Fluorescence Spectroscopy as a Tool for Investigating the Self-Organized Polyelectrolyte Systems - Self Organized Nanostructures of Amphiphilic Block Copolymers - page 212

c p =0.09 g/L

c HCl = 10 −3 M

c HCl , mol/L

c p , g/L

10 − 4

0.09

10 −3

0.19

10 −2

0.38

10 −1

0.75

10 − 1 10 0 10 1 10 2 10 − 1 10 0 10 1 10 2

τ

/ ms

Fig. 8 Relaxation time distributions for PS-PVP-PEO solutions in HCl aqueous solutions, mea-
sured ( left ) at the copolymer concentration, c p ,of0.09gL − 1 and HCl concentrations of 10 − 4 ,
10 − 3 ,10 − 2 and 10 − 1 mol L − 1 ;and( right )in10 − 3 M HCl, with copolymer concentrations of 0.09,
0.19, 0.38, and 0.75 g L − 1

Fig. 9 Hydrodynamic radius,
R H , of PS-PVP-PEO
micelles in acidic aqueous
solutions, as a function of pH

31

30

29

28

1 2 3 4

pH

of particles and the balance between individual micelles and aggregates shifts in
favor of aggregates with (a) increasing concentration of HCl and (b) increasing
copolymer concentration.
A strong effect of electrostatic screening is evident from the dependence of the
size of micelles on pH (Fig. 9 ) . In the pH range above 3, the concentration of ions
and the screening are negligible and R H increases with decreasing pH due to sub-
stantial protonization of PVP blocks. The maximum R H is reached at around pH 3.
Below this pH value, a decrease in R H is observed due to electrostatic screening by
an increasing concentration of small ions.