Entangled polymer-like micelles

If rj is independent of the shear rate y a liquid is called Newtonian. Water and other low molecular weight liquids typically are Newtonian. If rj decreases with increasing y, a liquid is termed shear thinning. Examples for shear thinning liquids are entangled polymer solutions or surfactant solutions with long rod-like micelles. The zero shear viscosity is the value of the viscosity for small shear rates ij0 = lim,> o tj y). The inverse case is also sometimes observed rj increases with increasing shear rate. This can be found for suspensions and sometimes for surfactant solutions. In surfactant solutions the viscosity can be a function of time. In this case one speaks of shear induced structures. 

The viscoelasticity of the worm-like micelles arises because of the entanglement of very long and flexible worm-like micelles to form a transient network, similar to a solution of flexible polymers. Unlike polymers, however, worm-like micelles break and re-form dynamically. When the network of worm-like micelles is deformed or the equilibrium conditions are suddenly changed, the relaxation occurs within a definite time, and the equilibrium condition is restored again. For a deformation with a hme period shorter than the relaxation time, Tr, the system... 

We have studied self-diffusion in polymer-like networks self-diffusion of transient chains (long entangled micelles) and tracer diffusion in the solvent (silica gels). Our results illustrate the role of reversible chain breaking and the scale-dependence of diffusion in the solvent. 

Entangled solutions of wormy micelles, like solutions of ordinary polymers, show pronounced viscoelastic effects. Figure 12-9 shows the storage and loss moduli for a solution of 15 mM cetylpyridinium salicylate (CPySal) with 11 mM added sodium salicylate. For this solution, the storage modulus is found to be comparable to the loss modulus over a... 

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