Chemistry Reference
In-Depth Information
Interfacial tension between two incompatible homopolymers can be reduced by
adding homopolymers containing functional side or end groups. In 1971, Patterson
et al. [
264
] investigated the effect of functionalized poly(dimethyl siloxane), PDMS,
additives on the interfacial tension between a commercial methyl-terminated PDMS
and a commercial polyoxyethylene/polyoxypropylene copolymer, P(OE-OP). Start-
ing with a high interfacial tension (8.3 dyn/cm), the presence of 10% carboxyl
groups on alkyl side chains attached to the PDMS molecules reduced the interfacial
tension by 63%. Doubling the number of carboxyl groups made this additive slightly
less, rather than more, effective (57% reduction). Incorporation of carboxyl end
groups on the PDMS chain provided a material that was capable of reducing
interfacial tension in the same system by 49%. In contrast, hydroxyl end groups
had no significant effect on the interfacial tension. Amino groups on the silicone
additives had only a small effect on the interfacial behavior: 1% amino groups on
alkyl side chains reduce interfacial tension by 28%, whereas increasing the amount
of polar substituents to 6% produced a higher rather than lower interfacial tension
value (18% reduction). In general, the interfacial activity of these additives is probably
due to specific interactions between the additive and the homopolymers; these
interactions increase compatibility and, consequently, reduce interfacial tension.
Patterson et al. [
264
] reported the effect of addition of PDMS-
b
-POE copoly-
mers on the interfacial tension between PDMS and P(OE-OP) as well. A 72%
reduction in interfacial tension was obtained with the addition of 2% of a 60/40
PDMS-
b
-POE block copolymer, as shown in Fig.
23
. Increasing the level of polar
polyether substitution from 40 to 75% did not result in any further reduction; it
rather showed less interfacial activity (64% reduction). This agreed with the
proposed maximum efficiency of symmetric copolymers [
257
,
258
,
265
]. Substitu-
tion of a POP for the POE in the 25/75 copolymer additive reduced its capability for
reducing interfacial tension (51% reduction).
The effect of the concentration of the copolymer emulsifier was studied for the
60/40 PDMS-
b
-POE (Fig.
23
). A major reduction in interfacial tension (55%) took
9
8
7
6
5
4
3
Fig. 23 Effect of the addition
of a 60/40 PDMS
b
POE
copolymer on the interfacial
tension between PDMS and a
P(OE OP) copolyether fluid
[
264
]
2
1
0
1
2
3
4
% Additive by Weight
