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Surface & Interfacial Tension Ph

oto  courtesy  of  M

ike,  Flickr  

Photo  courtesy  of  Joy  Ito,  Flickr  

Prepared & Presented by:

Professor Abd Karim Alias Universiti Sains Malaysia

 

Surface & Interfacial Tension by Prof. Abd Karim Alias is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

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} Surface tension is the property of a liquid in contact with air that makes it behave as if it was covered with a thin membrane under tension.

Surface & Interfacial Tension

Abd Karim Alias, 2013

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} The molecule inside the liquid interact equally with other molecule, from all sides, whereas the molecule at the surface is affected only by the molecule below it ⇒ the molecules exposed to air behave differently & try to contract to the smallest possible area (hence spherical shape).

Surface & Interfacial Tension

Abd Karim Alias, 2013

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} Surface tension (N/m) is defined as the force acting over the surface of the liquid per unit length of the surface perpendicular to the force.

Surface & Interfacial Tension

Abd Karim Alias, 2013

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AIR

LIQUID

Air-liquid interface

Surface & Interfacial Tension

Abd Karim Alias, 2013

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} Surface tension (γs) can also be defined as the amount of energy (∆E) required to increase the surface area between a liquid and a gas (e.g. air and water) by an amount ∆A:

∆E = γs∆A

} Interfacial tension (γi) is defined as the amount of energy required to increase the interfacial area between two immiscible liquids (e.g. oil & water).

Surface & Interfacial Tension

Abd Karim Alias, 2013

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}  One very important quality of the colloids is the large interfacial area between the dispersed & the continuous phase

Importance of Large Interfacial Area

Abd Karim Alias, 2013

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We have 20 cm3 of oil in 1 cm radius droplets. Each has a volume of (4/3.π.r3) 5.5 cm3 and a surface area of (4.π.r2) 12.5 cm2. ⇒ We can have about 3.6 droplets ∴ we would have a total area of 45.5 cm2

The same oil is split into 0.1 cm radius droplets, each has a volume of 0.004 cm3 and a surface area 0.125 cm2. ⇒ We can have about 5000 droplets ∴ we would have a total area of 625 cm2!

Importance of Large Interfacial Area

Abd Karim Alias, 2013