Below the cmc (I'm not sure what you mean by "beyond"), the viscosity should be close to that of the solvent (usually water). Above the cmc the viscosity can only increase, as far as I know. I am not sure that a Brookfield viscometer is sensitive enough for this job. It is challenging even with a true rheometer. What viscosity values are you measuring?

I want to mean concentration above CMC as beyond CMC and I want to measure bulk viscosity. 

Normally, viscosity  increases with surfactant concentration and it can be monitored using Brookfield viscometer.

what is the surfactant you are speaking about? Are you sure that micelles are formed or maybe you are below the Krafft temperature? What are the differences you measure?

All three type of surfactants. I think micelle formation makes it heavy and settle down at bottom which has not been sensed by viscosity meter spindle

micelles do not settle, undissolved ionic surfactants may settle, however, surfactant concentration in equilibrium with undissolved phase will not change, i.e. viscosity should not change either. Maybe best check your results with a different method.

I suggest that you make some glycerol/water or sugar/water mixtures, whose viscosity is given to high precision in the "Handbook of Chemistry and Physics" and see whether you measure the correct values with your Brookfield viscometer. Once you are sure that you can measure low viscosities accurately, we can discuss whether sedimentation of micelles is a problem.

Which solvent u are using? And what about the concentration of surfactant? Are u using any nano particle in surfactant solution?

Water as solvent , no nanoparticles. surfactant concentration is from below cmc to above cmc( 50-60 times of cmc)

what is the cmc value for SDS, CTAB solution?

CMC of CTAB: 0.92  mM

CMC of SDS: 8.2 mM.

Can u provide me a article from where this value has been given.

see the attachment. U can refer some paper related to this field

What shear rate do you use in the Brookfield?

If too high, you may have shear banding in the concentrated solutions of CTAB.

 What is the reason behind viscosity decrease beyond CMC of a surfactant solution?

When surfactant is added in the solvent may be water then the cohesive forces (CF) responsible for  higher surface tension and lower viscosity as the solvent is not entangled. Fundamentally the viscosity is caused by the frictional forces (FF) where fitting surfactant molecules redesign FF. So on increasing surfactant concentration the population of surfactants molecules is either aggregated but at CMC, emulsion could be ordered with higher FF. But beyond CMC, disordered surfactant molecules could be haphazard on making nano scale coalescence suitable for quick flow with less FF. However, in general, in case of emulsions the surface tension decrease and viscosity increase even beyond CMC.  However, product of  FF and CF is defined as friccohesity which clearly defines such trends.   http://www.sciencedirect.com/science/article/pii/S1878535211000025

http://www.sciencedirect.com/science/article/pii/S0021961413001985

Hello,

The viscosity of CTAB in water solutions increases with concentration as shown here using proper measurement technique (not my work):

http://pubs.rsc.org/En/content/articlelanding/2004/cp/b316621j#!divAbstract

see figure 1 and 2.

As several people said, a brookfield instrument is not appropriate to do such measurements. The only viable solutions around c* to perform such delicate measurements (viscosity~1-10 times that of water) are either a modern rheometer, or preferably, a Ubeholde viscometer.

Generally, viscosity is not sensitive for micelle formation. But sometimes, e.g. in case of formation of large micelles or micelle-polymer (polyelectrolite-like) complexes, it may be quite sensitive tool.

In some polymer-surfactant systems, the zero-zhear viscosity can go through a maximum, just beyond CMC, and then dip slightly (PEO-SDS is a swell-studied example). Although this is due to the polymer chain becoming saturated with surfactant, there are also instances where there is a transition in the type of micelle that the surfactant will form. This could cause a sort of transition in the observed viscosity, particularly if only measuring at one shear rate, as in with a Brookfield viscometer.

 Survismeter measures viscosity, surface tension, interfacial tension, wetting coefficient most accurately. Please use survismeter for measuring such data of such solutions.

Sir, 

      How much does it cost a survismeter as you have patented the technology

Sir, have a look at the following site.

vakilspremedia.com/borosil/files/assets/basic-html/page116.html

it is available in borosil catalogue 2015-16 at page no. 110-111.

Krishnayan Haldar

Man Singh

Erik Miller

Mikhail Y. Pletnev

Francois Caton

Jasila Karayil

Alan Parker

Brookfield viscometer can create a laminar or turbulent regime in the solution. If you measure the viscosity of surfactant solutions in the turbulent regime and when they have formed cylindrical micelles 50-60 times greater than СМС1, then the viscosity will decrease. This is a known phenomenon of viscosity decrease in the presence of high-molecular water-soluble substances, which is used by fish and tried to be used for boats to increase speed.