A helical shape of polyoxypropylene chain for extended surfactant molecule at the water/oil interface: Theoretical and experimental study

•A helical shape of long polypropylene chain in a row of 4 units at the water/oil interface was proposed.•A new method to analytically describe the detailed interfacial alignment of long polypropylene chains was used.•Long enough polypropylene chain played an important role in producing the ultralow interfacial tension.