We have used mechanically generated capillary wave and
ellipsometric techniques to investigate interfacial
viscoelastic properties of adsorbed monolayers of
polystyrene-b-poly(methacrylic acid) diblock
copolymer
at an air−water interface, as a function of both the overall
molecular weight, M
w, and the nominal
interfacial
number density of the copolymer. This experiment is a follow-up of
our earlier experiment, in which we
studied adsorbed monolayers of the same diblock copolymer at the
toluene−water interface (Macromolecules
1993, 26, 6595). Now we have changed the
environment of the polystyrene block from toluene to air
and
have studied the effect of such a change. The most prominent
effect of this change is that it is more difficult
to attain equilibrium at the air−water interface. Unlike the
toluene−water case, no clear saturation of
surface pressure is observed at the air−water interface. The
maximum surface pressure values measured
at the air−water interface are smaller than the saturation surface
pressure values in the toluene−water
case for all the three molecular weights we have investigated.
Ellipsometric study shows that only a very
small fraction of the copolymer molecules added to the system is
adsorbed at the air−water interface.
However, substantial changes in the longitudinal elasticity and
longitudinal viscosity are observed.
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