This document discusses the HLB (hydrophilic lipophilic balance) system for classifying surfactants. It explains that HLB values indicate whether a surfactant is more hydrophilic or lipophilic. Methods for estimating a surfactant's HLB value involve assigning group numbers to different parts of the molecule. Required HLB values can predict whether a surfactant will form a stable oil-in-water or water-in-oil emulsion with a given oil. However, the HLB system has limitations and does not consider surfactant concentration which also impacts emulsion stability.

1. IIIrd Semesester B. pharmacy
Physical Pharmaceutics-I
Unit-III
Surface and Interfacial tension [Part-5]
(HLB System, Solubilization )
Miss. Pooja D. Bhandare
(Assistant professor)
Kandhar college of pharmacy

2. HLB SYSTEM
• Griffin devised an arbitrary scale of values to serve as measure of the
Hydrophilic Lipophile Balance (HLB) of surface active agent.
• HLB is the ratio of oil soluble and water soluble portion of a molecule.
• HLB value Hydrophilic nature
• Higher the HLB number the more hydrophilic is the surfactant.
• Lower the HLB number the more lipophilic is the surfactant.

4. • At the top end of the scale, the surfactant are hydrophilic (water
soluble) and acts as solubilizing agents, detergents and oil/water
emulsifiers.
• Oil soluble surfactants that possess a low HLB value act as water-in-
oil emulsifier.

5. Method of estimation
• Method 1 : The chemical structure of a molecule is spilt into different
component groups. Each group is assigned a number. The algebriac sum
of these number for their respective groups permits the calculation of its
HLB value.
• The equation is
• ( ℎ𝑦𝑑𝑟𝑜𝑝ℎ𝑖𝑙𝑖𝑐 𝑔𝑟𝑜𝑢𝑝 𝑛𝑢𝑚𝑏𝑒𝑟) − (𝑙𝑖𝑝𝑜𝑝ℎ𝑖𝑙𝑖𝑐 𝑔𝑟𝑜𝑢𝑝 𝑛𝑢𝑚𝑏𝑒𝑟) + 7

6. • Tables containing various groups and group numbers are available in
handbook. For example, the calculation of HLB value of sodium lauryl
sulphate is as follows. The structure of sodium lauryl sulphate is
𝐶𝐻3(𝐶𝐻2)11 𝑆𝑂4
−
𝑁𝑎+.
• HLB = 38.7 – (0.4758 X 12) + 7
= 38.7 – 5.7 + 7
= 40
Group Group number
𝑺𝑶 𝟒
−
𝑵𝒂+ 38.7
𝑪𝑯 𝟑 0.475
𝑪𝑯 𝟐 0.475

7. Method 2
• In this method, each atom or group has been assigned a constant. They are
used for calculation, thus experimental estimates can be avoided. For
example, when a surfactant contain polyoxyethylene chains, the HLB value
can be estimated by
HLB =
𝑬+𝑷
𝟓
Where E = percent by weight of ethylene oxide chains.
P = percent by weight of polyhydric alcohol groups
( examples are glycerol, sorbitol)

8. Method 3
• If the surfactant contain ester functional groups, such as glyceryl
monostearate, the HLB value can be estimated using the equation.
HLB = 20 ( 1 -
𝑺
𝑨
)
Where S = saponification number of ester
A = acid number of the fatty acid.

9. Required HLB
• Normally , a blend of surface active agent are used in the preparation
of emulsion. The HLB of the blend is estimated based on the nature of
the oil phase.
• Required HLB is the hydrophilic- lipophilic value that is desired in
order to prepare a stable emulsion of o/w or w/o type.
• Occasionally it is also know as ‘critical HLB’. The required HLB
value is calculated based on the type of emulsion. A few example with
their RHLB are given below.

10. Oil phase o/w w/o
Cotton seed oil 6-7 -
Mineral oil 10-12 5-6
Bees wax 9-11 5
Paraffin wax 10 4

11. Disadvantages
1. HLB system provides information regarding the nature of the surfactant
used, but the concentration of such surfactant is equally important.
2. The HLB system neglects the concentration of surfactant required for the
optimum stability of emulsion.
3. Though HLB of a surfactant indicates the solubility properties, it is an
over-simplification. It cannot be always realistic. Because, in general,
solubility depends on the nature of solvent, temperature and presence or
absence of additives.

12. Thank you!