Wormlike Micelles of Pentaoxyethylene Tetradecyl Ether C14E5 and Hexaoxyethylene Hexadecyl Ether C16E6

Abstract

ABSTRACT:Micelles of pentaoxyethylene tetradecyl C 14 E 5 and hexaoxyethylene hexadecyl C 16 E 6 ethers in dilute aqueous solutions were characterized by static (SLS) and dynamic light scattering (DLS) experiments at several temperatures T between the LCST and UCST phase boundaries. The SLS results were successfully analyzed with the aid of the thermodynamic theory formulated with wormlike spherocylinder model for SLS of micelle solutions, yielding the molar mass M w of the micelles as a function of concentration c and the cross-sectional diameter d. 1-6 we have investigated micellar characteristics by static (SLS) and dynamic light scattering (DLS) measurements and viscometry. We have determined the values of the molar mass M w ðcÞ of the micelles at a specific c along with the cross-sectional diameter d from the analysis of the SLS data by using a molecular thermodynamic theory 7,8 formulated with the wormlike spherocylinder model. It is then found that molar mass M w dependence of the mean-square radius of gyration hS 2 i, hydrodynamic radius R H , and intrinsic viscosity ½ is quantitatively represented by the chain statistical 9 and hydrodynamic 10-13 theories based on the wormlike chain and spherocylinder models, respectively, thereby yielding the values of the stiffness parameter À1 and/or d. These analyses have demonstrated that the C i E j micelles assume a shape of flexible cylinder. We have so far characterized micelles of the surfactants C i E j with various i and j, and examined effects of the hydrophobic i and hydrophilic chain length j on size, structure, and flexibility of the micelles. It has been shown that the C i E j micelles grow in size with raising temperature and increasing surfactant concentration, and that intermicellar thermodynamic and hydrodynamic interactions strongly increase with concentration.The values of LCST (lower critical solution temperature) determined in our previous and present studies are summarized in Table I, in which the column and row represent variations in the length of the alkyl and oxyethylene chains of C i E j molecule, i.e., i and j, respectively. The LCST decreases with increasing i at fixed j and with decreasing j at fixed i, reflecting that the micellar size varies with the hydrophobic and hydrophilic chain length i and j. The phase behavior may be in good correspondence with the observations for polymer solutions in which LCST decreases with increasing polymer molecular weight. Although the solution properties of micelles are analogous to those of polymer solutions, the micelles are essentially different from polymers in the point that the micellar size or length is not chemically fixed but, in general, depends on surfactant concentration. For this reason, analyses of the scattering data for micelle solutions encounter difficulties in the performance for separate determination of concentration-dependent micellar growth and intermicellar interactions. In order to circumvent this problem, we have utilized the molecular thermodynamic theory 7,8 for unequivocal...

Characterization of Wormlike Pentaoxyethylene Dodecyl Ether C12E5 Micelles Containing n-Dodecanol

“…Figure 8b shows that the length L w at fixed c significantly increases with raising temperature. This finding is in line with our previous results [1][2][3][4][5][6][7] for the micelles of the single surfactant C i E j . It is also in qualitative agreement with the results reported by Menge et al 23 for the C 12 E 5 + n-decane micelles and those by Kwon and Kim 31 for the C 12 E 5 + phospholipid micelles.…”

“…The weight average molecular weight of the C 12 E 5 + n-dodecanol mixture calculated with a given w d was used as the surfactant molecular weight M 0 required in the theoretical analysis. 1=2 in the range of c examined, as in the case of the previous findings for the micelles formed with single surfactant of various type, [1][2][3][4][5]7 for those formed with binary C i E j mixtures, 8,9 and the C 10 E 5 micelles containing n-dodecanol. 18 These results are in good correspondence with simple theoretical predictions derived from the thermodynamic treatments of multiple equilibria among micelles of various aggregation numbers.…”

“…The experimental procedure is the same as described before. [1][2][3][4][5][7][8][9]18 In the present study, we have treated the micelle solutions as the binary system which consists of micelles containing n-dodecanol as a solute and water as a solvent.…”

Wormlike Micelles of Polyoxyethylene Alkyl Ethers CiEj

“…[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.…”

“…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. It has then found that the molar mass M w dependence of mean-square radius of gyration hS 2 i, hydrodynamic radius R H , and intrinsic viscosity [] for the micelles of pure C i E j with various i and j [22][23][24][25][26][27][28] and their binary mixtures 29,30 is quantitatively represented by the chain statistical 39 and hydrodynamic theories [40][41][42][43] based on the wormlike chain and spherocylinder models, respectively. In particular, it has been demonstrated that the fuzzy cylinder theory [44][45][46][47] is favorably applied to analyze the apparent hydrodynamic radius R H,app , which is directly obtained from DLS experiment, as a function of the micelle concentration, thereby yielding the concentration-dependent micellar growth by separating contributions of the enhancement of hydrodynamic interactions among micelles with increasing concentration.…”