Notes

Question 1

Material Dispersions

Answer 1

Multiple constituent (phase) system in which one phase is contained within a continuous phase.

Question 2

Short Range Forces

Answer 2

• Electromagnetic by nature
• Vander Waals forces
• ions<1nm (nanoscale)

Question 3

Long Range Forces

Answer 3

Electrical and Magnetic

1nm-10um in size (microscale)

Question 4

Gravitational Forces

Answer 4

10um-mm) Macroscale

Question 5

Colloids

Answer 5

A state of subdivision with a dispersed particle (phase) dispersed with at least 1 direction of a dimension (1nm-1um)

Question 6

Lyophilic

Answer 6

• Solvent-loving
• Colloids: behave like a single phase solution, which can contain macro-molecules (polymers and proteins) and association colloids (self assembled structures like micelles)
• Causes no true interface - solvent particles all around molecules
• THERMO and KINETICALLY stable

Question 7

Lyophobic

Answer 7

• solvent-fearing
• Colloid particle (discontinuous phase) well defined by interface

THERMODYNAMICALLY stable, not kinetically

Question 8

Protected Lyophobic

Answer 8

Stabilized with surface chemistry to increase kinetic stability

Question 9

Forming Colloid Particles (Top Down)

Answer 9

-Breaking down bulk materials

Question 10

Comminution

Answer 10

• wet and dry

- Mechanical disintegration

Question 11

Forming Colloid Particles (Bottom Up)

Answer 11

• Start with solution or gas mixture with rxn precursors
• Induced to nucleate through reaction and precipitate or be stabilized to form our desired particles
• Process
  1) Precursors –> controlled precipitation: supersaturated solution in which particle size grows –> insoluble salt
  2) Chemical rxn that produces particles

Question 12

Electrostatic Stabilization

Answer 12

Existence of a layer of charge on particle surface surrounded by a diffuse “cloud” of oppositely charged counterions

*Repulsion of these like charges causes stabilization

Question 13

Steric Effects

Answer 13

Particles coated with stabilizing or capping agent (surfactant or ligand) causes repulsion of neighboring particles

Question 14

Ostwald Ripening

Answer 14

Inhomogeneous phases leading to precipitation of larger particles, coming from smaller particles, due to energy factors
-Surface atoms desire proper coordination to minimize cohesive energy

Question 15

Limiting Ostwald Ripening

Answer 15

1) Arrested Precipitation

2) Stabilizing Agent

Question 16

6 Prevalent Strategies to Synthesize Colloids

Answer 16

1) Controlled Precipitation
2) Reduction of Metal Complexes
3) Sol-gel Process
- Hydrolysis of a metal salt
- Condensation/evaporation to remove the water
4) Emulsion and Dispersion Polymerization (to form colloidal polymer particles)
5) Template Controlled Growth

Ex: Colloidal Semiconductors (Quantum Dots)
-Formed through arrested precipitation

Question 17

Three “Rules” of Quantum Confinement

Answer 17

1) Motion of electron inside the well increases in energy in 1 dimension
2) Electrons behave like waves - “particle-wave duality”
3) Standing waves will have an amplitude of 0 at the walls

Question 18

Size vs. Energy for Nanoparticles

Answer 18

Smaller particles have high energy!

Question 19

Aggregation

Answer 19

“small” particles clump together, do NOT fuse into a new particle

*No significant surface reduction

Question 20

Coalescence

Answer 20

-2 or more particles fuse together to form a single larger particle

• Reduced Surface Area
• Ostwald Ripening takes place
• Solid particles: Sintering

Question 21

Flocculation

Answer 21

• Chains of particles that aggregate together

- A “flock” of particles

Question 22

Coagulation

Answer 22

Compact aggregate, possibly at the bottom of solution

Question 23

Aggregate Reversal Examples

Answer 23

• Dispersion
• Deflocculation
• Peptization

Question 24

Creaming

Answer 24

Concentration of particles move upward in a dispersion to the surface (based on density)

Question 25

Sedimentation

Answer 25

- Settling of dispersed particles under the action of gravity or a centrifugal field - Should be done at constant Temperature

Question 26

RCF

Answer 26

Relative Centrifugal Force

Question 27

Ultracentrifuge (particles they are useful for)

Answer 27

nanoparticles and lyophilic colloids

Question 28

Sedimentation Coefficient (Units, Definition)

Answer 28

- Seconds | - Sedimentation velocity per unit of centrifugal acceleration

Question 29

Diffusion

Answer 29

Tendency to keep things dispersed

Question 30

Surface Energy

Answer 30

Atoms on the surface are at a lower energy state - They have stronger lateral bonds, causing surface tension - Surface energy refers to solids, surface tension refers to liquids - Good indicator of wettability by liquids - High SE --> more wettable - Polymers have low SE, while metal solids and clean glass have high SE

Question 31

Work of Cohesion

Answer 31

Work required to pull apart a material by overcoming attraction between atoms

Question 32

γ (lowercase gamma)

Answer 32

- Measure of resistance of a surface to increase its area | - Force operating perpendicular and inward from a surface boundary

Question 33

Contact Angle

Answer 33

Angle measured in the liquid that is formed at the junction of the 3 phases

Question 34

Goniometer

Answer 34

- Used to measure the contact angle when a liquid droplet is placed on a solid surface - A digital camera will record the contact angle with respect to different droplets

Question 35

Variation in γLV due to what intermolecular forces?

Answer 35

Metallic Bonding Hydrogen Bonding Polar Molecules "Keesom" London Dispersion Forces γLV = Σγforces As T is increased, γLV is decreased due to less interaction

Question 36

Capillary Effect

Answer 36

Rise or fall of liquid in a small diameter tube inserted in liquid

Question 37

Micelle

Answer 37

Self-assembled ordered structure

Question 38

CMC

Answer 38

- Critical Micelle Concentration - Gibb's Monolayer is formed, number density of molecules at the surface will increase with concentration until the CMC is hit

Question 39

Surface Excess (Γ)

Answer 39

Difference in solute concentration between the bulk and surface

Question 40

Aggregation Number (n)

Answer 40

- Number of molecules to form a micelle | - Influenced by headgroup repulsion and hydrophobic tail attraction

Question 41

Krafft Point

Answer 41

Sharp increase in solubility of surfactant -The longer the hydrophobic taill, the higher the Krafft Point temperature