Article,
Static light scattering studies on xanthan in aqueous solutions
Macromolecules, 29 (10): 3491 -- 3498 (May 1996)
Abstract
A commercial sample of xanthan was (i) sonicated and fractionated
by GPC on Sepharose C1-2B with 0.1 M NaCl as eluant/solvent. The
angular dependence of scattered light was measured (offline) and
interpreted in terms of the wormlike chain model using the ''master
curve procedure''. The persistence length was estimated as L(P) approximate
to 150 nm. The mass per unit length M(L) approximate to 2000 g/mol
. nm indicates double-stranded chains. (ii) The parent sample was
studied at various ionic strengths I (0.01 mol/L less than or equal
to I less than or equal to 0.3 mol/L). The conditions for optimum
solubility and clarification (ultracentrifugation/membrane filtration)
were checked. At higher ionic strength, the sample was only partly
soluble and the solution contained supermolecular structures even
after clarification. Good solubility was observed in 10 mM NaCl.
The Zimm procedure was used to obtain the average molar mass M(W),
the second virial coefficient, and the radius of gyration R(g). The
interpretation of the scattering function led to M(W) = 2.88 x 10(6)
g/mol, R(g) = 241 nm, L(P) = 149 nm, a polydispersity sigma(M) =
0.5, and double-stranded chains. At room temperature, solutions revealed
a tendency for aggregation, which could be prevented by storage at
elevated temperature.
