Tuning the assembly of amphiphilic block copolymers through instabilities of solvent/water interfaces in the presence of aqueous surfactants

The influence of the water-soluble surfactant sodium dodecyl sulfate (SDS) on the self-assembly of amphiphilic block copolymers through hydrodynamic instabilities of organic solvent/water interfaces was studied. Micropipette aspiration measurements performed on evaporating chloroform droplets containing polystyrene-b-poly(ethylene oxide) (PS-PEO) revealed that interfacial instabilities were correlated to an approach of the organic/water interfacial tension to zero. The addition of SDS to the aqueous phase lowered the interfacial tension, thereby facilitating the onset of instability at lower concentrations of PS-PEO within the droplets. Further, increased amounts of SDS led to qualitatively different mechanisms of interfacial instability and correspondingly different morphologies of the resulting copolymer/surfactant assemblies. Similar, though less pronounced, effects were obtained using poly(vinyl alcohol) (PVOH) as a water-soluble surfactant, reflecting its more weakly concentration-dependent surface activity. These results enabled a single PS-PEO or polybutadiene-PEO block copolymer of fixed composition to be processed into aggregates that could be easily tuned from multi-vesicular particles to wormlike micelles and to spherical micelles.