Change in Characteristics of Wormlike Micelles of Hexaoxyethylene Tetradecyl and Decyl Ethers (C14E6 and C10E6) with Uptake of n-Dodecane

Abstract

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 ...

Wormlike Micelles of Polyoxyethylene Alkyl Ethers CiEj

“…They have shown that the apparent molar mass M app of the wormlike micelles formed in the L 1 phase increases with c in the range of small c, passing through a maximum, and then decreases with increasing c at higher c. Here, M app includes two contributions, i.e., concentration-dependent molar mass M w ðcÞ of the micelles and concentration dependent structure factor Sðc; q ¼ 0Þ (q the magnitude of scattering vector) which reflects thermodynamic interactions among micelles. We have also investigated solution properties of the wormlike micelles of various C i E j containing n-dodecanol, -octanol, and n-dodecane, [32][33][34][35][36][37] by applying the same technique as in the case of the micelles of C i E j and their mixtures described above.…”

“…[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] In the work, we have been able to determine the concentration-dependent characteristics of the micelles by separating contributions of the intermicellar thermodynamic and hydrodynamic interactions to the SLS and DLS results with the aid of the corresponding theories. We have determined the weight-average molar mass M w of the micelles as a function of surfactant mass concentration c along with the cross-sectional diameter d from the SLS data by using a molecular thermodynamic theory 21,38 formulated with the wormlike spherocylinder model.…”

“…The studies have been extended to the C i E j micelles containing n-dodecanol, n-octanol, and ndodecane in order to explore effects of uptake of n-alcohol and n-alkane into the micelles on the micellar characteristics. [31][32][33][34][35][36][37] The SLS and DLS results were successfully analyzed in a similar fashion to the micelle solutions of single C i E j and their binary mixtures.…”

Light Scattering from Hydrophobe-Uptake Spherical Micelles near the Critical Micelle Concentration

“…The hydrophobe-uptake micellization has been investigated for many systems, − because hydrophobe uptake is one of the most important phenomena, which relates to extensive applications in detergents, paints, and drugs as well as potential applications to nanocarriers and nanoreactors. Many studies were interested in the micellization at surfactant concentrations much higher than the critical micelle concentration (cmc) and characterized the micellar structure in detail by scattering techniques and electron microscopy. − However, near the cmc, it is difficult to apply these techniques to study the association–dissociation equilibrium behavior of the surfactants.…”

“…On the other hand, when the amount of the surfactant is still larger than the amount of the hydrophobe but the surfactant concentration is near the cmc, large colloidal particles of the hydrophobe appear in the solution because of the difficulty of the spherical micelle formation. The formation of the large colloidal particles enormously increases light scattering intensity. − ,, Even if no hydrophobe is added to the solution, a tiny amount of impurity in the surfactant sample may act as a hydrophobe and light scattering intensity increases unexpectedly near the cmc. , This strong scattering intensity from the large colloidal particles makes it difficult to analyze the association–dissociation equilibrium behavior of the surfactants using the light scattering data.…”