Surfactant Micelles and Scattering Techniques

Flashcards reviewing key concepts about surfactant behavior in solutions and methods for studying micelles.

What happens when surfactants are added to water?

Surfactants initially disperse as monomers, then the interface becomes full, reducing surface tension linearly until the CMC is reached, after which micelles form and can eventually lead to native crystalline species.

What is surface access?

The concentration of surfactant is higher at the interface than in the solution or air.

What can you calculate from the surface access?

Calculate the area of a head group of a surfactant molecule.

Why do ionic surfactants tend to have bigger head groups?

Ionic surfactants typically have larger head groups due to waters of hydration and repulsion between charged species.

What techniques are used to study micelles and their properties?

Techniques like microscopy and scattering.

What is a key problem with using electron microscopy to study micelles?

It requires a vacuum, which can distort the micelles.

How can electron microscopy be used to accurately measure micelles?

Cryo-EM, where the solution is frozen before imaging.

What is a limitation of cryo-EM?

The contrast between water and surfactant is not very strong.

What is the 'two-headed rhino' issue in microscopy?

Images are 2D representations of 3D objects, leading to potential misinterpretations of shape.

How can the reliability of microscopy be improved?

Combining it with other techniques like scattering.

How do scattering techniques work?

By shooting radiation at the sample and collecting the scattering pattern.

What is required for scattering objects to be seen?

The composition must be different from the bulk.

Why is light scattering not great for small surfactant micelles?

Light scattering is not ideal because of wavelength differences.

What factors affect the amount of scattering observed?

The amount of particles, their size, shape, and interactions, and the contrast between the particles and the medium.

What does contrast depend on when using light scattering?

The difference in refractive index between the particle and the medium.

What does contrast depend on when using X-ray scattering?

The electron density difference.

What makes neutron scattering unique?

The interaction of neutrons with the nucleus.

How is high contrast achieved in neutron scattering?

Using hydrogenated surfactants in deuterium oxide.

What type of light scattering measures changes in scattered light versus time at a fixed angle?

DLS (Dynamic Light Scattering).

What are some of the problems with DLS?

The contrast is quite low, and it's tricky to deal with non-spherical particles.

How can you quickly get a number from the DLS machine?

By putting it in a cuvette inside the DLS machine.

How Sex and Sains analysis can tell you if you have whole show my cells.

The difference in turnaround point of the techniques.

How can you watch things happen inside the cell over time?

By heating it up or cooling it down, or adding something else in.

Why is using 'Q' a better scale?

Q is better than two theta because it allows comparison irrespective of wavelength.

What does a higher CMC imply?

A higher CMC implies less solubility in the solvent (water).

What should you consider to argue about detergency or solubility?

Consider the head group and chain to determine solubility.

What happens to CMC as salinity increases?

CMC decreases because the charges are screened, effectively salting out the surfactant.

How do face diagrams behave?

Behaves like maps, showing composition variations and how they change relative to temperature.