+ All Categories
Home > Documents > VA. Superhydrophobicity and Shark Skin

VA. Superhydrophobicity and Shark Skin

Date post: 22-Oct-2014
Category:
Upload: janinarhea
View: 90 times
Download: 2 times
Share this document with a friend
Popular Tags:
33
Lotus Effect: Surfaces with Roughness- Induced Superhydrophobicity, Self-Cleaning and Low Adhesion Prof. Bharat Bhushan [email protected] (Collaborators – Dr. Y. C. Jung, Prof. Mike Nosonovsky and Prof. Kerstin Koch) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics © B. Bhushan Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 1
Transcript
Page 1: VA. Superhydrophobicity and Shark Skin

Lotus Effect: Surfaces with Roughness-Induced Superhydrophobicity, Self-Cleaning

and Low AdhesionProf. Bharat Bhushan

[email protected]

(Collaborators – Dr. Y. C. Jung, Prof. Mike Nosonovsky and Prof. Kerstin Koch)

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

© B. BhushanNanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 1

Page 2: VA. Superhydrophobicity and Shark Skin

Micro/nanoscale studies

Techniques

Bio/nanotribology Bio/nanomechanics Biomimetics

Materials sci., biomedical eng., physics & physical chem.

NanoindentorMicrotriboapparatusAFM/STM

Materials/DeviceStudies

• Materials/coatings• SAM/PFPE/Ionic liquids• Biomolecular films• CNTs

• Micro/nanofabrication

Collaborations

• MEMS/NEMS• BioMEMS/NEMS• Superhydrophobic surfaces• Reversible adhesion• Beauty care products• Probe-based data storage• Aging Mech. of Li-Ion Batt.

Applications

Numerical modeling and simulation

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 2

Page 3: VA. Superhydrophobicity and Shark Skin

Biomimetics – Lessons from Nature

Background

• Biomimetics means mimicking biology or nature. It is derived from a Greek word “biomimesis.” Other words used include bionics, biomimicry and biognosis.

• Biomimetics involves taking ideas from nature and implementing them in an application.

• Nature has gone through evolution over 3.8 billion years. It has evolved objects with high performance. Biological materials have hierarchical structure, made of commonly found materials.

• It is estimated that the 100 largest biomimetic products had generated $1.5 billion over 2005-08. The annual sales are expected to continue to increase dramatically.

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

M. Nosonovsky and B. Bhushan (2008), Multiscale Dissipative Mechanisms and Hierarchical Surfaces: Friction, Superhydrophobicity, and Biomimetics, Springer-Verlag, Heidelberg, Germany; B. Bhushan (2007), Springer Handbook of Nanotechnology, second ed., Springer-Verlag, Heidelberg, Germany; B. Bhushan, Phil. Trans. R. Soc. A 367, 1445-1486 (2009).

3

Page 4: VA. Superhydrophobicity and Shark Skin

Background

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

Biomimetics- examples from nature

4B. Bhushan. Phil Trans. R. Soc. A 367, 1631 (2009)

Janina
Highlight
Janina
Highlight
Page 5: VA. Superhydrophobicity and Shark Skin

Superhydrophobicity – definition and its importance• A surface is superhydrophobic if it has a water contact angle above 150 .• These surfaces are water repellent. These surfaces with low contact angle

hysteresis (less than 10º) also have a self cleaning effect, called “Lotus Effect”. Water droplets roll off the surface and take contaminants with them.

The self cleaning surfaces are of interest in various applications, e.g., self cleaning windows, windshields, exterior paints for buildings, navigation-ships and utensils, roof tiles, textiles, solar panels and reduction of drag in fluid flow, e. g. in micro/nanochannels. Also, superhydrophobic surface can be used for energy conservation and energy conversion.

Superhydrophobic surfaces can be achieved either by selecting low surface energy materials/coatings or by introducing roughness.

• When two hydrophilic surfaces come into contact, condensation of water vapor from environment forms meniscus bridges at asperity contacts which lead to an intrinsic attractive force. This may lead to high adhesion and stiction. Therefore, superhydrophobic surfaces are desirable.

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 5

Janina
Highlight
Janina
Highlight
Janina
Highlight
Janina
Highlight
Page 6: VA. Superhydrophobicity and Shark Skin

Examples of commercial MEMS with stiction issues

Microfabricated commercial MEMS components

B. Bhushan. Springer Handbook of Nanotechnology, Springer-Verlag, Heidelberg, second ed, 2007

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 6

Page 7: VA. Superhydrophobicity and Shark Skin

Objective and Approach

Objective• Develop roughness-induced superhydrophobic surfaces by

mimicing lotus effect.

• Use numerical model to develop optimized roughness distribution for a given contact angle.

• Study superhydrophobic and hydrophilic leaves to understand mechanism responsible for hydrophobicity

Fully characterize the surface of the leaves (contact angle, roughness, adhesion and friction)

• Fabricate and characterize micro-, nano- and hierarchical structured surfacesStudy the effect of micro-, nano- and hierarchical structures on contact angle and ability to form air pockets for superhydrophobicity.

• Fabricate and characterize biomimetic structures for fluid drag reductionStudy drag reduction efficiency on the surfaces in laminar and turbulent flows.

Approach

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 7

Page 8: VA. Superhydrophobicity and Shark Skin

)1cosθ(2)cosθ(cosθ1

θθθ0

adv0rec0recadvH +

−−≈−=

f

LAf

RfR

Wenzel’s equation:cos cosf oRθ θ=

Roughness optimization model for superhydrophobic and self cleaning surfaces

Droplet of liquid in contact with a smooth and rough surface

SL 0 LAcos cosfR f fθ θ= −

0 LA 0cos ( cos 1)f fR f Rθ θ= − +

Cassie-Baxter equation:

Composite interfaceComplete wetting For fluid flow, another property of interest -Contact angle hysteresis ( H)

Increase in fLA and reduction in Rf decrease H

α : Tilt angle

for high contact angle(θ 180 )

http://lotus-shower.isunet.edu/the_lotus_effect.htm

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 8

Page 9: VA. Superhydrophobicity and Shark Skin

Need for hierarchical structure for stability of air pockets

• Composite interface is metastable.• Capillary waves may lead to destabilization of the composite interface.

Condensation and accumulation of nanodroplets and surface inhomogeneity (with hydrophilic spots) may destroy the composite interface.

Microstructure resists capillary waves present at the liquid-air interface.Nanostructure prevents nanodroplets from filling the valleys between asperities and pin the droplet.

Hierarchical structure is required to resist these scale-dependent mechanisms and enlarges the liquid-air interface, resulting into high static contact angle and low contact angle hysteresis.

M. Nosonovsky and B. Bhushan, Microelectronic Eng. 84, 382 (2007); Ultramicroscopy 107, 969 (2007)Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 9

Page 10: VA. Superhydrophobicity and Shark Skin

Superhydrophobic leaves• Nelumbo nucifera (lotus) and colocasia

esculenta • The leaf surface consists of microbumps

formed by convex papilla epidermal cells covered with a 3-D epicuticular wax (crystalline tubules composed of a mixture of secondary alcohol nonacosan-10-ol and nonacosanediols) on surface which creates nanobumps.

• Combination of hierarchical structure of the rough surface and wax creates a superhydrophobic surface.

Hydrophobic leaves

Hydrophilic leavesNY Times, 1/27/05; ABCNEWS.com, 1/26/05; Z. Burton and B. Bhushan, Ultramicroscopy 106, 709 (2006); B. Bhushan and Y. C. Jung, Nanotechnology 17, 2758 (2006); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008)

Characterization of superhydrophobic and hydrophilic leaves

Many leaves exhibit superhydrophobic and hydrophilic properties.Characterize these to understand the mechanisms.

(Neinhuis and Barthlott, 1997; Wagner et al., 2003)

Hydrophilic leaves• Fagus sylvatica and magnolia grandiflora• Rather flat tabular cells with a 2-D thin wax

film (not continuous) on the surface

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 10

Page 11: VA. Superhydrophobicity and Shark Skin

Rolling off liquid droplet over superhydrophobic Lotus leaf with self cleaning ability

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 11

Page 12: VA. Superhydrophobicity and Shark Skin

SummaryContributions of bumps and wax

• A 3-D epicuticular wax exists on superhydrophobic leaves and a very thin wax layer (not continuous) exists on hydrophilic leaves.

• Superhydrophobic and self cleaning leaf surfaces have an intrinsic hierarchical structure.

• The lotus leaf surface consists of microbumps formed by convex papilla epidermal cells covered with a 3-D wax tubules composed of a mixture of secondary alcohol nonacosan-10-ol and nonacosanediols on surface which creates nanobumps.

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 12

Page 13: VA. Superhydrophobicity and Shark Skin

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

Fabrication and characterization of micropatterned silicon Transition for Cassie-Baxter to Wenzel regime depends upon the roughness spacing and radius of droplet. It is of interest to understand the role of roughness and radius of the droplet.

13

Transition from Cassie-Baxter regime to Wenzel regime

Cassie-Baxter to Wenzel Regime Transition criteria for patterned surfaces

• Geometry (P and H) and radius R govern transition. A droplet with a large radius (R) w.r.to pitch (P) would be in Cassie-Baxter regime.

If δ ≥ HR

D)P2(δ2−

Y. C. Jung, and B. Bhushan, Scripta Mater.57, 1057(2007); Y. C. Jung, and B. Bhushan, J.Microsc. 229, 127 (2008); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008)

• The curvature of a droplet is governed by Laplace eq. which relates pressure inside the droplet to its curvature. The maximum droop of the droplet

Page 14: VA. Superhydrophobicity and Shark Skin

Optical profiler surface height maps of patterned Si with PF3• Different surface structures with flat-top cylindrical pillars:

Series 1: Diameter (5 µm) and height (10 µm) pillars with different pitch values (7, 7.5, 10, 12.5, 25, 37.5, 45, 60, and 75 µm)

Series 2: Diameter (14 µm) and height (30 µm) pillars with different pitch values (21, 23, 26, 35, 70, 105, 126, 168, and 210 µm)

• MaterialsSample – Single-crystal silicon (Si)Hydrophobic coating – 1, 1, -2, 2, -tetrahydroperfluorodecyltrichlorosilane (PF3) (SAM)

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 14

B. Bhushan and Y. C. Jung, Ultramicroscopy 107, 1033 (2007); J. Phys.: Condens. Matter 20, 225010 (2008); B. Bhushan, M. Nosonovsky, and Y. C. Jung, J. R. Soc. Interf. 4, 643 (2007); Y. C. Jung, and B. Bhushan, Scripta Mater. 57, 1057 (2007); J. Microsc. 229, 127 (2008); Langmuir 24, 6262 (2008); M. Nosonovsky and B. Bhushan, Ultramicroscopy 107, 969 (2007); Nano Letters 7, 2633 (2007); J. Phys.: Condens. Matter 20, 225009 (2008); Mater. Sci. Eng.:R 58, 162 (2007) ; Langmuir 24, 1525 (2008)

Page 15: VA. Superhydrophobicity and Shark Skin

Static contact angle, contact angle hysteresis, and tilt angle on patterned Si surfaces with PF3

Droplet size = 1 mm in radius

• For the selected droplet, the transition occurs from Cassie-Baxter regime to Wenzel regime at certain pitch values for a given pillar height.

B. Bhushan, and Y. C. Jung, Ultramicroscopy 107, 1033 (2007); Y. C. Jung, and B. Bhushan, J. Microsc. 229, 127 (2008); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 15

Page 16: VA. Superhydrophobicity and Shark Skin

Ideal surfaces

Structure of ideal hierarchical surface

• As stated earlier, hierarchical surface is needed to develop composite interface with high stability.

• Proposed transition criteria can be used to calculate geometrical parameters for a given droplet radius. For example, for a droplet on the order of 1 mm or larger, a value of H on the order of 30 µm, D on the order of 15 µm and P on the order of 130 µm is optimum.

• Nanoasperities should have a small pitch to handle nanodroplets, less than 1 mm down to few nm radius. The values of h on the order of 10 nm, d on the order of 100 nm can be easily fabricated.

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 16

Page 17: VA. Superhydrophobicity and Shark Skin

Fabrication and characterization of hierarchical surfaces

Study the effect of hierarchical structure on superhydrophobicity

• Fabrication of microstructureReplication of Lotus leaf and micropatterned silicon surface using an epoxy resin and then cover with the wax material

B. Bhushan et al., Soft Matter 4, 1799 (2008); Appl. Phys. Lett. 93, 093101 (2008); Ultramicroscopy 109, 1029 (2009); Langmuir 25, 1659 (2009); Phil. Trans. R. Soc. A. 367, 1631 (2009); Koch et al., Soft Matter 5, 1386 (2009)

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 17

Page 18: VA. Superhydrophobicity and Shark Skin

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

Fabrication of nanostructure and hierarchical structure

• NanostructureSelf assembly of the Lotus wax deposited by thermal evaporation

Expose to a solvent in vapor phase for the mobility of wax molecules• Hierarchical structure

Lotus and micropatterned epoxy replicas and covered with the tubules of Lotus wax

Recrystallization of wax tubules

B. Bhushan et al., Soft Matter 4, 1799 (2008); Appl. Phys. Lett. 93, 093101 (2008); Ultramicroscopy 109, 1029 (2009); Langmuir 25, 1659 (2009); Phil. Trans. R. Soc. A. 367, 1631 (2009); Koch et al., Soft Matter 5, 1386 (2009)

18

Page 19: VA. Superhydrophobicity and Shark Skin

Nanostructures of nonacosan-ol wax tubules

Tubules of Lotus wax (0.8 µg/mm2)After seven days with ethanol vapor (50° C)

• Nanostructure is formed by tubules of Lotus wax.• Tubules are hollow structures and randomly orientated on the surface.• The tubular diameter varies between 100 and 150 nm and their length varies

between 1500 and 2000 nm.• The created nanostructures are comparable to the wax crystal morphology

found on superhydrophobic Lotus leaf.

K. Koch, B. Bhushan, Y. C. Jung and W. Barthlott, Soft Matter 5, 1386 (2009)Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 19

Page 20: VA. Superhydrophobicity and Shark Skin

Static contact angle, contact angle hysteresis, tilt angle and adhesive force on various structures

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

• Nano- and hierarchical structures with tubular wax led to high static contact angle of 167º and 173º and low hysteresis angle on the order of 6º and 1º.

• Compared to a Lotus leaf, hierarchical structure showed higher static contact angle and lower contact angle hysteresis.

K. Koch, B. Bhushan, Y. C. Jung and W. Barthlott, Soft Matter 5, 1386 (2009)20

Page 21: VA. Superhydrophobicity and Shark Skin

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

Self-cleaning efficiency of various surfaces

• As the impact pressure of the droplet is zero or low, most of particles on nanostructure were removed by water droplets, resulting from geometrical scale effects.

• As the impact pressure of the droplet is high, all particles which are sitting at the bottom of the cavities between the pillars on hierarchical structure were removed by the water droplets.

, B. Bhushan, Y. C. Jung and K. Koch, Langmuir 25, 3240 (2009)21

Page 22: VA. Superhydrophobicity and Shark Skin

Fabrication of mechanically durable CNT-composite hierarchical structure

• Since many applications operate in long-term exposure to various liquids and are exposed to rough operating conditions, hydrophobic surfaces should have mechanical strength and chemical stability. Therefore, it is necessary to perform durability studies on surfaces in order to identify fabrication techniques and materials.

• Study the durability of biomimetic structured surfaces on waterfall/jet and wear and friction tests

Lotus inspired hierarchical structuresCNT-composite hierarchical structures

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 22

Page 23: VA. Superhydrophobicity and Shark Skin

Fabrication of nanostructure and hierarchical structure• Nanostructure

Deposition of the CNT composite using a spray methodMixture of CNT, epoxy, and acetone

• Hierarchical structureMicropatterned epoxy replicas and covered with CNT composite

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 23

• CNT were well dispersed and embedded on flat and microstructured surfaces.• CNT diameter varied between 10 and 30 nm, and an aspect ratio varied between 160 and

200.Y. C. Jung and B. Bhushan, ACS Nano 3, 4155 (2009)

Page 24: VA. Superhydrophobicity and Shark Skin

Durability of the surfaces with CNT in waterfall/jet tests

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 24

• Superhydrophobic CNT composite structures showed good stability of wetting properties not only from long-term exposure to water but also high water pressure.

Y. C. Jung and B. Bhushan, ACS Nano 3, 4155 (2009)

Page 25: VA. Superhydrophobicity and Shark Skin

Durability of the surfaces with Lotus wax in waterfall/jet tests

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 25

• During increasing the exposure time and pressure, a portion of the wax nanostructured area started to be damaged, resulting in increasing contact angle hysteresis.

Y. C. Jung and B. Bhushan, ACS Nano (in press)

Page 26: VA. Superhydrophobicity and Shark Skin

Wear tests on the surfaces with CNT and Lotus wax using AFM

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 26

• With increasing the normal load to 10 µN, it was found that the wear depth on the nanostructure with CNT was not significantly changed.

• As the normal load of 100 nN was applied on the nanostructure with Lotus wax, the change in the morphology of the structured surface was observed, indicating that the wax nanostructure has weak mechanical strength at even small load.

Y. C. Jung and B. Bhushan, ACS Nano 3, 4155 (2009)

Page 27: VA. Superhydrophobicity and Shark Skin

Fabrication of biomimetic structures for fluid drag reduction

• To reduce pressure drop and volume loss in micro/nanochannels used in micro/nanofluidics, it is desirable to minimize the drag force in the solid-liquid interface. Therefore, it is of interest to study the effect of biomimetic structures on drag reduction in fluid flow.

• Study the effect of biomimetic structure on drag reduction in fluid flowLotus inspired hierarchical structuresAnother model surface from nature for a low drag surface is shark skin which is covered by very small individual tooth-like scales, ribbed with longitudinal grooves. These grooved scales reduce vortices formation present on a smooth surface, resulting in water moving efficiently over their surface.

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 27

Page 28: VA. Superhydrophobicity and Shark Skin

• Fabrication of hierarchical structureReplication of micropatterned silicon surface using an epoxy resin and then cover with Lotus wax

• Fabrication of shark skinReplication of shark skin surface using an epoxy resin

Y. C. Jung and B. Bhushan, J. Phys.: Condens. Matter 22, 035104 (2010)

• Fabrication of the flow channel for the measurement of pressure drop

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 28

Page 29: VA. Superhydrophobicity and Shark Skin

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 29

To observe the fluid drag reduction in the channel using water flow

• Hierarchical structure with highest static contact angle and lowest contact angle hysteresis provided the highest propensity of reduction of pressure in water flow.

• Drag reduction in turbulent flow with various structures is higher than that in laminar flow. In turbulent flow, the largest drop is in the case of shark skin replica.

Y. C. Jung and B. Bhushan, J. Phys.: Condens. Matter 22, 035104 (2010)

Page 30: VA. Superhydrophobicity and Shark Skin

Slip length on the surfaces with different wettabilities

Slip length in the channel:

35

2H

pWHQLb −

∆=

η

• The microstructure and shark skin replica had slip lengths of 56 and 35 µm, but nanostructure and hierarchical structures show higher slip lengths of 91 and 103 µm, respectively, which implies the boundary slip increases with increasing hydrophobicity of solid surfaces.

Y. C. Jung and B. Bhushan, J. Phys.: Condens. Matter 22, 035104 (2010)Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 30

Page 31: VA. Superhydrophobicity and Shark Skin

To investigate the effect of air flow in the channel and compare them to the water drag reduction

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 31

• Unlike the result of water flow in the channel, the pressure drop of microstructure, hierarchical structure, and shark skin replica became higher than that of hydrophilic flat surfaces and nanostructure with increasing Reynolds number.

• The structures on the surfaces may cause air to move around them, resulting in forming vortices and large fluid drag in air flow.

Y. C. Jung and B. Bhushan, J. Phys.: Condens. Matter 22, 035104 (2010)

Page 32: VA. Superhydrophobicity and Shark Skin

Summary• Increasing roughness on a hydrophilic surface decreases the contact angle, whereas an

increase on a hydrophobic surface increases contact angle. However, air pocket formation can change a hydrophilic surface to a hydrophobic surface.

• For fluid flow applications, for drag reduction, a surface should have high contact angle and low contact angle hysteresis. This condition should be achieved by high fLA and relatively low value of Rf.

• The transition occurs from Cassie-Baxter regime to Wenzel regime below a certain radius of droplet and/or above a certain pitch value.

• Hierarchical structures are produced using replication of micropattern and self assembly of hydrophobic alkanes and waxes, which provide flexibility in fabrication of variety of hierarchical structures.

• The created hierarchical surface shows a high static contact angle of 173 and low hysteresis angle of 1 which were superior to natural plant leaves including Lotus, and have superior resistance to the dynamic effects and maintanin stable composite solid-air-liquid interface for superhydrophobic and self-cleaning surfaces.

• Mechanically durable CNT-composite hierarchical structures are produced using spray method and show good stability of wetting properties from long-term exposure and high water pressure as well as high mechanical strength and wear resistance.

• Drag reduction efficiency on biomimetic structured surfaces has been investigated through pressure drop measurement in the channels using laminar and turbulent flows and increases with increasing hydrophobicity.

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 32

Page 33: VA. Superhydrophobicity and Shark Skin

References • M. Nosonovsky and B. Bhushan (2005), “Roughness optimization for biomimetic surperhydrophobic surfaces,” Microsyst. Technol. 11, 535-549• B. Bhushan and Y. C. Jung (2006), “Micro- and nanoscale characterization of hydrophobic and hydrophilic leaf surfaces,” Nanotechnology 17, 2758-2772• Y. C. Jung and B. Bhushan (2006), “Contact angle, Adhesion and Friction Properties of Micro- and Nanopatterned Polymers for Superhydrophobicity,” Nanotechnology 17, 4970-4980• B. Bhushan and Y. C. Jung (2007), “Wetting Study of Patterned Surfaces for Superhydrophobicity,” Ultramicroscopy 107, 1033-1041• B. Bhushan, M. Nosonovsky, and Y. C. Jung (2007), “Towards optimization of patterned superhydrophobic surfaces,” J. R. Soc. Interface 4, 643-648• Y. C. Jung and B. Bhushan (2007), “Wetting Transition of Water Droplets on Superhydrophobic Patterned Surfaces,” Scripta Mater. 57, 1057-1060• M. Nosonovsky and B. Bhushan (2007), “Hierarchical Roughness Makes Superhydrophobic Surfaces Stable,” Microelectronic Eng. 84, 382-386• M. Nosonovsky and B. Bhushan (2007), “Hierarchical roughness optimization for biomimetic superhydrophobic surfaces,” Ultramicroscopy 107, 969-979• M. Nosonovsky and B. Bhushan (2007), “Biomimetic Superhydrophobic Surfaces: Multiscale Approach,” Nano Letters 7, 2633-2637• M. Nosonovsky and B. Bhushan (2007), “Multiscale friction mechanisms and hierarchical surfaces in nano- and bio-tribology,” Mater. Sci. Eng.:R 58, 162-193• Y. C. Jung and B. Bhushan (2008), “Wetting Behavior During Evaporation and Condensation of Water Microdroplets on Superhydrophobic Patterned Surfaces,” J. Microsc. 229, 127-140• B. Bhushan and Y. C. Jung (2008), “Wetting, Adhesion and Friction of Superhydrophobic and Hydrophilic Leaves and Fabricated Micro/nanopatterned surfaces,” J. Phys.: Condens. Matter 20,

225010• M. Nosonovsky and B. Bhushan (2008), “Roughness-induced superhydrophobicity: a way to design non-adhesive surfaces,” J. Phys: Condens.Matter 20, 225009• M. Nosonovsky and B. Bhushan (2008), “Patterned Non-Adhesive Surfaces: Superhydrophobicity and Wetting Regime Transitions,” Langmuir 24, 1525-1533• M. Nosonovsky and B. Bhushan (2008), Multiscale Dissipative Mechanisms and Hierarchical Surfaces: Friction, Superhydrophobicity, and Biomimetics, Springer-Verlag, Heidelberg, Germany• K. Koch, B. Bhushan, and W. Barthlott, (2008), “Diversity of Structure, Morphology, and Wetting of Plant Surfaces (invited),” Soft Matter 4, 1943-1963• K. Koch, B. Bhushan, and W. Barthlott, (2009), “Multifunctional Surface Structures of Plants and Their Occurrence in Various Environments: An Inspiration for Biomimetics (invited),” Prog. Mater.

Sci. 54, 137-178• Y. C. Jung and B. Bhushan (2008), “Dynamic Effects of Bouncing Water Droplets on Superhydrophobic Surfaces,” Langmuir 24, 6262• B. Bhushan, K. Koch, and Y. C. Jung (2008), “Nanostructures for Superhydrophobicity and Low Adhesion,” Soft Matter 4, 1799-1804• B. Bhushan, K. Koch, and Y. C. Jung (2008), “Biomimetic Hierarchical Structure for Self-Cleaning,” Appl. Phys. Lett. 93, 093101• B. Bhushan, K. Koch, and Y. C. Jung (2009), “Fabrication and Characterization of the hierarchical Structure for Superhydrophobicity,” Ultramicroscopy 109, 1029-1034• B. Bhushan, Y. C. Jung, A. Niemietz, and K. Koch (2009), “Lotus-like Biomimetic Hierarchical Structures Developed by Self-assembly of Tubular Plant Waxes,” Langmuir 25, 1659-1666• K. Koch, B. Bhushan, Y. C. Jung, and W. Barthlott (2009), “Fabrication of artificial Lotus leaves and significance of hierarchical structure for superhydrophobicity and low adhesion,” Soft Matter 5,

1386-1393• B. Bhushan, Y. C. Jung, and K. Koch (2009), “Self-Cleaning Efficiency of Artificial Superhydrophobic Surfaces,” Langmuir 25, 3240-3248• B. Bhushan, Y. C. Jung, and K. Koch (2009), “Micro-, nano- and hierarchical structures for superhydrophobicity, self-cleaning and low adhesion,” Phil. Trans. R. Soc. A 367, 1631-1672• Y. C. Jung and B. Bhushan (2009), “Dynamic Effects Induced Transition of Droplets on Biomimetic Superhydrophobic Surfaces,” Langmuir 25, 9208-9218• Y. C. Jung and B. Bhushan (2009), “Wetting Behavior of Water and Oil Droplets in Three Phase Interfaces for Hydrophobicity/philicity and Oleophobicity/philicity,” Langmuir 25, 14165-14173. • Y. C. Jung and B. Bhushan (2010), “Biomimetic Structures for Fluid Drag Reduction in Laminar and Turbulent Flows,” J. Phys.: Condens. Matter 22, 035104.• M. Nosonovsky and B. Bhushan (2009), “Superhydrophobic surfaces and emerging applications: non-adhesion, energy, green engineering,” Curr. Opin. Colloid Interface Sci. 14, 270-280• Y. C. Jung and B. Bhushan (2009), “Mechanically Durable CNT-Composite Hierarchical Structures with Superhydrophobicity, Self-Cleaning, and Low-Drag,” ACS Nano 3, 4155-4163.

http://www.mecheng.osu.edu/nlbb/

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 33


Recommended