Nonlinear Rheology of CTAB/NaSal Aqueous Solutions:  Finite Extensibility of a Network of Wormlike Micelles

Abstract

The nonlinear rheology of aqueous solutions of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) was investigated. The concentration of CTAB was fixed at 0.1 mol L(-1), and the concentration of NaSal was varied from 0.07 to 0.4 mol L(-1). For all test solutions, dynamic moduli were described with the Maxwell model having a single relaxation time, tau. Time evolutions of the shear stress, sigma, and the first normal stress difference, N(1), after inception of the steady shear flow were measured. For solutions having low NaSal concentrations, strain-hardening was observed and sigma and N(1) diverged at a certain strain when the shear rate, , exceeded tau(-1). For solutions with high NaSal concentrations, stress overshoot similar to that of ordinary entangled polymer solutions was observed at between tau(-1) and a certain critical rate, (C), while the strain-hardening was observed at > (C). A simple relationship for elastic solids, N(1)/sigma = gamma with gamma being the strain imposed by shear flow, held for all the solutions in the strain-hardening regime. The strain-hardening was attributable to the strain-dependent shear modulus and well described with the network theory considering the finite extensibility of network strands. The segment size of network strands was successfully determined. Thus, the stress-strain relationship obtained after the inception of fast flows is useful for characterizing the network properties.

Effect of Surface Treatments on Viscoelastic Measurements of Thread-like Micellar Solutions

“…1,12) Concentration of CTAB, C D , and concentration of NaSal, C S , were fixed at C D = 0.1 M and C S = 0.1 M. All solutions were kept quiescently at room temperature prior to the tests for at least for two days for equilibration.…”

Nonlinear Viscoelastic Behavior of Aqueous Hybrid Threadlike Micellar Solutions

“…Thus, the shear thinning behavior is usually observed in entangled polymer systems. According to Inoue et al, 25,26) the strain-hardening behavior observed in the threadlike micellar system, CTAB:P(St/NaSS)/W, is attributed to the finite extensibility of the hybrid threadlike micelles forming fused temporal cross-links at entanglements as assumed in the phantom-crossing model. 13) Consequently, the relaxation mechanism for the hybrid threadlike micellar system is essentially explained with the phantom-crossing model as proposed in the previous study.…”

“…Inoue et al 25) have analyzed the strain-hardening behavior of the ordinary threadlike micellar system of CTAB:NaSal/W using a three-(freely jointed)-chain model. 28,29) In this model, threadlike micelles were regarded as non-gaussian freely jointed chains with a finite segment number giving finite …”

“…9) In the ordinary threadlike micellar systems, strain-hardening behavior was observed in their shear stress under stress relaxation measurements at large strains and also start-up shear flows at high shear rates, i.e., the initial shear modulus was higher than the linear value under large step strains, and the shear stress increased enormously and exhibited a marked overshoot much higher than the linear response at the onset of start-up shear flow. [23][24][25][26] Inoue et al 25,26) has reported that the significant strain-hardening behavior observed in an ordinary threadlike micellar system is attributed to the finite extensibility of threadlike micelles forming sticky temporal cross-links at entangling points which are not simple topological entanglements as those formed in the entangled polymer systems, but are temporal fused crosslinks as assumed in the phantom-crossing model. Since the molecular origin of strain-hardening behavior observed either in ordinary or hybrid threadlike micellar systems is directly related to characteristics of micellar structures, nonlinear viscoelastic measurements in the CTAB:P(St/NaSS)/W system provide useful information for the understanding of structure and dynamics of hybrid threadlike micelles.…”

Creep Behavior of a Maxwell Element Type Supramolecular Polymeric System

“…These suggest that relaxation experiments at large strains belonging to the nonlinear regime 41,42) as the behavior of networks consisting of chainlike strands with finite extensibility 38) . From these, the essential characteristics of networks formed with threadlike micelles in the CTAB:NaSal/W system are possibly similar to those in the DO 3 B/C 10 system in aspects of both linear and nonlinear viscoelastic responses.…”