Chemistry Reference
In-Depth Information
the copolymer and
s
and
f
are determined by (
119b
) together with (
115b
), (
117a
)
(or
117b
), and (
118b
) (or (
118c
), respectively);
Dg
is evaluated by (
113b
). Due to
the asymmetric architecture of the graft copolymers and in view of the respective
experimental data [
56
], two situations were considered: (1) when the AB
2
diblock is
added to the B homopolymer (e.g., an I
2
S graft added to the PI phase [
56
]); and (2)
when it is added to the A homopolymer (I
2
S added to PS [
56
]).
Although the assumptions involved did not allow a quantitative comparison with
the data [
56
], the behavior of the estimated
Dg
when graft copolymers of varying
compositions were introduced into the PI or PS homopolymer phase (at constant
additive concentration) resembled the experimental data for the molecular para-
meters of the experimental systems [
56
]. When the I
2
S graft copolymers are added
to the PI homopolymer, there are no micelles formed for high values of
f
PI
, and the
copolymer chains at the interface are at equilibrium with chains homogeneously
mixed within the PI phase. The surface density of chains increases with decreasing
f
PI
(from its high value) and the interfacial tension decreases. At lower values of
f
PI
,
micelles are also present and
s
does not increase (and even decreases) as
f
PI
decreases further; as a result the interfacial tension does not decrease further (and
even increases). Similarly, when the I
2
S copolymer is added to the PS homopoly-
mer, there are no micelles formed for low values of
f
PI
, and the copolymer chains at
the interface are at equilibrium with chains homogeneously mixed with PS. The
surface density of chains increases with increasing
f
PI
and the interfacial tension
decreases. At higher values of
f
PI
, micelles are also present and
s
ceases to increase
as
f
PI
increases further; as a result the interfacial tension does not decrease further.
The
Dg
values were more or less in the range of the experimental values, although
the apparent functional forms of the curves were different from the experimental
ones [
56
]. For example, the dependencies in the region where micelles are present
are apparently different to the experimental values. This is most probably due to the
assumptions involved in the estimation of the chemical potentials for the copolymer
chains in micelles (dry brush behavior was assumed). Even more, the value of the
interaction parameter used affects both the location of the minimum (with respect to
f
PI
) and the values of
Dg
. No fitting was attempted because the aim of the theoretical
analysis was to obtain only the trends in order to understand the behavior of the
experimental data. Indeed, it is evident that the calculation indicates a behavior very
similar to that shown by the experimental data, with the origin of this trend evidently
related to the behavior of the estimated surface density of adsorbed chains.
5 Concluding Remarks
Mixing two or more components that have complementary properties is largely
utilized to improve the performance of polymeric materials for many important
industrial applications. In spite of the great interest in homogeneous blends, a more
desirable situation is that of a non-miscible system, i.e., a heterophase mixture
wherein each of the constituents retains its own properties. In addition, the final
