ISSN:
1435-1536
Keywords:
Dynamic light scattering
;
CTAB: NaSal micelles
;
semidilute regime
;
cooperative diffusion coefficient
;
first cumulant
;
relaxation mode
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Dynamic light scattering measurements are made on networks formed by elongated threadlike micelles of cetyltrimethylammonium bromide (CTAB) in aqueous sodium salicylate (NaSal) solutions at 25°C. The surfactant concentrationC D of the samples is varied from 0.006 to 0.3 M and the ratio of the salt concentrationC s toC D is fixed at unity. The time correlation functionA q (t) of light intensity scattered from the solutions exhibits transition from the unimodal to the bimodal distribution of the decay rate Γ at aroundC D=0.05 M. The dependence of the first cumulant Γe on the scattering vectorq for the samples withC D≦0.03 M is described by the dynamic scaling law. The cooperative diffusion coefficientD c is obtained from extrapolation of Γe/q2 for the samples withC D≦0.03 M and of Γf/q2 forC D≧0.05 M where Γf is the first cumulant from the fast mode. TheD c is found in proportion toC D 0.45, being in agreement with the theoretical prediction for a rigid rod in the semidilute regime by the scaling law. The decay rate Γs characteristic of the slow mode is independent ofq, and Γ s −1 roughly agrees with the mechanical relaxation time τ estimated from a fit of the dynamic viscoelastic data of the same samples by a Maxwell type of model with the single relaxation time τ.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00658893
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