Super-strong segregation limit

In most cases block copolymers form spherical micelles in dilute solution. In only a few studies was the formation of non-spherical aggregates reported. For example, cylindrical or worm-like micelles were observed for polystyrene-polybutadiene-polystyrene (PSt-PB-PSt) triblock copolymers in ethylacetate [148], PSt-PI (polyisoprene) in N,N-dimethylformamide (DMF), or PEO-PPO-PEO triblock copolymers in aqueous solutions [149]. Conditions for the formation of non-spherical micelles currently seem to be clear only for ionic block copolymers. Due to enormous interfacial tension these systems are in a thermodynamic state close to the super-strong segregation limit (SSSL) [150]. Under these conditions, a sequence of shape transitions from spherical - cylindrical - lamellar is possible. Such transitions can be induced by increasing the ionic strength of the solution or by increasing the relative length of the core block. 

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