EXTRAORDINARY PROPERTIES OF SYNTHETIC AND BIOLOGICAL POLYELECTROLYTES IN DEIONIZED SOLUTION .2. EXPANSION OF CARBOXYLIC-ACID TYPE GELS

Steady-flow viscosities of carboxylic acid type gels are measured in deionized solutions and in the presence of a small amount of NaOH and NaCl. The plots of shear stress (S) of the net structure of the gels against shear rate (q) show the following features: (1) at very small values of q (smaller than 1 s-1), 5 increases very sharply with increasing q. The S-q curve is S-shaped, and the rigidity (G) of the gels is roughly evaluated from the plots of S against qt/2 (shear strain), where t is time. The G values are between 260 and 730 Pa. (2) The sharp increase in S ceases above the critical q values, and then S decreases and begins to increase again. (3) The log (viscosity, η) vs log q plots support the netlike nature of the gels; log η decreases linearly as log q increases with a slope of -1. (4) Viscosities of deionized gels are unexpectedly high compared with the partially neutralized gels with NaOH, which is explained by the important contribution of the expanded Debye screening length. (5) On the addition of NaOH, the gels transform partially from the netlike to the liquidlike structures. (6) Addition of a small amount of NaCl shrinks the gel conformation by the shielding effect in the electrical double layers. Expansion of the gels is explained with the electrostatic intersegment repulsion and the expanded Debye screening length in the deionized system. © 1990 American Chemical Society.