ABSTRACT:Wormlike micelles formed with the surfactant hexaoxyethylene decyl C 10 E 6 and tetradecyl C 14 E 6 ethers were studied by static (SLS) and dynamic light scattering (DLS) experiments to examine variation of the micellar characteristics with uptake of n-dodecanol. The SLS results have been analyzed by the light scattering theory for micelle solutions to yield the molar mass M w ðcÞ as a function of concentration c along with the cross-sectional diameter d of the micelle. The apparent hydrodynamic radius R H,app ðcÞ determined by DLS as a function of c is also successfully analyzed by a fuzzy cylinder theory which takes into account the hydrodynamic and direct collision interactions among micelles, allowing us to evaluate the stiffness parameter À1 . It has been found that the micellar length increases with increasing surfactant weight fraction w s or with raising temperature T irrespective of the composition of n-dodecanol content in the micelles. The length of the micelles at fixed w s and T steeply increases with increasing weight fraction w d of n-dodecanol. The length of the C 14 E 6 micelles is extremely larger than that of the C 10 E 6 micelles. In the previous work on micellar solutions of nonionic surfactant polyoxyethylene alkyl ethers H(CH 2 ) i (OCH 2 CH 2 ) j OH (abbreviated C i E j ) and their binary mixtures, we have studied characteristics of the micelles by static (SLS) and dynamic light scattering (DLS) measurements and viscometry. [1][2][3][4][5][6][7][8][9] It has been demonstrated that the SLS results (Rayleigh ratios) as a function of surfactant concentration are well represented by a molecular thermodynamic theory 10,11 formulated with the wormlike spherocylinder model to yield the values of M w ðcÞ at a specified surfactant concentration c along with the cross-sectional diameter d of the micelles. The molar mass M w dependence of the mean-square radius of gyration hS 2 i, hydrodynamic radius R H , and intrinsic viscosity [] is quantitatively represented by the chain statistical 12 and hydrodynamic 13-16 theories based on the wormlike chain and spherocylinder models, respectively, thereby providing us with the values of the stiffness parameter À1 . Following the work, We have also studied C 12 E 6 , C 10 E 5 , and C 12 E 5 micelles containing n-dodecanol to explore effects of uptake n-alcohol into the micelles on the micellar characteristics. [17][18][19] It has been then found that the SLS and DLS results are successfully analyzed as in the case of the micelle solutions of simple C i E j or their binary mixtures. In particular, it has been demonstrated that the fuzzy cylinder theory [20][21][22] is applied in a favorable way to analyze the apparent hydrodynamic radius R H,app as a function of the micelle concentration, thereby obtaining the concentration-dependent micellar growth by separating contributions of the enhancement of hydrodynamic interactions among micelles.The present work extends the studies to micelles in the C 10 E 6 + n-dodecanol + water and C 14 E 6 + ndodecanol +...

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.