Wormlike Micelles of Polyoxyethylene Dodecyl C12Ej and Heptaoxyethylene Alkyl CiE7 Ethers. Hydrophobic and Hydrophilic Chain Length Dependence of the Micellar Characteristics

Abstract

ABSTRACT:The micelles formed with pentaoxyethylene C 12 E 5 and heptaoxyethylene C 12 E 7 dodecyl ethers and heptaoxyethylene tetradecyl ether C 14 E 7 in dilute aqueous solutions were characterized by static (SLS) and dynamic light scattering (DLS) experiments at several temperatures T below the critical points. The SLS results were successfully analyzed by using a thermodynamic theory formulated with wormlike spherocylinder model for SLS of micelle solutions, thereby yielding the molar mass M w of the micelles as a function of c along with the cross-sectional diameter d. The radius of gyration hS 2 i 1=2 and the hydrodynamic radius R H of the micelles as functions of M w were found to be also well described by the corresponding theories for the wormlike spherocylinder or wormlike chain models. Combining the present and previous results for various C i E j (polyoxyethylene alkyl ether) micelles, effects of the hydrophobic (alkyl) i and hydrophilic (oxyethylene) 1-4 we have investigated micelle characteristics such as the weightaverage molar mass M w , mean-square radius of gyration hS 2 i, and hydrodynamic radius R H as functions of surfactant mass concentration c by static (SLS) and dynamic light scattering (DLS) measurements. 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 5,6 formulated with the wormlike spherocylinder model. It is then found that molar mass M w dependence of hS 2 i and R H is quantitatively represented by the chain statistical 7 and hydrodynamic 8-10 theories based on the wormlike chain and spherocylinder models, respectively, thereby yielding the values of the stiffness parameter À1 . 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 10 E 5 , C 10 E 6 , C 12 E 6 , C 14 E 6 , C 16 E 7 , C 18 E 7 , C 14 E 8 , C 16 E 8 , and C 18 E 8 , and examined effects of the hydrophobic i and hydrophilic chain length j on size, structure, and flexibility of the micelles. Solution properties of the C i E j micelles have been the subject of considerable research. 11-24 Brown and his coworkers 11-13 studied solution properties of C 12 E 5 , C 12 E 6 , C 12 E 7 , and C 12 E 8 micelles by SLS, DLS, and pulsed field gradient NMR measurements. Similar studies were performed for C 12 E 5 , C 12 E 6 , and C 12 E 8 micellar solutions by Kato et al. 16,17 They showed that the C i E j micelles grew in size with raising temperature and increasing surfactant concentration, and that intermicellar thermodynamic and hydrodynamic interactions strongly increase with concentration. Bernheim-Groswasser et al.24 realized by cryo-TEM observations that in the growth of the C 12 E 5 micelles thread-like or polymer-like micelles were evolved in the solutions examined, especially to the greater length in the vicinity of the lower consolute point.Although the solution properties of mice...

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

“…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.…”

“…As in the previous studies, [1][2][3][4][5][7][8][9]18 the SLS results Kc=ÁR 0 successfully analyzed with the aid of the theory 10 for light scattering of micelle solutions formulated with wormlike spherocylinder model, to yield the molar mass M w ðcÞ as a function of c along with the cross-sectional diameter d of the micelle. It has been found that the mean-square radius of gyration hS 2 i as a function of M w is well described by the Benoit-Doty equation 12 for the wormlike chain model.…”

“…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.…”