Viscoelastic Properties of Aqueous Solutions of Amylose in Ultrasonic Frequencies Region

Abstract

The viscoelastic properties of dilute aqueous solutions of amylose in ultrasonic frequencies region were investigated by a torsional method using quartz crystal resonator.
Both G/andnLns showed a minimum between pH II and 11.5and in addition, a maximum was observed for n-n, at a slight1y lower pH value. These results are similar to the behavior o-f intinsic viscosity reported by Rao and Foster and by Doppert and Staverman and suggest that the pH-dependent heliX-coil transition of amylose occurs in water.
In the range aboye pH 13, where amylQs is said to show bshavior, similar to a polyelectrolyte, the cgncentrqtion dependences of G' and n-n were larger than those for the aqueous solution of sodiun aL1ginat-e whigh behaves as polyelectrolyte in solution as reported pretiiously by the authors. Therefore electrostatic repulsion between amylose chains does not seem to be so strong.04 the gther hand, in the range below pH 10, where amylose exists essentially in a helical conformation, the concentration dependences of G' and n'-n, were more remarkVable.
In the range above pH 13, the experimentaHy obtained frequency dependences of viscoelastic functions at an infinite silution agreed well with the curves predicted by the Rouse theory or the Techoegl theory for a random coil polymer in a dilute solution. Unexpectedly, in the range below pH 10, the results were closer to the Rouse theory rather than the Kirkood-Auer theory for a rod-like polymer, Therefore, in the low pH renge, amylose chain is thought to take a loose, extended helical conformation.