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copolymers
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The Influence of the Macromolecular Architecture on the Micellization in Block
*
Copolymer / Homopolymer BlendsTPD
1,2*
1
UE. PavlopoulouUP
P, K. ChrissopoulouP P, S. H. AnastasiadisP
4
5
5
G. PortaleP P, H. IatrouP P, S. PispasP N. HadjichristidisP
1
PFoundation for Research and Technology – Hellas, I.E.S.L., Heraklion, Crete, Greece
2
PUniversity of Crete, Dept. of Materials Science and Technology, Heraklion, Crete, Greece
3
PAristotle University of Thessaloniki, Dept. of Chemical Engineering, Thessaloniki, Greece
4
PESRF, DUBBLE beamline, Grenoble Cedex, France
5
PUniversity of Athens, Dept. of Chemistry, Zografou, Athens, Greece
*epavl@iesl.forth.gr
Micellization of block copolymers in a selective solvent or in a homopolymer matrix has attracted the attention of the
scientific community in the recent years [1]. The increasing interest in such systems arises from the influence of the
micellization and of the micellar characteristics on phenomena like the modification of interfacial activity, controlled drug
delivery, formation of metal nanoparticles and others. Micelles are stable aggregates formed by the self-assembly of the
copolymers whereas micellization often occurs via a procedure which leads to a dynamic equilibrium between micelles, with
a narrow mass and size distribution, and dispersed copolymer molecules. The majority of the studies on block copolymer
micelle, however, concern micellization either in a selective solvent and/or micelles formed by linear diblocks [2,3].
Herein we investigate the effect of macromolecular architecture on micellar formation and micelle characteristics
of block copolymers in homopolymer matrices. A series of (polyisoprene)B2B(polystyrene), IB2BS, graft copolymers with constant
total molecular weight and varying composition, fBPSB, and a series of symmetric (polyisoprene)BnB(polystyrene)BnB, IBnBSBnB,
miktoarm star block copolymers, with n identical pairs of arms, are added to a low molecular weight polyisoprene
homopolymer matrix and the blends are investigated by small-angle X-ray scattering (SAXS) and dynamic light scattering as
a function of copolymer concentration and fBPSB or n, respectively. SAXS measurements have been carried out at the
Daresbury Synchrotron Radiation Source (SRS), UK, and at the Dutch-Belgian Beamline (DUBBLE) at the European
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Synchrotron Radiation Facility (ESRF) in Grenoble, France, covering a very wide scattering vector range 0.04 < q < 3.7 nmP
1
P. The scattered intensity was corrected for background and transmission whereas measurement of a standard sample
(Lupolen) was utilized for intensity normalization. Analysis of the SAXS scattered intensity [4] allows the measurement of
the form factor of the micelles and, thus, the polystyrene core radius, RBcB, the micellar aggregation number, QBmB, and the
micelle number density, N, can be calculated.
At 2wt% concentration of the IBnBSBnB (with 19k polystyrene and 15k polyisoprene blocks), spherical
micelles are obtained (Figure 1) with a micellar core radius that is independent of n whereas the aggregation number
-1
decreases with n following an nP law (Figure 2). The number density of micelles in the mixture and the polystyrene
fraction in the core are constant as well. These findings signify that, in the range of molecular weights investigated, the
functionality of the junction point of the copolymer does not influence the micellar characteristics. A simple thermodynamic
model has been developed that describes theoretically the micellization of ABnBBBnB within a B homopolymer
matrix. The model agrees very well with the experimental data both qualitatively and quantitatively [5], see Figure 2.
1,3
5
Intensity (cm -1 )
10 -4
10 0
10 0 ESRF
SRS
10 -2
10 -2
10 -4
10 0
10 -2
10 -4
10 0
10 -2
10 -4
10 0
10 -2
10 -4
0.1 1
q (nm -1 )
IS
25
20
15
Experimental
Theoretical
I 2
S 2
10
5
I 4
S 4
0
0 2 4 6 8 10 12 14 16 18
Experimental
250
n
Theoretical
100
200
-1
150
10
1 10
I 6
S 6
I 16
S 16
Q m
R c
(nm)
100
50
Q m
0
0 2 4 6 8 10 12 14 16 18
n
n
Figure 1: The SAXS intensity curves as a function of the
scattering vector q for the 2wt% blends of the various IBnBSBnB
miktoarm copolymers in PI. The curves obtained at ESRF
are presented shifted by an order of magnitude for clarity.
Figure 2: The core radius (RBcB) and the aggregation number
(QBmB) for the IBnBSBnB versus the number of arms n. The
triangles correspond to the theoretical values whereas the
solid circles to the experimental ones with the error bars
determined by the polydispersity in the radii.
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