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motion of the probe with respect to micelle upon excitation. Because the solvent
relaxation processes are very specific and complex, we have not yet attempted to
perform the corresponding computer simulations.
3.4
Study of Shell-Forming Chain Conformations
by Nonradiative Energy Transfer
3.4.1
Studies of Reference Systems of Nonmodified Weak Polyelectrolyte
Shells in Solutions with Low Ionic Strength
Motivation
The properties of PE micelles in aqueous solutions are determined by the behav-
ior of micellar shells, which can be regarded as convex PE brushes. Depending
on the degree of charging and ionic strength, the PE brush can undergo several
patterns of behavior. In systems where the density of charge on the PE chains is
high, the electrostatic force acting on counterions is strong and prevents their es-
cape in bulk solvent, which means that the brush remains electrically neutral. At low
ionic strength, the osmotic pressure is high and individual brush-forming chains are
strongly stretched. The brush is swollen and obeys the osmotic regime. In solutions
with high ionic strength, the excess of small ions screens electrostatic interactions
and the brush collapses, obeying the salted brush regime. We have been systemat-
ically studying the behavior of both hydrophobically modified and unmodified PE
shells by a combination of several experimental techniques. Even though we have
been interested mainly in modified systems, which we studied using fluorescence
techniques, first we had to study the corresponding unmodified micelles as refer-
ence systems for comparison.
Outline of Experimental Studies and the Most Important Observations
The micelles were prepared by stepwise dialysis of diblock copolymer PS-PMA
from mixed solvents to pure water. The copolymer contains one PS and one PMA
block with an almost identical number of monomeric units (about 200). Further ex-
characterized by static light scattering (SLS) and DLS. The Zimm plot of experi-
mental data in a borate buffer is regular and we used it for the evaluation of the
weight average molar mass (
M
w
)
of micelles and their radius of gyration. The scat-
tering functions depend almost linearly on
q
2
(scattering vector), which indicates
that the micelles interact weakly with each other and that their interaction can be
described by the excluded volume effect only. The monodisperese spherical mi-
celles were further visualized by atomic force microscopy after their deposition on
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