CONTACT ANGLES
ARVIND TOMAR
Sr-08471
Contact angle
FACTORS AFFECTING CONTACT
ANGLE
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SURFACE TENSION
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SURFACE ENERGY OF SOLID SURFACES
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INTERACTION FORCES BETWEEN LIQUID
MOLECULES
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SURFACE ROUGHNESS
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TEMERATURE OF LIQUID
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
DUE TO SURFACE TENSION A NEEDLE CAN FLOAT
ON A LIQUID
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SURFACE TENSION =FORCE/LENGTH
=WORK DONE /AREA
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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
SURFACES BENDS TO BALANCE
FORCES
YOUNG-LAPLACE EQUATION
ΔP=σ[1/Rx +1/Ry]
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HIGHER THE SURFACE TENSION HIGHER WILL
BE CONTACT ANGLE
SURFACE ENERGY
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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
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
WATER PROOF FABRICS
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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
NON-WETTING FABRIC
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 NONWETTING
VERY WEAK
VERY STRONG
SURFACE ROUGHNESS
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WITH INCREASING SURFACE ROUGHNESS
CONTACT ANGLE DECREASES FOR
HYDRO-PHILIC SURFACE
WITH INCREASING SURFACE ROUGHNESS
CONTACT ANGLE INCREASES FOR HYDROPHOBIC SURFACE
TEMPERATURE
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WITH INCREASING OF TEMPERATURE
SURFACE TENSION DECREASES AS
INTERMOLECULER FORCE DECREASES
THUS WITH INCREASING OF
TEMPERATURE CONTACT ANGLE
DECREASES
BALANCE OF FORCES
YOUNG'S EQUATION
γsl +γlg*cosθc =γsg
TWO DIFFRENT LIQUIDS
METHODS FOR MEASURING
CONTACT ANGLE
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THE STATIC SESSILE DROP METHOD
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THE DYNAMIC SESSILE DROP METHOD
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DYNAMIC WILHELMY METHOD
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POWDER CONTACT ANGLE METHOD
Young-dupre equation
γ(1+cosθc)= ∆Wsl
Here,
∆Wsl=solid-liquid adhesion energy per unit area
CALCULATION FOR CONTACT
ANGLE
θc=arcCOS[rAcosθA+rRcosθR/rA+rR]
Where,
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
Calculation of Θa and Θr on a tilted
plane
Hysteresis angle
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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
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Increased liquid penetration leads to increased
hysteresis
THANK YOU