Questions from class - Lecture 3 Flashcards
How does gel permeation chromatography work and which quantities can be determined?
GPC consists of a column of a gel with a wide pore distribution. The polymer solution is supplied to the top of the column. Below a detector measures the eluted volume as time proceeds. Due to the pore size distribution the large polymers will elute first and the smaller polymers later. This is because the large polymers are excluded from most of the pores, where as the smaller polymer use time to “explore” a higher proportion of the pores.
Molar mass distribution, and from a weighted integral also the number average and weight average molar masses.
How does osmometry work?
Which average molar mass is determined?
Osmometry work by relating the osmotic pressure to the number average of polymers.
The osmotic pressure arises when two chambers, one with a polymer solution and one with only solvent, is separated by a semipermeable membrane. The solvent will flow through this membrane until the chemical (µ) is the same in the two chambers. This gives a pressure difference, which in term can be related to the number average of our polymers.
Sketch a light scattering setup and give a typical plot to determine M_w.
The different combinations of concentration and scattering angle can be plotted in the Zimm-diagram. The lines are then extrapolated to c=0 and theta= 0 and the interception gives 1/M_w.
Which quantity gives the scattering contrast in light/X-ray and neutron scattering?
In light/x-ray scattering the contrast is given by the interaction with the electron, whereas in neutron scattering the nucleus determines the scattering. Bigger nuclei gives higher degree of scattering.
