Lect 7-8_Surface I_Adhesion n Wetting_print(1)

8/11/2019 Lect 7-8_Surface I_Adhesion n Wetting_print(1)

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3/27/2014

MSE 598/494 Bio-inspired Materials and Biomaterials MSE 598/494 Bio-inspired Materials and Biomaterials

Instructor: Ximin He

TA: Xiying Chen Email: [email protected]

2014-03-27

Lecture 7 & 8. Biomimetic Surfaces I

Adhesion & Wetting

Surface Science

As old as civilization

Administering oil to the surface of wooden planksin ships to reduce friction with water

Deposition of poison on arrowheads

…

Innovations aimed to endow surfaces with desiredproperties through modifying their structures,

compositions, and molecular organizations.2



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3

Adhesive

Climb the wall

A "glue" to stick minerals back on eroded teeth

Adhesive in water

4



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5

Minimizeflow resistance

Swim faster

V.S.

See clearly

6



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Anti-reflection (AR)

7

Superior Anti-reflection Lens

“nano-bumps”

8

Moth’s Eyes



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SURFACE

Anti-• Scratch• Water• Smudges• Reflection• Dust

…

9

More colorful…life

10



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Fluid transport

Ultra-Slipperiness Water-RepellencyFluid Harvesting

Smart AdhesiveStructural Colors

Anti-Fogging

Bio-inspired

SURFACE/INTERFACEscience & engineering

11

What you will learn in the next 90 minutes?

Lecture 7. Adhesion

• Dry adhesion: gecko feet

• Wet adhesion: mussel glue

Lecture 8. Wetting

• Liquid repellent: lotus leaf, pitcher plant • Antifogging:moth’s eye

• Water vapor harvesting: namib desert beetle 12





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Structure Functionattachment, detachment, self-cleaning…

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Structures?• Hierarchical

Fundamental Study: Johnson et al. developed the Johnson–Kendall–Roberts(JKR) model by considering interactions between adhesive elasticspheres, in which the size of the contact area was determined viaa balance betweenelastic and surface energies

Micro-hairs: setaeNano-hairs: spatulae

Experimental: Adhesion Characteristics 1. Anisotropic Adhesion. Gecko’s toes can actively switch its toedirection for easy attachment and detachment .2. Low Normal Detaching Force. The detaching force required for liftingthe gecko–foot–toe from the contacted surface nearly equals zero.3. High Compatibility. Gecko exhibits high adhesion capability to wet ordry and molecularly smooth or very rough surfaces.4. Self-cleaning and Anticollapse Properties.Gecko’s setae are made ofelastic protein with a modulus of 2–4 GPa; β-keratin can prevent theimpure contaminations from adsorbing

Hoon, E. J.; Kahp, Y. S. Nano Today 2009 , 4, 335.

Structural Requirement for Synthetic Dry Adhesives

1. Small Fibril Radius.Contact Splitting theory: the adhesion force α the fibril radius2. High Aspect Ratio.Mechanism of crack propagation in rubbery materials: a high aspectratio ↑ No. of fibrils to contact the surface, ↓ Modulus foreffective elastic energy dissipation3. Slanted Structures.Shear and normal contact experiments: an angled structure

significantly lowers the effective modulus of the surface. A directional angle of the nanostructured fibers is a crucial factorfor anisotropic, reversible dry adhesive (i.e., strong attachment andeasy detachment)

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Fabrication of Synthetic Dry Adhesives

Two main approaches:1. micro/nanoscale casting (polymers)using a variety of lithography techniques: e-beam lithography,photolithography, electrochemical etching, etc

2. gas phase growth (CNTs)

indenting a wax with an AFM tip and then molding polymerinto that wax mold

Metin, S.; Ronalds, F. J. Adhes. Sci. Technol . 2003 , 17, 1055..

i) Structures of High Aspect Ratio (HAR)

• PDMS: limited the mechanical stability of HAR pillars2.5 to 25 μm in radius and 2.5 to 80 μm in height with the aspectratio between 0.5 and 4. Critical AR >0.5 ↑ AR ↔ ↑ adhesion• E-beam lithography: HAR but slow and expensive

An array of micropillars made bymicropatterning polyimide hairs.Scale bars: 2 μm.

(b) Upon several detachment–attachmentcycles, its adhesive property degradeddue to hairs breaking and lateral bunching .

Geim, A. K.; Dubonos, S. V.; Grigorieva, I. V.; Novoselov, K.S.; Zhukov, A. A.; Shapoval, A. A. Nat. Mater . 2003 , 2, 461.



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i) Structures of High Aspect Ratio (HAR)

• Capillarity-driven Rigiflex Lithography aided by modulatedinterfacial tensions

stretched PMMA nanohairs on PET film

Jeong, H. E.; Lee, S. H.; Kim, P.; Suh, K. Y. Nano Lett . 2006 , 6, 1508.

ii) Directional Structure

A directional angle of the nanostructure is another crucial factor for• Anisotropic (strong attachment and easy detachment) and reversible

dry adhesions.• Significantly lower the effective modulus of a hair surface and

prevent structural bucking under a preload

• a diameter of 8 μm and a tilting angle of 25 o with a good flexibilityand a normal adhesion of 2.5–3.2 N/cm 2

• Good adhesion on glass but difficult demolding without fracturing Aksak, B.; Murphy, M. P.; Sitti, M. Langmuir 2007 , 23, 3322.



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Thermal annealing

E-beam irradiation

CO 2gas

A greater adhesion hysteresis:• the strong shear attachment when pulled from the bent direction (31 N/cm2)• contrasted with the easy detachment from the opposite direction (4.1 N/cm2)

Jeong, H. E.; Kim, T.; Kang, T. J.; Yoon, H.; Char, K.; Suh, K. Y.; Tahk, D. Nano Today 2009 , 4, 385.


• Shear force: Forward v.s. Reversedfor easy attachment and detachment

22 Kim, T.; Jeong, H. E.; Suh, K. Y.; Lee, H. H. Adv. Mater . 2009 , 21, 2276..



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• Tilting angle ↔ Shear force

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(a) Si master substrates (left) and formed PUA nanohairs (right) with different leaningangles, Scale bar = 400 nm. (b) Measured macroscopic shear adhesion force with anadhesive patch having PUA nanohairs with different leaning angles against a smoothglass surface upon removing preload of 0.3 N/cm.

Jeong, H. E.; Lee, J. K.; Kwak, M. K.; Moon, S. H.; Suh, K. Y. Appl. Phys. Lett . 2010 , 96, 043704.

iii) Tips structures

• Observed in different animals: spherical, conical, filament-like,band-like, sucker-like, spatula-like, flat, and toroidal tip

• Heavier animals exhibit Finer adhesion

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Beetle Fly Spider GeckoTerminal elements (circled areas) in animals with hairy design of attachment pads

Arzt, E.; Gorb, S.; Spolenak, R. Proc. Natl. Acad. Sci. U.S.A . 2003 , 100, 10603.



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iii) Tip structures

• various micro-to-nanoscale structures

25del Campo, A.; Greiner, C.; Alvarez, I.; Arzt, E. Adv. Mater . 2007 , 19, 1973.

3-D Structure with Special Mushroom-Headed

• Mushroom-shaped head was demonstrated to yield the mostsignificant enhancement of adhesion

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polyurethane fibers cast from a negative silicone rubber mold produced by acommercial acrylic master mold

Sameoto, D.; Menon, C. Smart Mater. Struct . 2010 , 19, 103001.



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3-D Structure with Special Mushroom-Headed

• The combination of the tilted fibers and mushroom-shaped tipscan allow for a significant load of 1 kg/cm2 in shear direction.

• Exhibit directional characteristics of gripping when loaded in onedirection, but self-releasing behavior when loaded in the oppositeshear direction.

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34 o 90 o

23 o 23 o

35 μm diameter

Michael, P. M.; Burak, A.; Sitti,M. Small 2009 , 5, 170.

iv) Multilevel Complex Hierarchical Structures

• Challenge: adhere to surfaces with varyingroughnesses

• Each of the fibers deforms independently ,allowing them to access deeper recessions tomake an intimate contact with the surface

• Spring-based models predicted: appropriatemultilevel hierarchical structuresshouldexhibit a higher adhesive force due toimproved adaptation and attachment ability.

two-step photolithography and soft molding

two-step UV-assisted capillary force lithography28 Jeong, H. E.; Lee, J. K.; Kim, H. N.; Moon, S. H.; Suh, K. Y. Proc. Natl. Acad. Sci . 2009 , 106, 5639.



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iv) Multilevel Complex Hierarchical Structures

Three-level hierarchical polyurethane fibers:(a) 400 μm Ø curved base fibers; (b) base fiber tip with midlevel Ø 50 μm fibers(c) midlevel fibers in detail; (d) terminal third level fibers at the tip of the midlevelfibers are 3 μm Ø and 20 μm in height and have 5 μm Ø flat mushroomtips.

Increased adhesion andinterface toughness :suggesting that a hierarchicalstructure could adhere withhigher strength to unevensurfaces with the roughnessamplitude on the same scaleas the length of the base

fibers

Murphy, M. P.; Kim, S.; Sitti, M. ACS Appl. Mater. Interfaces 2009 , 1, 849.

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Gecko-foot-inspired ‘dry’ adhesive patch

Jeong, H. E. et al. Adv. Mater. 2011

A dense array of PDMS ‘micropillars’optimal adhesion to skin.

Gecko patch v.s. Conventional patch:• Multiple usage• Smoother ‘peel-off’(slight tilting efficient disengagement)

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Glue on Wet Surface?

• Adhesive proteins containing a high content of the catecholicamino acid 3,4-dihydroxy-L-phenylalanine (DOPA)

• DOPA forms extraordinarily strong yet reversiblebonds withsurfaces (adhesive force 800 pN/20nN)

Wet Adhesive: mussels

The reduced catechol form of dopa binds surfaces directly for adhesive bonding (left). Theoxidized states of dopa, the semiquinone and quinone, may be reduced by a thiol-rich partnerprotein to regain surface-binding ability. Cohesion within the bulk material (right) can be broughtabout by metal ion templating and oxidation chemistry, including radical-radical coupling.

J. Wilker, Nature Chemical Biology 2011



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• High amounts of DOPA: key to the extraordinary adhesion properties• Fe(III) in the byssus imparts strength and self-healing properties via DOPA:Fe(III)

cross-links. Al(III), Ga(III) and In(III)

Long-last water proof with novel Poly (dopaminemethacrylamideco-methoxyethyl acrylate) (p(DMA-co-MEA)

Synthetic Wet Adhesive

Birkedal, H. et al. PNAS (2011); Biomacromolecue (2013)

Messersmith, P. et al.Nature (2007); PNAS (2006)

Dual dry/wet adhesives

1. Achieve autonomous switching of adhesion2. Single-molecule mechanics on different oxide/metal surface

Smart Switchable Adhesive inspired bymussels and geckos



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Summary

35

Lecture 7. Adhesion

• Dry adhesion: gecko feet – Mechanism

– Structure, Feature, Properties

– Synthetic dry adhesive: fabrication – CNTs based; Other functions: self-healing (option for Lit Rev Presentation)

• Wet adhesion: mussel glue – Mechanism,

– Chemistry

– Synthetic wet (/dry) adhesives – Applications (option for Lit Rev Presentation)

36



3/27/2014

MSE 598/494 Bio-inspired Materials and Biomaterials MSE 598/494 Bio-inspired Materials and Biomaterials

Instructor: Ximin He

TA: Xiying Chen Email: [email protected]

2014-03-27

Lecture 8. Biomimetic Surfaces I

Wetting

PinningEdge

Liquid

When Liquid “sees” an Solid Edge: Pinning

Study Pinning: Micro to NanoControl Pinning: Devices and Materials

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The Need for Highly Repellent Materials – The “Sticky” Problems

Marine Fouling

Ice NucleationDrag Creation

Bacterial Fouling

Contamination

Blood Coagulation

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Parker &Lawrence 2001

NamibDesert Beetle

Deegan et al. 1997

Coffee Rings

Nature’s Strategy in Controlling Fluid-Surface Interactions

Bohn and Fedele 2004

Nepenthes Pitcher Plants

Neinhuis & Barthlott 1997

Lotus



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Vapor Liquid

θ a

∆ θ = θ a – θ r Hysteresis:

α

Solid

θ

Vapor Liquid

Contact Angle (CA): θ

Contact Angle, θ

Contact Angle Hysteresis, ∆ θ

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Ideal Solid

θ Vapor Liquid

Contact Angle (CA): θ

Contact Angle: How Much the Fluid “Likes”/“Hates” the Solid

γ LVcos θ = γ SV – γ LS Young (1805): Ideal Flat

Wenzel (1936): cos θ * = r cos θ Texture, Wetted

θ *

θ max ~ 120 o

(Nishino et al.,1999 )

Surface Chemistry :

Surface Chemistry + Physical Roughness:

Cassie-Baxter (1944): cos θ * = –1 + Φ s (cos θ + 1)

Texture, Non-wetted

θ * D

γ LV

γ SVγ LS

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MSNBC, a mantis

θ or θ *alone does not quantifyLiquid Repellency43

Microscopic Origin:

θ

Solid

θ

β

θ a

Contact Line Pinning Resists Liquid Mobility

2. Physical Edge1. Chemical Edge

θ aθ a

Liquidθ a

α Johnson & Dettre (1964)

Microscopic Origin:

θ

Heterogeneous Solid

Liquidθ a

α

Gibbs (1875)44



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Pinning Leads to Contact Angle Hysteresis

Vapor Liquid

θ a

∆ θ = θ a – θ r Hysteresis:

α

Gravity

Minimizing ∆ θ (i.e., Removing Pinning)is the KEY to Design Surfaces with

Extreme Liquid Repellency

Furmidge (1962)

γ LV(cos θ r – cos θ a ) =mg sin α

Dwidth

Retention Force Gravitational Force

45

The Lotus Effect

Barthlott & Neinhuis (1997): The Lotus Effect

Image Credit: Burton, Z. & Bhushan, B. (2005)

Dancing Water Droplet(Ben Hatton and Lidiya Mishchenko, Harvard)

High Water Mobility

46Mobile

Lotus Effect: “Air-cushion”

θ *Cassie-Baxter (1944)cos θ * = –1 + Φ s (cos θ + 1)

Liquid

Air Superhydrophobic State:θ * > 150 o & ∆θ * < 10 o

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Year

N o .

o f C i t a t i o n s

Impact of The Lotus Effect

>2500 papers since the inception of the Lotus Effect

Credit: Thomson Reuters ISI Web of Knowledge

T e ch n

ol o

gi c

al P r o

gr e

s s

Technological Limits

47

48

Technological Limits of the “Lotus” Technologies

Mobile

Lotus Effect:“Air-cushion”

θ *

Liquid

Air

Wenzel State

Cassie State

Non-Mobile

∆t TimeMobile

2. Repellency of Complex Fluids

1. Pressure Stability

Liquid

Air Liquid

Pressure

Low γ LV

Pentane released from a height of 10 cm

3. Self-healing/repairing Physical Textures

Tokay Gecko

Autumn, K., et. al . (2000) Nature 405, 681-685.

Is The Lotus Effect the only way to createliquid-repellent material (i.e., minimizing ∆θ )?48



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A Liquid Surface: Smooth and Chemical Homogeneous

Textured Solid

Water

Silicon Micro-textures

Canola Oil

Thin-liquid film, (i.e., θ * ~ 0o

)

Proof-of-Concept Experiment: The Kitchen Experiment

Thin LiquidFilm

Pitcher Plant Surface

Credits: Bohn & Federle, PNAS (2004)

Adhesive Fluid:Water-in-Oil

Emulsion

Secretion of Adhesive Fluid

Lessons Learned from Nature:

• Stable Lubricating Film

• Immiscibility

Pitcherplant:

Ant:

Inspiration from Nature: Nepenthes Pitcher Plants

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Chemical Affinity: “Like” Likes “Like”

Solid A

Solid B Liquid BLiquid A

Stable FilmFilm

Disrupted

Likes

Likes

Formation of Stable Lubricating Film:

Roughness Amplifies Chemical Affinity

Di s

p en

si n

g

S yr i n

g e

Di s

p en

si n

g

S yr i n

g e

Liquid Liquid

51

Liquid BLiquid A

Solid with Roughness R

h H

L

Assumptions: 1) L < Lcapillary ; 2) h < hcapillary ; 3) H > h; 4) Immiscibility and Non-reactivity

For Stable Film Formation , ∆E 1 > 0 & ∆E 2 > 0, where

∆E 1 = R (γ Bcos θ B – γ Acos θ A) – γ AB; ∆E 2 = R (γ Bcos θ B – γ A cos θ A) + γ A – γ B

Design Principle: Modeling the Film Stability

E A = R γ SA + γ A

E 2 = R γ SB + γ B

Dry Partial Wetting

E 1 = R γ SB + γ AB + γ A

Complete Wetting

∆E 2 = E A – E 2 ∆E 1 = E A – E 1

Vapor

52



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Silanized EpoxyNon-Silanized Epoxy

T = 0s T = 5s T = 10s

Dyed Pentane

Stable FilmFilm

Disrupted

1 cm

Lubricating Film

Design Principle: Experimental Verification

∆E 1 > 0and

∆ E 2 > 0

∆E 1 < 0and

∆ E 2 < 0

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Regular Nano-array

5 μm

Random Nanofibers

5 μm

Examples of Porous Solids

FunctionalizedPorous/Textured Solid

Lubricating Film Liquid

Tilt

SLIPS: Slippery Liquid-Infused Porous Surfaces

Direct Mimicry of Nature: Insect Repellency

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Technological Performance Comparison

Lotus Leaf-Inspired Technology Pitcher Plant-Inspired Technology

VS

1.Omniphobicity2.Self-Healing3.Pressure Stability4.Repellency to Complex Fluids

55

56

1. Omniphobicity and Ultra-Liquid Repellency

Lotus Leaf Inspired Technology

Pitcher Plant Inspired Technology


θ *

Liquid

Air

Low γ LV Liquid

Pitcher Plant Effect:“Liquid-cushion”

θ *

Liquid Low γ LV Liquid

Liquid Liquid56



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Comparison with Best Synthetic Lotus Surface

1. Omniphobicity and Ultra-Liquid Repellency

SLIPS

Hexane

α = 3.0

t = 0.00 s

t = 0.77 s

Hexane

SLIPS

1 mm

α

Liquid Repellency at Ultra-low Tilt

57

58

2. Self-Healing




θ *

Liquid

Air

Damage Liquid


θ *

Liquid Damage Liquid

Liquid Liquid



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2. Self-healing and Optical Transparency

5 mm

Damage

Self-healed

T = 0 ms

T = 150 ms

59

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3. Pressure Stability




θ *

Liquid

Air

Pressure Liquid


θ *

Liquid Pressure Liquid

Liquid Liquid





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Blood P. aeruginosa (bacteria)

4. Repellency to Complex FluidsCrude Oil

S L I P

S

L o

t u s - I n s p

i r e d S u r f a c e

4a. Persistent Resistance to Biofilm Formation24 hours 7 days

Under Flow Condition

SLIPS

Lotus-Inspired Surface

Bacteria

Bacteria

Bacteria:Pseudomonas aeruginosa (Sepsis)Staphylococcus aureus (Pneumonia, Sepsis)Escherichia coli (Food Poisoning)



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Self-cleaning

Ice-Repellency Anti-StickingSLIPS – What’s More

65

Porous/Textured Solid Lubricating Film Liquid

Tilt

Oil RepellentBlood Repellent Biofilm-Resistant

Self-Healing Self-Cleaning

Ice Repellent

Pressure StableSLIPS

Transparent

Summary

Wong, T.-S. et al., Nature , 477: 443 – 447 (2011)Best Inventions using Biomimicry of Year 2011



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SLIPS as the Next Wave of Functional Materials

Anti-Soiling

Anti-Soiling

Anti-Biofouling

Reduced Friction

Anti-Icing

Anti-Graffiti

Defrosting

Reduced Friction

Antiseptic

Anti-Soiling

Anti-Stick

Range of ApplicationsSLIPS

S O L I D

L U B R

I C A N T

RoughnessPorosityTransparency

ViscosityTransparencyBoiling Pt.Freezing Pt.Biocompatibility

67

• Lives in one of the driest deserts: southwest Africa, but obtains all of the water it needs fromocean fog due to the unique surface of its back

• Microscopic bumps with hydrophilic (waterattracting) tips and hydrophobic (waterrepelling) sides cover its hardened forewings,which it aims at oncoming fog each morning

Namib desert beetle ( Stenocara gracilipes )

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Homework of Lecture 7-8

1. Please describe the mechanism of gecko-feet dry adhesion fromthe aspect of the structure, feature and functions.

2. Please state the principal of wetting at solid-liquid-air interface.

• Due by 04/08/2014• Hand in hard copy of homework at the TA, Xiying Chen, at the

beginning of the 04/08 class• Please contact [email protected] for questions.

Documents

Lect 7-8_Surface I_Adhesion n Wetting_print(1)