Folie 1

1

• Light Scattering from Polyelectrolytes in
  Aqueous Solution
• sources
• www.tulane.edu/wreed/research/Polyel.props/Polyel
  ectrolytes.pdf
• 2. Macromolecules, 2006, 39 (2), 731-739

Problem if you are interested only in particle
analytics Even dilute samples show structure
factor contributions due to long-range Coulomb
repulsion Simple solution add enough salt!
2
Polyelectrolytes - Properties
Important parameters Bjerrum length Debye
screening length
mi mol/L added univalent charges
3
Static structure factor and positional
interparticle correlation
4
2nd Virial Coefficient A2
A2 gt 0 good solvent gt swollen polymer coil /
increased chain stiffness
5
Apparent electrostatic persistence length
gt Stiffness of polymer chain increases with
increasing Coulomb repulsion
6
The electroviscous effect decrease and increase
in polymer density due to counterion and added
ion (salt) contributions
7
Slow modes in dynamic light scattering
Can be removed by proper filtering -gt aggregates ?
8
But recent experiments by Paul Russo and
coworkers DLS in dialysis equilibrium
Macromolecules, 2006, 39 (2), 731-739
At low salt small intercept, two relaxation modes
9
(No Transcript)
10
Apparent fast and slow diffusion coefficients
At high salt conc., when the Coulomb repulsion is
screened, one single diffusion coefficient
(Stokes-Einstein) is obtained
11
Further Insight into these Modes Dialysis
Fluorescence Photobleaching Recovery, Tracer
Diffusion of Labelled Polyelectrolytes
12
Increase in single particle mobility
(selfdiffusion) with the amount of added
salt (calculations wormlike chain model,
stiffness changing with salt conc.)
13
Comparison of DLS and FPR
Data rescaled for different length scales (DLS
2p/q 621 nm, FPR 2p/K 107 700 nm
14
Combined Diffusion Coefficient of DLS and FPR
15
Model Temporal Aggregates, Sampled by the
Diffusion Labelled Chain
16
Conclusions by Russo and Coworkers on the
Physical Origin of Fast and Slow DLS Modes in
Polyelectrolyte Solutions at Low Amount of Added
Salt
fast DLS mode probably easiest to understand
as the response of an osmotically stiff system to
spontaneous fluctuations. slow DLS mode may
represent multimacroion domains that last long
enough as integral bodies to dephase scattered
light in DLS by traveling the small distance
2p/q. Said domains are postulated to be loosely
structured, such that the residence time of a
single chain is shorter than the time required to
travel the distance 2p/K to erase the imposed
fluorophore contrast in FPR. The effectively
single decay mode detected by FPR reflects a
weighted average of the multimacroion diffusion
coefficient and the self-diffusion coefficient of
single chains.