The effects of different cationic surfactants (n-undecylammonum chloride, UDACl and dodecyldimethyl (dodecyloxymethyl) ammonium chloride, DDMDDACl) on fully hydrated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) vesicles have been studied. In the studied systems the molar ratio (x) of DPPC/surfactant ranged between x=0.0164-0.82 and from x=0.0352-1.76 for DPPC/DDMDDACl and DPPC/UDACl, respectively. For both systems, the enthalpy associated with the phase transition significantly decreases even at the lowest surfactant concentration. Also the main phase transition temperature is shifted towards lower temperatures.
The structural parameters of the phases have been characterised by small angle X-ray scattering (SAXS). The SAXS results have proved that UDACl at x=0.0352 molar ratio significantly influences the DPPC lamellar structure, while its total disappearance was observed for x=0.176. The presence of DDMDDACl causes a total disappearance of the DPPC lamellar structure already at the lowest molar ratio (x=0.0352). Each surfactant in the system with DDPPC leads to a mixed micellar phase formation.