Surface Tension of Liquids
Surface Tension of Liquids
Surface Tension of Liquids
Adhesion and Surface Tension: Adhesion and Surface Tension: Adhesion and Surface Tension: Adhesion and Surface Tension:
Adhesion and surface tension together can produce
capillary action Capillary action occurs when the capillary action. Capillary action occurs when the
adhesion to the walls is stronger than the
cohesive forces between the liquid
molecules Adhesion of water to the walls of a molecules. Adhesion of water to the walls of a
vessel results in an upward force on the liquid at
the edges. The surface tension keeps the surface
intact so the whole liquid surface is dragged intact, so the whole liquid surface is dragged
upward.
Cont... Cont...
Atoms Atoms,
- Chemical bonding
unsatisfied bonds of top surface layer
Th i h i ht t hi h th Th i h i ht t hi h th The maximum height to which the The maximum height to which the
liquid will rise through capillary liquid will rise through capillary
action is given by action is given by
h = 2 h = 2cos cos/( /(gr gr)) h 2 h 2cos cos/( /(gr gr). ).
Effect of Surfactants on wetting . Effect of Surfactants on wetting . gg
((An example ) An example )
Surface Tension Values of Some Surface Tension Values of Some
Solvents: Solvents: Solvents: Solvents:
Surface Energy of Diff. Substrates Surface Energy of Diff. Substrates Surface Energy of Diff. Substrates Surface Energy of Diff. Substrates
S.N. Substrates Description Surface Energy
1
LDPE Film
31
2
HDPE Film
32
3
BOPP Film
32
4
PET Films
42
5
PP Films
29
6
PVC Film
38
77
PLA Films
..
Testing Of Substrate Surface Energy Testing Of Substrate Surface Energy
i.e. Dyne Label i.e. Dyne Label
Dyne Solution or Dyne Pens to be Used Dyne Solution or Dyne Pens to be Used
Preparing Formula for Dyne Sol Preparing Formula for Dyne Sol Preparing Formula for Dyne Sol. Preparing Formula for Dyne Sol.
Testing Of Dyne Label : Testing Of Dyne Label : Testing Of Dyne Label : Testing Of Dyne Label :
Wetting of same ink over different Wetting of same ink over different
Substrates: Substrates:
Condition for Good Adhesion of Condition for Good Adhesion of
Inks : Inks :
Transfer and spreading of an ink on a
substrate depends on the surface energy of
the material delivering the ink, the surface
t i f th i k dth f tension of the ink, and the surface energy
of the substrate receiving the ink. The
substratemust haveasurfaceenergy substrate must have a surface energy
higher than the ink, with forces of
attractiongreat enoughtopromotegood attraction great enough to promote good
transfer and spreading, which in turn
facilitates good adhesion.
..
Examples Examples
f of
S f T i Surface Tension
Walking on Water: Walking on Water: Walking on Water: Walking on Water:
Small insects such as the water strider
can walk on water because their weight is
not enough to penetrate the surface. g p
This interesting insect (See Next Slide
)can freely run along the surface of a quiet ) y g q
pond. It's tiny mass and the geometry of
its legs allow it to be supported by the g pp y
high surface tension of water.
Surface Tension and the Water Surface Tension and the Water
Strider Strider
Floating a needle: Floating a needle: Floating a needle: Floating a needle:
f ll l d h f If carefully placed on the surface, a
small needle can be made to
fl h f f float on the surface of water
even though it is several times as
d If h f dense as water. If the surface is
agitated to break up the surface
h dl ll kl tension, then needle will quickly
sink.
Dont touch the tent! Dont touch the tent! Don t touch the tent! Don t touch the tent!
Common tent materials are
somewhat rainproof in that the
surface tension of water will
bridge the pores in the finely
woven material. But if you touch y
the tent material with your
finger, you break the surface g , y
tension and the rain will drip
through. g
Soaps and Detergents Soaps and Detergents Soaps and Detergents Soaps and Detergents
Help the cleaning of clothes by
l h f lowering the surface tension
of the water so that it more of the water so that it more
readily soaks into pores and
soiled areas.
Washing with Cold Water: Washing with Cold Water: Washing with Cold Water: Washing with Cold Water:
The major reason for using hot
water for washing is that its water for washing is that its
surface tension is lower and it is
a better ettin a ent B t if the a better wetting agent. But if the
detergent lowers the surface
tension, the heating may be
unnecessary. y
Surface Tension Disinfectants: Surface Tension Disinfectants: Surface Tension Disinfectants: Surface Tension Disinfectants:
Disinfectants are usually solutions of s ecta ts a e usua y so ut o s o
low surface tension. This allow
them to spread out on the cell them to spread out on the cell
walls of bacteria and disrupt them.
One such disinfectant, S.T.37, has a
name which points to its low p
surface tension compared to the
72 dynes/cm for water 72 dynes/cm for water.
Some More Examples: Some More Examples:
Add some drops of Gasoline into Add some drops of Gasoline into
water and see,.. water and see,..
Writing with Pen Writing with Pen Writing with Pen Writing with Pen
Any questions ? Any questions ? Any questions ? Any questions ?