An　equally-charged　mixture　of　an　anionic　gemini　surfactant,　O,O′-bis(sodium　2-tetradecylcarboxylate)-p-azodiphendiol　(G14-azo),　and　a　cationic　surfactant,　cetyltrimethylammonium　bromide　(CTAB),　was　dissolved　in　cyclohexane　to　form　reverse　worm-like　micelles.　Samples　with　different　surfactant　concentrations　and　amounts　of　added　water　were　studied　using　rheological　measurements.　The　amount　of　water,　represented　as　the　molar　ratio　of　water　to　total　surfactants　W0,　was　c.　13　(at　its　minimum)　in　these　equally　charged　systems　of　G14-azo　(200　mmol　L-1)/CTAB.　The　low　shear　viscosity　ηL　of　this　system　reached　4370　Pa　s　at　W0　=　13　and　the　dynamic　rheological　result　showed　typical　surfactant　gel　behaviour.　Under　UV-light　irradiation,　the　transparent　sample　(G14-azo　(300　mmol　L-1)/CTAB　(600　mmol　L-1))　at　W0　=　40　became　turbid,　during　which　ηL　was　rapidly　reduced　from　the　original　285　Pa　s　to　0.3　Pa　s,　indicating　a　transition　of　aggregate　morphology　from　reverse　worms　into　simple　reverse　micelles.　Then　the　sample　was　returned　to　its　original　homogeneous　state　with　c.　290　Pa　s　viscosity　under　visible　light　irradiation.　However,　this　transition　cannot　be　well　achieved　at　low　W0　due　to　the　interior　cores　being　too　small.　This　limit　has　been　attributed　to　both　the　Gemini　type　of　surfactant　molecule　and　to　the　inverted　structure　of　aggregates.　©　2016　The　Royal　Society　of　Chemistry.