1. CONTACT ANGLES
ARVIND TOMAR
Sr-08471

2. Contact angle

3. FACTORS AFFECTING CONTACT ANGLE
SURFACE TENSION
SURFACE ENERGY OF SOLID SURFACES
INTERACTION FORCES BETWEEN LIQUID MOLECULES
SURFACE ROUGHNESS
TEMERATURE OF LIQUID

4. SURFACE TENSION

5. SURFACE TENSION IS A CONTRACTIVE TENDENCY OF SURFACE OF A LIQUID
THIS ALLOWS IT TO RESIST AN EXTERNAL FORCE
DUE TO SURFACE TENSION A LIQUID ACQUIRE MINIMUM SURFACE AREA
DUE TO SURFACE TENSION LIQUID SURFACE BAHAVES AS A STRECHED SKIN
SURFACE TENSION IS CAUSED BECAUSE OF MOLECULER ATTRACTION FORCES
IN GENERAL DISSOLVED CONTAMINATION IN WATER REDUCES SURFACE TENSION, HENCE ALSO THE CONTACT ANGLE

6. DUE TO SURFACE TENSION A NEEDLE CAN FLOAT ON A LIQUID

7. SURFACE TENSION =FORCE/LENGTH
=WORK DONE /AREA
TO SEPRATE TWO LIQUID SURFACES WE HAVE TO DO WORK
THIS PER UNIT AREA WORK IS CALLED SURFACE TENSION
THIS WORK INCREASES POTENTIAL ENERGY OF LIQUID

8. AS SURFACE TENSION REDUCES, DROPLETS TENDS TO SPREADS AND CONTACT ANGLE DECREASES
GREATER THE PORTION OF POLAR GROUPS,HIGHER THE ATTRACTIVE FORCES,HIGHER SURFACE TENSION AND HIGH WILL BE THE CONTACT ANGLE
EX. WATER HAS HIGHER CONTACT ANGLE AS COMPARED TO OILS

9. SURFACES BENDS TO BALANCE FORCES

10. YOUNG-LAPLACE EQUATION
ΔP=σ[1/Rx +1/Ry]

11. HIGHER THE SURFACE TENSION HIGHER WILL BE CONTACT ANGLE

12. SURFACE ENERGY HIGHER THE SURFACE ENERGY LOWER WILL BE CONTACT ANGLE
HIGH SURFACE ENERGY OVERCOMES SURFACE TENSION AND LIQUID DROPLET SPREADS OVER SURFACE
HIGHER THE SURFACE ENERGY HIGHER THE ADHESION
SURFACE IS ALWAYS AT HIGHER ENERGY AS COMPARED TO BULK

13. DEPENDENCE OF CONTACT ANGLE ON SURFACE ENERGY AND SURFACE TENSION

14. SURFACE ENERGY DEPENDS ON CHEMICAL COMPOSITION AT SURFACE
POLAR GROUPS CAUSES HIGH SURFACE ENERGY
CLEAN METALIC SURFACES HAVE HIGH SURFACE ENERGY
BONDING BETWEEN HYDROCARBON MOLECULES IS LESS
POLYETHYNES HAVE LESS SURFACE ENERGY AND HIGHER CONTACT ANGLE

15. FOR UNPOLISHED SURFACE THERE ARE SO MANY POLAR GROUP(EX
FOR UNPOLISHED SURFACE THERE ARE SO MANY POLAR GROUP(EX. O-H) SO HAD HIGHER ENERGY
SURFACE ENERGY OF SURFACE CAN BE REDUCED BY POLISHING WAX

16. WATER PROOF FABRICS
FLOURINATED FABRICS, WHICH ARTIFICIALLY MAKE A SURFACE LOW ENERGY ONE
THUS MORE CONTACT ANGLE AND SURFACE IS NON-WETTING
BY FORMING OXYGEN CONTAINING COMPOUNDS AT SURFACE A LOW ENERGY SURFACE CAN BE CONVERTED INTO A HIGH ENERGY ONE
THIS CAN BE ACHEIVED BY EXPOSURE TO UV-RADIATION,CORONA/PLASMA DISHCHARGE, ACID TREATMENT etc.

17. NON-WETTING FABRIC

19. INTERACTION FORCES BETWEEN LIQUID MOLECULES
CONTACT ANGLE
(IN DEGREES)
DEGREE OF WETTING
SOLID-LIQUID INTERACTION
LIQUID-LIQUID INTERACTION
θ=0
PERFECT WETTING
VERY STRONG
VERY WEAK
0<θ<90
HIGH WETTING
STRONG
WEAK
90≤θ<180
LOW WETTING
θ=180
PERFECTLY NON-WETTING

20. SURFACE ROUGHNESS
WITH INCREASING SURFACE ROUGHNESS CONTACT ANGLE DECREASES FOR HYDRO-PHILIC SURFACE
WITH INCREASING SURFACE ROUGHNESS CONTACT ANGLE INCREASES FOR HYDRO- PHOBIC SURFACE

22. TEMPERATURE
WITH INCREASING OF TEMPERATURE SURFACE TENSION DECREASES AS INTERMOLECULER FORCE DECREASES
THUS WITH INCREASING OF TEMPERATURE CONTACT ANGLE DECREASES

23. BALANCE OF FORCES

24. γsl +γlg*cosθc =γsg
YOUNG'S EQUATION

25. TWO DIFFRENT LIQUIDS

26. METHODS FOR MEASURING CONTACT ANGLE
THE STATIC SESSILE DROP METHOD
THE DYNAMIC SESSILE DROP METHOD
DYNAMIC WILHELMY METHOD
POWDER CONTACT ANGLE METHOD

27. Young-dupre equation γ(1+cosθc)= ∆Wsl Here,
∆Wsl=solid-liquid adhesion energy per unit area

28. CALCULATION FOR CONTACT ANGLE
θc=arcCOS[rAcosθA+rRcosθR/rA+rR]
Where,
CALCULATION FOR CONTACT ANGLE

29. ΘA= advancing angle
ΘR= receding angle
ADVANCING ANGLE:- largest contact angle possible without increasing solid-liquid interfacial area by adding volume dynamically
RECEDING ANGLE:- if in above case you start removing volume then smaalest possible angle is called receding angle

31. Calculation of Θa and Θr on a tilted plane

32. Hysteresis angle H=Θa-Θr
Hysteresis angle for an ideal solid surface is zero i.e. Θa=Θr
With increasing roughness H increases
With increasing roughness Θa increases and Θr decreases
Increased liquid penetration leads to increased hysteresis

33. THANK YOU