17. Self-Assembly Micelles Flashcards
What are amphiphiles
Molecules which have a water-soluble head group and a hydrophobic tail group. They are also known as lipophilic molecules/surfactants.
State a benefit of amphiphiles
They can drastically reduce the cost of an interface as they have a hydrophobic tail and a hydrophilic tail.
When amphiphilic molecules are added to water they migrate to ___ ______ to reduce unfavourable contact.
The surface
Why do micelles form?
To shield hydrophobic tails from an aqueous environment.
What is the critical micelle concentration?
The concentration of amphiphilic molecules at which aggregates (micelles) start to form.
What is the optimum size of a micelle?
What two things contribute to the optimum headgroup area?
- Electrostatic or steric effects
- Hydrophobic interactions
These balance to determine the optimum area occupied by each head group.
What are the electrostatic or steric effects that impact the headgroup area?
A repulsion between the head groups that acts to force neighbouring molecules apart.
What are the hydrophobic interactions that impact the headgroup area?
The grouping of head groups that prevents the hydrocarbon tails from being exposed to too much water.
What are the three shapes of micelles?
- Spheres
- Cylinders
- Bi-layers
Give the equation for the geometric packing parameter of amphiphiles
H = geometric packing parameter
v = tail volume
lc = tail length
a0 = head area
What is the geometric packing parameter required to form a spherical micelle?
H ≤ 1/3
What is the geometric packing parameter required to form a cylindrical micelle?
1/3 < H ≤ 1/2
What is the geometric packing parameter required to form a bi-layer micelle?
1/2 < H ≤ 1
What is a vesicle?
A bi-layer that has folded around to close itself off. This offsets the excess energy associated with any exposed hydrophobic tail groups.
