Dear Uchenna,

Please read the following text taken from the publication contained in the link depicted at the end of this answer:

The joint self-assembly of polymers and surfactants usually starts at a well-defined surfactant concentration, the ‘critical aggregation concentration’ (cac). One of the most consistent experimental observations in polymer–surfactant systems is that the cac is found to be lower than the ‘critical micellar concentration’ (cmc) of the polymer-free surfactant solution. Consequently, polymer–surfactant systems are commonly divided into two categories: (i) polyelectrolyte and oppositely charged ionic surfactant, where the cac can become several orders of magnitude lower than the cmc; (ii) neutral polymer and ionic surfactant, where the cac is lower than, but comparable to the cmc. Less common are systems containing a polyelectrolyte and a non-ionic surfactant, which can be included in the second category as their cac is comparable to the cmc. Systems where both species are neutral exhibit a very weak effect.

Interactions of Surfactants with Polymers and Proteins, edited by E. D. Goddard and K. P. Ananthapadmanabhan, (CRC, Boca Raton, FL) 1993.

M. Vasilescu, D. F. Anghel, M. Almgren, P. Hansson and S. Saito, Langmuir, 13 (1997). 6951. D. F. Anghel, S. Saito, A. Baran ˜ and A. Iovescu, Langmuir, 14 (1998) 5342.

http://arxiv.org/pdf/cond-mat/9903050.pdf

Hoping this will be helpful,

Rafik

CMC (critical micelle concentration, for those unfamiliar) can be thought of as a type of CAC (critical aggregation concentration). CMC is specific to the formation of micelles, whereas CAC is the formation of any type of aggregate, regardless of any definite shape or morphology. Sometimes these are one and the same; it really depends upon the system. For example, in many of the polymer systems I study, lower concentrations lead to ill-defined aggregates (as determined by dynamic light scattering), but above a certain threshold (which I define as the CMC), definite monodisperse micelles are formed. Alternatively, for a system with similar behavior but that forms vesicles instead of micelles, it would be inaccurate to use the term CMC. However, I've seen both terms used interchangeably throughout the literature. I would be especially wary of which one I used when different morphologies are possible as a function of concentration.