Part 3 - Functionalization of nanoparticles

Question 1

What two main types of functionalization is there?

Answer 1

1. Direct functionalization (during synthesis)

2. Post-synthesis functionalization

Question 2

How is adsorption quantified?

Answer 2

By adsorption isotherms.

Question 3

Derive the Langmuir adsorption isotherm.

Answer 3

See slides.

Question 4

What are the assumptions of the Langmuir isotherm?

Answer 4

1. Adsorption does not exceed monolayer coverage.
2. All adsorption sites are equivalent, and the surface is completely uniform.
3. Adsorption to a given adsorption site is indepedent of the surface coverage (no lateral interactions between adsorbate molecules)
4. No surface diffusion among localized adsorbate molecules.
5. Completely reversible adsorption

Question 5

What kind of solvents do we have?

Answer 5

Good solvent, where the FH-parameter is approx. 0
Theta solvent, where the FH-parameter is 0.5
Poor solvent, where the FH-parameter is > 0.5

Question 6

What steps must adsorbing molecules pass through in an adsorption process?

Answer 6

1. Transport towards surface.
2. Attachment
3. Spreading

Question 7

Which assumptions of the Langmuir isotherm is perhaps the most wrong for polymers?

Answer 7

3. Adsorption to a given adsorption site is indepedent of the surface coverage (no lateral interactions between adsorbate molecules)
4. No surface diffusion among localized adsorbate molecules.

Question 8

Why is the Langmuir isotherm often applied to polymers, despite the obvious breaches of the assumptions?

Answer 8

Because it often fits the data set. Science woo!

Question 9

What determines the layer thickness of polymer adsorption?

Answer 9

The deposition time vs. spreading time. If the molecules are deposited faster than it spreads, it’s going to be a thicker layer. And if it spreads faster, then its going to be a thinner layer.

Question 10

How is the adsorption of proteins affected by pH?

Answer 10

It has a much higher adsorption at the isoelectric point.

Question 11

What can happen to proteins adsorbing onto a surface?

Answer 11

It can:

• move laterally
• dissociate
• reversible denaturation and changes in protein conformation
• dissociation of altered protein
• denaturation that results in irreverisble adsorption

Question 12

How possibility of protein adsorption on coated surfaces can happen?

Answer 12

1. Protein binds to passivating layer.
2. Protein is repelled from passivating layer.
3. Protein displaces passivating layer.
4. Protein adsorbs to substrate through defects.

Question 13

Write down the Sauerbrey equation.

Answer 13

∆m = - C∆f / n,

∆m - change of mass
C - constant for crystal
∆f - change in frequency
n - overtone number (usually 3!)

Question 14

Write down the equation for the dissipation factor for QCM.

Answer 14

Ediss / 2pi*Estor

Ediss = dissociated energy
Estor = stored energy

Question 15

What does a higher D-value tell us from QCM measurements?

Answer 15

More energy is dissipated. Usually from thicker layers.

Question 16

What information can we get from D-f plots in QCM measurements?

Answer 16

• Different kinetic processes during adsorption.
• Conformational changes during adsorption
• Formation of multilayers during adsorption
• Interaction with surface/passivating layer
• Rigidity of adsorbed layer

Question 17

What does the value |∆D / ∆f | tell us in QCM measurements?

Answer 17

Provides a relative measure of rigidity. The smaller this value, the more rigid layer.