EST

Question 1

Chemical equations to manufacture SLS

Answer 1

Sulfonation:
Lauryl alcohol + SO3 -> Hydrogen lauryl sulfate

Neutralisation
Hydrogen lauryl sulfate + NaOH or NA2-CO3 -> Na-C12-H25-SO4 (SLS)

Question 2

Chemical equations to manufacture SLES

Answer 2

Ethoxylation:
ROH + n C2-H4-O -> R(O-C2-H4)n-OH

Sulfonation:
R(O-C2-H4)n-OH + SO3 -> R(O-C2-H4)n-O-SO3-H

Neutralisation:
R(O-C2-H4)n-O-SO3-H + NaOH -> R(O-C2-H4)n-O-SO3-Na (SLES) + H2O

Question 3

What is the main application for SLES?

Answer 3

Personal care products like toothpaste and shampoo

Question 4

What is the main application for SLS?

Answer 4

It is a powerful grease remover

Question 5

Explain hydrodynamic lubrication

Answer 5

Majority of the load rests on a thick film of lubricant between the two sliding surfaces/

Friction is at the lowest because of the lack of contact between the two surfaces.

Bulk viscosity and thickness is important.

Any friction found is within the lubricant itself, as molecular structures slide past each other.

Question 6

Explain elastohydrodynamic lubrication

Answer 6

Lubrication film is only a few molecules thick

Lubricant exhibits new-Newtonian behavior (i.e. viscosity is not constant)

Lubricant viscosity increases due to high pressure

Question 7

Suggest one method to maintain hydrodynamic lubrication at high temperatures

Answer 7

To maintain viscosity and film thickness at high temperatures, a viscosity modifier can be added.

The modifier is a specialty polymer. At high temperatures, the polymer expands, maintaining the lubricant viscosity and thickness.

Question 8

Explain boundary lubrication

Answer 8

Majority of the load rests on areas of direct contact between the irregularities of two sliding surfaces.

Friction is at the highest because of areas of direct contact between the 2 surfaces

Question 9

What is a boundary layer?

Answer 9

Lubricating action is the result of an adsorbed monomolecular film at one or both surfaces that reduce adhesive forces

Question 10

Explain chemical lubrication

Answer 10

At extreme load, speed and temperature, normal lubricants break down.

Sacrificial lubricants react with fresh metal surfaces formed by wear to produce a new inorganic chemical layer that can be more easily sheared, thereby preventing permanent cold weld.

Graphite contains planar molecular sheets which reduce friction

Question 11

Give 2 examples of chemical lubricants

Answer 11

Graphite, molybdenum disulfide

Question 12

What is the principle behind defoamers?

Answer 12

Hydrophobic defoamer molecules reach into the liquid membrane of the bubble.

It displaces the original surfactants from the gas-liquid membrane of the bubble.

Surface tension of bubble decreases due to high defoamer concentration on surface of lamallae.

Surface tension at bulk liquid is higher.

Hence, water from lamallae will be drained to the bulk liquid due to Marangoni effect.

Rapid thinning of membrane is accelerated by significantly lowered surface tension and gravity.

Bubble ruptures.

Question 13

What is one consequence of using too much defoamers?

Answer 13

The foam will be re-stabilised

Question 14

What is the most important property of a defoamer

Answer 14

The ability to lower the surface tension of the lamallae surface

Question 15

What are the two main classes of defoamer?

Answer 15

Silicones/fluorosilicones and polyglycols

Question 16

Hydrophobised silica particles are sometimes used with defoamers. Explain how they work.

Answer 16

Silica particles pierce the foam bubbles, causing them to coalesce when the defoamer spreads at the interface

Question 17

How would you test the performance of a defoamer?

Answer 17

1. Make foam in a cylinder
2. Add the defoamer
3. Measure time taken to fully break the foam

Question 18

Explain how foams remain stable, using the Marangoni effect

Answer 18

Gibbs elasticity, E = 2A dy/dA

As bubble surface area expands, surface tension at the top of the bubble increases

Water transfers from the bulk to the lamallae, avoiding thinning and rupture

Bubble remains stable as long as E remains positive when bubble expands or contracts

Question 19

Explain why surface tension of water is high

Answer 19

Surface tension of water is high because of the strong intermolecular forces of water, which consists of van der Waals forces and hydrogen bonding.

Question 20

Explain how a surfactant reduces the surface tension of water

Answer 20

Forces of attraction between polar head and water is weaker than forces of attraction between water and water. Interaction between polar head and water may be dipole-dipole interaction which is weaker than the hydrogen bonds between water molecules.

Question 21

How does temperature affect the efficiency of the surfactants?

Answer 21

At increased temperature, the efficiency of surfactants will increase.

Dynamic of surfactant molecules increases due to higher thermal energy.

Surface tension will also decrease.

This will make it easier to form new surfaces, increasing the efficiency of surfactants.

Question 22

Provide an example of an oil dispersant and the chemical pathway to synthesize it

Answer 22

Alkyl polyoxyethylene polyether can be synthesized using ethoxylation.

Dodecanol - C11H23(CH2)OH

Ethylene Oxide - C2H4O (gas at room temperature and pressure)

C11H23(CH2)OH + n C2H4O → C11H23(CH2)(OCH2CH2)n-OH

with CH3ONA as catalyst

If n = 10, compound is largely soluble, and has good surfactants properties.

Question 23

Explain how surfactants break up the oil spill from the perspective of interfacial tension and agitation created by sea waves

Answer 23

When surfactant mixes with the hydrocarbon (oil), it will lower the oil-water interfacial tension by wrapping around the oil molecules.

With the help of mechanical agitation from sea waves, surfactant molecules wrapping the oil molecules will break away from the main oil slick and become independent.

Oil globules are stabilised by the interaction between the polar heads and the surrounding seawater.

Waves provide agitation and energy required to overcome the interfacial tension between the hydrocarbon and water.

When a small part of the oil breaks away, fresh surfaces are created on the original oil slick.

More surfactant molecules have the chance to insert themselves between oil molecules present on the new surface.

With frequent breaking out, a continuous stream of independent oil globules will be carved out from the oil slick.

These small oil globules, being less dense than sea water, will tend to stay on the sea surface. This will make the subsequent task of cleaning up the small oil globules much easier.