green tribology biomimetics, energy conservation and sustainability

These problems include tribologicaltechnology that mimics living nature biomimetic surfaces and thus is expected to be environment-friendly, the control of friction and wear that is of i

Green Energy and Technology

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Michael Nosonovsky • Bharat Bhushan Editors

Green Tribology

Biomimetics, Energy Conservation and Sustainability

123

Prof Michael Nosonovsky

Department of Mechanical Engineering

201 West 19th AvenueColumbus

OH 43210-1142USA

e-mail: bhushan.2@osu.edu

DOI 10.1007/978-3-642-23681-5

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Tribology (from the Greek word sqíbx ‘‘tribo’’ meaning ‘‘to rub’’) is the disciplinary area of science and technology that involves the study of the inter-action of solid surfaces in relative motion Typical tribological studies coverfriction, wear, lubrication, and adhesion These studies involve the efforts ofmechanical engineers, material scientists, chemists, and physicists The word

inter-‘‘tribology’’ was coined in the 1960s when it was realized that it may be beneficialfor engineers and scientists studying friction, lubrication, and wear to collaborate

in the framework of the new interdisciplinary area Since then, many new areas oftribological studies have been suggested, which are at the interface of variousscientific disciplines These areas include nanotribology, biotribology, the tribol-ogy of magnetic storage devices, and micro/nanoelectromechanical systems Theresearch in these areas is driven mostly by the advent of new technologies and newexperimental techniques for surfaces characterization

Green tribology is a new, separate research area that is emerging, and it isdefined as the science and technology of the tribological aspects of ecologicalbalance and of environmental and biological impacts There are a number oftribological problems that can be put under the umbrella of green tribology, andthey are of mutual benefit to one another These problems include tribologicaltechnology that mimics living nature (biomimetic surfaces) and thus is expected to

be environment-friendly, the control of friction and wear that is of importance forenergy conservation and conversion, environmental aspects of lubrication andsurface modification techniques, and tribological aspects of green applicationssuch as wind-power turbines, tidal turbines, or solar panels

Since the 2000s, there have been several publications dealing with the nomic and social implications of the ecological aspects of tribology Most of thesepapers were prepared by economists and people involved in the strategic planning

eco-of research The first scientific volume completely devoted to green tribology,which emphasized scientific rather than societal and economic aspects, appeared in

2010, and it was the theme issue of the Philosophical Transactions of the RoyalSociety, Series A (Volume 368, Number 1929) edited by M Nosonovsky and

B Bhushan In that volume, three areas of green tribology were identified:

v

biomimetic tribology, eco-friendly lubrication and materials, and tribologicalaspects of sustainable energy applications The assumption was that combiningthese three areas, rather than focusing on narrow issues such as biodegradablelubrication, would mutually enhance them and establish new connections Severalworkshops, conference sections, and symposia took place after that, which con-firmed this inclusive approach, as well as the interest in green tribology in general.The present publication in Springer to a certain degree extends that work:whereas some authors who participated in that volume also submitted their newresults into the present volume, new authors participated as well Prominentexperts in various areas were invited that fit the definition of Green Tribology Theinternational group of authors include tribologists from the U.S., the U.K., Austria,Australia, Canada, India, South Africa, China, Israel, and Malaysia Some of theauthors are from academic institutions, while others are practical engineers fromthe industry At University of Wisconsin–Milwaukee (UWM) a big group oftribologists has worked since 2009 on various aspects related to green tribology,and the results of their efforts are presented in the current volume The biomimeticsurfaces, including those using the Lotus, rose petal, gecko, and shark skin effects

as well as tribology of human skin and hair were studied actively at the Ohio StateUniversity (OSU) in the past decade

After a review of the current state of green tribology and its history, the maincontent of this book is divided into three parts First, biomimetics in tribology isdiscussed, including biomimetic surfaces, materials, and methods Biomimeticapproaches follow the ways found in living nature and thus are expected to be eco-friendly This includes non-adhesive surfaces mimicking flower (e.g., Lotus androse) leaves, wetting transitions on these surfaces, biomimetic adhesion control forantifouling, polymeric and metal-based composite materials, and surfaces capable

of friction-induced organization (lubrication, cleaning, and healing) as well as biomimetics in nanotribology Second, green and sustainablematerials and lubricants are reviewed This involves water, ice, and natural oil-based lubrication, eco-friendly products for tribological applications involvingnatural fiber reinforced composites, fly ash, cements, and lubricant additives Thethird part includes tribology of eco-friendly applications, such as wind turbines,biorefinaries, and marine wave energy collectors Some of the chapters emphasizethe review of the current state of the area, while others stress the research con-ducted by the investigators

self-We would like to thank our colleagues, the authors, who responded to ourinvitations and contributed to this edited book In addition, we would like toacknowledge help in preparation of the manuscripts of Ms Caterina Runyon-Spears (OSU) and Mr Mehdi Mortazavi (UWM)

Bharat Bhushan

Michael Nosonovsky and Bharat Bhushan

Michael Nosonovsky and Bharat Bhushan

Michael Nosonovsky and Vahid Mortazavi

of Biofouling: Cell Adhesions to Three-Dimensional

Chang-Hwan Choi and Chang-Jin Kim

I C Gebeshuber

Edward Bormashenko and Gene Whyman

Vahid Hejazi and Michael Nosonovsky

vii

8 Polymer Adhesion and Biomimetic Surfaces

Mehdi Mortazavi and Michael Nosonovsky

Anne-Marie Kietzig

Pradeep L Menezes, Michael R Lovell, M A Kabir,

C Fred Higgs III and Pradeep K Rohatgi

K R Sathwik Chatra, N H Jayadas and Satish V Kailas

Pradeep L Menezes, Pradeep K Rohatgi and Michael R Lovell

R Pai and D J Hargreaves

W Li, X H Kong, M Ruan, F M Ma, X H Zuo and Y Chen

Konstantin Sobolev

Pradeep K Rohatgi, Pradeep L Menezes and Michael R Lovell

Pradeep L Menezes, Pradeep K Rohatgi and Michael R Lovell

Elon J Terrell, William M Needelman and Jonathan P Kyle

19 Ecological Aspects of Water Desalination Improving

Tyler G Hurd, Saman Beyhaghi and Michael Nosonovsky

P L de Vaal, L F Barker, E du Plessis and D Crous

Andrew Fronek, Michael Nosonovsky, Ben Barger and Ilya Avdeev

53211-0413, USA, e-mail: avdeev@uwm.edu

Wisconsin–Milwaukee, North Cramer Street 3200, Milwaukee, WI 53211-0413,USA, e-mail: bdbarger@uwm.edu

Africa, e-mail: Leslie.barker@eskom.co.za

Wisconsin–Milwaukee, North Cramer Street 3200, Milwaukee, WI 53211-0413,USA, e-mail: beyhagh2@uwm.edu

OH 43210-1142, USA, e-mail: bhushan.2@osu.edu

Samaria, P.O.B 3, Ariel 40700, Israel, e-mail: edward@ariel.ac.il

Science, Bangalore 560 012, India, e-mail: sathwikchathra@gmail.com

Reuse, School of Chemical and Materials Engineering, Huangshi Institute of nology, Huangshi 435003, People’s Republic of China, e-mail: ychen21@163.com

on Hudson, Stevens Institute of Technology, Hoboken, NJ 07030, USA, e-mail:Chang-Hwan.Choi@stevens.edu

Pretoria, South Africa, e-mail: i_dc_i@yahoo.com

xi

P L de Vaal Department of Chemical Engineering University of Pretoria,Pretoria, South Africa, e-mail: pdv@up.ac.za

Silverton 0127, South Africa, e-mail: producut@icon.co.za

Wisconsin–Milwaukee, North Cramer Street 3200, Milwaukee, WI 53211-0413,USA, e-mail: ajfronek@gmail.com

(IMEN), Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Selangor,Malaysia, e-mail: ille.gebeshuber@mac.com; ille.gebeshuber@ukm.my

University of Technology, P.O Box 2434, Brisbane 4001, Australia, e-mail:d.hargreaves@qut.edu.au

Milwaukee, North Cramer Street 3200, Milwaukee, WI 53211-0413, USA, e-mail:vhejazi@uwm.edu

University, 5000 Forbes Avenue, Pittsburgh, PA 15213-3890, Australia, e-mail:higgs@andrew.cmu.edu

Wisconsin–Milwaukee, North Cramer Street 3200, Milwaukee, WI 53211-0413,USA, e-mail: tghurd@uwm.edu

Sci-ence and Technology, Ernakulam 682 022, India, e-mail: jayadasnh@cusat.ac.in

e-mail: mohd.kabir@netl.doe.gov

of Science, Bangalore 560 012, India, e-mail: satish.kailas@gmail.com;satvk@mecheng.iisc.ernet.in

anne.kietzig@mcgill.ca

University of California, 3610 University Street, Los Angeles, CA 90095, USA,e-mail: cjkim@seas.ucla.edu

Reuse, School of Chemical and Materials Engineering, Huangshi Institute of nology, Huangshi 435003, People’s Republic of China, e-mail: xkong@ualberta.ca

Jonathan P Kyle Mechanical Engineering Department, Columbia University,S.W Mudd, Room 220B 500 West 120th St., New York, NY 10027, USA, e-mail:jpk2128@columbia.edu

Reuse, School of Chemical and Materials Engineering, Huangshi Institute of nology, Huangshi 435003, People’s Republic of China, e-mail: wenl@ualberta.ca

53201, USA, e-mail: mlovell@uwm.edu

Reuse, School of Chemical and Materials Engineering, Huangshi Institute of nology, Huangshi 435003, People’s Republic of China, e-mail: fmma1@yahoo.cn

Milwaukee, Milwaukee, WI 53211-0413, USA, e-mail: menezesp@uwm.edu

Wisconsin–Milwaukee, North Cramer Street 3200, Milwaukee, WI 53211-0413,USA, e-mail: mortaza3@uwm.edu

Wisconsin–Milwaukee, North Cramer Street 3200, Milwaukee, WI 53211-0413,USA, e-mail: mortaza2@uwm.edu

NY 11743, USA, e-mail: bill.needelman@donaldson.com

of Wisconsin–Milwaukee, North Cramer Street 3200, Milwaukee, WI

53211-0413, USA, e-mail: nosonovs@uwm.edu

Manipal Institute of Technology, Manipal University, 5000 Forbes Avenue,Manipal 576104, India, e-mail: raghuvir.pai@manipal.edu

Composites, University of Wisconsin–Milwaukee, P.O Box 784, Milwaukee,

WI 53201, USA, e-mail: prohatgi@uwm.edu

Reuse, School of Chemical and Materials Engineering, Huangshi Institute of nology, Huangshi 435003, People’s Republic of China, e-mail: rm@126.com

Wisconsin–Milwaukee, EMS 939 3200 North Cramer Street, P.O Box 784,Milwaukee, WI 53211, USA, e-mail: sobolev@uwm.edu

Elon J TerrellMechanical Engineering Department, Columbia University, S.W.Mudd, Room 220C 500 West 120th St., New York, NY 10027, USA, e-mail:eterrell@columbia.edu

P.O.B 3, Ariel 40700, Israel, e-mail: gevaiman@ariel.ac.il

Reuse, School of Chemical and Materials Engineering, Huangshi Institute of nology, Huangshi 435003, People’s Republic of China, e-mail: xhzuo@126.com

Part I Introduction

Chapter 1

Green Tribology, its History, Challenges,

and Perspectives

Michael Nosonovsky and Bharat Bhushan

areas of tribology is discussed as well as other ‘‘green’’ disciplines, namely, greenengineering and green chemistry The twelve principles of green tribology areformulated: the minimization of (1) friction and (2) wear, (3) the reduction orcomplete elimination of lubrication, including self-lubrication, (4) natural and(5) biodegradable lubrication, (6) using sustainable chemistry and engineeringprinciples, (7) biomimetic approaches, (8) surface texturing, (9) environmentalimplications of coatings, (10) real-time monitoring, (11) design for degradation,and (12) sustainable energy applications Three areas of green tribology are furtherdefined: (1) biomimetics for tribological applications, (2) environment-friendlylubrication, and (3) the tribology of renewable energy application The integration

of these areas remains a primary challenge for this novel area of research Thechallenges of green tribology and future directions of research are also discussed

1.1 Introduction

Tribology (from the Greek word sqi9bx ‘‘tribo’’ meaning ‘‘to rub’’) is defined bythe Oxford dictionary as ‘‘the branch of science and technology concerned withinteracting surfaces in relative motion and with associated matters (as friction,

M Nosonovsky

College of Engineering and Applied Science, University of Wisconsin,

Milwaukee, WI 53201, USA

B Bhushan ( &)

Nanoprobe Laboratory for Bio- and Nanotechnology and Biomimetics (NLB2),

The Ohio State University, 201 W 19th Avenue,

Columbus, OH 43210-1142, USA

e-mail: bhushan.2@osu.edu

M Nosonovsky and B Bhushan (eds.), Green Tribology,

Green Energy and Technology, DOI: 10.1007/978-3-642-23681-5_1,

 Springer-Verlag Berlin Heidelberg 2012

3

wear, lubrication, and the design of bearings—Oxford English Dictionary)’’ Theword ‘‘tribophysics’’ was used already in the 1940s by David Tabor and Philip

The term ‘‘tribology’’ was officially introduced in 1966 by Prof H Peter Jost, thenthe chairman of a working group of lubrication engineers, in his published reportfor the U.K Department of Education and Science It was reported that huge sums

of money had been lost in the UK annually due to the consequences of friction,wear, and corrosion Therefore, it was strongly recommended to unite multidis-ciplinary scientific and engineering efforts in these areas, so that they could benefitfrom one another As a result, several centers for tribology were created in manycountries Since then the term has diffused into the international engineering field;various tribological organizations and societies have been established, such as theSociety of Tribologists and Lubrication Engineers (STLE), and many specialistsnow claim to be tribologists

Typical tribological studies cover friction, wear, lubrication, and adhesion andinvolve the efforts of mechanical engineers, material scientists, chemists, and

ago, many new areas of tribological studies have developed which are at theinterface of various scientific disciplines, and various aspects of interacting sur-faces in relative motion have been the focus of tribology These areas include, forexample, nanotribology, biotribology, the tribology of magnetic storage devicesand micro/nanoelectromechanical systems (MEMS/NEMS), and adhesive contact

technologies and new experimental techniques for surface characterization.Few researchers have reported the need for ecological or ‘‘green’’ tribology

the environment are the most important aspects of ecotribology In the course ofrelevant practices savings of basic resources and materials, optimum design,optimum operation, reduced energy consumption and the protection of the envi-ronment have to be covered… Using environmentally acceptable lubricants is thekey factor for this.’’ He suggested a diagram which he called ‘‘ECO-Balance-

the need for ecological tribology, which he considered a response to the worldeconomic and financial crisis of 2008 as well as the global worming crisis asreflected by the ‘‘Kyoto Protocol.’’ The new concept of ‘‘green tribology’’ has beendefined as ‘‘the science and technology of the tribological aspects of ecological

need for green tribology and has mentioned that the influence of economic,market, and financial triumphalisms have retarded tribology and could retard

‘green tribology’ from being accepted as a not-unimportant factor in its field…Therefore, by highlighting the economic benefits of tribology, tribology societies,groups and committees are likely to have a far greater impact on the makers ofpolicies and the providers of funding than by only preaching the scientific logic…Tribology societies should highlight to the utmost the economic advantage of

tribology It is the language financial oriented policy makers and markets, as well

as governments, understand

These earlier mentions by researchers called scientists to pay attention to greentribology; however, they did not define the field in a rigorous scientific or aca-demic manner The first scientific volume on green tribology emerged in 2010,when Philosophical Transaction of the Royal Society A, the oldest (published since1666) and one of the most prestigious research journals in the world, decided todevote a theme issue to ‘‘green tribology,’’ edited by M Nosonovsky and B.Bhushan In that volume, the editors defined green tribology in quite a broad way,

so that it encompassed biomimetic tribology (which follows the ways of livingnature to solve engineering problems, eco-friendly lubrication, and clean and

these areas under the umbrella of green tribology could enhance them all and help

to benefit from one another by establishing new links

Ten chapters were published in the theme issue Nosonovsky and Bhushan

wetting transitions on biomimetic superhydrophobic surfaces, while Bhushan and

effect and rose petal effect regimes Shark-skin effect surfaces were discussed by

reviewed the tribological aspects of wind power turbines, whereas Wood et al

lubricants

Several workshops, conference sections, and symposia took place after that,which confirmed the volume’s inclusive approach, as well as the interest in greentribology in general Green tribology topics have been covered at a number of

The specific field of green or environment-friendly tribology emphasizes theaspects of interacting surfaces in relative motion, which are of importance forenergy or environmental sustainability or which have impact upon today’s envi-ronment This includes tribological technology that mimics living nature (biomi-metic surfaces) and thus is expected to be environment friendly, the control offriction and wear that is of importance for energy conservation and conversion,environmental aspects of lubrication and surface modification techniques, andtribological aspects of green applications, such as wind-power turbines, tidal

prob-lems could be put under the umbrella of ‘‘green tribology’’ and are of mutualbenefit to one another

1.2 Green Tribology and Green Chemistry and Engineering

Green tribology can be viewed in the broader context of two other ‘green’ areas:green engineering and green chemistry The US Environmental Protection Agency(EPA) defined green engineering as ‘‘the design, commercialization and use ofprocesses and products that are technically and economically feasible whileminimizing (1) generation of pollution at the source (2) risk to human health and

in design involve: (1) process research and development, (2) liminary design, and (3) detailed design pollution prevention; process heat/energy

Another related area is green chemistry, also known as sustainable chemistry,which is defined as ‘‘the design of chemical products and processes that reduce or

chemistry is on minimizing the hazard and maximizing the efficiency of anychemical choice It is distinct from environmental chemistry which focuses onchemical phenomena in the environment While environmental chemistry studies thenatural environment as well as pollutant chemicals in nature, green chemistry seeks

to reduce and prevent pollution at its source Green chemistry technologies provide anumber of benefits, including reduced waste, eliminating costly end-of-the-pipetreatments, safer products, reduced use of energy and resources, and improvedcompetitiveness of chemical manufacturers and their customers Green chemistryconsists of chemicals and chemical processes designed to reduce or eliminate neg-ative environmental impacts The use and production of these chemicals may involvereduced waste products, non-toxic components, and improved efficiency

which provided a road map for chemists to implement green chemistry:

1 Prevention of waste is better than cleaning up

2 Maximum incorporation into the final product of all materials used in the process

3 Chemical synthesis should incorporate less hazardous or toxic materials, whenpossible

Fig 1.1 The paradigm of green tribology: renewable energy (represented by a wind turbine), biomimetic surfaces (represented by the gecko foot), and biodegradable lubrication (represented

by natural vegetable oil)

4 Chemical products should be designed to reduce toxicity.

5 Auxiliary substances, such as solvents, should be safe whenever used

6 Energy efficiency requirements should be recognized Synthetic methodsshould be conducted at ambient temperature and pressure, whenever possible

7 A raw material or feedstock should be renewable, whenever possible

8 Reduce unnecessary derivatives

9 Catalytic reagents are superior to stoichiometric reagents

10 Chemical products should be degradable at the end of their function

11 Real-time analysis, monitoring and control should be implemented to preventthe formation of hazardous substances

12 Substances and their use in the chemical process should be chosen to mize the risk of accidents and prevent fires, explosions, spills, etc

mini-A number of green chemistry metrics have been suggested to quantify theenvironmental efficiency of a chemical process These metrics include the envi-ronmental factor (‘‘E-factor’’), which is equal to the total mass of waste divided by

Attempts are made not only to quantify the ‘‘greenness’’ of a chemical processbut also to factors in other parameters such as chemical yield, the price of reactioncomponents, safety in handling chemicals, hardware demands, energy profile, andease of product workup and purification Green chemistry is increasingly seen as apowerful tool that researchers must use to evaluate the environmental impact ofnanotechnology As nanomaterials are developed, the environmental and humanhealth impacts of both the products themselves and the processes to make themmust be considered to ensure their long-term economic viability While manyscientists use the term ‘‘green chemistry,’’ there are also critics who argue thatgreen chemistry is no more than a public relations label, since some chemists usethe term green chemistry without relating it to the green chemistry principles

Green tribology may have to deal with the same problem

Since tribology is an interdisciplinary area which involves, among other fields,chemical engineering and materials science, the principles of green chemistry areapplicable to green tribology as well However, since tribology involves not onlythe chemistry of surfaces but also other aspects related to the mechanics andphysics of surfaces, there is a need to modify these principles The principles ofgreen tribology will be formulated in the following section

1.3 Twelve Principles of Green Tribology

can be formulated, similar to the principles of green chemistry Some principlesare related to the design and manufacturing of tribological applications (3–10),while others belong to their operation (1–2, 11–12)

1 Minimization of heat and energy dissipation Friction is the primary source ofenergy dissipation According to some estimates, about one-third of the energyconsumption in the US is spent to overcome friction Most energy dissipated

by friction is converted into heat and leads to heat pollution of the atmosphereand the environment The control of friction and friction minimization, whichleads to both energy conservation and the prevention of damage to the envi-ronment due to the heat pollution, is a primary task of tribology It is rec-ognized that for certain tribological applications (e.g., car brakes and clutches)high friction is required; however, ways of effective use of energy for theseapplications should be sought as well

2 Minimization of wear is the second most important task of tribology which hasrelevance to green tribology In most industrial applications wear is undesir-able It limits the lifetime of components and therefore creates the problem oftheir recycling Wear can lead also to catastrophic failure In addition, wearcreates debris and particles which contaminate the environment and can behazardous for humans in certain situations For example, wear debris gener-ated after human joint replacement surgery is the primary source of long-termcomplications in patients

3 Reduction or complete elimination of lubrication and self-lubrication.Lubrication is a focus of tribology since it leads to the reduction of friction andwear However, lubrication can also lead to environmental hazards It isdesirable to reduce lubrication or achieve the self-lubricating regime, when noexternal supply of lubrication is required Tribological systems in living natureoften operate in the self-lubricating regime For example, joints form essen-tially a closed self-sustainable system

4 Natural lubrication (e.g., vegetable oil-based) should be used in cases whenpossible, since it is usually environmentally friendly

5 Biodegradable lubrication should also be used when possible to avoid ronmental contamination In particular, water lubrication is an area whichattracted researchers in recent years Natural oil (such as canola) lubrication isanother option, especially discussed in the developing countries

envi-6 Sustainable chemistry and green engineering principles should be used for themanufacturing of new components for tribological applications, coatings, andlubricants

7 Biomimetic approach should be used whenever possible This includes mimetic surfaces, materials, and other biomimetic and bio-inspired approa-ches, since they tend to be more ecologically friendly

bio-8 Surface texturing should be applied to control surface properties tional engineered surfaces have random roughness, and the randomness is thefactor which makes it extremely difficult to overcome friction and wear Onthe other hand, many biological functional surfaces have complex structureswith hierarchical roughness, which defines their properties Surface texturingprovides a way to control many surface properties relevant to making tribo-systems more ecologically friendly

9 Environmental implications of coatings and other methods of surface fication (texturing, depositions, etc.) should be investigated and taken intoconsideration.

modi-10 Design for degradation of surfaces, coatings, and tribological components.Similar to green chemistry applications, the ultimate degradation/utilizationshould be taken into consideration during design

11 Real-time monitoring, analysis, and control of tribological systems duringtheir operation should be implemented to prevent the formation of hazardoussubstances

12 Sustainable energy applications should become the priority of the tribologicaldesign as well as engineering design in general

1.4 Areas of Green Tribology

The following three focus areas of tribology have the greatest impact on ronmental issues, and therefore, they are of importance for green tribology: (1)biomimetic and self-lubricating materials/surfaces; (2) biodegradable and envi-ronment-friendly lubricants, coatings, and materials; and (3) tribology of renew-able and/or sustainable sources of energy Below, the current state of these areasand their relevance for the novel field of green tribology are briefly discussed

envi-1.4.1 Biomimetic Surfaces

Biomimetics (also referred to as bionics or biomimicry) is the application of logical methods and systems found in nature to the study and design of engineeringsystems and modern technology It is estimated that the 100 largest biomimeticproducts generated approximately US $1.5 billion over the years 2005–2008

biological materials have remarkable properties which can hardly be achieved byconventional engineering methods For example, a spider can produce hugeamounts (compared with the linear size of his body) of silk fiber which is strongerthan steel without any access to the high temperatures and pressures which would

be required to produce such materials as steel using conventional humantechnology These properties of biomimetic materials are achieved due to their

organization provides biological systems with the flexibility needed to adapt to thechanging environment As opposed to the traditional engineering approach, bio-logical materials are grown without the final design specifications, but by using therecipes and recursive algorithms contained in their genetic code The difference ofnatural versus engineering design is the difference of growth versus fabrication

[29, 54, 55] Hierarchical organization and the ability of biological systems togrow and adapt also provides a natural mechanism for the repair or healing ofminor damage in the material.

The remarkable properties of the biological materials serve as a source ofinspiration for materials scientists and engineers indicating that such perfor-mance can be achieved if the paradigm of materials design is changed While

in most cases it is not possible to directly borrow solutions from living natureand to apply them in engineering, it is often possible to take biological systems

as a starting point and a source of inspiration for engineering design Molecularscale devices, superhydrophobicity, self-cleaning, drag reduction in fluid flow,energy conversion and conservation, high adhesion, reversible adhesion, aero-dynamic lift, materials and fibres with high mechanical strength, biological self-assembly, antireflection, structural coloration, thermal insulation, self-healing,and sensory-aid mechanisms are some of the examples found in nature that are

of commercial interest

Biomimetic materials are also usually environmentally friendly in a naturalway, since they are a natural part of the ecosystem For this reason, the biomimeticapproach in tribology is particularly promising In the area of biomimetic surfaces,

1 The lotus effect based non-adhesive surfaces The term ‘‘lotus effect’’stands for surface roughness-induced superhydrophobicity and self-cleaning.Superhydrophobicity is defined as the ability to have a large ([150) watercontact angle and, at the same time, low contact angle hysteresis The lotusflower is famous for its ability to emerge clean from dirty water and to repelwater from its leaves This is due to a special structure of the leaf

Adhesion is a general term for several types of attractive forces that actbetween solid surfaces, including the van der Waals force, electrostatic force,chemical bonding, and the capillary force due to the condensation of water atthe surface Adhesion is a relatively short-range force, and its effect (which isoften undesirable) is significant for microsystems which have contacting sur-faces The adhesion force strongly affects friction, mechanical contact, andtribological performance of such a system’s surface, leading, for example, to

microelectromechanical switches and actuators from proper functioning It istherefore desirable to produce non-adhesive surfaces, and applying surfacemicrostructure mimicking the lotus effect has been successfully used for thedesign of non-adhesive surfaces, which are important for many tribologicalapplications In some applications, high adhesion surfaces are of interest Highadhesion surfaces have been produced using the so-called ‘‘Petal effect,’’

2 The Gecko effect, which stands for the ability of specially structured chical surfaces to exhibit controlled adhesion Geckos are known for theirability to climb vertical walls due to a strong adhesion between their toes and anumber of various surfaces They can also detach easily from a surface when

surface The Gecko effect is used for applications when strong adhesion isneeded (e.g., adhesive tapes) or for reversible adhesion (e.g., climbing robot)[13,54]

Fig 1.2 a SEM micrographs (shown at three magnifications) of lotus (Nelumbo nucifera) leaf surface, which consists of microstructure formed by papillose epidermal cells covered with epicuticular wax tubules on the surface, which create nanostructure; b image of water droplet sitting on the lotus leaf [ 21 ]

Fig 1.3 Optical

micrographs of water droplets

on Rosa, cv Bairage at 0 and

180 tilt angles Droplet is

still suspended when the petal

is turned upside down [ 18 ]

3 Microstructured surfaces for underwater applications, including easy flow due

and anti-biofouling (the fish-scale effect) Biofouling and biofilming are theundesirable accumulation of microorganisms, plants, and algae on structureswhich are immersed in water Conventional antifouling coatings for ship hullsare often toxic and environmentally hazardous On the other hand, in livingnature there are ecological coatings (e.g., fish scale), so a biomimetic approach

4 Oleophobic surfaces capable of repelling organic liquids The principle can besimilar to superhydrophobicity, but it is much more difficult to produce anoleophobic surface, because surface energies of organic liquids are low, and

5 Microstructured surfaces for various optical applications, including reflective (the Moth-eye effect), highly reflective, colored (in some cases,including the ability to dynamically control coloration), and transparent sur-faces Optical surfaces are sensitive to contamination, so the self-cleaning

removal of frozen contaminant from a surface) and anti-icing (protectingagainst the formation of frozen contaminant) are significant problems for manyapplications that have to operate below the water freezing temperature: air-crafts, machinery, road and runway pavements, traffic signs and traffic lights,etc The traditional approaches to de-icing include mechanical methods, heat-ing, the deposition of dry or liquid chemicals that lower the freezing point ofwater Anti-icing is accomplished by applying a protective layer of a viscousanti-ice fluid All anti-ice fluids offer only limited protection, dependent uponfrozen contaminant type and precipitation rate, and it fails when it can nolonger absorb the contaminant In addition to limited efficiency, these de-icingfluids, such as propylene glycol or ethylene glycol, can be toxic and raise

Fig 1.4 Tokay gecko has

the ability to climb walls and

detach from surfaces easily at

will

environmental concerns Anti-icing on roadways is used to prevent ice andsnow from adhering to the pavement, allowing easier removal by mechanicalmethods.

Ice formation occurs due to the condensation of vapor phase water and furtherfreezing of liquid water For example, droplets of supercooled water that exist instratiform and cumulus clouds crystallize into ice when they are struck by thewings of passing airplanes Ice formation on other surfaces, such as pavements

or traffic signs also occurs via the liquid phase It is therefore suggested that a

super-hydrophobic surface is wetted by water, an air layer or air pockets are usuallykept between the solid and the water droplets After freezing, ice will not adhere

to solid due to the presence of air pockets and will be easily washed or blownaway

7 Microelectromechanical system (MEMS)-based dynamically tunable surfacesfor the control of liquid/matter flow and/or coloration (for example, mimickingthe coloration control in cephalopods), used for displays and other applications,

8 Various biomimetic microtextured surfaces to control friction, wear and

10 Self-repairing surfaces and materials, which are able to heal minor damage

11 Various surfaces with alternate (and dynamically controlled) wettingproperties for micro/nanofluidic applications, including the Darkling beetleeffect, e.g., the ability of a desert beetle to collect water on its back usingthe hydrophilic spots on the otherwise hydrophobic surface of its back

system A specimen is first

immersed in water, and then

an oil droplet is gently

deposited using a

microsyringe, and the static

contact angle is measured;

b opticalmicrographs of

droplets at

three-different-phase interfaces on a

micropatterned surface (shark

skin replica) without and with

C20F42[ 39 ]

Fig 1.7 The principle of

applying of surface

microstructure for de-icing

13 The ‘‘sand fish’’ lizard effect, able to dive and ‘‘swim’’ in loose sand due to

14 Composite and nanocomposite materials tailored in such way that they canproduce required surface properties, such as self-cleaning, self-lubrication,and self-healing Metal-matrix composites, and polymeric composites as well

as ceramics (including concrete) have been recently used for this purpose.Natural fiber-reinforced composites are among these materials The differencebetween microstructured surfaces and composite materials is that the latterhave hydrophobic reinforcement in the bulk and thus can be much more wear-resistant than microstructured surfaces, which are vulnerable even to moderatewear rates

15 Green biomimetic nanotribology, including cell adhesion, nanoornamentics,and biochemistry is another new area associated with green tribology

Fig 1.8 The

water-capturing surface of the fused

overwings (elytra) of the

desert beetle Stenocara sp.

a Adult female, dorsal view;

peaks and valleys are evident

on the surface of the elytra;

b SEM image of the textured

surface of the depressed areas

[ 61 ]

Environmental engineers have only just started paying attention to biomimetic

burdens associated with using the lotus effect based self-cleaning surfaces Theyfound that while the use phase benefits are apparent, production burdens canoutweigh them when compared with other cleaning methods, so a more thoughtfuland deliberate use of bio-inspiration in sustainable engineering is needed Clearly,more studies are likely to emerge in the near future

1.4.2 Biodegradable Lubrication, Coatings, and Materials

In the area of environment-friendly and biodegradable lubrication several ideashave been suggested:

Fig 1.9 a Water strider

(Pond skater, G remigis)

walking on water; b SEM

images of a pond skater leg

showing (top) numerous

oriented microscale setae and

(bottom) nanoscale grooved

structures on a seta [ 31 ]

1 The use of natural (e.g., vegetable-oil based or animal-fat based) biodegradablelubricants This involves oils that are used for engines, hydraulic applications,and metal cutting applications In particular, corn, soybean, coconut oils havebeen used so far (the latter is of particular interest in tropical countries such asIndia) These lubricants are potentially biodegradable, although in somecases chemical modification or additives for best performance are required.Vegetable oils can have excellent lubricity, far superior than that of mineral oil.

In addition, they have a very high viscosity index and high flash/fire points.However, natural oils often lack sufficient oxidative stability, which means thatthe oil will oxidize rather quickly during use, becoming thick and polymerizing

to a plastic-like consistency Chemical modification of vegetable oils and/or the

2 Ionic liquids for green molecular lubrication Common industrial lubricantsinclude natural and synthetic hydrocarbons and perfluoropolyethers (PFPEs),where the latter is widely used in commercial applications requiring extremeoperating conditions due to their high temperature stability and extremely lowvapor pressure However, PFPEs exhibit low electrical conductivity, makingthem undesirable in some nanotechnology applications Ionic liquids (ILs) havebeen explored as lubricants for various device applications due to theirexcellent electrical conductivity as well as good thermal conductivity, where

volatile organic compounds, they are regarded as ‘‘green’’ lubricants

3 Powder lubricants and,in particular, boric acid lubricants In general, these tend

to be much more ecologically friendly than the traditional liquid lubricants

oil Friction and wear experiments show that the nanoscale (20 nm) particleboric acid additive lubricants significantly outperformed all of the otherlubricants with respect to frictional and wear performance In fact, the nano-scale boric acid powder based lubricants exhibited a wear rate more than an

4 Self-replenishing lubrication that uses oil-free environmentally benign powdersfor lubrication of critical components such as bearings used in fuel cell com-

5 Water lubrication of bearings and other tribological components Recently, a lot

of attention has been paid to water lubrication which is considered an friendly method

eco-6 New eco-friendly coating materials for tribological applications

7 Environmental effect of wear particles It has been suggested that

data obtained with animal experiments revealed that the inhaled metallic ticles remain deposited in the lungs of rats 6 month after the exposure Thepresence of inhaled particles had a negative impact on health and led toemphysema (destroyed alveoli), inflammatory response, and morphologicalchanges of the lung tissue

1.4.3 Renewable Energy

The tribology of renewable sources of energy is a relatively new field of bology Today, there are meetings and sessions devoted to the tribology of windturbines at almost every tribology conference, and they cover certain issuesspecific for these applications Unlike in the case of the biomimetic approachand environment-friendly lubrication, it is not the manufacturing or operation,but the very application of the tribological system which involves ‘‘green’’issues, namely, environmentally friendly energy production The following issuescan be mentioned

1 Wind power turbines have a number of specific problems related to their bology, and constitute a well-established area of tribological research Theseissues include water contamination, electric arcing on generator bearings, issuesrelated to the wear of the mainshaft and gearbox bearings and gears, the erosion

2 Tidal power turbines are another important way of producing renewableenergy, which involves certain tribiological problems Tidal power turbines areespecially popular in Europe (particularly, in the U.K.), which remains theleader in this area, although several potential sites in North America have beensuggested There are several specific tribological issues related to tidal powerturbines, such as their lubrication (seawater, oils, and greases), erosion, cor-rosion, and biofouling, as well as the interaction between these modes of

3 Besides tidal, the ocean water flow and wave energy and river flow energy(without dams) can be used with the application of special turbines, such as the

independent of the direction of the current flow These applications also involvespecific tribological issues

4 Geothermal energy plants are used in the US (in particular, at the Pacific coastand Alaska); however, their use is limited to the geographical areas at the edges

with Philippines (2.0 GW) and Indonesia (1.0 GW) in the second and third

energy sources which are discussed in the literature

synthesis is performed is it possible to see green tribology as a coherent and sustained field of science and technology, rather than a collection of several topics

self-of research in tribology and surface engineering There is potential synergy in theuse of biomimetic approach, microstructuring, biodegradable lubrication,self-lubrication, and other novel approaches as well as in developing methods oftheir applications to sustainable engineering and energy production Clearly,more research should be performed for the integration of these fields Some ideascould be borrowed from the related field of green chemistry, for example,developing quantitative metrics to assess the environmental impact of tribologicaltechnologies

The creator of the periodic table of elements, chemist Mendeleev used to saythat science starts when the measurement begins This saying should apply togreen tribology as well It is important to develop quantitative measures andmetrics which would allow comparison of which tribological material, technology,

or application is ‘‘greener,’’ i.e., produces smaller carbon footprint, less chemical,

or thermal pollution of the environment

Green tribology should be integrated into world science and make its impact onthe solutions for worldwide problems, such as the change of climate and the

of the new discipline: ‘‘the application of tribological principles alone will, ofcourse, not solve these world-wide problems Only major scientific achievementsare likely to be the key to their solution, of which I rate Energy as one of the mostimportant ones For such tasks to be achieved, the application of Tribology, andespecially of green tribology can provide a breathing space which would enablescientists and technologists to find solutions to these, mankind’s crucial problemsand allow time for them to be implemented by governments, organizations andindeed everyone operating in this important field Consequently, this important—albeit limited—breathing space may be extremely valuable to all working for thesurvival of life as we know it However, the ultimate key is science and itsapplication Tribology—especially green tribology can and—I am confident—willplay its part to assist and give time for science to achieve the required solutionsand for policy makers to implement them.’’

1.6 Conclusions

Green tribology is a novel area of science and technology It is related to otherareas of tribology as well as other ‘‘green’’ disciplines, namely, green engineeringand green chemistry The twelve principles of green tribology are formulated, andthree areas of tribological studies most relevant to green tribology are defined Theintegration of these areas remains the primary challenge of green tribology anddefines the future directions of research

3 Anonymous, Green Engineering (2010) http://www.epa.gov/oppt/greenengineering/

4 Y Bar-Cohen, Biomimetics: Nature-Based Innovation (CRC Press, Boca Raton, 2011)

5 W.J Bartz, Ecotribology: Environmentally Acceptable Tribological Practices Tribol Int 39, 728–733 (2006)

6 W.M.J Batten, A.S Bahaj, A.F Molland, J.R Chaplin, The Prediction of the Hydrodynamic Performance of Marine Current Turbines Renew Energ 33, 1085–1096 (2008)

7 E.R Bertani, World Geothermal Generation in 2007 Geo Heat Cent Bull 28, 8–19 (2007)

8 B Bhushan, Tribology and Mechanics of Magnetic Storage Devices, 2nd edn (Springer, New York, 1996)

9 B Bhushan, Principles and Applications of Tribology (Wiley, New York, 1999)

10 B Bhushan, Mechanics and Reliability of Flexible Magnetic Media, 2nd edn (Springer, New York, 2000)

11 B Bhushan, Modern Tribology Handbook, Vol 1–Principles of Tribology; Vol 2–Materials, Coatings, and Industrial Applications (CRC Press, Boca Raton, 2001)

12 B Bhushan, Introduction to Tribology (Wiley, New York, 2002)

13 B Bhushan, Adhesion of Multi-level Hierarchical Attachment Systems in Gecko feet.

J Adhesion Sci Technol 21, 1213–1258 (2007, invited)

14 B Bhushan, Biomimetics: Lessons from Nature—an overview Phil Trans R Soc A 367, 1445–1486 (2009)

15 B Bhushan, Springer Handbook of Nanotechnology, 3rd edn (Springer, Heidelberg, 2010)

16 B Bhushan, Nanotribology and Nanomechanics I-Measurement Techniques and Nanomechanics, II-Nanotribology, Biomimetics, and Industrial Applications, 3rd edn (Springer, Heidelberg, 2011)

17 B Bhushan, B.K Gupta, Handbook of Tribology: Materials, Coatings, and Surface Treatments (McGraw-Hill, New York, 1991)

18 B Bhushan, E.K Her, Fabrication of Superhydrophobic Surfaces with high and low Adhesion Inspired from rose petal Langmuir 26, 8207–8217 (2010)

19 B Bhushan, Y.C Jung, Natural and biomimetic artificial surfaces for superhydrophobicity, self-cleaning, low adhesion, and drag reduction Prog Mater Sci 56, 1–108 (2011)

20 B Bhushan, M Nosonovsky, The rose petal effect and the modes of superhydrophobicity Phil Trans Royal Soc A 368, 4713–4728 (2010)

21 B Bhushan, Y.C Jung, K Koch, Micro-, nano- and hierarchical structures for superhydrophobicity, self-cleaning and low adhesion Phil Trans R Soc A 367, 1631–1672 (2009)

22 E Bormashenko, Wetting transitions on biomimetic surfaces Phil Trans Royal Soc A.

368, 4695–4712 (2010)

23 M.A Bucaro, P.R Kolodner, A Taylor, A Sidorenko, J Aizenberg, T.N Krupenkin, Tunable liquid optics: electrowetting-controlled liquid mirrors based on self-assembled janus tiles Langmuir 25, 3876–3879 (2009)

24 L Cao, A.K Jones, V.K Sikka, J Wu, D Gao, Anti-icing superhydrophobic coatings Langmuir 25, 12444–12448 (2009)

25 L.D Chambers, K.R Stokes, F.C Walsh, R.J.K Wood, Modern approaches to marine antifouling coatings Surf Coat Tech 201, 3642–3652 (2006)

26 D.J.C Constable, A.D Curzons, L.M Freitas dos Santos, G.R Geen, R.E Hannah, J.D Hayler, J Kitteringham, M.A McGuire, J.E Richardson, P Smith, R.L Webb, M Yu, Green chemistry measures for process research and development Green Chem 3, 7–9 (2001)

27 B Dean, B Bhushan, Shark-skin surfaces for fluid drag reduction in turbulent flow Phil Trans Royal Soc A 368, 4775–4806 (2010)

28 E Favret, N.O Fuentas, Functional Properties of Bio-inspired Surfaces: Characterization and Technological Applications (World Scientific, Hackensack, 2009)

29 P Fratzl, Biomimetic materials research: what can we really learn from nature’s structural materials? J R Soc Interf 4, 637–642 (2007)

30 P Fratzl, R Weinkamer, Nature’s hierarchical materials Prog Mater Sci 52, 1263–1334 (2007)

31 X.F Gao, L Jiang, Biophysics: water-repellent legs of water striders Nature 432, 36 (2004)

32 J Genzer, K Efimenko, Recent developments in superhydrophobic surfaces and their relevance to marine fouling: a review Biofouling 22, 339–360 (2006)

33 A Gombert, B Blasi, The Moth-Eye-Effect—from Fundamentals to Commercial Exploitation, in Functional Properties of Bio-inspired Surfaces: Characterization and Technological Applications, ed by E Favret, N.O Fuentas (World Scientific Publishing Co., Hackensack, 2009), pp 79–102

34 S Gorb, Functional Surfaces in Biology: Mechanisms and Applications, in Biomimetics: Biologically Inspired Technologies, ed by Y Bar-Cohen (Taylor and Francis, Boca Raton, 2006), pp 381–397

35 A.N Gorban’, A.M Gorlov, V.M Silantyev, Limits of the turbine efficiency for free fluid flow ASME J Energ Resour Technol 123, 311–317 (2001)

36 N.N Greenwood, J.A Spink, An antipodean laboratory of remarkable distinction Notes Rec.

46 M.R Lovell, M.A Kabir, P.L Menzes, C.F Higgs III, Influence of boric acid additive size

on green lubricant performance Phil Trans Royal Soc A 368, 4851–4868 (2010)

47 J.K Mannekote, and S.V Kailas, Performance evaluation of vegetable oils as lubricant in a four stroke engine, in Proceedings Fourth World Tribology Congress, Kyoto, 6–11 Sept

on Tribology TriboBr-2010-17172, 24–26 Nov 2010, Rio de Janeiro (2010b)

51 M Nosonovsky, Towards ‘green tribology’: self-organization at the sliding interface for biomimetic surfaces, in Proceedings ASME 10th Biennial Conference on Engineering Systems Design and Analysis, 12–14 July 2010, Istanbul, Turkey, ESDA2010-25047 (2010c)

52 M Nosonovsky, B Bhushan, Biomimetic superhydrophobic surfaces: multiscale approach Nano Lett 7, 2633–2637 (2007)

53 M Nosonovsky, B Bhushan, Multiscale friction mechanisms and hierarchical surfaces in nano- and bio-tribology Mater Sci Eng R 58, 162–193 (2007)

54 M Nosonovsky, B Bhushan, Multiscale Dissipative Mechanisms and Hierarchical Surfaces: Friction, Superhydrophobicity, and Biomimetics (Springer, Heidelberg, 2008)

55 M Nosonovsky, B Bhushan, Multiscale effects and capillary interactions in functional biomimetic surfaces for energy conversion and green engineering Phil Trans R Soc A 367, 1511–1539 (2009)

56 M Nosonovsky, B Bhushan, Superhydrophobic surfaces and emerging applications: adhesion, energy, green engineering Curr Opin Colloid Interface Sci 14, 270–280 (2009)

non-57 M Nosonovsky, B Bhushan, Thermodynamics of surface degradation, self-organization, and self-healing for biomimetic surfaces Phil Trans R Soc A 367, 1607–1627 (2009)

58 M Nosonovsky, B Bhushan, Green tribology: principles, research areas and challenges Phil Trans Royal Soc A 368, 4677–4694 (2010)

59 M Nosonovsky, and B Bhushan, Towards the ‘Green Tribology:’ Biomimetic Surfaces, Biodegradable Lubrication, and Renewable Energy, in Proceedings STLE/ASME 2010 International Joint Tribology Conference, 17–20 Oct 2010, San Francisco, IJTC2010-41157 (2010b)

60 P Palacio, B Bhushan, A review of ionic liquids for green molecular lubrication in nanotechnology Tribol Lett 40, 247–268 (2010)

61 A.R Parker, C.R Lawrence, Water capture by a desert beetle Nature 414, 33–34 (2001)

62 L Raibeck, J Reap, B Bras, Investigating environmental burdens and benefits of biologically inspired self-cleaning surfaces CIRP J Manufact Sci Technol 1, 230–236 (2009)

63 I Rechenberg, A.R El Khyeri, The sandfish of the Sahara A model for friction and wear reduction (Department of Bionics and Evolution Techniques, Technical University of Berlin, Berlin), See http://www.bionik.tu-berlin.de/institut/safiengl.htm

64 W.E Reif, Squamation and ecology of sharks Cour Forschung Senck 78, 1–255 (1985)

65 L Rybach, Geothermal sustainability Geo Heat Cent Q Bull 28, 2–7 (2007)

66 M Salta, J.A Wharton, P Stoodley, S.P Dennington, L.R Goodes, S Werwinski, U Mart, R.J.K Wood, K.R Stokes, Designing biomimetic antifouling surfaces Phil Trans Royal Soc A 368, 4729–4754 (2010)

67 S Sasaki, Environmentally friendly tribology (eco-tribology) J Mech Sci Technol 24, 67–

71 (2010)

68 M Scherge, S Gorb, Biological Micro- and Nanotribology: Nature’s Solutions (Springer, Heidelberg, 2001)

69 R.A Sheldon, Organic synthesis: past, present and future Chem Ind 23, 903–906 (1992)

70 A Sidorenko, T Krupenkin, A Taylor, P Fratzl, J Aizenberg, Reversible switching of hydrogel-sctuated nanostructures into complex micropatterns Science 315, 487–490 (2007)

71 B.M Trost, The atom economy—a search for synthetic efficiency Science 254, 1471–1477 (1991)

72 A Tuteja, W Choi, M Ma, J.M Mabry, S.A Mazzella, G.C Rutledge, G.H McKinley, R.E Cohen, Designing superoleophobic surfaces Science 318, 1618–1622 (2007)

73 A Tuteja, W Choi, J.M Mabri, G.H McKinley, R.E Cohen, Robust omniphobic surfaces Proc Nat Acad Sci U S A 105, 18200–18205 (2008)

74 M Varenberg, S Gorb, Hexagonal surface micropattern for dry and wet friction Adv Mater.

21, 483–486 (2009)

75 R.J.K Wood, A.S Bahaj, S.R Turnock, L Wang, M Evans, Tribological design constraints

of marine renewable energy systems Phil Trans Royal Soc A 368, 4807–4828 (2010)

76 E.Y.A Wornyoh, V.K Jasti, C.F Higgs III, A review of dry particulate lubrication: powder and granular materials ASME J Tribol 129, 438–449 (2007)

77 R Yun, Y Lu, P Filip, Application of extension evaluation method in development of novel eco-friendly brake materials SAE Int J Mater Manuf 2, 1–7 (2010)

Part II Biomimetics Surfaces, Materials and Methods

Chapter 2

Lotus Versus Rose: Biomimetic

Surface Effects

Michael Nosonovsky and Bharat Bhushan

investigation by scientists, as they involve different modes of the interaction ofwetting with roughness The contact angle (CA) and CA hysteresis are twoparameters, which characterize the hydrophobicity/philicity of a solid surface.Lotus-effect surfaces have a high CA and low CA hysteresis However, it wasfound recently that a high CA can coexist with strong adhesion between water and

a solid surface (and high CA hysteresis) in the case of the so-called ‘‘rose petaleffect.’’ It is clear now that wetting cannot be characterized by only the CA, sinceseveral modes or regimes of wetting of a rough surface can exist, including theWenzel, Cassie, Lotus, and Petal regimes This is due to the hierarchical structure

of rough surfaces built of micro- and nanoscale roughness, so that a compositeinterface can exist at the microscale, while a homogeneous interface can exist atthe nanoscale or vice versa The understanding of the wetting of rough surfaces isimportant in order to design non-adhesive surfaces for various applications,including environmental

M Nosonovsky

College of Engineering and Applied Science, University of Wisconsin,

Milwaukee, WI 53201, USA

B Bhushan ( &)

Nanoprobe Laboratory for Bio- and Nanotechnology and Biomimetics (NLB2),

The Ohio State University, 201 W 19th Avenue, Columbus,

OH 43210-1142, USA

e-mail: bhushan.2@osu.edu

M Nosonovsky and B Bhushan (eds.), Green Tribology,

Green Energy and Technology, DOI: 10.1007/978-3-642-23681-5_2,

Ó Springer-Verlag Berlin Heidelberg 2012

25