Effect of Amino‐Acid‐Based Polar Oils on the Krafft Temperature and Solubilization in Ionic and Nonionic Surfactant Solutions

Abstract

The Krafft temperature and solubilization power of ionic and nonionic surfactants in aqueous solutions are strongly affected by added polar oils such as amino-acid-based oils (e.g., N-acylamino acid esters, AAE), because they tend to be solubilized in the surfactant palisade layer. The Krafft temperatures of 5 wt.% sodium dodecyl sulfate (SDS)-water and octaoxyethylene octadecyl ether (C 18 EO 8 )-water systems largely decreases upon addition of AAE and 1-hexanol, whereas it decreases very slightly in isopropyl myristate (IPM) and n-dodecane. The lowering of the Krafft temperature can be explained by the same mechanism as the melting-temperature reduction of mixing two ordinary substances. Namely, the polar oils are solubilized in the surfactant palisade layer of micelles and reduce the melting temperature of hydrated solid-surfactant (Krafft temperature). On the other hand, non-polar oil such as dodecane is solubilized deep inside micelles and makes an oil pool. The solubilization of non-polar oil is enhanced by mixing surfactant with AAE due to an increase in micellar size.

Formation of intermediate micellar phase between hexagonal and discontinuous cubic liquid crystals in brine/N-acylamino acid surfactant/N-acylamino acid oil system

“…likely to behave as polar or non-polar oil depend on the occasion. We had found that this semi-polar oil behaves as co-surfactant in the polyoxyethylene-type nonionic surfactant (C 12 EO 8 ) [1][2][3] and sodium dodecyl sulfate (SDS) systems [3,4]. Afterwards, however, it was demonstrated that the solubilization sites of SLIP varies with its concentration in a homologous amino acid surfactant system: SLIP penetrates into the palisade layer at its low concentration, but further addition of SLIP leads to the solubilization in the micelle core [4].…”

Conformational Behavior of N-Acylamino Acid Oil and N-Acylamino Acid Surfactant in Aqueous Solution

“…We have previously reported that the addition of SLIP causes the different type of phase transition in the SDS/water system and in the Sar/water system 4) . In the hexagonal liquid crystal phase (H 1 ), SLIP penetrates in the palisade layer of the surfactant for both systems.…”

“…and sodium dodecyl surfate (SDS) systems 4) to cause the phase transition from hexagonal liquid crystal (H 1 ) to lamellar liquid crystal phase (La); the use of SLIP as a cosurfactant in various applications seemed to be very promising. However, it was demonstrated that the solubilization sites of SLIP varied with its concentration in the homologous sodium N-dodecanoyl sarcosinate (or sodium N-dodecanoyl-N-methylglycinate, Sar) system 5) .…”