Effect of Polyoxyethylene Chain Length on the Physicochemical Properties of N,N‐Dimethyl‐N‐dodecyl Polyoxyethylene Amine Oxide Hybrid Surfactants (C₁₂EO_nAO, with n = 1–4)

Abstract

In order to determine the structure-performance relationship of nonionic-zwitterionic hybrid surfactants, N,N-dimethyl-N-dodecyl polyoxyethylene (n) amine oxides (C 12 EO n AO) with different polyoxyethylene lengths (EO n , n = 1-4) were synthesized. For homologous C 12-EO n AO, it was observed that the critical micelle concentration (CMC), the maximum surface excess (C m ), CMC/ C 20 , and the critical micelle aggregation number (N m,c ) decreased on going from 1 to 4 in EO n . However, there were concomitant increases in surface tension at the CMC (c CMC ), minimum molecular cross-sectional area (A min ), adsorption efficiency (pC 20 ), and the polarity ([I 1 /I 3 ] m ) based on the locus of solubilization for pyrene. The values of log CMC and N m,c decreased linearly with EO n lengthening from 1 to 4, although the impact of each EO unit on the CMC of C 12 EO n AO (n = 1-4) was much smaller than that typically seen for methylene units in the hydrophobic main chains of traditional surfactants. Compared to the structurally related conventional surfactant N,N-dimethyl-N-dodecyl amine oxide (C 12 AO), C 12 EO n-AO (n = 1-4) have smaller CMC, A min , and CMC/C 20 , but larger pC 20 , C m , and N m,c with a higher [I 1 /I 3 ] m . This may be attributed to the moderately amphiphilic EO n (n = 1-4) between the hydrophobic C 12 tail and the hydrophilic AO head group. Keywords Hybrid surfactant Á N,N-dimethyl-N-dodecyl polyoxyethylene (n) amine oxide Á Structure-performance relationship Electronic supplementary material The online version of this article (

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