Readings

Question 1

What is the wavelength equation for a particle in a well?

Answer 1

Lambda = 2*L/n ; n=1,2,3…

Amplitude = 0 at walls

Question 2

How do position and momentum relate on the quantum level?

Answer 2

The more precisely something’s position is determined, the less precisely its momentum is known, and vice versa.

Question 3

What is a Quantum Dot?

Answer 3

• Semiconducting
• Confined in all three dimensions
• 1 to 10 nanometer scale

Question 4

What is a Quantum Wire?

Answer 4

• Semiconducting
• Confined in two dimensions
• 1 to 10 nanometer scale

Question 5

What is a Quantum Well?

Answer 5

• Semiconducting
• Confined in one dimension
• 1 to 10 nanometer scale

Question 6

Explain how an Exciton is formed

Answer 6

An electron is promoted from the valence band to the conduction band

• This electron leaves a “hole” behind in the valence band
• “hole” is thought of as a particle with a +1 charge and some mass

The promoted electron and the “hole” are bound together and considered a quasiparticle - Exciton!

Question 7

Periodic Trend of Bandgap Energy of a solid (Eg)

Answer 7

As you go down the periodic table, the bandgap energy of the solid atom decreases

Question 8

Techniques used to Measure Quantum Dot Size

Answer 8

• Transmission Electron Microscopy (TEM)
• Line-broadening of X-ray Diffraction lines of Quantum Dot powders
• Electronic Absorption Spectroscopy

Question 9

What are the two ways that Quantum Dots can be made?

Answer 9

• Colloidal solutions

- Grown on solid substrates

Question 10

Creaming

Answer 10

• When the density of the solvent is > the density of the particle
• The particle will move upward in solution

Question 11

What is the friction factor of a spherical particle?

Answer 11

f = 6pimu*R

Question 12

What is the Boundary Zone?

Answer 12

• The area between sedimented particles and space above which contains no particles.
• The C at the base&raquo_space;» C in the upper zone

Question 13

How does an Ultracentrifuge work?

Answer 13

• Cell is rotated at very high speeds in a horizontal position
• g is increased by a factor of ~10^5
• Used for characterization of colloidal materials

Question 14

Explain the difference between Analytical and Preparative ultracentrifuge techniques.

Answer 14

Analytical:

• Requires small samples (.1-1mL)
• Optical systems are used to measure the Concentration or change in Concentration

Preparative:

• Requires larger samples (5-100mL)
• Samples removed after time
• fractionation for preparation or purification of samples

Question 15

Surface Active Agent

Answer 15

Known as:

• Surfactant
• Lipids (fatty acids)
• amphiphiles

Compounds that reduce surface tension of water in aqueous solutions >30mN/m

Surfactants reduce surface tension in in non-aqueous media, just not as significantly

Question 16

Surface Active Agent Composition

Answer 16

Head group - hydrophilic portion of compound

Tail - hydrophobic portion of compound

Head group and tail are segregated from each other

Question 17

Detergent

Answer 17

A synthetic surfactant such as a fatty sulfate, sulfonate, or long chain quaternary ammonium salts

Question 18

Anionic Surfactants

Answer 18

• Ionized salts
  
  • The anion possesses the long hydrophobic chain
  • The hydrophilic head groups are exposed to the water, increasing the hydrophilicity of the solid surface.

-Tend to shun dense absorption onto solid surfaces from water because these surfaces are often negatively charged

Question 19

Hydrophobic Bonding

Answer 19

The non-specific desire of the hydrophobic portions of molecules to “get out” of the water

Question 20

Cationic Surfactants

Answer 20

• Ionized salts
  
  • The cation (+) is the surfactant species
• Good bacterial properties
• Head-down, tail-out absorption
• Most are nitrogen-containing compounds

Question 21

Anionic Surfactant Examples

Answer 21

Sodium Stearate
Sodium Dodecyl Sulfate (SDS)
Sodium Dodecyl Benzene Sulfonate

Question 22

Cationic Surfactant Examples/Uses

Answer 22

• Waterproofers and anti-stats

- Quaternary ammonium compounds (synthesized through the reaction of ammonia with fatty alcohols)

Question 23

Nonionic Surfactants

Answer 23

• Various alkyl poly(ethylene oxide)’s
• Derived from the condensation of ethylene oxide with fatty acids or alcohols
• CnEm (n and m are subscripts)
  
  • As the m/n ratio increases, the surfactants become more hydrophilic
• resistant to hard water
• generally low foamers
• may be soluble in organic solvents
• polydisperse

Question 24

Nonionic Surfactant Examples/Uses

Answer 24

• Formulating injet printing inks
• Emulsifiers
• Wetting agents and dispersants

Question 25

Amphoteric Surfactants

Answer 25

• Anionic or Cationic (pH dependent)

- Proteins and natural surfactants

Question 26

Zwitterionic Surfactants

Answer 26

-ionic head group contains (+) and (-) charges in close proximity

Question 27

Gemini Surfactants

Answer 27

Two single-tail surfanctants whose heads are connected by a hydrophilic or hydrophobic spacer chain

Question 28

Telechelic Surfactants

Answer 28

Two hydrophobic groups are connected by a hydrophilic chain

Question 29

Boloform Surfactants

Answer 29

Hydrophobic chains with hydrophilic groups on each end

Question 30

function-changing Surfactants

Answer 30

Amphoteric or nonionic surfactants with PEO hydrophilic head groups
-Surfactant characteristics can change with changes in pH or Temperature

Question 31

Cleavable Surfactants

Answer 31

Intentionally designed with weak linkage
-susceptible to cleavage under low/high pH

Cleavability is motivated in part to:

• biodegradability
• aid to removal of surfactants from a system

Question 32

Gibbs Monolayer

Answer 32

When the surface of the solution is saturated with vertically oriented molecules
-The slope will be a constant

Question 33

Traube’s Rule

Answer 33

The longer the hydrocarbon chain length, the more efficient the surfactant
-valid for nonionic and some ionic surfactants