Abstract: In order to investigate the surfactivity of the linear dodecyl polyoxyethylene polyoxypropylene ether series (LSmn), the surface tensions of LS36, LS45 and LS54 have been respectively measured at 298, 303, 313 and 323 K in aqueous solution. Their phase diagrams in water have also been separately made. The critical micelle concentration(cmc) and the corresponding surface tension at such concentration (γcmc) are determined from their γ－lgc curves, which is in the ranges 4.44×10－6～17.3×10－6 mol•L－1 and 30.1～33.5 mN•m－1, respectively. The thermodynamic functions on surface adsorption at cmc and on micellization have also been calculated, in which the adsorption and the micellization free energies (ΔGadΘ and ΔGmΘ) respectively are in the ranges －40.0～－49.5 kJ•mol－1 and －27.2～－33.1 kJ•mol－1 in the studied temperature range. The thermodynamic data show that both the adsorption and the micelliration processes for the studied surfactants are driven by entropy and that LS36 is much different from LS45 and LS54 in many aspects, due to its less component of polyoxyethylene group which has strong hydrophilic capacity in its hydrophilic segment.

Key words: Linear dodecyl polyoxyethylene polyoxypropylene ether (LS_mn), 　Nonionic surfactants, Surface tension, Phase diagram