CONTACT ANGLES

1. ARVIND TOMAR Sr-08471 CONTACT ANGLES

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

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. 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

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

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,

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 Θron 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