Bridging interactions due to telechelic linkers balanced by screened Coulombicrepulsions

Abstract

When telechelic polymers (poly-ethyleneoxide grafted at both ends with an aliphatic chain)are added to a microemulsion of decane droplets in water stabilized by a surfactant filmthey can link the droplets and thus introduce an effective attractive interaction between thedroplets, eventually leading to a phase separation. Starting from a neutral microemulsionwe show that this attractive interaction can be offset by adding minute quantities of anionic surfactant, thus introducing a repulsive Coulombic interaction. This opens up thepossibility of ‘weighting’ an unknown effective attraction against a well known repulsion.The phase behaviour and the small angle neutron scattering spectra of different samplesillustrate this point. The spectra are simulated assuming the interaction potentials to bethe sum of attractive and repulsive contributions and a good agreement is foundbetween the experimental and simulated spectra in the neutral microemulsion, inthe charged microemulsion and in the charged and connected microemulsion.