Abstract
Samples of carboxylated scleroglucan, sclerox, with a degree of carboxylation
in the side-chains varying from 10 to 50% were made in order to investigate
the potential of using carboxylation as a means to control subsequent
gelation by heavy metal ions. The storage and loss moduli of aqueous
solutions of sclerox samples as a function of time were determined
at T = 20 degrees C and 30 degrees C after addition of trivalent
chromium ions. The theological characterization showed a transition
from a viscoelastic liquid to a gel with a characteristic time depending
on the chromium concentration and the degree of carboxylation. For
20% carboxylation, the rate of change in the storage modulus could
be controlled within nearly three orders of magnitude from 10(-3)
to 1 Pa min(-1), using total chromium concentrations ranging from
0.3 to 6 mM. This rate was decreased by a factor of 2-5 by reducing
the degree of carboxylation to 10%. The present study indicates that
carboxylation of scleroglucan can be used to control the rate of
gelation mediated by heavy metal ion complexation. This finding suggests
that extension of the application range of this polysaccharide from
an efficient viscosifer for polymer flooding to profile modification
of high temperature oil reservoirs is attainable.
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