Solvent Blends Can Control Cationic Reversed Micellar Interdroplet Interactions. The Effect of n-Heptane:Benzene Mixture on BHDC Reversed Micellar Interfacial Properties: Droplet Sizes and Micropolarity

Abstract

We have investigated, for the first time, the effect of the composition of the nonpolar organic media on the benzyl-n-hexadecyl-dimethylammonium chloride (BHDC) reversed micelles (RMs) properties at fixed temperature. To achieve this goal we have used the solvatochromic behavior of 1-methyl-8-oxyquinolinium betaine (QB) as absorption probe and dynamic light scattering (DLS), to monitor droplet sizes, interfacial micropolarity, and sequestrated water structure of water/BHDC/n-heptane:benzene RMs. DLS results confirm the formation of the water/BHDC/n-heptane:benzene RMs at every n-heptane mole fraction (X(Hp)) investigated, that is, X(Hp) = 0.00, 0.13, 0.21, 0.30, and 0.38. Also, DLS was used to measure the RMs diffusion coefficient and to calculate the apparent droplet hydrodynamic diameter (d(App)) at different compositions of the nonpolar organic medium. The data suggest that as the n-heptane content increases, the interdroplet attractive interactions also increase with the consequent increment in the droplet size. Moreover, the interdroplet attractive interactions can be "switched on (increased)" or "switched off (decreased)" by formulation of appropriate n-heptane:benzene mixtures. Additionally, QB spectroscopy was used to obtain the "operational" critical micellar concentration (cmc) and to investigate both the RMs interfacial micropolarity and the sequestrated water structure in every RMs studied. The results show that BHDC RMs are formed at lower surfactant concentration when n-heptane or water content increases. When the interdroplet interaction "switches on", the RMs droplet sizes growth expelling benzene molecules from the RMs interface, favoring the water-BHDC interaction at the interface with the consequent increases in the interfacial micropolarity. Therefore, changing the solvent blend is possible to affect dramatically the interfacial micropolarity, the droplet sizes and the structure of the entrapped water.

Droplet–droplet interactions investigated using a combination of electrochemical and dynamic light scattering techniques. The case of water/BHDC/benzene:n-heptane system

“…To nd out the size and properties of the interface we studied water/BHDC/benzene:n-heptane RMs using dynamic light scattering (DLS) and the solvatochromism of 1-methyl-8-oxyquinolinium betaine (QB) at a xed temperature. 34 We demonstrated that the BHDC RM sizes and interfacial composition change upon n-heptane addition, as it was previously shown for AOT RMs with a nonpolar phase blend. 31 Thus, for BHDC RMs formed in benzene:n-heptane mixtures, droplet sizes, interfacial micropolarity and the water-polar head surfactant interaction increase as the n-heptane content increases.…”

Effect of the Cationic Surfactant Moiety on the Structure of Water Entrapped in Two Catanionic Reverse Micelles Created from Ionic Liquid‐Like Surfactants

“…[1] The amount of water dispersed in the organized system can be expressed by the ratio W 0 (W 0 = [Water]/[Surfactant]). BHDC forms RMs without the addition of cosurfactants [1][2][3][4][5] but CTAB needs the presence of a cosurfactant, usually an alcohol, to generate RMs. BHDC forms RMs without the addition of cosurfactants [1][2][3][4][5] but CTAB needs the presence of a cosurfactant, usually an alcohol, to generate RMs.…”

“…This IL-like surfactant was isolated from the original surfactant mixture (and elimination of NaCl) and showed properties absolutely different from Na-AOT and BHDC. [3,4,26] It is motivating to explore the interaction between the entrapped water and the interface formed by catanionic surfactants in RMs, in which both anionic and cationic polar head groups are present. Thus, we investigated its ability to form RMs in nonpolar solvents and spontaneous large unilamellar vesicles (LUVs) in water.…”

Solvent dependent interactions between droplets in water-in-oil microemulsions

“…Recently, Salabat et al 21 used dynamic light scattering to monitor the apparent diffusion coefficient and effective microemulsion droplet diameter, and found that the interdroplet attractive interactions could be tuned by formulation of appropriate solvent mixtures using heptane, toluene, and dodecane. Myakonkaya et al 22 and Agazzi et al 23 also found that the properties of microemulsions and possibly also the droplet interaction can be controlled by changing the solvent blend composition. However, until now, no direct experimental evidence involving the solvent dependent enthalpy interactions between the microemulsion droplets has been reported to clarify the existence of some ambiguities and contradictories.…”