Physical Pharmaceutics -I Sem-III

1. Surface &
Interfacial
Phenomenon
Kiran C Rodge
Shivlingeshwar college of Pharmacy,
Almala, Tq-Ausa,Dist-Latur,Maharashtra

2. Interface
2
The boundary that forms between two phases say solid &
liquid is called Interface.
Surface
The term surface is normally used to denote interface,
when one of the phase is Gas.
Boundary
An imaginary line which separate two state of matter.

3. 3
Surface tension
The force in dynes acting on the surface of the liquid at
right angle to any line in 1 cm.
Interfacial tension
It is the force per unit length that exist at the interface
between two immiscible liquid phases.

4. 4
Cohesive forces
“Intermolecular attractions between like molecules”
Adhesive forces
“Intermolecular attractions between unlike molecules”

5. 5
Surface Free Energy
“The energy required to increase the area of a liquid
by 1 sq cm”
W = ϒ * Δ A
Spreading Coefficient
“The capacity of oil to spread over the surface of water”

6. Surface & interfacial
determination method
1) Capillary Rise Method
2) Drop Formation Method
a) Drop weight Method
b) Drop count Method
3)Maximum Bubble Pressure Method
4)Ring Detachment Method
6

7. Adsorption
“The attachment of Gas or Liquid at Solid Surface ”
Desorption
“The Detachment of Gas or Liquid from Solid Surface ”
Absorption
“The penetration of substance in to the material ”

8. 8
Adsorbent
“The substance that deposit at the surface ”
Adsorbate
“The Solid on whose surface the deposition occurs ”

9. “
9
Adsorption of
Liquid Interface

10. 10
Positive Adsorption
“when the added molecules move on their accord to the
interface this process is called Positive adsorption ”
Negative Adsorption
“when the added molecules remain in the bulk of solution
this process is called Negative adsorption ”

11. What is the effect of
type of adsorption on
surface tension ?
11

12. Surface Active Agent
12
Surfactants are compounds that lower the surface
tension (or interfacial tension) between two liquids,
between a gas and a liquid, or between a liquid and a
solid.

13. 13
Structure of Surfactant
Hydrophilic
“Those compound shows affinity towards
Water are refereed as Hydrophilic compound”
Lipophilic
“Those compound shows affinity towards oils/
organic solvents are refereed as Lipophilic
compound”
Amphiphilic
“Those compound shows affinity towards both
water & oils solvents are refereed as
Amphiphilic compound”

14. 14

15. Types of Surfactants
Anionic
Cationic
Zwitterionic
Non-ionic
SLS
Cetrimide, BKC
Lecithin
Spans, Tweens

16. Applications of Surfactant
16
Solubilizing Agent
Wetting Agent
Detergents
Suspending Agent
Emulsifying Agent
Foaming Agent

17. Selection of Surfactant
Hydrophilic-lipophilic balance
The hydrophilic-lipophilic balance of
a surfactant is a measure of the degree to
which it is hydrophilic or lipophilic,
determined by calculating values for the
different regions of the molecule, as described
by Griffin in 1949.

18. 18

19. Determination Method of HLB value
19
1. HLB =Σ (Hydrophilic Group No) – Σ (Lipophilic group No) + 7
2. HLB = E + P
5
3. HLB = 20 ( 1 - S )
A

20. Adsorption of Gas
Interface

21. 21

22. Adsoprtion Isotherms
22
As the plots drawn between the amount of gas
adsorbed on a solid against the equilibrium
pressure at a constant temperature.

23. Types of Isotherms
23
Type I
This isotherms represent a significant
increase in the adsorption with
increasing pressure & followed by
leaving off.
This leaving off is due to the saturation of
available specific chemical groups or entire
surface is covered by monomolecular layer.

24. 24
Type II
This isotherms is sigmoidal in shape &
occurs when gases undergo physical
adsorption onto nonporous solid.
The first inflection point represent the
formation of a monolayer, when the
pressure increased further, multilayer
formation is observed.

25. 25
Type III
This is seen rarely. The heat of
adsorption of gas in the first layer is
less than the latent heat of
condensation of subsequent layers.

26. 26
Type IV
This plot represent the adsorption of gases on
porous solids. First point of inflection
extrapolated to Zero represent the
monomolecular layer adsorption.
Condensation within the pores of the solid
& the multimolecular layer is represented
by further adsorption.

27. 27
Type V
This is seen rarely & indicates capillary
condensation. Here the adsorption reaches a
limiting value before Ps is attained.

28. 28

29. Assumption of Langmuir Adsorption
29
1. Fixed number of active sites for the adsorption of gases.
2. Monomolecular thick layer
3. The rate of adsorption α number of sites unoccupied
4. The rate of desorption α number of sites occupied

30. At particular pressure P,
Sites occupied = θ
Sites unoccupied = (1- θ)
Rate of adsorption = r1 =Pk1(1-θ)
Rate of desorption = r2 = k2θ
30
r1 = r2
Pk1(1-θ) = k2θ
k1P – k1Pθ = k2θ
k1P = k2θ + k1Pθ
k1P = θ(k2 + k1P)
θ = k1P / k2 + k1P
θ = ( k1 / k2 )P / (k2/k2) + k1 / k2 P
θ = ( k1 / k2 )P / 1+ k1 / k2 P
Now assume that
k1 / k2 = b & θ=y/ym
y/ym = bp / 1+ bp
y= (bp / 1+ bp)ym

31. Braunauer,Emmette,Teller (BET)Equation
for multimolecular adsorption
31

32. Freundlich Adsorption Isotherm
32

33. 33

34. 34
Thanks!
Any questions?
You can find me at:
kirunitu@gmail.com
9579827675