AMITY UNIVERSITY

MICELLE PRESENTATION PRESENT BYSUBHRANGSU SEKHAR DEY In Presences ofDR. RENU UPODHYAY AND DR. SHASHI VERMA

.

Contents of this Presentation:

••

•

•

Definition.How to form?Surfactant

Some video for example

“”

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).

Micelles (“Aggregation colloids”)

3 - 50 nmOutlineHydrophilic headgroup

Hydrophobic tail

H2O

1. Surfactants

Ionic surfactants Hydrophilic headgroup(“loves water”)Br

+N

cationic

Hydrophobic tail(“hates water”)Non-ionic surfactants (“Niotenside”)

„Brij“OHm

On

Pluronics: PEO - PPO - PEOO

mnϕ

1. Surfactants

Zwitterionic surfactants: Phospholipids

Phospholipids are the building block ofbiological membranes

Phosphatidylcholin (Lecithin)

Introduction: Self-assembly of surfactants in water

Formation of liquid crystals („lyotropic mesophases“) uponincrease in the surfactant concentration

L1 H1 Lα

Surfactant volume fraction φ

Why are micelles/self-assembled structures of interest at all?

Cells = vesicles1) Living organisms:

2) Applications of surfactants:Cleaning/Detergents (40%), Textiles, Cosmetics,Paper Production, Paint, Food, Mining (Flotation)......

Surfactant production per year: ~40 billion tons

3) Chemical reactions in micelles:Micelles as „nanoreactors“

Emulsion polymerisation

4) New materialsEtOH/H2O

through templating/casting

SiO24

Porous material

Si(OH)

Washing / Solubilization of other substances

What happens during washing?

Solubilizationmicelles

by

Different shapes of micelles

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 arrangedFor normal surfactants, micelles

are not shape-persistent

A more realistic illustration of micelles:

H2O H2OH2O

H2O ...H2O

H2OH2O

Pluronics: up to 30% of the core is water

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)

Shape persistent micelles

„The first accountof a structurally persistent micelle“

Specific interactions / covalent linkages can leed to micelles, which donot change their size/shape!

Entropie/enthalpy of micellization

Low-molecular weight surfactants:

• Δ H ca. + 1-2 kJ/molMicellization is unfavorable with respect

to the enthalpy!!

• Δ S ca. + 140 J /K: The entropy of micellization is POSITIVE

Specific features of the solvent (water) enablemicellization!

***

High surface tension,very high cohesion energy,high dielectric constant, high boiling point, etc etc

ΔG = ΔH – T ΔS

Water is not a normal liquid! The “iceberg model”

A) Nonpolar solutes create a clathrate-like cage of first-shell waters aroundthe 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)

Thank you!