This document discusses surface and interfacial phenomena, including definitions of interphase, surface tension, and interfacial tension. It provides three key methods for measuring surface tension and interfacial tension: 1) the capillary rise method, which measures the height liquid rises in a capillary tube; 2) the Du Nouy ring tensiometer, which measures the force required to detach a platinum-iridium ring from a liquid surface; and 3) the drop count method using a stalagnometer, which counts drops formed from a liquid passing through a capillary tube.

1. surface and interfacial phenomenon
Inter phase: it is the boudery between two or more phases together.
Several types of inter phases can exist depending on whether the two
adjacent phases are in solid,liquid or gas state.
Important of interfacial phenomenon in pharmacy:
 Adsorption of drugs
 Penetration of molecules through Biological membranes.
 Emulsion formation and stability.
The dispersion insoluble particles in liquid media to form suspension
Cohesive forcees: The attraction forces like molecules(liuid-liquid or solid
solid particles)
Adhesive forces: The attraction forces between unlike molecules

2. SURFACE AND INTERFACIAL TENSION:
The molecules in bulk liquid experiences only cohessive forces.
The molecules at surface (at the liquid and air interface) experiences
Cohessive and adessive forces.

3. SURFACE TENSION(Y): It is tension exist at surface of liuid.
• or
• It is force per unit length that must be applied parallel to the surface so as to
counter balance inword force.
• Units: dynes/cm.
• Inetrfacial tension: ): It is tension exist at interface of two immiscible
liquids.
• or
• It is force per unit length excisting at interfae between two immscible liquid
phases.
• units : dynes/cm
• Inter facial tension(IT) is less than surface tension(ST) when adhessive
forces are greater in bulk liuids.
• If two liquids are miscible completely no IT excist between them.
• Greater ST reflects heigher intermolecular force of attraction thus increses
H-bonds.

4. METHODS FOR MEASURING OF ST AND IT:
1.CAPILLARY RISE METHOD.
2.RING(Du Nouy) TENSIOMETER.
3.DROP COUNT METHOD(STALAGNOMETER)
The choice of method for measuring ST and IT depends on following
 whether ST or IT is to be determined.
 the accurecy desired.
 Size of sample.
1.CAPILLARY RISE METHOD:
 when capillary tube is placed in a liquid it rises up the tube a certaine
distance by measuring this rise it is possible to determine the ST of the
liquid.
 capillary rise method is not used for dtermination of IT.
PRINCIPLE:
When the force of adhession is greater than cohession the liquid rising in
the tube. The rising of the liquid continuous due to ST, untill the upword
moment is just balanced by the downword force of gravity due to weight of
the liquid.

5. The upword component of the force:
The ST of liuid at any point on circumference is given by
a = y cosø
Thus the total upword force around the inside circumference of the tube is
a = 2πr y cosø
Where,
r = radioud of the capiillary.
ø = the contact angle between the surface of the liquid and capillary wall.
2πr = the inside circumference of the capillary.
For water angle ø is insignificant ,that is the liquid wets the capillary wall so
that cosø is unity.
The downword force of gravity: the mass × accelaration is given by
πr2 h (P-P0)g+w
Where,
πr2 = cross sectional area of tube
h = the height of the liquid coloumn(rising liquid)
P-P0 =the difference in the density of the liquid and its vapour
g= accelaration of gravity w=the weight of upper part of miniscus.

6. At maximum height:
the opposing forces are equilibrium
2πr y cosø = πr2 h (P-P0)g+w
Ø, P0 and W can usually be disregarded
hence the ST can be calculated
2πr y = πr2 hpg
After rearrengment the equation for
y = ½ rhpg
Where y = surface tension

7. 2.Ring(Du-Nouy) Tensiometer:
 It is equipment used for measuring of surface and interfacial tensions.
principle:
The equipment containe one sample holder.
In that have to kept sample and immerse a
platinum -irridium ring. Then apply some force
to dettach the ring from surface or interface.
While removing the ring measure the required
force recorded on a calibrated dial in
units of dynes/cm.
The surface tension is given by
γ = f/2 π(R1+R2)
F= The dettachment force
R1&R2=The inner and outer radious of the ring
3.Drop count method(with stalagnometer):