Dynamic light scattering from semidilute cellulose-tri-carbanilate solutions

Abstract

A series of cellulose-tri-carbanilates (CTC) with a range of M w = 130 000 to 1 000 000 has been studied in dioxane at 20°C by static and dynamic light scattering. CTC is a semiflexible chain with a persistence length of 110 Å. In two cases ( M w = 130 000 and 1 000 000) a concentration region from dilute to 20c∗ was covered, where c∗ = 1 |η| is taken as the coil overlap concentration. Up to 3c∗ usual dilute solution behaviour was found. At about 3c∗ a sharp decrease in 1 M app [ = Kc R (q = 0)] and in the apparent diffusion coefficient D( c) (determined from the first cumulant of the time correlation function ( TCF)) was observed. Simultaneously, the mean square radius of gyration increases. Analysis of the TCF reveals two modes of motion: the mode which is fast, increases with c with an exponent of about 1.0 ± 0.1 and may be attributed to the cooperative diffusion coefficient of an entangled network. The other, which is slow, decreases with an exponent of about −2.6 ± 0.2 and thus is appreciably larger in value than −1.75 which is predicted for the self-diffusion of single chains. Master curves are obtained for M M app and D(c) D 0 as function of c c∗ . The observed behaviour indicates that there is no transient network formation. The results are, however, consistent with a model of entangled clusters existing in the region c∗ ⩽ c ⩽ 10c∗.