Effect of Polyoxyethylene Chain Length on the Physicochemical Properties of N , N ‐Dimethyl‐ N ‐dodecyl Polyoxyethylene Amine Oxide Hybrid Surfactants (C 12 EO n AO, with n = 1–4)

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 (Γ 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 ( γ CMC ), minimum molecular cross‐sectional area ( A min ), adsorption efficiency (p C 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 p C 20 , Γ 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.