Lamellar Micelles as Templates for the Preparation of Silica Nanodisks

Abstract

We have reported earlier that silica nanodisks are formed by the reverse micelle solÀgel (RMSG) method, from ternary Aerosol OT (AOT)/nheptane/water mixtures. These nanodisks are formed from the ternary mixtures with higher water contents and containing a significant concentration of FeCl 3 . Such mixtures undergo a phase separation. The present work seeks to identify the origin of these nanodisks. They are found to be produced from the lower, water-rich layer and not from the upper, oil-rich layer or from the interfacial region. Further, upon increasing the water content by a factor of 10, the phase separation is achieved in the absence of the salt as well. In the next step, the naodisks are observed to form from concentrated aqueous AOT solutions, with no involvement of organic solvents. Polarized optical microscopy and infrared studies reveal the occurrence of lamellar AOT micelles in these media. These micelles act as the templates for the nanodisks. This phenomenon paves the way for the soft chemical preparation of nanodisks in the aqueous phase, without the need of using salt or organic solvents.

Anisotropic dynamics of guest molecules in aerosol OT lamellar structures

“…15,22,26 The mixture is then shaken thoroughly to aid dissolution and subsequently left undisturbed for 1-2 days so as to attain equilibrium and complete phase separation with a clear water rich layer. Ternary mixtures of w 0 , a measure of molar ratio of water to AOT, 300 and 150 are prepared in a separating funnel by mixing required amount of AOT in nheptane and water containing C153.…”

“…In water, however, AOT molecules aggregate to form two dimensional flat lamellar structures. 15 Even though the fundamental structural aspects of these lamellar assemblies are similar to regular micelles, changes in degree of hydration and connectivity of water pools have been observed due to loss of dimensionality. 14 These lamellar structures are anisotropic and therefore, exhibit birefringence, unlike regular micelles.…”

“…16,20,21,22,23 4 Among these studies, the two that are most closely related to the present one are by Verma et al 16 and ourselves. 15 These structures have been characterized by several methods like POM, SAXS and Cryo TEM. The reason why coumarin dyes are used for such studies is that they undergo charge transfer in the excited state, leading to the formation of a dipole.…”

AOT/isooctane reverse micelles with a microaqueous core act as protective shells for enhancing the thermal stability of Chromobacterium viscosum lipase

“…The solution was then mixed vigorously for 1 min to obtain a transparent micellar solution. The desired water content was defined as the R value, which indicates the molar ratio of water to surfactant ([H 2 O]/[surfactant]) (Banerjee, Ghosh, & Datta, 2011), and the glycerol content was defined as the G value, which indicates the molar ratio of glycerol to surfactant ([glycerol]/[surfactant]) (Park et al, 2010). The R and G values were calibrated by considering the amount of water inherently present in the isooctane, glycerol, and AOT.…”

Silica nanodisks as platforms for fluorescence lifetime-based sensing of pH

“…In the present work, we have adopted a similar approach as Weisner and co-workers, but have used anisotropic silica nanodisks prepared using lamellar micelles as templates. [20][21][22] These nanodisks are likely to have important applications in drug delivery and sensing in biological media, as Mitragotri and co-workers have shown that anisotropic structures are less prone to phagocytosis by macrophages and consequent ejection from the body. 23,24 Further, we have used these core-shell nanoconjugates as a platform to explore the feasibility of pH sensing with the fluorescence lifetimes, in addition to the ratios of intensities.…”