Wetting behaviors of a c h si o film coated nano scale structured surface
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Wetting Behaviors of a-C:H:Si:O Film Coated Nano-scale Structured Surface. Tae-Young Kim * , *** , Bialuch Ingmar **, Klaus Bewilogua **, Kyu Hwan Oh ***and Kwang-Ryeol Lee * * Future Technology Research Division, KIST, KOREA ** New Tribological Coating, Fraunhofer IST, GERMANY

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Wetting behaviors of a c h si o film coated nano scale structured surface

Wetting Behaviors of a-C:H:Si:O Film Coated Nano-scale Structured Surface

Tae-Young Kim*,*** , Bialuch Ingmar **, Klaus Bewilogua **,

Kyu Hwan Oh ***and Kwang-Ryeol Lee *

* Future Technology Research Division, KIST, KOREA

** New Tribological Coating, Fraunhofer IST, GERMANY

***Department of Materials Engineering, SNU, KOREA


Lotus surface
Lotus Surface

  • Properties of Lotus leave

    • Water wetting angle exceeds 150o

    • Wetting angle hysteresis is below 10o

  • Water repellent and/or surface self cleaning effect


Lotus surface1
Lotus Surface

50μm

20μm

Planta, 202,(1998) 1

  • Surface Material - cuticular wax

  • Surface morphology – very rough in micrometer scale

Control of surface chemical and structure enhances hydrophobic property


Super hydrophobic surface
Super-hydrophobic Surface

  • Water repellent surface

  • Self cleaning of surface

  • Surface energy induced drop motion

  • Low resistance coating against liquid flow


Super hydrophobic
Super Hydrophobic

What is super-hydrophobic?

Super

hydrophobic

hydrophobic

hydrophilic

150o

90o

Flat surface

chemical control

Surface chemical+roughness

control

120o


Just rough surface
Just Rough Surface??

Which surface is more hydrophobic?


Just rough surface1
Just Rough Surface?

Water droplets behave differently on tilted surfaces because of the contact angle and contact angle hysteresis.

Wetting angle hysteresis = advancing wetting angle –receding wetting angle


Purpose of this work
Purpose of This Work

  • Super hydrophobic surface generation

    • Hydrophobic DLC coating

    • Surface roughness controlled by Si etching process

  • Goal

    • Static wetting angle >150o

    • wetting angle hysteresis < 10o

  • Optimizing surface roughness structure

    • Mono roughness

    • Double roughness


Experimental process
Experimental Process

Thin metal(Cu) film deposition

Metal dot formation

by heat treatment

Si wafer

Plasma etching conditions

CF4+O2etched surface is flat

CF4formation of nano post on etched

surface


Plasma si etching
Plasma Si Etching

Plasma source gas : CF4

Nano post formation

Plasma source gas : CF4+O2

Flat etched surfac


Surface structure manipulation

Si wafer

Si wafer

Si wafer

Surface Structure Manipulation

CF4+O2 plasma

Si wafer

CF4+O2 plasma

CF4 plasma

CF4 plasma

Si wafer

Hydrophobic a-C:H:Si:O deposition


Wetting angle analysis
Wetting Angle Analysis

  • Static wetting angle (apparent wetting angle)

    • Water drop volume : 5μL

    • Gently drop on the surface

  • Dynamic wetting angle

    • Water drop size continuously changed (0.053 μL/sec)

    • Advancing angle (AA): 0 to 5 μL

    • Receding angle (RA): 5 to 0 μL

    • Wetting angle hysterisis : AA-RA


Static wetting angle

DLC coated nano post

Static Wetting Angle

DLC coated Si(110)


Static wetting angle1

DLC coated big post

DLC coated DRS

Static Wetting Angle


Dynamic wetting angle

DLC coated nano post

Dynamic Wetting Angle

DLC coated Si(110)


Dynamic wetting angle1

DLC coated big post

DLC coated DRS

Dynamic Wetting Angle


Double rough structure effect

DRS

BP

Double Rough Structure Effect

DRS is more hydrophobic and suitable for moving droplet application than BP.

The difference in structure is just bottom nano post in DRS DRS effect


Summary
Summary

  • We fabricated double rough structure by nano structuring of Si.

  • Double rough structure shows high static wetting angle and low wetting angle hysteresis.

  • Double rough structure could be effective structure for moving droplet application.

But why?


Thermodynamical calculation
Thermodynamical Calculation

  • System idealization

    • Surface structure : circular post type

    • Variables : post radius(Pr), post height(Ph), solid fractional factor (f), roughness factor (r), water drop radius(R), young contact angle(θy)

R

Pr

Ph


Thermodynamical calculation1
Thermodynamical Calculation

R

Pr

Ph

Lamgmuir 2004, 20, 10015

Langmuir 2003, 19, 8343


Calculations
Calculations

System definition:

Pr (205nm), Ph(413nm), f (0.5)

(93o), R (5*109)


Drs calculation
DRS calculation

0<z<h: calculation results same with BP



Small post structure
Small Post Structure

System definition:

Pr (35nm), Ph(131nm), f (0.5)

(93o), R (5*109)


Big post structure
Big Post Structure

System definition:

Pr (2565nm), Ph(393nm), f (0.065)

(93o), R (5*109)


Double rough structure
Double Rough Structure

System definition:

Pr (201nm), Ph(436nm), f (0.08)

(93o), R (5*109)

(134o)


Hysteresis and energy barrier w c

BP

DRS

Hysteresis and Energy Barrier (WC)


Conclusion
Conclusion

  • We fabricated double rough structure by nano structuring of Si.

  • Double rough structure shows high static wetting angle and low wetting angle hysteresis.

  • Double rough structure could be effective structure for moving droplet application.

  • Low hysteresis in DRS would caused by decrement of detaching energy barrier.


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