Robust and Programmable Superhydrophobic Surfaces

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School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2017-10-06
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Authors

Date

2017

Department

Kemian ja materiaalitieteen laitos
Department of Chemistry and Materials Science

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Mcode

Degree programme

Language

en

Pages

77 + app. 59

Series

Aalto University publication series DOCTORAL DISSERTATIONS, 181/2017

Abstract

This thesis deals with design, fabrication and characterization of robust and programmable superhydrophobic surfaces. The content is divided into two main categories. The first part is dedicated to fabrication of durable superhydrophobic surfaces and their performance characterization, including blood compatibility. The second part focuses on programmable superhydrophobic/superhydrophilic surfaces. A new fabrication process was introduced to produce durable superhydrophobic silicon surfaces, based on geometrical modification of the surface without any hydrophobic coating. The fabrication process is based on a combination of inductively coupled plasma-reactive ion etching (ICP-DRIE) and metal-assisted chemical etching (MaCE). Elimination of hydrophobic coating made the surface chemically and thermally robust, but due to use of silicon, the mechanical fragility issue remained. A biomimetic approach inspired by the exoskeleton of insects such as Armadillidium, was introduced to tackle the mechanical robustness. The new hybrid material consists of elastomeric overhang nanostructures covered by a thin layer of metal oxide. The elastomer part can bend and deform without breaking, while the hard metal oxide layer protects the surface from mechanical damage. We used atomic layer deposition (ALD) and replica moulding to produce such hybrid PDMS/titania surfaces. Our new fabrication process is based on sacrificial etching of the aluminum template and the transfer of titania film from the template to the PDMS. Subjecting the surfaces to a battery of mechanical, thermal, chemical and radiation tests demonstrated extremely durable superhydrophobicity. As an extension to replica moulding/sacrificial template process, we introduce a new way to make hydrophobic and hemophobic elastomeric tubes. The tubes showed a dramatic drag reduction for water and blood droplets compared to control tubes. A programmable superhydrophobic surface was introduced using hierarchical silicon micro and nanostructures covered by photo-switchable materials. Combination of ICP-DRIE and RIE were used to produce silicon T-shaped microstructures. Colloidal deposition was done to introduce nanoscale roughness. These structures were then conformally coated with photoactive titania using ALD. Fast and reversible transition of superhydrophobic to hydrophobic, hydrophilic and superhydrophilic state was demonstrated using UV-exposure and thermal annealing.

Description

Supervising professor

Franssila, Sami, Prof., Aalto University, Department of Chemistry and Materials Science, Finland

Thesis advisor

Jokinen, Ville, Dr., Aalto University, Department of Chemistry and Materials Science, Finland

Keywords

superhydrophobic, superhydrophilic, durable, switchable, restorable

Other note

Parts

  • [Publication 1]: Hoshian, Sasha; Jokinen, Ville; Somerkivi, Villeseveri; Lokanathan, Arcot, R.; Franssila, Sami. 2015. Robust superhydrophobic silicon without a low surface-energy hydrophobic coating. American Chemical Society. Applied Materials & Interfaces, volume 7 (1), pages 941-949. ISSN 1944-8244.
    DOI: 10.1021/am507584j View at publisher
  • [Publication 2]: Hoshian, Sasha; Jokinen, Ville; Franssila, Sami. 2016. Robust hybrid elastomer/metal-oxide superhydrophobic surfaces. Royal Society of Chemistry. Soft Matter, volume 12, issue 31, pages 6526-6535. ISSN 1744-6848. Fulltext at Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-201610135008.
    DOI: 10.1039/C6SM01095D View at publisher
  • [Publication 3]: Hoshian, Sasha; Kankuri, Esko; Jokinen, Ville; Franssila, Sami. 2017. Water and Blood Repellent Flexible Tubes. Minor revision in Scientific Reports.
  • [Publication 4]: Hoshian, Sasha; Jokinen, Ville; Hjort, Klas; Ras, Robin H. A.; Franssila, Sami. 2015. Amplified and localized photoswitching of TiO2 by micro- and nanostructuring. American Chemical Society. Applied Materials & Interfaces, volume 7 (28), pages 15593-15599. ISSN 1944-8244.
    DOI: 10.1021/acsami.5b04309 View at publisher

Citation

Permanent link to this item

https://urn.fi/URN:ISBN:978-952-60-7627-0

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[diss] Kemian tekniikan korkeakoulu / CHEM