Pre-micellar interaction or direct monomer to micelle transition for zwitterionic sulfobetaine surfactant in water? A comparative fluorescence study with cationic surfactant

•Drastic difference of HPTS fluorescence quenching was observed between cationic and zwitterionic surfactant.•The monomer-micelle transition behavior depends critically on the initial concentration of HPTS taken.•The zwitterionic surfactant behaves like a neutral surfactant as monomer but more like a cationic micelle when forms micelle.