AdvMat:AP

Question 1

Briefly describe how the correlation function is generated?

Answer 1

-PCS/DLS will give and speckled pattern of light as light intensity fluctuates across a sample
-Measure light intensity of a spot and a given time and at very small time intervals to get an intensity vs t graph with a slope. From this graph we can get the correlation function.
Using this we can get the decay constant which in-turn can give us the self-diffusion coefficient. This can then give us the radius.

Question 2

Shear Thinning

Answer 2

-Arises from the allignement of particles in the system
-To begin with particles cant move around each other (high viscosity)
-Shear stress alines the particle, shear planes now present in system
-The system can now flow/planes over each other
(draw graph of viscosity v shear stress)

Question 3

Shear Thickening

Answer 3

• As we increase the stress further, now we are trying to move the particles more quickly than they can actually move in the system to avoid each other
• Increase stress-increase thickening
• high shear rates, transient clusters form in system, to big to move around each other

Question 4

Gloss Paint

Answer 4

• When paints are applied, the shear stress created by the brush will allow the point to thin out on the surface evenly
• Once applied, the paint regains their higher viscosity, which avoids drips and runs
• To avoid drips from gravitational forces, viscosity must be high (larger polymer) so the stress value is lower than the yield stress

Question 5

Shear stress

Answer 5

Resistance of material to applied force

Question 6

Dynamic viscosity

Answer 6

Tendency of a material to resist flow

Question 7

GPC limitations

Answer 7

• MWt limit, some molecules to big to pass through in time limit
• Compared to standards to give MWt of molecules but only a comparison of size (different MWts for same Volume
• No info on shape

Question 8

Term given to properties between Hookean Solid and Newtonian fluid

Answer 8

Viscoelastic

Question 9

Newtonian Fluid

Answer 9

Application of stress gradually increase strain. On removal of applied stress, the strain does not return to zero, flow has occured.

Question 10

Hookean solid

Answer 10

Application of stress results in instant deformation. Complete elastic recovery of the strain.

Question 11

GPC

Answer 11

• Size based on the time taken for the polymer to travel through the column of porous beads
• Smaller molecules can enter the pores of the beads and therefore take longer time to pass through the column
• Larger molecules flow over the beads, short time
• Times compared to standards to give MWt

Question 12

Theta Solvent

Answer 12

The conditions that give a random coil

Question 13

A poor solvent

Answer 13

P-P>P-S, volume occupied is reduced and the chain collapses. Leads the

Question 14

A good solvent

Answer 14

P-P

Question 15

Surface tensions relates to Polymer/surfactant

interactions

Answer 15

Draw surface tension vs surfactant conc.
3 regions of where micelles and polymer interact
-first point- onset of micelle formation on polymer
-polymer becomes saturated with micelles
-second point-micelles form in solution

Question 16

What info EPR can provide

Answer 16

Include and EPR probe in the surfactant. EPR will give info on hydration and local viscosity. As polymer interacts with surfactant it hydration and viscosity of the head group. Signal will change showing the point of interaction.

Question 17

Neutron scattering vs fluoresence/Electron methods (pertubation)

Answer 17

Neutron scattering does not cause any changes to the molecule (perturbation) as it does not interact with the molecule when scattering.
Other techniques may exited the molecule or ionise in extreme cases. This will cause structural changes to the molecule.

Question 18

Contrast variation experiment

Answer 18

Neutron scattering is isotopically dependent.
Hydrogen and deuterium are two isotopes that give a large difference in intensity and therefore a large contrast.
To achieve contrast in a system of polymer/surfactant/solution use hydrogen and deuterium. To show polymer wrapped around surfactant use 1H surfactant and polymer and a deuterated solvent or vise versa.

Question 19

TEM

Answer 19

• Beam of electrons transmitted through specimen to form an image. Image is formed from the interaction with the electrons with the sample as the beam passes through
• Need ultra thin samples
• Not a bulk technique, how representative is surface of bulk

Question 20

SEM

Answer 20

• produces images of a sample by scanning the surface with a focused beam of electrons.
• electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample.