Transient Networks by ABA Triblock Copolymers and Microemulsions: A Rheological Study

The theological properties of microemulsion-triblock copolymer [poly(oxyethylene)-b-polyisoprene-b-poly(oxyethylene)] transient networks were studied by oscillatory shear measurements. The chemical nature of the surfactants (ionic or nonionic) seems not to affect the principal viscoelastic feature of our systems. The main differences between both systems are caused by the individual phase behavior of the underlying microemulsions: within a particular temperature region the temperature dependences of the mechanical properties are opposite for ionic and nonionic systems. Also, specific interactions between the surfactants and the hydrophilic poly(oxyethylene) blocks of the network links lead to a significant effect on the formation of network structures and on the lifetimes of network crosslinks. These lifetimes are connected with characteristic relaxation times derived from the mechanical spectra. Model considerations yielded the definition of a persistence length of the triblock copolymer molecules dissolved in microemulsions.