- Micelles are aggregates of surfactant molecules that form spherical structures in water, with the hydrophilic "heads" facing outwards and the hydrophobic tails sequestered in the inner core. - They are typically 3-50 nm in size and form as a result of the packing behavior of single-tailed lipids, which leads to aggregation that allows accommodation of the head groups at the interface while filling the interior volume. - Micelles have various applications including in detergents, cosmetics, and as nanoreactors for chemical reactions, and their formation is driven entropically by the ordering of water molecules despite the enthalpic cost of aggregation.

1. AMITY UNIVERSITY
MICELLE
PRESENTATION
PRESENT BY
SUBHRANGSU SEKHAR DEY
In Presences of
DR. RENU UPODHYAY AND DR. SHASHI VERMA

2. .
Contents of this Presentation:
•
•
•
•
Definition.
How to form?
Surfactant
Some video for example

3. “
”
Definition of Micelle
A micelle (/maɪˈsɛl/) or micella (maɪˈsɛlə) (plural micelles or micellae, respectively) is an
aggregate of surfactant molecules dispersed in a liquid colloid. A typical micelle
in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact
with surrounding solvent, sequestering the hydrophobic single-tail regions in the micelle
centre. This phase is caused by the packing behavior of single-tail lipids in a bilayer. The
difficulty filling all the volume of the interior of a bilayer, while accommodating the area
per head group forced on the molecule by the hydration of the lipid head group, leads to
the formation of the micelle. This type of micelle is known as a normal-phase micelle (oil-
in-water micelle).

4. Micelles (“Aggregation colloids”)
3 - 50 nm
Outline
Hydrophilic headgroup
Hydrophobic tail
H2O

5. 1. Surfactants
Ionic surfactants Hydrophilic headgroup
(“loves water”)Br
+
N
cationic
Hydrophobic tail
(“hates water”)Non-ionic surfactants (“Niotenside”)
„Brij“OH
m
O
n
Pluronics: PEO - PPO - PEO
O
mn
ϕ

6. 1. Surfactants
Zwitterionic surfactants: Phospholipids
Phospholipids are the building block of
biological membranes
Phosphatidylcholin (Lecithin)

7. Introduction: Self-assembly of surfactants in water
Formation of liquid crystals („lyotropic mesophases“) upon
increase in the surfactant concentration
L1 H1 Lα
Surfactant volume fraction φ

8. Why are micelles/self-assembled structures of interest at all?
Cells = vesicles
1) Living organisms:
2) Applications of surfactants:
Cleaning/Detergents (40%), Textiles, Cosmetics,
Paper Production, Paint, Food, Mining (Flotation)......
Surfactant production per year: ~40 billion tons

9. 3) Chemical reactions in micelles:
Micelles as „nanoreactors“
Emulsion polymerisation
4) New materials
EtOH/H2O
through templating/casting
SiO2
4
Porous material
Si(OH)

10. Washing / Solubilization of other substances
What happens during washing?
Solubilization
micelles
by

11. Different shapes of micelles

12. A didactic excursion: wrong illustrations of micelles
Standard figure seen in textbooks:
Wrong:
1.
2.
3.
There is no denser core!
The heads are not so perfectly arranged
For normal surfactants, micelles
are not shape-persistent
A more realistic illustration of micelles:
H2O H2OH2O
H2O
...H2O
H2O
H2O
Pluronics: up to 30% of the core is water

13. Visualization of self-assembled structures
Cylindrical micelles forming a stable 2D hexagonal lattice in a SiO2 matrix
50 nm
SiO2
Pore structures can be seen as „cast“ of the micellar structure (Nanocasting)

14. Shape persistent micelles
„The first account
of a structurally
persistent micelle“
Specific interactions / covalent linkages can leed to micelles, which do
not change their size/shape!

15. Entropie/enthalpy of micellization
Low-molecular weight surfactants:
• Δ H ca. + 1-2 kJ/mol
Micellization is unfavorable with respect to the enthalpy!!
• ΔS ca. + 140 J /K: The entropy of micellization is POSITIVE
Specific features of the solvent (water) enable
micellization!
*
*
*
High surface tension,
very high cohesion energy,
high dielectric constant, high boiling point, etc etc
ΔG = ΔH – T ΔS

16. Water is not a normal liquid! The “iceberg model”
A) Nonpolar solutes create a clathrate-like cage of first-shell waters around
the solute.
Large entropic cost to order the hydrogen bonds into a more open
“iceberg”-like structure (low temperature).
High-Temperatures break hydrogen bonds to gain entropy, at the cost
of the enthalpy.
Analogy: Clathrate formation of rare gases in water.
B)
C)
D)

17. Thank you!