Variation of characteristics of pentaoxyethylene decyl C10E5 and hexaoxyethylene tetradecyl C14E6 ether micelles with uptake of n-octanol

Wormlike micelles of the surfactant pentaoxyethylene decyl C10E5 and hexaoxyethylene tetradecyl C14E6 ethers were characterized by static (SLS) and dynamic light scattering (DLS) experiments to examine effects of uptake of n-octanol on the micellar characteristics. The SLS results have been successfully analyzed by the light scattering theory for micelle solutions to yield the molar mass Mw(c) as a function of concentration c along with the cross-sectional diameter d of the micelle. The apparent hydrodynamic radius RH,app(c) determined by DLS as a function of c has also been successfully analyzed by a fuzzy cylinder theory which takes into account the hydrodynamic and direct collision interactions among micelles, providing us with the values of the stiffness parameter lambda(-1). It has been found that the micellar length Lw increases with increasing surfactant weight fraction ws and increasing n-octanol content wo in the micelles or with raising temperature T. The values of d and lambda(-1) are found to increase with increasing wo, whereas the spacing s between hydrophilic tails of adjacent surfactant molecules on the micellar surface decreases with increasing wo. Comparison with our previous results for the C10E5 and C14E6 micelles containing n-dodecanol has revealed the salient features in change of the micellar characteristics with uptake of n-alcohols as follows: (i) The Lw values increase more significantly for the C14E6 micelles containing n-dodecanol than those containing n-octanol, whereas Lw of the C10E5 micelles increases by including n-dodecanol and n-octanol without a significant difference for the two alcohols. (ii) The values of d and lambda(-1) of the C10E5 and C14E6 micelles increase with uptake of n-octanol and n-dodecanol into the micelles. They are larger for the C10E5 micelles than for the C14E6 micelles, and their increase with alcohol content is less significant for the C14E6 micelles in comparison with the C10E5 micelles. (iii) The s values of the C10E5 and C14E6 micelles decrease with uptake of n-octanol and n-dodecanol into the micelles. They are somewhat larger in the latter micelles than in the former. (iv) The variation in d, s, and lambda(-1) with uptake of n-alcohol occurs with no difference in the effects for the two alcohols n-octanol and n-dodecanol.