Rheological properties of an interpolymer complex formed between poly(acrylic acid) and methyl cellulose

Some rheological properties of an interpolymer complex formed in the mixtur es of aqueous solutions of poly(acrylic acid) and methyl cellulose are inve stigated. In a diluted state, the complex exhibits polyelectrolyte properti es, and in the shear field, it flows like a pure poly(acrylic acid) solutio n. From the experimental data obtained from the mixture flow in a longitudi nal field, an effective relaxation time was calculated, It turned out to be higher than that for the initial components. The deviation of the experime ntal values of the viscosity from the calculated additive ones allowed us t o determine the critical molecular weight of the poly(acrylic acid) below w hich the complex is not formed: M-cr approximate to 6 x 10(4), which is one order of magnitude higher than for the mixtures of spatially complementary macromolecules. The increase of the total polymer concentration in the mix ture first leads to an increase of the complex size. Further increase of th e polymer concentration and transition to the semidiluted state decreases t he complex size and also decreases its solubility in water. (C) 1999 John W iley & Sons, Inc.