Wormlike micelles of the surfactant hexaoxyethylene tetradecyl and decyl ethers C 14 E 6 and C 10 E 6 were characterized by static (SLS) and dynamic light scattering (DLS) experiments to examine effects of uptake of n-dodecane on the micellar characteristics. The SLS results have been successfully 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 has also been successfully analyzed by the fuzzy cylinder theory which takes into account the hydrodynamic and direct collision interactions among micelles, providing us with the values of the stiffness parameter À1 . It has been found that although the micellar length L w increases with increasing surfactant mass concentration c and the d and À1 values increase with increasing n-dodecane content w d , as in the case of various C i E j micelles containing n-alcohol, the values of M w , L w , and R H,app for all the micelles examined decrease or hardly vary with increasing w d contrary to the micelles containing n-alcohol. This finding may reflect the fact that the addition of n-dodecane into the micelles weakens hydrophilic interactions among polyoxyethylene chains of the surfactant molecules and water, making the micelles unstable, and then leading to collapse them into micelles of the smaller size. In this series of work on micelle solutions of nonionic surfactant polyoxyethylene alkyl ethers H(CH 2 ) i (OCH 2 CH 2 ) j -OH (abbreviated C i E j ), we have characterized the wormlike C i E j micelles with various i and j containing n-alcohols, ndodecanol or n-octanol, 1-5 and n-dodecane 6 by static (SLS) and dynamic light scattering (DLS) measurements in order to explore effects of uptake of n-alcohol or n-dodecane into the micelles on the micellar characteristics. It has been demonstrated that the SLS results (the excess Rayleigh ratio) as a function of surfactant concentration c are successfully analyzed by a molecular thermodynamic theory 7,8 formulated with the wormlike spherocylinder model to provide us with molar mass M w ðcÞ of the micelle at a specified c along with the crosssectional diameter d of the spherocylinder, as in the case of the micelle solutions of pure C i E j and binary C i E j mixtures. 9-16The DLS results have been also successfully analyzed in a similar fashion to the micelle solutions of pure C i E j and their binary mixtures with the aid of the fuzzy cylinder theory, [17][18][19][20] thereby yielding the concentration-dependent micellar growth by separating contributions of the enhancement of hydrodynamic interactions among micelles with increasing concentration to the apparent hydrodynamic radius R H,app , which is directly obtained from DLS experiment. The analyses have yielded the values of the stiffness parameter À1 and shown that the molar mass M w dependence of the hydrodynamic radius R H is quantitatively represented by the ...