Flexibility and Cross-Sectional Structure of an Anionic Dual-Surfactant Wormlike Micelle Explored with Small-Angle X-ray Scattering Coupled with Contrast Variation Technique

Abstract

The contrast variation technique by adding sucrose to aqueous solvents as an electron density adjusting reagent was applied to small-angle X-ray scattering (SAXS) from a dual surfactant wormlike micelle consisting of sodium lauryl ether sulfate and coconut fatty acid amido propyl betaine in order to evaluate the flexibility and the cross-sectional structure of the micelle. The salt concentration dependence of the zero-shear and dynamic viscosities were found not to be affected by the cation species nor the presence of sucrose in the solution. SAXS showed that the scattering profile [I(q)] can be fitted a double layer cylinder model. By systematically changing the sucrose concentration (CS), a "matching composition" was found in which the shell layer can become invisible in SAXS for each sodium cation concentration ([Na+]). From this composition, the electron densities of the shell (rhoS) and core (rhoC) layers were evaluated to be 370 and 216 e/nm(-3), respectively. These values were consistent with the chemical structure of the surfactant. At these matching compositions, I(q) was measured at low q range (0.03 nm(-1)<q<4 nm(-1)) and the data points were perfectly fitted with a single layer rigid cylinder model, except for [Na+]>1.02 M. In these larger [Na+], the I(q) showed an up-turn deviation from the rigid rod limit (i.e., I(q) proportional, variant q(-1)) at low q, indicating appearance of the flexibility of the cylinder. By applying a wormlike cylinder theory, the Kuhn statistical segment length was evaluated as a function of [Na+]. At the infinite limit of [Na+], the intrinsic Kuhn length (excluding of the electrostatic interactions) can be evaluated to be about 20-40 nm. This value was comparable with that of the wormlike micelles made of nonionic surfactants.

Medical contrast media as possible tools for SAXS contrast variation

“…particles composed of segregated zones of different electron density) can by probed efficiently with SAXS experiments by varying sol . Historically, several small electron-rich molecules have been used to modify the solvent electron density, including sucrose (Garcia-Diez et al, 2016;Bolze et al, 2003;Kiselev et al, 2001;Ballauff, 2001;Dingenouts & Ballauff, 1993), glycerol (Hickl et al, 1996;Bolze et al, 1996) and salt (Naruse et al, 2009;Fernandez et al, 2008). The value of sol can usually be varied between 0.335 e Å À3 (pure water) and a maximum of about 0.41 e Å À3 , which has been reached for 'conventional' contrast agents, e.g.…”

“…sucrose at 1.8-2.0 M [50-55%(w/w)] (Jeffries et al, 2016; Kiselev et al, 2003Kiselev et al, , 2001Dingenouts & Ballauff, 1993;Kirste & Stuhrmann, 1967) and 100% glycerol (Wolf et al, 1989;Kirste & Stuhrmann, 1967). High molar NaCl solutions provide electron densities up to 0.38 e Å À3 but in practice are problematic since they may perturb the structural integrity of many systems (Chen et al, 2017;Naruse et al, 2009;Fernandez et al, 2008).…”

Chain architecture and flexibility of α-cyclodextrin/PEG polyrotaxanes in dilute solutions

“…When we compare this value with typical semiflexible chains such as schizophyllan (153), 14,15 poly(n-hexyl isocyanate) (46), 16 sodium hyaluronate (8.2) 17 and a polystyrene polymacromonomer (3-4), 9 the present system has a similar flexibility to those of polystyrene polymacromonomer and cylindrical lipid micelles. 18 During our iteration process to fit the data, we had to choose a shorter L than that of the PEG chain template. As shown in Figure 3a, we did not observe a clear Guinier region (that is, I(q)∝q − 0 at the lower q, and with increasing q, IðqÞpexpðÀ 4 3 R 2 g q 2 Þ, where R g is the radius of gyration).…”

Study of the internal structure of polymer micelles by anomalous small-angle X-ray scattering at two edges

“…Small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) have been used for structural analyses of polymer micelles (Feigin & Svergun, 1987;Hamley, 1998Hamley, , 2005. Among the various methods used in SAXS and SANS experiments, the contrast variation technique is a powerful tool for accurate analysis of the internal structure of polymer micelles because it can distinguish between the contributions from the hydrophobic core and the hydrated corona to the scattering profile of the whole micelles (Hickl et al, 1996;Naruse et al, 2009;Pedersen et al, 2000Pedersen et al, , 2003. In SANS experiments, contrast variation can be readily achieved by adjusting the deuteration levels to render a specific phase visible or invisible.…”

“…In SANS experiments, contrast variation can be readily achieved by adjusting the deuteration levels to render a specific phase visible or invisible. The contrast variation technique can also be applied to SAXS experiments by tuning the electron density of a solvent through addition of a contrast tuning agent (Hickl et al, 1996;Naruse et al, 2009). However, the application of contrast variation in SAXS to the structural analysis of polymer micelles is quite limited because the additives used to tune the electron density might cause structural change in the polymer micelles.…”