Surfactants (Soaps and Detergents) and Physicochemical Properties - Surface and Colloid Chemistry: Principles and Applications - page 64

nonionic) behave as a micro phase, where the inner core behaves as (liquid) alkane,
while the surface area behaves as a polar phase. The inner core is also found to exhibit
liquid- alkane-like characteristics. The inner core thus has been found to exhibit
alkane-like properties while being surrounded by a water phase. In fact, micelles
are nanostructures . What this then suggests is that surfactant solution systems can
be designed in water, which can have both aqueous and alkane-like properties. This
unique property is one of the main applications of surfactant micelle solutions in all
kinds of systems. Further, in ionic surfactant micelles, one can additionally create
nano-reactor systems. In the latter reactors, the counterions are designed to bring
two reactants in very close proximity (Birdi, 2007).
The most useful characteristic of the micelle arises from its inner (alkyl chain)
part (Figure 3.17). The inner part consists of alkyl groups that are closely packed. It
is known that these clusters behave as liquid parafin (Cn H 2 n+2). The alkyl chains
are thus not fully extended. Hence, one would expect that this inner hydrophobic
part of the micelle should exhibit properties that are common to alkanes, such as
ability to solubilize all kinds of water-insoluble organic compounds. The solute
enters the alkyl core of the micelle and it swells. Equilibrium is reached when the
ratio between moles solute:moles detergent is reached corresponding to the thermo-
dynamic value.

Water Insoluble
Organic Molecule

Polar
Outer Core

Polar
Outer Core

Apolar Core Apolar Core

(A) (B)

Polar
Outer Core

Water
Soluble Ion

Apolar Core

(C)

FIGure 3.17 Micelle structure: (A) (inner part = liquid paraffin-like; outer polar part); (B)
solubilization of apolar molecule; (C) binding of counterion to the polar part (schematic).