Biomedical Engineering Reference
In-Depth Information
in interfacial tension was also observed for polymers bearing side groups
in systems such as PDMS(-g)-NH
2
/PEO, PDMS(-g)-COOH/PEO [21] and
PDMS(-g)-NH
2
/PB [22]. In a PB/PDMS-NH
2
system, a decrease in the in-
terfacial tension as a function of Mn
-1
was observed but not the expected
Mn
-2
/
3
relationship generally encountered for surfactant activity. Moreover,
the addition of NH
2
-terminated PDMS in a PB/PDMS system showed a lin-
ear relationship between the interfacial tension and the proportion of added
PDMS-NH
2
(up to 75%). These phenomena led the authors to conclude that
the end-group effect is a bulk effect and not an interfacial one. Their con-
clusion is based on the fact that a surfactant does not involve such linear
relationships and only a few percent is required to observe interfacial ac-
tivity. Interaction parameters deduced from theory or obtained from cloud
point curves allowed the authors to suggest that the observed compatibiliza-
tion is more likely due to repulsion between the PDMS backbone and its
amine end groups rather than to unexpected attractive interactions between
the amine groups and the PB. The addition of functional PDMSs such as
PDMS-NH
2
,PDMS-g-NH
2
, PDMS-COOH or PDMS-g-COOH in a PA/PDMS
blend has been patented [23]. For example, the addition of 1 wt % of carboxy-
terminated polysiloxane to a 75
25 (wt.%) PA/PDMS system reduced the
diameter of the PDMS phase from 35
/
m(SEMmeasurements).
The inventors observed that the diameters of the dispersed particles in the
polysiloxane phase were much smaller in the presence of the additive than
without it. Moreover, the mechanical properties [tensile elongation and Izod
strength (impact resistance)] were enhanced. Finally, Li et al. [24] compatibi-
lized PDMS and polyvinylpyridine (PVP) via hydrogen bonding interactions
that they obtained by functionalization of the PDMS with carboxylic acid
groups. Using FT-IR, DSC and XPS measurements, the authors concluded that
a minimum of 23 mol % was required to obtain a compatibilized blend.
µ
mto1-2
µ
3
Compatibilization of Polymer Blends Using Copolymers
The use of copolymers as surfactants is widespread in macromolecular chem-
istry in order to compatibilize immiscible blends. These additives are some-
times named “surfactants”, “interfacial agents” or more usually “compatibi-
lizers”. Their effect on improving different properties is observed: interfacial
tension and domain size decrease, while there is an increase in adhesion
between the two phases and a post-mixing morphology stabilization (coales-
cence prevention). The aim of the addition of such copolymers is to obtain
thermodynamically stable blends, but the influence of kinetic parameters
hastobekeptinmindaslongastheyhavetobemasteredtoreachthe
equilibrium. Introducing a copolymer can be achieved either by addition of
a pre-synthesized copolymer or by in-situ surfactant synthesis via a fitted re-
