Interpolyelectrolyte Complexes Based on Polyionic Species of Branched Topology - Self Organized Nanostructures of Amphiphilic Block Copolymers - page 138

1 z = 0.0

z = 0.3
z = 0.5
z = 0.7
z = 0.9

2

0.2

3

5

4

5

6

1

4

6 Single

neutral star

0.1

2

3

3

4

2

0.0 0

5 10 15 20 25

r

Fig. 5 Fraction P of the terminal monomer units located at a distance r from the center of a
star-shaped PE at different contents of a linear PE. z is the degree of charge compensation, which
reflects the linear PE content. Reprinted from [ 89 ] with permission from the American Chemical
Society

Thus, the results of MD simulations provide ultimate support for the core-corona
[the core comprises domains (a) and (b), as revealed in MD simulations] model of
the structural organization of IPECs based on the star-shaped PEs, which was sug-
gested on the basis of experimental findings [ 80 ]. Together, experimental results
and MD simulations provide evidence for a compartmentalized micelle-like struc-
ture that results from a pronounced nonuniform distribution of chains of the linear
PE within the volume occupied by a molecule of the star-shaped PE.
The MD simulations [ 89 ] also gave another very important insight into the
structure of IPECs based on the star-shaped PEs that would be difficult to obtain
experimentally. Following from the radial distributions of the end monomer units
demonstrated in Fig. 5 , a progressive repartitioning of the arms of the star-shaped
PE from the periphery region to the complex coacervate domain was observed with
an increase in content of the linear PE. Figure 6 clearly illustrates the pronounced
segregation of the arms of the star-shaped PE into two populations, one of which
forms the complex coacervate domain together with chains of the linear PE, and the
other builds up the corona domain.
The MD-predicted intramolecular segregation of the arms of the star-shaped PE
into two populations (collapsed and extended ones) provides an explanation for the
experimentally observed absence of a dependence (or relatively weak dependence)
of the hydrodynamic size of the IPEC species on the number of incorporated chains
of the linear PE.
Simple scaling arguments [ 89 ] enable a rationalization of the origin of the parti-
tioning of arms of the star-shaped HPE between the core and the corona domains:
the free energy of the core (complex coacervate) domain is controlled (in the main
part) by the total number of positively and negatively charged monomer units form-
ing the complex coacervate core, i.e., by the degree of charge compensation of the