Water is among the most vital substances on earth. Despite being an everyday element, prominently interesting phenomena occur when water is in contact with a surface. Superhydrophobic surfaces are ones that do not wet. In the extreme, they repel water to such a large degree that water does not stick to even nearly horizontal planes. Nowadays, many researchers pursue the magnificent examples set by nature, such as the extraordinary water repellency of a lotus leaf. Even though the basis of the study of wetting dates back to the 1800s, many elementary concepts remain unexplored. This thesis combines fundamental notions of wetting to experimental material science and demonstrates applications based on these materials, ranging from memory devices and sensors to pellets, which facilitate environmental clean-up. Publication I studies the fundamental concepts of surface wetting characterization and introduces a quantitative method for measuring the receding contact angle using the sessile-drop method. Theory and experiments together with calculations evaluate the validity of the developed model, and good agreement between theory and experiments is found. Furthermore, a novel definition for superhydrophobicity is proposed. Publication II introduces a growth model for the synthesis of silicone nanofilaments, which are one-dimensional nanostructures used to create superhydrophobic surfaces. In contrast to the previous studies, the present model explains the break of symmetry occurring in the initial phase of the growth, which has so far been implicitly assumed. Publication III demonstrates a hierarchically rough surface, which exhibits bi-stable superhydrophobic wetting states under water. A rapid local wetting transition occurs simply by locally applying pressure or suction onto the surface. Theoretical considerations explain the phenomena and a simple display demonstrates the concept. Publications IV and V introduce nanocellulose aerogels coated by atomic layer deposition with inorganic thin films. These materials are further employed as a resistive/capacitive humidity sensor and for oil spill cleanup from a water surface. The porosity and high surface area of the structures together with the wetting properties of the inorganic coating account for the observed properties. In addition, the study evaluates different drying methods for the nanocellulose aerogels based on the aggregation of the fibrils. Combining basic principles of wetting and superhydrophobicity to novel materials, as shown in this study, can lead to applications from myriad fields of technology. The concepts and applications demonstrated hopefully inspire future research towards many wetting-based applications.
|Translated title of the contribution||Kastuvuustutkimuksia: Peruskäsitteistä ja kuitumaisista nanorakenteista sovelluksiin|
|Publication status||Published - 2013|
|MoE publication type||G5 Doctoral dissertation (article)|
- humidity sensor
- oil absorption