Chemistry Reference
In-Depth Information
PMMA mixed with a few percent of diblock copolymer were spin coated separately
and, using the floating method, the assembly was built. The films were annealed to
let the copolymer migrate to the interface and reach thermodynamic equilibrium.
Figure
21
shows the volume fraction profile of a dPS-
b
-PMMA copolymer (262
segments) with a deuterated PS sequence at the interface between PS (18,000
segments) and PMMA (13,000 segments). At the concentrations studied, the excess
number of copolymer chains per unit area at the polymer polymer interface varied
linearly with
f
c
, the volume fraction of copolymer chains in the bulk. The results
were compared with predictions based on a modification of the mean field argu-
ments of Leibler [
75
] (discussed in Sect.
4.3.3
). For low density of copolymer
chains at the interface, the predictions are in a good agreement with the experimen-
tal behavior.
Neutron reflectivity was used to investigate the segment density distribution of
symmetric diblock copolymers of PS and PMMA [
39
] (molecular weights of about
100,000) at the interface between PS and PMMA homopolymers (molecular
weights of about 100,000). Selective deuterium labeling of either a block of the
PS-
b
-PMMA or of the PS or PMMA homopolymers provided the contrast neces-
sary to isolate the distribution of the segments of the individual components at the
interface. Results from a series of experiments were used simultaneously to yield
the density profiles of the PS and PMMA segments of the homopolymers, and of the
copolymer blocks at the interface (Fig.
22
).
It was found that the effective width of the interface between the PS and PMMA
segments was 75
˚
, i.e., it was 50% broader than that found between the PS and
PMMA homopolymers in the absence of the diblock copolymer (50
5
˚
[
261
])
and between the PS and PMMA lamellar microdomains of the pure PS-
b
-PMMA in
the bulk (50
4
˚
)[
261
,
262
]. The area occupied by the copolymer at the interface
between the homopolymers is 30% larger than that of the copolymers in the bulk
lamellar microstructure [
39
]. In that study, the amount of diblock copolymer at the
interface was (approximately) equivalent (
200
˚
) to half of the long period of
the neat ordered copolymer. The same PS/PS-
b
-PMMA/PMMA system was subse-
quently investigated by a lattice-based self-consistent field model that was extended
0.010
Fig. 21 Volume fraction
profile of dPS
b
PMMA
copolymer chains segregated
to the PS PMMA interface.
The
shaded region
indicates
the interface excess. The
volume fraction of copolymer
chains in the PS phase (
x <
0)
is
f
c
PS
0.0033. The volume
fraction of copolymer chains
in the PMMA phase (
x
0.008
0.006
0.004
0.002
>
0) is
f
c
PMMA
0.0044. The
sample was annealed at
162
C for 100 h [
40
]
0.000
−
4000
−
2000
0
x (Å)
2000
4000
