Lecture 8: self assembly & Networks

Question 1

Self-assembly

Answer 1

A process in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of specific, local interactions among the components themselves, without external direction; i.e. spontaneously

Question 2

Name an example of self-assembly

Answer 2

● Lipid molecules forming oil droplets in water
● Polypeptides folding to form a functional protein
● The way RNA and ribosomal proteins combine to form a functional
ribosome
● Formation of crystalline structure
● Formation of the lipid bilayer

Question 3

What 3 forces drive self-assembly

Answer 3

○ Electrostatic intramolecular and intermolecular interactions, though mostly hydrogen
bonding
○ External forces such as electric, magnetic, flow, osmotic and gravitational forces
○ Interface forces, both electrostatic and entropic

Question 4

What is gibbs free energy equation?

Answer 4

ΔG=ΔH-TΔS

Question 5

What are networks composed of?

Answer 5

Networks are combinations of various nodes (elements) linked together through edges (the lines between elements).

Question 6

Name 2 hydrophobic regimes

Answer 6

Wenzel regime, Cassie-Baxter regime

Question 7

Name the characteristics of the Wenzel regime

Answer 7

● micro-structures into which the water droplet embeds itself
● smaller contact angle than Cassie-Baxter

Question 8

Name the characteristics of the Cassie-Baxter regime

Answer 8

● nano-structures over which the water “floats”
● larger contact angle than Wenzel

Question 9

Describe the concept of super-hydrophobicity ?

Answer 9

Result of micro- and nano-structured patterns. Hierarchical structures increase hydrophobicity.
Contact angle needs to be greater than 90 degrees on a superhydrophobic surface.

Question 10

What are some applications of superhydrophobic surfaces ?

Answer 10

Oil-water separation: Filter is superhydrophobic, allowing only oils to pass, leaving clean water behind.
Self-cleaning materials : ability to easily wash away dirt from surface.
Anti-corrosion: Air bubbles formed between the surface and corrosive liquid act as a protectant.

Question 11

What do spontaneous reactions require to occur ?

Answer 11

Negative Gibbs free energy.

Question 12

What will happen if the entropy is positive and the enthalpy is negative to the Gibbs free energy?
What about when S < 0 and H < 0?
What about when S > 0 and H > 0?
What about when S < 0 and H > 0?

Answer 12

1. Always spontaneous.
2. Spontaneous if temperature is low.
3. Spontaneous if temperature is high.
4. Never spontaneous (G > 0 always)