Water loading driven size, shape, and composition of cetyltrimethylammonium/hexanol/pentane reverse micelles

Abstract

Cetyltrimethylammonium bromide (CTAB)/hexanol reverse micelles have found a variety of applications that demand control over physical parameters. Water content or loading is among the most basic tunable components and is the major driver of the physical properties of these systems. This study uses small-angle scattering with contrast variation to characterize these systems as a function of water loading. The scattering data were analyzed with a variety of approaches, resulting in converging physical specifications. Equations that describe basic physical parameters were determined that allow for characterization and manipulation of the CTAB/hexanol reverse micelle surfactant system. The shape of the reverse micelles was revealed to be slightly ellipsoidal and varies slightly through the water loading range. The surfactant shell is shown to contain a higher fraction of hexanol upon addition of water. Analysis reveals that the size, shape, and surfactant/cosurfactant composition are directly tunable by variation of the water content and that these properties are consequences of the balance of forces present in the reverse micelles.

Slow Proton Transfer in Nanoconfined Water

“…This slowing down cannot be explained from surface effects. It was shown with small-angle neutron scattering (SANS) experiments that the shape of the studied nanodroplets is nearly spherical or only slightly ellipsoidal . For such a shape, only a small part of the water molecules will be in close contact with the surface effects (∼20% of the volume for a droplet with a diameter of 7.4 nm).…”

“…It was shown with small-angle neutron scattering (SANS) experiments that the shape of the studied nanodroplets is nearly spherical or only slightly ellipsoidal. 29 For such a shape, only a small part of the water molecules will be in close contact with the surface effects (∼20% of the volume for a droplet with a diameter of 7.4 nm). The limited effect of the surface is further confirmed by the low fraction of water molecules showing a slower vibrational relaxation as a result of their location near the surface of the reverse micelle (see Supporting Information ).…”

“…Without HBr this procedure yields nearly spherical monodisperse nanodroplets with a water pool diameter d w = 0.26 × w 0 (nm). 29 , 65 , 66 We estimate the size of the water nanodroplets with a particular w 0 to become 1.4 ± 0.2 times smaller when the water is replaced by an aqueous 7 M HBr solution, which implies that d w = 0.19 × w 0 (nm) (see Supporting Information , Figure S9). We also performed experiments with a lower HBr concentration (3 M).…”

“…Here we study the vibrational and structural dynamics of hydrated protons in water nanodroplets of cationic reverse micelles using polarization-resolved femtosecond infrared (fs-IR) transient absorption spectroscopy. We use a positively charged surfactant system consisting of CTAB (cetyltrimethylammonium bromide) and hexanol, where the addition of hexanol as a cosurfactant allows to prepare much more stable and monodisperse nanodroplets. , Recent small-angle neutron scattering (SANS) studies showed that water nanodroplets stabilized by these surfactants in an apolar solvent have an ellipsoid shape with an axial ratio between 1.7 for small nanodroplets ( w 0 < 17) and 1.1–1.3 for large nanodroplets ( w 0 > 20). Since the shape is near-spherical, we will further use the diameter d w of a sphere of equal volume to refer to the size of the studied nanodroplet (for details, see the Methods section).…”

Influence of different parameters on reverse micelle extraction combined with acetone precipitation to purify sn-1,3 extracellular lipase from Aspergillus niger GZUF36

“…The increase in water content resulted in an increase in the size of the reverse micelles, which could further dissolve more protein and extract more protein with higher molecular weight. It was reported that changes in water content can modulate the size, shape and surfactant/cosurfactant composition of CTAB)/hexanol reverse micelles (Fuglestad et al 2019). Adding lipophilic alcohols weakened the repulsive force between micelles, and this condition was more favorable for the protein into the reverse micelles (Krei and Hustedt 1992).…”