Structure and rheology of gel nanostructures from a vitamin C-based surfactant

Abstract

The structure and rheology behaviour of gels produced by water dispersions of a vitamin C-derived surfactant (ascorbyl-6-O-dodecanoate) were investigated by means of SAXS and rheology experiments for the first time. The gel state is formed upon heating and is due to an anisotropic expansion of the tightly compact lamellar structure. The phase transition involves primarily the melting of the alkyl chains and a significant increment in the interlamellar water layer. In particular, our results show that in the gel the hydrophobic chains are in a liquid-like state, as in the core of a micelle, while the head groups release their acidic proton, become negatively charged and determine the onset of strong electrostatic interactions between facing lamellae. The full hydration of the anionic head groups and the uptake of a significant amount of water increase the interlamellar thickness and stabilise the gel structure. Rheology and SAXS measurements together provide an updated picture for the gel state. Moreover, for the first time we show the presence of a concentration threshold, above which the self-assembled aggregates interact more strongly and deplete some of the water that is retained in the interlamellar region.

Organogels from Double‐Chained Vitamin C Amphiphilic Derivatives

“…Previously,w ee xtensively investigated the solid-state and selfassembly properties of amphiphilic single-chained alkanoyl-6-O-ascorbic acid esters (ASCn;8 n 18), [1][2][3][4][5][6][7][8] bolaforms, [9,10] and branched derivatives. [11] In these compounds,ah ydrophobic side chain is linked through an ester bond to the ÀOH group in position6of the lactoner ing.…”

Ascorbyl‐6‐O‐oleate: A Bioconjugate Antioxidant Lipid

“…This result indicates that, if the hydrocarbon chains are oriented perpendicularly with respect to the plane formed by the headgroups, the interdigitation degree can be estimated at about 60%. Saturated single chained vitamin C surfactants (abbreviated as ASCn, where “n” refers to the number of carbons in the side chain) usually show a lower interdigitation degree . In the present case the interdigitation is more extended.…”

“…Saturated single chained vitamin C surfactants (abbreviated as ASCn, where "n" refers to the number of carbons in the side chain) usually show a lower interdigitation degree. [20,21] In the present case the interdigitation is more extended. This is probably because of the large cross-section area of the heads that allows a deeper mutual interpenetration of the fluid oleoyl chains in the hydrophobic pocket.…”

“…This is a typical behavior in ascorbyl‐based surfactants, in fact saturated analogues, e. g . ascorbyl palmitate, that bear a quite long alkyl chain, in water form stiff coagels (i. e. semicrystalline hydrated lamellae) that turn into gel‐like transparent phases upon heating …”

“…This is a typical behavior in ascorbyl-based surfactants, in fact saturated analogues, e. g. ascorbyl palmitate, that bear a quite long alkyl chain, in water form stiff coagels (i. e. semicrystalline hydrated lamellae) that turn into gel-like transparent phases upon heating. [7,8,20,21,30,32,[35][36][37][38] The enthalpy changes increase almost linearly with the concentration of the lipid. From the experimental enthalpy change of fusion for bulk water (ΔH exp , see Table 1) we calculated the amount of water that is strongly bound to the headgroups (W b ) as: [36]…”