Multifunctional Superhydrophobic Nanoparticle Coatings for Cellulose-based Substrates by Liquid Flame Spray

Wettability of a solid surface by a liquid plays an important role in several phenomena and applications, for example in adhesion, printing, and coating. Especially, wetting of rough surfaces has attracted a great scientific interest in recent decades. Superhydrophobic surfaces, which possess extraordinary water repellency properties due to their low surface energy chemistry and specific nano- and microscale roughness, are of particular interest due to the great variety of potential applications ranging from self-cleaning surfaces to microfluidic devices. Another driving force for the extensive scientific work on superhydrophobicity has been a desire for detailed understanding of wetting phenomena on different types of superhydrophobic surfaces, for example on natural superhydrophobic surfaces of lotus leaves where easy mobility of water droplets results in self-cleaning effect, rose petals where water droplets firmly adhere to the surface, and butterfly wings which possess directional water droplet adhesion. This thesis work reviews recent aspects on different modes of superhydrophobicity and explores a variety of functional anti-wetting/wetting properties on both natural and artificial superhydrophobic surfaces. In addition, fabrication techniques, properties, and potential applications of superhydrophobic surfaces and coatings are examined with focus on cellulose-based substrate materials on which an extensive literature survey is executed. In recent years, a great number of different approaches ranging from simple one-step methods to sophisticated multi-step procedures to fabricate superhydrophobic coatings on cellulose-based substrate materials such as cotton or paper have been reported. Potential applications for the cellulose-based superhydrophobic materials vary from water- and stain-repellent, self-cleaning and breathable clothing to cheap and disposable lab-on-a-chip devices. The experimental section of this work focuses on fabrication of functional superhydrophobic and superhydrophilic nanoparticle coatings on cellulose-based substrate materials by liquid flame spray (LFS) and examination of the coating properties. LFS proved itself straightforward and versatile one-step method to fabricate broad range of functional nanoparticle coatings on various substrate materials in an atmospheric roll-to-roll process. It has established itself among the most potential candidates for large-scale production of superhydrophobic coatings on affordable cellulose-based substrates

Adhesion Mechanism of Water Droplets on Hierarchically Rough Superhydrophobic Rose Petal Surface

Extremely hydrophobic surfaces, on which water droplets sit in a spherical shape leaving air entrapped into the roughness of the solid, are often called superhydrophobic. Hierarchically rough superhydrophobic surfaces that possess submicron scale fine structures combined with micron scale structures are generally more hydrophobic, and water droplet adhesion to those surfaces is lower in comparison with surfaces possessing purely micrometric structures. In other words, usually a fine structure on a superhydrophobic surface reduces liquid-solid contact area and water droplet adhesion. Here we show that this does not apply to a high-adhesive superhydrophobic rose petal surface. Contrary to the present knowledge, the function of the fine structure on the petal surface is to build up the high adhesion to water droplets. Understanding of the specific adhesion mechanism on the rose petal gives insight into an interesting natural phenomenon of simultaneous superhydrophobicity and high water droplet adhesion, but, in addition, it contributes to more precise comprehension of wetting and adhesion mechanisms of superhydrophobic surfaces overall

Multifunctional Superhydrophobic Nanoparticle Coatings for Cellulose-based Substrates by Liquid Flame Spray

Wettability of a solid surface by a liquid plays an important role in several phenomena and applications, for example in adhesion, printing, and coating. Especially, wetting of rough surfaces has attracted a great scientific interest in recent decades. Superhydrophobic surfaces, which possess extraordinary water repellency properties due to their low surface energy chemistry and specific nano- and microscale roughness, are of particular interest due to the great variety of potential applications ranging from self-cleaning surfaces to microfluidic devices. Another driving force for the extensive scientific work on superhydrophobicity has been a desire for detailed understanding of wetting phenomena on different types of superhydrophobic surfaces, for example on natural superhydrophobic surfaces of lotus leaves where easy mobility of water droplets results in self-cleaning effect, rose petals where water droplets firmly adhere to the surface, and butterfly wings which possess directional water droplet adhesion. This thesis work reviews recent aspects on different modes of superhydrophobicity and explores a variety of functional anti-wetting/wetting properties on both natural and artificial superhydrophobic surfaces. In addition, fabrication techniques, properties, and potential applications of superhydrophobic surfaces and coatings are examined with focus on cellulose-based substrate materials on which an extensive literature survey is executed. In recent years, a great number of different approaches ranging from simple one-step methods to sophisticated multi-step procedures to fabricate superhydrophobic coatings on cellulose-based substrate materials such as cotton or paper have been reported. Potential applications for the cellulose-based superhydrophobic materials vary from water- and stain-repellent, self-cleaning and breathable clothing to cheap and disposable lab-on-a-chip devices. The experimental section of this work focuses on fabrication of functional superhydrophobic and superhydrophilic nanoparticle coatings on cellulose-based substrate materials by liquid flame spray (LFS) and examination of the coating properties. LFS proved itself straightforward and versatile one-step method to fabricate broad range of functional nanoparticle coatings on various substrate materials in an atmospheric roll-to-roll process. It has established itself among the most potential candidates for large-scale production of superhydrophobic coatings on affordable cellulose-based substrates

Grafting Silicone at Room Temperature — a Transparent, Scratch-resistant Nonstick Molecular Coating

Silicones are usually considered to be inert and, thus, not reactive with surfaces. Here we show that the most common silicone, methyl-terminated polydimethylsiloxane, spontaneously and stably bonds on glass—and any other material with silicon oxide surface chemistry—even at room temperature. As a result, a 2–5 nm thick and transparent coating, which shows extraordinary nonstick properties toward polar and nonpolar liquids, ice, and even super glue, is formed. Ten microliter drops of various liquids slide off a coated glass when the sample is inclined by less than 10°. Ice adhesion strength on a coated glass is only 2.7 ± 0.6 kPa, that is, more than 98% less than ice adhesion on an uncoated glass. The mechanically stable coating can be easily applied by painting, spraying, or roll-coating. Notably, the reaction does not require any excess energy or solvents, nor does it induce hazardous byproducts, which makes it an ideal option for environmentally sustainable surface modification in a myriad of technological applications

Planar fluidic channels on TiO2 nanoparticle coated paperboard

A new design for permanent, low-cost, and planar fluidic channels on TiO2 nanoparticle coated paperboard is demonstrated. Initially superhydrophobic TiO2 nanoparticle coatings can be converted to hydrophilic by ultraviolet (UVA) light, and fluidic channels can be generated. A simple water treatment after the UVA illumination converts the channels permanent when nanoparticles are removed from the illuminated and wetted areas as shown by water contact angle, FE-SEM, XPS, and ToF-SIMS analysis. This suggests new routes for inexpensive, easy to use point-of-care diagnostics based on planar fluidic channels

Paper-Based Microfluidics: Fabrication Technique and Dynamics of Capillary-Driven Surface Flow

Paper-based devices provide an alternative technology for simple, low-cost, portable, and disposable diagnostic tools for many applications, including clinical diagnosis, food quality control, and environmental monitoring. In this study we report a two-step fabrication process for creating two-dimensional microfluidic channels to move liquids on a hydrophobized paper surface. A highly hydrophobic surface was created on paper by TiO₂ nanoparticle coating using a high-speed, roll-to-roll liquid flame spray technique. The hydrophilic pattern was then generated by UV irradiation through a photomask utilizing the photocatalytic property of TiO₂. The flow dynamics of five model liquids with differing surface tensions 48–72 mN·m^–1 and viscosities 1–15 mN·m^–2 was studied. The results show that the liquid front (<i>l</i>) in a channel advances in time (<i>t</i>) according to the power law <i>l</i> = <i>Zt</i>^0.5 (<i>Z</i> is an empirical constant which depend on the liquid properties and channel dimensions). The flow dynamics of the liquids with low viscosity show a dependence on the channel width and the droplet volume, while the flow of liquids with high viscosity is mainly controlled by the viscous forces