Progressive Freezing-in
of the Junctions in Self-Assembled
Triblock Copolymer Hydrogels during Aging
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Abstract
The evolution with time was investigated for self-assembled
networks
formed by triblock copolymers in aqueous solution. The polymers consisted
of a central hydrophilic poly(acrylic acid) block and two hydrophobic
end-blocks formed by random copolymers of 50% acrylic acid and 50% <i>n</i>-butyl acrylate units. The rheological properties of the
systems at steady state were strongly influenced by the degree of
ionization (α) and thus by the pH. This allows one to obtain
systems ranging from low viscosity solutions to hydrogels just by
varying α. However, steady state was not reached instantaneously
when α was changed, but proceeded through a slow progressive
increase of the viscosity. The rate at which the systems aged was
independent of α and of the polymer concentration and is attributed
to slow reorganization of the cores formed by the self-assembled hydrophobic
blocks
