The wormlike micelles formed with the surfactant pentaoxyethylene decyl ether C10E5 containing n-dodecanol were characterized by static (SLS) and dynamic light scattering (DLS) experiments. The SLS results have been analyzed with the aid of the light scattering theory for micelle solutions, thereby yielding the molar mass Mw(c) as a function of concentration c along with the cross-sectional diameter d of the micelle. The observed Kc/DeltaR0 as a function of c and the hydrodynamic radius RH as functions of Mw have been well described by the theories for the wormlike spherocylinder model. It has also been demonstrated that the apparent hydrodynamic radius RH,app(c) as a function of c is well described by a fuzzy cylinder theory which takes into account the hydrodynamic and direct collision interactions among micelles. Our previous results for the hexaoxyethylene dodecyl ether C12E6 micelles containing n-dodecanol were reanalyzed in the same scheme. It has been found that the micellar length increases with increasing concentration c or with raising temperature T irrespective of the composition of the C10E5 + n-dodecanol and C12E6 + n-dodecanol systems. The length of the micelles at fixed c and T steeply increases with increasing weight fraction wd of n-dodecanol in both systems. The growth of the micelles accompanies the increase of the cross-sectional diameter d of the micelles and the results that the surfactant molecules are more densely assembled with increasing wd in order to keep n-dodecanol molecules inside the micelles.

ABSTRACT:Variation of characteristics of the wormlike micelles formed with the surfactant pentaoxyethylene dodecyl ether C 12 E 5 with uptake of n-dodecanol were examined by static (SLS) and dynamic light scattering (DLS) experiments. The SLS results have been analyzed with the aid of 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 concentration c or with raising temperature T irrespective of the composition of the C 12 E 5 + n-dodecanol system. The length of the micelles at fixed c and T steeply increases with increasing weight fraction w d of n-dodecanol. and their binary mixtures, we have investigated micellar characteristics such as the weightaverage molar mass M w , mean-square radius of gyration hS 2 i, hydrodynamic radius R H , and intrinsic viscosity ½ as functions of surfactant mass concentration c by static (SLS) and dynamic light scattering (DLS) measurements and viscometry. [1][2][3][4][5][6][7][8][9] In these work, we were able to determine the concentration-dependent characteristics of the micelles unequivocally by separating the contributions of the thermodynamic and hydrodynamic interactions to the SLS and DLS results with the aid of the corresponding theories. We have determined the values of M w ðcÞ at a specified c along with the cross-sectional diameter d of the micelles from the analysis of the SLS data by using a molecular thermodynamic theory 10,11 formulated with the wormlike spherocylinder model. The molar mass M w dependence of hS 2 i, R H , and ½ is quantitatively represented by the chain statistical 12 and hydrodynamic 13-16 theories based on the wormlike chain and spherocylinder models, respectively, thereby yielding the values of the stiffness parameter À1 . The salient features found for the C i E j micelles are summarized as: (i) The micelles grow in length to a greater extent for larger i and smaller j. À1 decreases with increasing i at fixed j and increases with increasing j at fixed i.We have also studied C 10 E 5 and C 12 E 6 micelles containing n-dodecanol to explore effects of uptake n-alcohol into the micelles on the micellar characteristics. 17,18 It has been then found that the SLS and DLS results are successfully analyzed in a similar fashion to the micelle solutions of single C i E j or their binary mixtures. In particular, it has been demonstrated that the fuzzy cylinder theory [19][20][21] is applied in a favorable way to analyze the apparent hydrodynamic radius R H,app , thereby obtaining the concentrationdependent micellar growth by separating contributions of the enhancement of hydrodynamic inter...

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.

Wormlike micelles of the surfactant penta-, hexa-, and heptaoxyethylene dodecyl ethers C12 E5, C12 E6, and C12 E7 were characterized by static light scattering (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 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 the fuzzy cylinder theory which (-1). It has been found that the micellar length Lw increases with increasing surfactant mass concentration c and the values of d and lambda(-1) increase with increasing n-dodecane content wd, as in the case of various CiEj micelles containing n-alcohol. On the other hand, the values of Mw, Lw, and RH,app for all the micelles examined decrease with increasing wd contrary to the micelles containing n-alcohol. This finding may be attributed to 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 them to collapse into smaller micelles.