2.80). The volume fraction is anisotropic, and two major species of SNFs are quantified to contribute equally to the overall surface area. Spatial statistics reveals a self-avoiding growth pattern of SNFs over the substrate, and a 3D model of the data is rendered. The presented analysis therefore significantly advances the understanding of SNF surface coatings with regard to their structure at the nano- and microscale. Finally, the described procedure may serve as a useful tool to analyze other surface-bound 1D nanostructures of similar complex arrangement

Superficial Dopants Allow Growth of Silicone Nanofilaments on Hydroxyl-Free Substrates

We report new types of silicone nanostructures by a gas-phase reaction of trichloromethylsilane: 1-D silicone nanofilaments with a raveled end and silicone nanoteeth. Filaments with a raveled end are obtained on poly­(vinyl chloride), which is superficially doped with the detergent Span 20. Silicone nanoteeth grow on sodium chloride using dibutyl phthalate as superficial dopant. Without dopants, no structures are observed. The dopants are identified by mass spectroscopy and the silicone nanostructures are analyzed by infrared spectroscopy and energy-dispersive analysis of X-rays. The growth of silicone nanostructures on a hydrophobic substrate (poly­(vinyl chloride)/Span 20) and a substrate free of hydroxyl groups (sodium chloride/dibutyl phthalate) questions the currently discussed mechanisms for the growth of 1-D silicone nanofilaments, which is discussed. We suggest superficial doping as an alternative pretreatment method to oxidizing activation and prove this principle by the successful coating of copper, which is superficially doped with Span 20

Life Cycle Assessment of a New Technology To Extract, Functionalize and Orient Cellulose Nanofibers from Food Waste

A new technology for the production of cellulose nanofibers from vegetable food waste has been developed. The fibers are liberated enzymatically, given a functionalized coating and oriented using spinning techniques. We performed a laboratory-scale life cycle assessment (LCA) to assess the various routes of the entire production process from an environmental perspective. The results indicate that the electrospinning process has a higher impact than the alternative wet spinning process under the conditions described. Furthermore, to improve the liberation process of the microfibrillated cellulose, the enzymatic treatment step requires development; this could be through optimization of energy use in the heating process, mainly by reducing heat loss and water use. A comparative LCA with the results of other published studies, using different starting materials and chemical processes to obtain nanocellulose, provides a deeper understanding of our processes. From this comparison, we conclude that our technology has the potential to become a competitive alternative, outperforming other nanocellulose technologies from an environmental perspective

Polysiloxane Nanotubes

The synthesis of polysiloxane nanotubes using trifunctional organosilanes is reported. Tubular nanostructures were formed via a chemical vapor deposition technique at room temperature when ethyltrichlorosilane is used or via a liquid phase method when methyltriethoxysilane is used as precursor. In the chemical vapor deposition process the shape of the tubes was controlled by changing the water content in the reaction chamber prior to coating. The diameter varied between 60 and 4000 nm. While in the case of the liquid phase method nanotubes with very high aspect ratios of 800 are produced. Parameters, such as length and diameter of the various tubes, were investigated using scanning electron microscopy and transmission electron microscopy. Additionally, the chemical composition of produced structures was analyzed using attenuated total reflectance-infrared and energy-dispersive X-ray spectroscopy. Glass substrates coated with such structures exhibit extreme superhydrophobic properties

Polysiloxane Nanotubes

The synthesis of polysiloxane nanotubes using trifunctional organosilanes is reported. Tubular nanostructures were formed via a chemical vapor deposition technique at room temperature when ethyltrichlorosilane is used or via a liquid phase method when methyltriethoxysilane is used as precursor. In the chemical vapor deposition process the shape of the tubes was controlled by changing the water content in the reaction chamber prior to coating. The diameter varied between 60 and 4000 nm. While in the case of the liquid phase method nanotubes with very high aspect ratios of 800 are produced. Parameters, such as length and diameter of the various tubes, were investigated using scanning electron microscopy and transmission electron microscopy. Additionally, the chemical composition of produced structures was analyzed using attenuated total reflectance-infrared and energy-dispersive X-ray spectroscopy. Glass substrates coated with such structures exhibit extreme superhydrophobic properties

Evaporation-Induced Transition from <i>Nepenthes</i> Pitcher-Inspired Slippery Surfaces to Lotus Leaf-Inspired Superoleophobic Surfaces

The newly developed <i>Nepenthes</i> pitcher (NP)-inspired slippery surfaces, formed by immobilizing fluoroliquids on lotus leaf (LL)-inspired superoleophobic surfaces, are of great general interest, whereas there are many interesting phenomena and fundamental scientific issues remaining to be unveiled. Here we present our findings of the effects of evaporation of the fluoroliquid, an inevitable process in most cases, -induced transition from NP-inspired to LL-inspired surfaces on the wettability, transparency, and self-cleaning property of the surfaces. The transition is controlled by regulating the evaporation temperature of the model fluoroliquid, Krytox100. The evaporation of Krytox100 has great a influence on the wettability, transparency, and self-cleaning property. An intermediate “sticky” state is observed in the transition process. We believe that our findings in the transition process are helpful in understanding the similarities and differences between the NP-inspired and LL-inspired surfaces and in designing new bioinspired antiwetting surfaces and exploring their potential applications

Protein Biomineralized Nanoporous Inorganic Mesocrystals with Tunable Hierarchical Nanostructures

Mesocrystals with the symmetry defying morphologies and highly ordered superstructures composed of primary units are of particular interest, but the fabrication has proved extremely challenging. A novel strategy based on biomineralization approach for the synthesis of hematite mesocrystals is developed by using silk fibroin as a biotemplate. The resultant hematite mesocrystals are uniform, highly crystalline, and porous nanostructures with tunable size and morphologies by simply varying the concentration of the silk fibroin and iron­(III) chloride in this biomineralization system. In particular, we demonstrate a complex mesoscale biomineralization process induced by the silk fibroin for the formation of hematite mesocrystals. This biomimetic strategy features precisely tunable, high efficiency, and low-cost and opens up an avenue to access new novel functional mesocrystals with hierarchical structures in various practical applications

Superwetting Double-Layer Polyester Materials for Effective Removal of Both Insoluble Oils and Soluble Dyes in Water

Inspired by the mussel adhesive protein and the lotus leaf, Ag-based double-layer polyester (DL-PET) textiles were fabricated for effective removal of organic pollutants in water. The DL-PET textiles are composed of a top superamphiphilic layer and a bottom superhydrophobic/superoleophilic layer. First, the PET textiles were modified with a layer of polydopamine (PDA) and deposited with Ag nanoparticles to form the PET@PDA@Ag textiles. The top superamphiphilic layer, formed by immobilizing Ag₃PO₄ nanoparticles on the PET@PDA@Ag textile, shows excellent visible-light photocatalytic activity. The bottom superhydrophobic/superoleophilic layer, formed by modifying the PET@PDA@Ag textile using dodecyl mercaptan, is mechanically, environmentally, and chemically very stable. The water-insoluble oils with low surface tension can penetrate both layers of the DL-PET textiles, while the water with soluble organic dyes can only selectively wet the top layer owing to their unique wettability. Consequently, the water-soluble organic contaminants in the collected water can be decomposed by the Ag₃PO₄ nanoparticles of the top layer under visible-light irradiation or even sunlight in room conditions. Thus, the DL-PET textiles can remove various kinds of organic pollutants in water including both insoluble oils and soluble dyes. The DL-PET textiles feature unique wettability, high oil/water separation efficiency, and visible-light photocatalytic activity