BIOLOGICAL AND MEDICAL PHYSICS,BIOMEDICAL ENGINEERING

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Bharat Bhushan

BiomimeticsBioinspired Hierarchical-Structured Surfacesfor Green Science and Technology

Second Edition

123

Bharat BhushanNanoprobe Laboratory for Bio- andNanotechnology and Biomimetics(NLBB)

The Ohio State UniversityColumbus, OHUSA

ISSN 1618-7210 ISSN 2197-5647 (electronic)Biological and Medical Physics, Biomedical EngineeringISBN 978-3-319-28282-4 ISBN 978-3-319-28284-8 (eBook)DOI 10.1007/978-3-319-28284-8

Library of Congress Control Number: 2016930053

1st edition: © Springer-Verlag Berlin Heidelberg 20122nd edition: © Springer International Publishing Switzerland 2016This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or partof the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations,recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmissionor information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilarmethodology now known or hereafter developed.The use of general descriptive names, registered names, trademarks, service marks, etc. in thispublication does not imply, even in the absence of a specific statement, that such names are exempt fromthe relevant protective laws and regulations and therefore free for general use.The publisher, the authors and the editors are safe to assume that the advice and information in thisbook are believed to be true and accurate at the date of publication. Neither the publisher nor theauthors or the editors give a warranty, express or implied, with respect to the material contained herein orfor any errors or omissions that may have been made.

Printed on acid-free paper

This Springer imprint is published by SpringerNatureThe registered company is Springer International Publishing AG Switzerland

To my sons Ankur and Corrado, daughtersNoopur and Subha, granddaughters Sahanaand Joya, and my grandson Ashwin.

Foreword

Our planet has a unique biological diversity of about 1.8 million different species ofliving organisms that have been scientifically documented. The overwhelmingdiversity of plants and animals in shape, color, and function has fascinated studentsand scientists. What is more, it is estimated that the real number of species is muchhigher; on the order of 10 million species.

Each of these approximately 10 million species has optimized “technical”solutions to particular environmental conditions. The results of millions of years ofbiological evolution of millions of species are freely available to scientists thatbegin looking to nature’s solutions for ideas. The most exciting of these solutionshappen on surfaces, the boundary layer, and interface between solids and theirgaseous or liquid environment. Surfaces define the boundaries for thewell-structured world of solids, and it is surfaces that define their interactions.

Concise and systematic research in biology and technical innovations startedonly in the 1970s. “Bionics,” “biomimicry,” and “biomimetics” are the terms usedfor this field. Until the 1980s, bionics concentrated on mechanical functions such asrobotics and airplane development. Surfaces did not really play a role—despite thefact that surfaces are an essential part of all solids.

In 1977, when I discovered the functions of biological hierarchical structuringand the self-cleaning abilities of certain plant surfaces such as lotus leaves, Ipublished the results in German in a purely academic journal—exotic for anengineering audience. Nobody took any notice. Then, it was difficult for scientiststo talk across disciplines: different languages and seemingly different aims. Today,the cross-disciplinary field of biomimetics has changed this situation dramaticallyfor the better: engineers listen to biologists—and biologists are aware of technicalpotentials in their research and discuss them with materials scientists.

There is one outstanding scientist who has reinforced this process: ProfessorBharat Bhushan. Bharat, a materials engineer/physicist by education and practice andnot a botanist, became interested in bionics in the 1990s. He recognized the enormousimportance of biomimetic materials and their surfaces for technical applications.When the first edition of his “Biomimetics—Bioinspired Hierarchical-Structured

vii

Surfaces” appeared in 2012, it was an inspiration to scientists; for students this wasthe first time a comprehensive textbook was available.

Now, the amended second edition is available that recapitulates and expands onthe first edition to provide a comprehensive review of the field. It covers not onlytopics such as lotus leaves, rose petals, and salvinia leaves, but is pushingboundaries looking at low drag and antifouling properties of shark skin, rice leaves,and butterfly wings. The book covers broad biomimetic topics from solid expla-nations of superphobic/superphilic, self-cleaning, and antifouling surfaces (lotus,rose petal, salvinia, rice leaf, and butterfly wings), to more discrete topics includingstructural coloration (butterfly wings), mechanical toughness and durability (nacre),and reversible adhesion (gecko feet). The book even ventures beyond the sciencesto discuss the influence of biomimetics on art and architecture. As a biologist, Icongratulate him and I am convinced it will be a great success and an importantresource for all scholars of biomimetics.

Bonn Dr. Wilhelm BarthlottProfessor Emeritus of Botany and Former Director

of the Nees Institute for Biodiversity of PlantsUniversity of Bonn

Member of the National Academy of Sciences LeopoldinaMember of the Academy of Sciences and Literature Mainz

Foreign Member of the Linnean Society of London

viii Foreword

Preface (Second Edition)

The field of biomimetics or bioinspired hierarchically structured surfaces started totake off in the late 1990s with major developments in nanoscience and nanotech-nology. The latter made it possible to create natural surfaces with features rangingfrom the molecular scale to the macroscale. The interest in green science andtechnology has also provided impetus for advancement. The field is highly inter-disciplinary, spanning from biology, physics, chemistry, materials science, andengineering. As of 2015, the field contains only a handful of visionaries andcontributors.

Since the early 2000s, there have been significant advances in research, andmany ideas have started to be commercialized. With continued understanding of themechanisms relevant in species of living nature and development of new materialsand nanofabrication techniques, rapid advancements are expected in the next dec-ade and beyond. It is expected that new inventions will play a major role in humanlife. This author is fortunate to be one of the early pioneers in the field.

The second edition of the book provides a state of the art of the biomimetics fieldprimarily related to interface science. The book is targeted to various audiencesincluding novices as well as experts in the field, practitioners, solution seekers, andthe curious. It should help in advancement of the field.

The book is based on the work of past and present collaborators. These includethe following:

Past and present students:

Zach Burton, Yong Chae Jung, James Hunt, Robert A. Sayer, and Eun Kyu Her(Seoul National University, Korea); Brian Dean, Daniel Ebert, Gregory D. Bixler,and Srimala Perara (University of Moratuwa, Sri Lanka); Andrew Theiss and ShanPeng (Wuhan University of Science and Technology, China); and Samuel Martin.

Past and present postdoctoral fellows and visitors:

Dr. Michael Nosonovsky (University of Wisconsin, Milwaukee), Dr. Andrei G.Peressadko (Russia), Dr. Tae-Wan Kim (Pukyong National University, Korea),

ix

Prof. Kerstin Koch (University of Bonn, Germany), Dr. Manuel L. B. Palacio(Western Digital Corp., San Jose, California), Dr. Hyungoo Lee, Dr. P.K. Muthiah,Dr. Yongxin Wang, and Dr. Philip S. Brown.

External Collaborators:

Professor Wilhelm Barthlott (University of Bonn, Germany), Dr. E.S. Yoon (KIST,Korea), Dr. Patrick Hoffman (EPFL, Lausanne, Switzerland), Dr. Andre Meister(CSEM, Switzerland), Prof. Scott. C. Schricker (Ohio State University, Columbus,Ohio), Prof. Joao F. Mano (University of Minho, Guimaraes, Portugal), Dr. JiyuSun (Jilin University, China), Prof. Shunsuke Nishimoto (Okayama University,Japan), Prof. Stanislav N. Gorb (University of Kiel, Germany), Prof. Eduard Arzt(Max Planck Institute for Metals Research, Stuttgart, Germany), and Prof.Stephen C. Lee (Ohio State University, Columbus, Ohio).

Next, the author would like to thank Renee L. Ripley for many importantcontributions during preparation of the manuscript including major edits in themanuscript, architectural content, figure drawings, and constant input based on hervast experience. Finally, author would like to thank his wife Sudha for her constantsupport and encouragement.

Columbus, Ohio Bharat Bhushan

x Preface (Second Edition)

Preface (First Edition)

Nature has developed materials, objects, and processes that function from themacroscale to the nanoscale. The emerging field of biomimetics allows one tomimic biology or nature to develop nanomaterials, nanodevices, and processeswhich provide desirable properties. Hierarchical structures with dimensions offeatures ranging from the macroscale to the nanoscale are extremely common innature to provide properties of interest. The biologically inspired materials andstructured surfaces are eco-friendly or green with minimum human impact on theenvironment and are being explored for various commercial applications. Thisrecognition has led to “Green Science and Technology,” the term used for the firsttime in this book.

There are a large number of objects including bacteria, plants, land and aquaticanimals, and seashells with properties of commercial interest. The book presents anoverview of the general field of biomimetics and biomimetics-inspired surfaces. Itdeals with various examples of biomimetics, which include surfaces withroughness-induced superomniphobicity, self-cleaning, antifouling, and controlledadhesion. It primarily focuses on the lotus effect which exhibits superhydropho-bicity, self-cleaning, antifouling, low adhesion, and drag reduction. The book alsoincludes the floating water fern which floats over water, rose petal effect which canprovide either low adhesion or high adhesion, oleophobic/oleophilic surfacesinspired from aquatic animals, shark skin which exhibits low drag and antifouling,and gecko feet which exhibits reversible adhesion.

The book provides theoretical background, characterization of natural objects,and relevant mechanisms and inspired structured surface of commercial interest.We hope the book would serve as a catalyst for further innovations as well as serveas a useful reference in the emerging field of biomimetics. The book should alsoserve as an excellent text for a one-semester graduate course in biomimetics or as acompanion text for a general course in nanotechnology. Given the interdisciplinarynature of the discipline, the appeal of the book is expected to be broad.

The work reported in the book is largely based on the pioneering contributionsmade by former and present students, postdoctoral fellows, and visiting scholars.

xi

Special mention is deserved by Dr. Yong Chae Jung, a former Ph.D. studentworking in fabrication and characterization; Prof. Michael Nosonovsky, a formervisiting scholar and an ongoing collaborator in theoretical modeling; and Prof.Kerstin Koch of Nees Institute for Biodiversity of Plants at University of Bonn,Germany, who spent a sabbatical year in the author’s laboratory. All of themcontributed immensely to the research on the lotus effect. Dr. Tae-Wan Kim, avisiting scholar, contributed immensely on theoretical modeling of GeckoAdhesion. Brian Dean, a graduate student, contributed to the understanding of themechanisms of the shark skin effect. Other postdoctoral fellows and students whohave contributed include Dr. Andrei G. Peressadko (gecko adhesion), Zack Burton(lotus effect), Eun Kyu Her (rose petal effect), Robert Sayer (gecko adhesion),James Hunt (salvinia effect), Daniel Ebert (lotus effect), and Dr. Hyungoo Lee(gecko adhesion). Finally, the author would like to thank Caterina Runyon-Spearsfor administrative support.

My special thanks go to my wife Sudha, who has been forbearing of my 24/7commitment to science.

Columbus, Ohio Bharat Bhushan

xii Preface (First Edition)

Contents

1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Lessons from Nature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.4 Golden Ratio and Fibonacci Numbers. . . . . . . . . . . . . . . . . . . 71.5 Biomimetics in Art and Architecture—Bioarchitecture . . . . . . . 121.6 Industrial Significance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161.7 Research Objective and Approach . . . . . . . . . . . . . . . . . . . . . 191.8 Organization of the Book . . . . . . . . . . . . . . . . . . . . . . . . . . . 19References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2 Roughness-Induced Superliquiphilic/phobic Surfaces:Lessons from Nature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232.2 Wetting States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232.3 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252.4 Natural Superhydrophobic, Self-cleaning,

Low Adhesion/Drag Reduction Surfaces with Antifouling . . . . . 272.5 Natural Superhydrophobic and High Adhesion Surfaces . . . . . . 282.6 Natural Superoleophobic Self-cleaning and Low Drag Surfaces

with Antifouling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292.7 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3 Modeling of Contact Angle for a Liquid in Contactwith a Rough Surface for Various Wetting Regimes . . . . . . . . . . . 353.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353.2 Contact Angle Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . 353.3 Homogeneous and Heterogeneous Interfaces

and the Wenzel, Cassie-Baxter and Cassie Equations . . . . . . . . 37

xiii

3.3.1 Limitations of the Wenzel and Cassie-BaxterEquations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

3.3.2 Range of Applicability of the Wenzeland Cassie-Baxter Equations . . . . . . . . . . . . . . . . . . . 45

3.4 Contact Angle Hysteresis . . . . . . . . . . . . . . . . . . . . . . . . . . . 493.5 Stability of a Composite Interface and Role of Hierarchical

Structure with Convex Surfaces . . . . . . . . . . . . . . . . . . . . . . . 513.6 The Cassie-Baxter and Wenzel Wetting Regime Transition . . . . 553.7 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

4 Lotus Effect Surfaces in Nature . . . . . . . . . . . . . . . . . . . . . . . . . . 634.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634.2 Plant Leaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634.3 Characterization of Superhydrophobic and Hydrophilic

Leaf Surfaces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664.3.1 Experimental Techniques. . . . . . . . . . . . . . . . . . . . . . 664.3.2 SEM Micrographs . . . . . . . . . . . . . . . . . . . . . . . . . . 674.3.3 Contact Angle Measurements. . . . . . . . . . . . . . . . . . . 674.3.4 Surface Characterization Using an Optical

Profiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 704.3.5 Surface Characterization, Adhesion,

and Friction Using an AFM. . . . . . . . . . . . . . . . . . . . 714.3.6 Role of the Hierarchical Roughness . . . . . . . . . . . . . . 774.3.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

4.4 Various Self-cleaning Approaches . . . . . . . . . . . . . . . . . . . . . 794.4.1 Comparison Between Superhydrophobic

and Superhydrophilic Surface Approachesfor Self-cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

4.4.2 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 824.5 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

5 Nanofabrication Techniques Used for Lotus-Like Structures . . . . . 855.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855.2 Roughening to Create One-Level Structure . . . . . . . . . . . . . . . 865.3 Coatings to Create One-Level Structures . . . . . . . . . . . . . . . . . 905.4 Methods to Create Two-Level (Hierarchical) Structures. . . . . . . 925.5 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

6 Fabrication and Characterization of Micro-,Nano- and Hierarchically Structured Lotus-Like Surfaces . . . . . . . 976.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 976.2 Experimental Techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

xiv Contents

6.2.1 Contact Angle, Surface Roughness,and Adhesion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

6.2.2 Droplet Evaporation Studies . . . . . . . . . . . . . . . . . . . 1006.2.3 Bouncing Droplet Studies . . . . . . . . . . . . . . . . . . . . . 1006.2.4 Vibrating Droplet Studies . . . . . . . . . . . . . . . . . . . . . 1006.2.5 Microdroplet Condensation and Evaporation Studies

Using ESEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1016.2.6 Generation of Submicron Droplets . . . . . . . . . . . . . . . 1016.2.7 Waterfall/Jet Tests . . . . . . . . . . . . . . . . . . . . . . . . . . 1046.2.8 Wear and Friction Tests . . . . . . . . . . . . . . . . . . . . . . 1056.2.9 Transmittance Measurements . . . . . . . . . . . . . . . . . . . 106

6.3 Micro- and Nanopatterned Polymers . . . . . . . . . . . . . . . . . . . . 1066.3.1 Contact Angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1086.3.2 Effect of Submicron Droplet on Contact Angle . . . . . . 1096.3.3 Adhesive Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1106.3.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

6.4 Micropatterned Si Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . 1116.4.1 Cassie-Baxter and Wenzel Transition Criteria. . . . . . . . 1146.4.2 Effect of Pitch Value on the Transition . . . . . . . . . . . . 1166.4.3 Observation of Transition During the Droplet

Evaporation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186.4.4 Another Cassie-Baxter and Wenzel Transition

for Different Series . . . . . . . . . . . . . . . . . . . . . . . . . . 1226.4.5 Contact Angle Hysteresis and Wetting/Dewetting

Asymmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1246.4.6 Contact Angle Measurements During

Condensation and Evaporation of Microdropletson Micropatterned Surfaces . . . . . . . . . . . . . . . . . . . . 128

6.4.7 Observation of Transition During the BouncingDroplet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

6.4.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1366.5 Ideal Surfaces with Hierarchical Structure . . . . . . . . . . . . . . . . 1366.6 Hierarchically Structured Surfaces with Wax Platelets

and Tubules Using Nature’s Route . . . . . . . . . . . . . . . . . . . . . 1376.6.1 Effect of Nanostructures with Various

Wax Platelet Crystal Densitieson Superhydrophobicity . . . . . . . . . . . . . . . . . . . . . . 142

6.6.2 Effect of Hierarchical Structure with WaxPlatelets on the Superhydrophobicity . . . . . . . . . . . . . 146

6.6.3 Effect of Hierarchical Structure with WaxTubules on Superhydrophobicity . . . . . . . . . . . . . . . . 150

6.6.4 Self-cleaning Efficiency of Hierarchically StructuredSurfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

Contents xv

6.6.5 Observation of Transition During the BouncingDroplet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

6.6.6 Observation of Transition During the VibratingDroplet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

6.6.7 Measurement of Fluid Drag Reduction . . . . . . . . . . . . 1676.6.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

6.7 Mechanically Durable Superhydrophobic Surfaces . . . . . . . . . . 1696.7.1 CNT Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . 1706.7.2 Nanoparticle Composites with Hierarchical

Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1796.7.3 Nanoparticle Composites for Optical

Transparency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1866.8 Superhydrophobic Paper Surfaces. . . . . . . . . . . . . . . . . . . . . . 1976.9 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198

7 Fabrication and Characterization of MicropatternedStructures Inspired by Salvinia molesta . . . . . . . . . . . . . . . . . . . . . 2057.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2057.2 Characterization of Leaves and Fabrication of Inspired

Structural Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2077.3 Measurement of Contact Angle and Adhesion . . . . . . . . . . . . . 209

7.3.1 Observation of Pinning and Contact Angle . . . . . . . . . 2097.3.2 Adhesion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210

7.4 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212

8 Characterization of Rose Petals and Fabricationand Characterization of Superhydrophobic Surfaceswith High and Low Adhesion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2138.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2138.2 Characterization of Two Kinds of Rose Petals and Their

Underlying Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2148.3 Fabrication of Surfaces with High and Low Adhesion

for Understanding of Rose Petal Effect . . . . . . . . . . . . . . . . . . 2218.4 Fabrication of Mechanically Durable, Superhydrophobic

Surfaces with High Adhesion. . . . . . . . . . . . . . . . . . . . . . . . . 2308.4.1 Samples with Hydrophilic ZnO Nanoparticles

(Before ODP Modification) . . . . . . . . . . . . . . . . . . . . 2318.4.2 Samples with Hydrophobic ZnO Nanoparticles

(After ODP Modification) . . . . . . . . . . . . . . . . . . . . . 2338.4.3 Wear Resistance in AFM Wear Experiment . . . . . . . . . 237

8.5 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240

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9 Modeling, Fabrication, and Characterization of Superoleophobic/Philic Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2439.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2439.2 Strategies to Achieve Superoleophobicity in Air. . . . . . . . . . . . 247

9.2.1 Fluorination Techniques . . . . . . . . . . . . . . . . . . . . . . 2489.2.2 Re-entrant Geometry. . . . . . . . . . . . . . . . . . . . . . . . . 250

9.3 Model to Predict Oleophobic/Philic Nature of Surfaces . . . . . . . 2529.4 Validation of Oleophobicity/Philicity Model for Oil

Droplets in Air and Water . . . . . . . . . . . . . . . . . . . . . . . . . . . 2559.4.1 Experimental Techniques. . . . . . . . . . . . . . . . . . . . . . 2559.4.2 Fabrication of Oleophobic/Philic Surfaces . . . . . . . . . . 2569.4.3 Characterization of Oleophobic/Philic Surfaces. . . . . . . 2579.4.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264

9.5 Mechanically Durable Nanoparticle Composite Coatingsfor Superoleophobicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2649.5.1 Experimental Details. . . . . . . . . . . . . . . . . . . . . . . . . 2719.5.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 2739.5.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281

9.6 Mechanically Durable Nanoparticle Composite Coatingsfor Superliquiphilicity and Superliquiphobicity UsingLayer-by-Layer Technique. . . . . . . . . . . . . . . . . . . . . . . . . . . 2829.6.1 Experimental Details. . . . . . . . . . . . . . . . . . . . . . . . . 2859.6.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 2889.6.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

9.7 Mechanically Durable Superoleophobic AluminumSurfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2999.7.1 Experimental Details. . . . . . . . . . . . . . . . . . . . . . . . . 3039.7.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 3059.7.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314

9.8 Mechanically Durable Superoleophobic Polymer Surfaces . . . . . 3149.8.1 Experimental Details. . . . . . . . . . . . . . . . . . . . . . . . . 3159.8.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 3169.8.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

9.9 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

10 Shark-Skin Surface for Fluid-Drag Reduction in TurbulentFlow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32710.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32710.2 Fluid Drag Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

10.2.1 Mechanisms of Fluid Drag . . . . . . . . . . . . . . . . . . . . 32910.2.2 Shark Skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

10.3 Experimental Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33210.3.1 Flow Visualization Studies . . . . . . . . . . . . . . . . . . . . 33410.3.2 Riblet Geometries and Configurations . . . . . . . . . . . . . 334

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10.3.3 Riblet Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . 33610.3.4 Drag Measurement Techniques . . . . . . . . . . . . . . . . . 34110.3.5 Riblet Results and Discussion . . . . . . . . . . . . . . . . . . 34610.3.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361

10.4 Fluid Flow Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36210.4.1 Riblet Geometry Models . . . . . . . . . . . . . . . . . . . . . . 36410.4.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 36710.4.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370

10.5 Application of Riblets for Drag Reduction and Antifouling . . . . 37310.6 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377

11 Rice Leaf and Butterfly Wing Effect . . . . . . . . . . . . . . . . . . . . . . . 38311.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38311.2 Inspiration from Living Nature. . . . . . . . . . . . . . . . . . . . . . . . 383

11.2.1 Ambient Species—Lotus Effect . . . . . . . . . . . . . . . . . 38311.2.2 Aquatic Species—Shark Skin and Fish Scales

Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38411.2.3 Ambient Species—Rice Leaf and Butterfly

Wing Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38411.3 Sample Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386

11.3.1 Actual Sample Replicas. . . . . . . . . . . . . . . . . . . . . . . 38611.3.2 Rice Leaf Inspired Surfaces . . . . . . . . . . . . . . . . . . . . 387

11.4 Pressure Drop Measurement Technique. . . . . . . . . . . . . . . . . . 39211.5 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395

11.5.1 Surface Characterization . . . . . . . . . . . . . . . . . . . . . . 39611.5.2 Pressure Drop Measurements . . . . . . . . . . . . . . . . . . . 40011.5.3 Wettability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41111.5.4 Drag Reduction Models . . . . . . . . . . . . . . . . . . . . . . 413

11.6 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420

12 Bio- and Inorganic Fouling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42312.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42312.2 Fields Susceptible to Fouling . . . . . . . . . . . . . . . . . . . . . . . . . 42312.3 Biofouling and Inorganic Fouling Formation Mechanisms . . . . . 427

12.3.1 Biofouling Formation . . . . . . . . . . . . . . . . . . . . . . . . 42812.3.2 Inorganic Fouling Formation . . . . . . . . . . . . . . . . . . . 43012.3.3 Surface Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430

12.4 Antifouling Strategies from Living Nature . . . . . . . . . . . . . . . . 43312.5 Antifouling: Current Prevention and Cleaning Techniques . . . . . 437

12.5.1 Prevention Techniques . . . . . . . . . . . . . . . . . . . . . . . 43712.5.2 Self-cleaning Surfaces and Cleaning Techniques. . . . . . 440

12.6 Bioinspired Rice Leaf Surfaces for Antifouling . . . . . . . . . . . . 441

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12.6.1 Fabrication of Micropatterned Samples . . . . . . . . . . . . 44312.6.2 Anti-biofouling Measurements . . . . . . . . . . . . . . . . . . 44412.6.3 Anti-inorganic Fouling Measurements . . . . . . . . . . . . . 44512.6.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 44612.6.5 Anti-biofouling and Anti-inorganic Fouling

Mechanisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44912.7 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452

13 Gecko Adhesion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45713.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45713.2 Hairy Attachment Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 45813.3 Tokay Gecko. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462

13.3.1 Construction of Tokay Gecko . . . . . . . . . . . . . . . . . . 46213.3.2 Adhesion Enhancement by Division of Contacts

and Multilevel Hierarchical Structure . . . . . . . . . . . . . 46413.3.3 Peeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46613.3.4 Self Cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470

13.4 Attachment Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47213.4.1 van der Waals Forces . . . . . . . . . . . . . . . . . . . . . . . . 47313.4.2 Capillary Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474

13.5 Adhesion Measurements and Data . . . . . . . . . . . . . . . . . . . . . 47613.5.1 Adhesion Under Ambient Conditions . . . . . . . . . . . . . 47613.5.2 Effects of Temperature . . . . . . . . . . . . . . . . . . . . . . . 47813.5.3 Effects of Humidity . . . . . . . . . . . . . . . . . . . . . . . . . 47913.5.4 Effects of Hydrophobicity . . . . . . . . . . . . . . . . . . . . . 479

13.6 Adhesion Modeling of Fibrillar Structures . . . . . . . . . . . . . . . . 48013.6.1 Single Spring Contact Analysis . . . . . . . . . . . . . . . . . 48213.6.2 The Multi-level Hierarchical Spring Analysis . . . . . . . . 48413.6.3 Adhesion Results of the Multi-level Hierarchical

Spring Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48813.6.4 Capillary Effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . 494

13.7 Adhesion Data Base of Fibrillar Structures . . . . . . . . . . . . . . . 49813.7.1 Fiber Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49913.7.2 Single Fiber Contact Analysis . . . . . . . . . . . . . . . . . . 49913.7.3 Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50013.7.4 Non-fiber Fracture Condition . . . . . . . . . . . . . . . . . . . 50213.7.5 Numerical Simulation . . . . . . . . . . . . . . . . . . . . . . . . 50413.7.6 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 505

13.8 Fabrication of Gecko Skin-Inspired Structures . . . . . . . . . . . . . 50913.8.1 Single Level Roughness Structures . . . . . . . . . . . . . . . 51013.8.2 Multi-level Hierarchical Structures . . . . . . . . . . . . . . . 517

13.9 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524

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14 Structure and Mechanical Properties of Nacre. . . . . . . . . . . . . . . . 53114.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53114.2 Hierarchical Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533

14.2.1 Columnar and Sheet Structure . . . . . . . . . . . . . . . . . . 53314.2.2 Mineral Bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53514.2.3 Polygonal Nanograins . . . . . . . . . . . . . . . . . . . . . . . . 53614.2.4 Inter-Tile Toughening Mechanism . . . . . . . . . . . . . . . 537

14.3 Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53814.4 Bioinspired Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54214.5 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545

15 Structural Coloration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54915.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54915.2 Physical Mechanisms of Structural Colors . . . . . . . . . . . . . . . . 552

15.2.1 Film Interference . . . . . . . . . . . . . . . . . . . . . . . . . . . 55215.2.2 Diffraction Gratings . . . . . . . . . . . . . . . . . . . . . . . . . 55415.2.3 Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55515.2.4 Photonic Crystals . . . . . . . . . . . . . . . . . . . . . . . . . . . 55515.2.5 Coloration Changes . . . . . . . . . . . . . . . . . . . . . . . . . 556

15.3 Lessons from Living Nature . . . . . . . . . . . . . . . . . . . . . . . . . 55715.3.1 Film Interference . . . . . . . . . . . . . . . . . . . . . . . . . . . 55815.3.2 Diffraction Grating . . . . . . . . . . . . . . . . . . . . . . . . . . 56215.3.3 Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56515.3.4 Photonic Crystals . . . . . . . . . . . . . . . . . . . . . . . . . . . 56615.3.5 Coloration Changes . . . . . . . . . . . . . . . . . . . . . . . . . 569

15.4 Bioinspired Fabrication and Applications. . . . . . . . . . . . . . . . . 57115.5 Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573

16 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583

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Biography and Photograph of Author

Dr. Bharat Bhushan received an M.S. in mechanicalengineering from the Massachusetts Institute ofTechnology in 1971, an M.S. in mechanics and aPh.D. in mechanical engineering from the Universityof Colorado at Boulder in 1973 and 1976, respec-tively; an MBA from Rensselaer Polytechnic Instituteat Troy, NY, in 1980; Doctor Technicae from theUniversity of Trondheim at Trondheim, Norway, in1990; a Doctor of Technical Sciences from theWarsaw University of Technology at Warsaw,Poland, in 1996; and Doctor Honouris Causa from theNational Academy of Sciences at Gomel, Belarus, in

2000, and University of Kragujevac, Serbia, in 2011. He is a registered professionalengineer. He is presently an Ohio Eminent Scholar and The Howard D. WinbiglerProfessor in the College of Engineering, and the Director of the NanoprobeLaboratory for Bio- and Nanotechnology and Biomimetics (NLBB) and affiliatedfaculty in John Glenn College of Public Affairs at the Ohio State University,Columbus, Ohio. In 2013–14, he served as an ASME/AAAS Science andTechnology Policy Fellow, House Committee on Science, Space and Technology,United States Congress, Washington, DC. His research interests include funda-mental studies with a focus on scanning probe techniques in the interdisciplinaryareas of bio/nanotribology, bio/nanomechanics and bio/nanomaterials characteri-zation and applications to bio/nanotechnology, and biomimetics. He is an inter-nationally recognized expert of bio/nanotribology and bio/nanomechanics usingscanning probe microscopy and is one of the most prolific authors. He is consideredby some a pioneer of the tribology and mechanics of magnetic storage devices. Hehas authored 8 scientific books, 90+ handbook chapters, 800+ scientific papers(h-index—76+; ISI Highly Cited Researcher in Materials Science since 2007 and inBiology and Biochemistry since 2013; ISI Top 5 % Cited Authors for Journals inChemistry since 2011), and 60+ technical reports. He has also edited 50+ books and

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holds 20 US and foreign patents. He is co-editor of Springer NanoScience andTechnology Series and co-editor of Microsystem Technologies, and member ofeditorial board of PNAS. He has given more than 400 invited presentations on sixcontinents and more than 200 keynote/plenary addresses at major internationalconferences.

Dr. Bhushan is an accomplished organizer. He organized the Ist Symposium onTribology and Mechanics of Magnetic Storage Systems in 1984 and the Ist Int.Symposium on Advances in Information Storage Systems in 1990, both of whichare now held annually. He organized two international NATO institutes in Europe.He is the founder of an ASME Information Storage and Processing SystemsDivision founded in 1993 and served as the founding chair during 1993–1998. Hisbiography has been listed in over two dozen Who’s Who books including Who’sWho in the World and has received more than two dozen awards for his contri-butions to science and technology from professional societies, industry, and USgovernment agencies including Life Achievement Tribology Award and Institutionof Chemical Engineers (UK) Global Award. His research was listed as the top tenscience stories of 2015. He is also the recipient of various international fellowshipsincluding the Alexander von Humboldt Research Prize for Senior Scientists, MaxPlanck Foundation Research Award for Outstanding Foreign Scientists, andFulbright Senior Scholar Award. He is a foreign member of the InternationalAcademy of Engineering (Russia), Byelorussian Academy of Engineering andTechnology, and the Academy of Triboengineering of Ukraine; an honorarymember of the Society of Tribologists of Belarus and STLE; a fellow of ASME,IEEE, and the New York Academy of Sciences; and a member of ASEE, Sigma Xi,and Tau Beta Pi.

Dr. Bhushan has previously worked for Mechanical Technology Inc., Latham,NY; SKF Industries Inc., King of Prussia, PA; IBM, Tucson, AZ; and IBMAlmaden Research Center, San Jose, CA. He has held visiting professorship atUniversity of California at Berkeley; University of Cambridge, UK; TechnicalUniversity Vienna, Austria; University of Paris, Orsay; ETH Zurich; EPFLLausanne; Univ. of Southampton, UK; Univ. of Kragujevac, Serbia; TsinghuaUniv., China; Harbin Inst., China; and KFUPM, Saudi Arabia.

xxii Biography and Photograph of Author