Transient Gelation and Glass Formation of Reversibly Cross-linked Polymeric Micelles

Poly(ethylene oxide) (PEO) end-capped with a hexadecyl group at one (alpha-PEO) or both ends (alpha,omega)-PEO) are highly asymmetric diblock or triblock copolymers that form spherical micelles in aqueous solution. (alpha,omega-PEO) can bridge between two micelles leading to reversible association of the micelles. At a first critical concentration (C-p), the micelles percolate and a transient network is formed with an elastic modulus determined by the concentration of alpha,omega-PEO. C-p increases with increasing fraction of alpha-PEO and is insensitive to the temperature. At a second critical concentration (C-c), a liquid-solid transition occurs. C-c is independent of the fraction of alpha-PEO and increases with increasing temperature. There are indications that the solid state is formed by nucleation and growth of domains of dynamically arrested micelles. The properties of the transient network are almost the same in the liquid and in the solid state.