contact angles

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CONTACT ANGLES ARVIND TOMAR Sr-08471

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ARVIND TOMAR Sr-08471. CONTACT ANGLES. Contact angle . FACTORS AFFECTING CONTACT ANGLE. SURFACE TENSION SURFACE ENERGY OF SOLID SURFACES INTERACTION FORCES BETWEEN LIQUID MOLECULES SURFACE ROUGHNESS TEMERATURE OF LIQUID. SURFACE TENSION. - PowerPoint PPT Presentation

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Page 1: CONTACT ANGLES

CONTACT ANGLES

ARVIND TOMARSr-08471

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Contact angle

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FACTORS AFFECTING CONTACT ANGLE

SURFACE TENSION SURFACE ENERGY OF SOLID SURFACES INTERACTION FORCES BETWEEN LIQUID

MOLECULES SURFACE ROUGHNESS TEMERATURE OF LIQUID

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SURFACE TENSION

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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

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DUE TO SURFACE TENSION A NEEDLE CAN FLOAT ON A LIQUID

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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

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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

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SURFACES BENDS TO BALANCE FORCES

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ΔP=σ[1/Rx +1/Ry]

YOUNG-LAPLACE EQUATION

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HIGHER THE SURFACE TENSION HIGHER WILL BE CONTACT ANGLE

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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

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DEPENDENCE OF CONTACT ANGLE ON SURFACE ENERGY

AND SURFACE TENSION

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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

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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

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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.

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NON-WETTING FABRIC

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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 STRONG

WEAK WEAK

90≤θ<180 LOW WETTING WEAK STRONG

θ=180 PERFECTLY NON-WETTING

VERY WEAK VERY STRONG

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SURFACE ROUGHNESS

WITH INCREASING SURFACE ROUGHNESS CONTACT ANGLE DECREASES FOR HYDRO-PHILIC SURFACE

WITH INCREASING SURFACE ROUGHNESS CONTACT ANGLE INCREASES FOR HYDRO-PHOBIC SURFACE

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TEMPERATURE

WITH INCREASING OF TEMPERATURE SURFACE TENSION DECREASES AS INTERMOLECULER FORCE DECREASES

THUS WITH INCREASING OF TEMPERATURE CONTACT ANGLE DECREASES

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BALANCE OF FORCES

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YOUNG'S EQUATION

γsl +γlg*cosθc =γsg

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TWO DIFFRENT LIQUIDS

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METHODS FOR MEASURING CONTACT ANGLE

THE STATIC SESSILE DROP METHOD THE DYNAMIC SESSILE DROP METHOD DYNAMIC WILHELMY METHOD POWDER CONTACT ANGLE METHOD

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Young-dupre equation

γ(1+cosθc)= ∆Wsl

Here,

∆Wsl=solid-liquid adhesion energy per unit area

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CALCULATION FOR CONTACT ANGLE

θc=arcCOS[rAcosθA+rRcosθR/rA+rR]

Where,

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ΘA= advancing angleΘR= receding angleADVANCING 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

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Calculation of Θa and Θr on a tilted plane

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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

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THANK YOU