Chemistry Reference
In-Depth Information
interface. In contrast, when a PS-
b
-PMMA copolymer was added to the polyvinyl
chloride (PVC)/PS blend (the PMMA sequences are miscible with PVC), dispersion
of the copolymer within the PVC phase was observed instead of a preferential
adsorption to the interface. It was pointed out that a properly tailored decrease in the
interaction of the PMMA block with PVC (i.e., by controlling microstructure,
molecular weight, and composition) would restore a more favorable situation but
at the cost of a long optimization process. Thus, an important requirement for the
copolymer is that it should not be miscible as a whole molecule within one of the
homopolymer phases, because this would increase the amount of the copolymer
required to reach interesting sets of properties.
Shull et al. [
38
] used forward recoil spectrometry to quantify the interfacial
segregation of diblock copolymers consisting of deuterated polystyrene (dPS) and
poly(2-vinylpyridine) (P2VP) at interfaces between PS and P2VP homopolymers.
Figure
20
shows the equilibrium distribution of the diblock copolymer to the PS
P2VP interface after the appropriate annealing. The interfacial excess, estimated as
the hatched area in Fig.
20
, increased with increasing copolymer concentrations
within the PS layer and was compared to mean-field theory predictions, which
were quantitatively accurate for copolymer concentrations below the limiting value
associated with the formation of block copolymer micelles. The segregation behav-
ior in the regime where micelles were present was complicated by a strong tendency
for micelles to segregate to the free PS surface and by a weaker tendency for
micelles to segregate to the interfacial region. The effects of micelle formation
within the bulk homopolymer phases on the interfacial behavior will be discussed
further in the following sections.
Elastic recoil detection (ERD) was used by Green et al. [
40
] to study the
segregation of low molecular weight symmetric copolymers of PS, and PMMA to
the interface between PS and PMMA homopolymers. Bilayer films of PS and
0.10
0.08
Fig. 20 Copolymer
distribution for a dPS
b
P2VP
391 68 diblock copolymer
added at constant
concentration to the top PS
layer (overlaid onto a P2VP
layer) following by an 8
h annealing at 178
C. For this
sample, the final equilibrium
copolymer concentration in
the PS phase was 2.1%. The
interface copolymer excess,
zi
*, corresponding to the
shaded area
, was equal to 100
˚
[
38
]
Z
i
*
0.06
0.04
f
p
s
0.02
0.00
2000
0
2000
Depth (Å)
4000
6000
8000
−
