Superhydrophobic, Biomimetic Surfaces with High and Low Adhesion, Optical Transmittance, and

167 Pages·2016·7.64 MB·English

Superhydrophobic, Biomimetic Surfaces with High and Low Adhesion, Optical
Transmittance, and Nanoscale Mechanical Wear Resistance

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy
in the Graduate School of The Ohio State University

By
Daniel R. Ebert
Graduate Program in Mechanical Engineering

The Ohio State University
2016

Dissertation Committee:
Professor Bharat Bhushan, Advisor
Professor Terrence Conlisk
Professor Noriko Katsube
Professor Soheil Soghrati

Copyrighted by
Daniel R. Ebert
2016
ABSTRACT

Superhydrophobic surfaces (defined as surfaces having water contact angle greater
than 150°) show great promise for use in a rapidly growing number of engineering
applications, ranging from biomedical devices to fluid drag reduction in pipelines. In
nature, the surfaces of many organisms, such as certain plant leaves, are known to exhibit
superhydrophobicity. In some cases, droplet adhesion is very low (droplet rolls away
easily), while in other cases adhesion is high (droplet remains adhered when surface is
inverted). The recent advent and development of microscopes with resolution down to a
few nanometers (such as atomic force microscopes and scanning electron microscopes)
has allowed for in-depth understanding of the micro- and nanoscale mechanisms
employed by these plant leaves and other natural surfaces to achieve their particular
wetting properties. Biomimetics (or “mimicking nature”) is therefore a very promising
approach for the development of engineering surfaces with desired wetting
characteristics. However, research in creating biomimetic surfaces is still in its early
stages, and many of the surfaces created thus far are not mechanically robust, which is
required for many potential real-world applications. In addition, for applications such as
self-cleaning windows and solar panels, optical transparency is required.
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In this thesis, a set of original studies are presented in which superhydrophobic
surfaces were designed based on biomimetics and fabricated using a wide of variety of
techniques. The surfaces were characterized with regard to wetting characteristics such as
water contact angle and contact angle hysteresis, micro- and nanoscale mechanical
durability, and in some cases optical transmittance. Theoretical wetting models served as
guides both in the design and in the understanding of experimental results, especially in
regard to different wetting regime and regime transition. This work provides important
conclusions and valuable insight for identifying materials, techniques, and designs for
mechanically durable, optically transparent superhydrophobic surfaces.

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Dedicated to my parents

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ACKNOWLEDGMENTS

I would like to thank first and foremost my research advisor, Professor Bharat
Bhushan, for working with me at every step of this long journey. I have made enormous
strides professionally because of his guidance and tutelage. Next I would like to thank my
fellow researchers at NLBB, especially Dr. Manuel Palacio and Dr. Philip Brown, who
provided critical assistance with my work in the lab. I thank the graduate advising staff of
the mechanical engineering department, as well as my doctoral committee members,
Professor Terrence Conlisk, Professor Noriko Katsube, and Professor Soheil Soghrati. I
thank The Ohio State University for a full undergraduate scholarship, for countless
academic, research, and teaching opportunities, and for so many memorable experiences.
Lastly I want to thank my family, my true friends, and all of my teachers throughout my
life.

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VITA

2002………………………………………….……………...Beavercreek High School
Beavercreek, Ohio, USA
2008………………………………………….……………...B.S. Mechanical Engineering
The Ohio State University
2012……………………………………………………........M.S. Mechanical Engineering
The Ohio State University

PUBLICATIONS

1. Ebert, D. and Bhushan, B. (2012a), “Durable Lotus-effect surfaces with
hierarchical structure using micro- and nanosized hydrophobic silica particles,” J.
Colloid Interf. Sci. 368, 584-591
2. Ebert, D. and Bhushan, B. (2012b), “Wear-resistant rose petal-effect surfaces with
superhydrophobicity and high droplet adhesion using hydrophobic and
hydrophilic nanoparticles,” J. Colloid Interf. Sci. 384, 182-188
3. Ebert, D. and Bhushan, B. (2012c), “Transparent, Superhydrophobic, and Wear-
Resistant Coatings on Glass and Polymer Substrates Using SiO , ZnO, and ITO
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Nanoparticles,” Langmuir 28, 11391–11399
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4. Ebert, D.R. and Bhushan, B. (2013), “Methods of Fabricating Superhydrophobic,
Optically Transparent Surfaces,” U.S. Patent Pending
5. Ebert, D. and Bhushan, B. (2016), “Transparent, superhydrophobic, and wear-
resistant surfaces using deep reactive ion etching on PDMS substrates,” J. Colloid
Interf. Sci. 481, 82-90

FIELDS OF STUDY

Major Field: Mechanical Engineering

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TABLE OF CONTENTS

ABSTRACT ........................................................................................................................ ii
ACKNOWLEDGMENTS .................................................................................................. v
VITA .................................................................................................................................. vi
LIST OF TABLES ............................................................................................................ xii
LIST OF FIGURES ......................................................................................................... xiv
CHAPTER 1: Introduction ................................................................................................ 1
1.1 Significance of the problem ...................................................................................... 1
1.2 Overview of surface wettability and superhydrophobicity ....................................... 2
1.3 Biomimetics and extreme wettability found in nature ............................................ 14
1.4 Scope of the thesis ................................................................................................... 19
CHAPTER 2: Lotus Effect Surfaces with Superhydrophobicity and Low Droplet
Adhesion ........................................................................................................................... 23
2.1 Introduction ............................................................................................................. 23
2.2 Overview of wettability on a patterned surface ...................................................... 25
2.3 Sample preparation and characterization ................................................................ 27
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