Surfactants that can self-assemble to form worm-like micelles (WLM) are widely used in home and personal care products, inkjet printing, drag reduction agents or in enhanced oil recovery. Depending on the surfactant concentration, type of salt and salt/surfactant ratio, linear or branched structures can emerge in WLM solutions. Numerous technical processes exhibit complex flow fields with strong elongational components. In such elongational flows, structural changes occur, thus leading to a dramatic change of the flow behavior. Rheological methods such as the “Capillary Breakup Elongational Rheometry (CaBER)” and the “Optimized-Shape Cross-slot Extensional Rheometer (OSCER)“ are combined with birefringence and ”Particle Image Velocimetry (PIV)“ measurements, to investigate these flow-induced structural changes. Based on the results models can be developed, which enable to predict these structures depending on the material and flow parameters.