Abstract:

The critical micelle concentrations(CMCs)of the reversed demulsifiers poly(propylene oxide)-blockpoly(ethylene oxide)-block-poly(propylene oxide)(PPO-PEO-PPO),SP169,and DMEA169 were measuredby steady-state fluorescence spectroscopy,with cetylpyridinium chloride(CPC)as the quencher and pyreneas the fluorescent probe.The micellar aggregation numbers(N_agg)and the polarity of the micro-environmentsinside the micelles were obtained for the first time.The hydrodynamic diameters of the micelles at differentdemulsifier concentrations were determined by dynamic light scattering(DLS)and the corresponding micelleshapes were simulated by dissipative particle dynamics(DPD).The results indicate that the critical micellaraggregation numbers(N_m)can be extrapolated from the N_agg-c_s curves,with N_m(SP169)=28 and N_m(DMEA169)=18.Thehydrodynamic diameter of SP169 is smaller than that of DMEA169,while the acceleration of the former is fasterthan that of the latter.The simulations show that the micelle of SP169 is spherical while that of DMEA169 hasaclavate shape,because of the different interactions resulting from the initiators among the beads.Moreover,the simulations are in good agreement with the experiments in that they find a smaller hydrodynamic diameterand a less polar micro-environment inside the micelle of SP169 compared with that of DMEA169,while theaggregation number of the former is larger than that of the latter.

Key words: Reversed demulsifier, aggregation behaviour, Initiator, Dissipative particle dynamics, Fluorescence probe method, Dynamic light scattering method