Reprint of “Self-diffusion study of micelles in poly(oxyethylene)–polydimethylsiloxane diblock copolymer and poly(oxyethylene) alkyl ether systems” [J. Colloid Interface Sci. 300 (2006) 354–360

Abstract

Self-diffusion constants of amphiphilic molecules in D 2O solutions of mixed poly(oxyethylene)–polydimethylsiloxane diblock copolymer (POE–PDMS, Si m C 3 EO n ) and poly(oxyethylene) dodecyl ether ( C 12 EO n ) were measured by pulsed-field-gradient NMR method. In the D 2O/Si 25C 3EO 51.6/C 12EO 8 or D 2O/Si 52C 3EO 51.6/C 12EO 8 systems, small and large micelles coexist in a wide range of Si m C 3EO 51.6 fraction in total amphiphiles, whereas such a coexisting phenomenon does not take place in the D 2O/Si 5.8C 3EO 51.6/C 12EO 8 system. The coexisting phenomenon also takes place in the D 2O/Si 25C 3EO 51.6/C 12EO 5 system although the range of mixing fraction is limited. By obtaining each contribution of surfactant and copolymer molecules to the attenuation decay of the echo signal from the proton of the poly(oxyethylene) chain, we could evaluate the composition of the mixed micelles in the D 2O/Si 25C 3EO 51.6/C 12EO 8 system. The copolymer content in the mixed micelle increases proportionally to the copolymer mole fraction in the aqueous solution. From the series of self-diffusion measurements, we can conclude that the miscibility of Si m C 3 EO n and C 12 EO n in aqueous micelles becomes poor and the coexisting phenomenon takes place when the PDMS chain becomes much longer than the dodecyl chain of C 12 EO n or the POE chain of C 12 EO n becomes long. Furthermore it is also revealed that very few silicone copolymer molecules can be incorporated in small surfactant micelles.