Surfactants and Micelles Lecture Notes

Flashcards about surfactants, CMC, micelles, and liquid crystals.

What is the Critical Micelle Concentration (CMC)?

The concentration above which micelles start to form.

Why are micelles important in cleaning?

They compartmentalize dirt and oil, changing interfacial tension.

What factors influence micelle formation?

Temperature, solubility, and the presence of electrolytes.

When calculating changes in delta G, what must be remembered?

Mole fraction must be used.

Electrolyte strength has no effect on what type of surfactants?

non-ionic surfactants

What happens to ionic surfactants with the addition of electrolytes?

They become less soluble.

How does decreasing the hydrophobic chain length of a surfactant affect the CMC?

It increases the CMC.

How does increasing the hydrophobic chain length affect the CMC?

It decreases the CMC.

What effect does using methanol as a solvent have on CMC?

It also increases CMC.

In what solvents do reverse micelles form?

Solvents such as hexane.

What are liquid crystals?

These have some crystalline aspects but are also liquid.

For what are liquid crystals commonly used?

Viscosity modifiers in products like makeup.

What method is used to observe liquid crystalline structures?

Distinct and Polarizing Light Microscopy

X-ray diffraction can be applied to liquid crystals because they have…

Repeat distances.

What parameter gives an idea of how big micelles are?

Aggregation number.

What shape are simple chain surfactants likely to form?

Spherical.

More complicated surfactants tend to form what shape micelles?

Worm-like (elongated cylinders).

Adding salt causes surfactants to transition from spherical to rod-like micelles because…

repulsion between head groups decrease.

A bigger head group leads to what common geometry in micelles?

Larger head group

What is used to predict the shape and structure of a micelle?

Packing Parameter (P)

What is the the packing parameter for a sphere?

< 1/3.

What is the formula for the packing parameter (P)?

Volume of surfactant / (Area of headgroup * Length of tail)