α-Gel (α-Form Hydrated Crystal) Prepared by Eco-Friendly Cationic Surfactant.

We studied the structures and properties of gel samples prepared by mixtures of N-[3-(dimethylamino)propyl]docosanamide (APA-22) acid salt (APA-22 L-lactic acid), 1-octadecanol (C ₁₈ OH), and water. The gel samples prepared at the mole ratios [APA-22 L-lactic acid]:C ₁₈ OH = 1:3, 1:4, and 1:5 yielded two phases; one being the α-gel (α-form hydrated crystal) phase, incorporating a significant quantity of water between lamellar bilayers, and the other being the excess water phase. The lamellar d-spacing remained practically unaltered at these mole ratios, thus maintaining the quantity of water incorporated between the lamellar bilayers relatively constant. Starting at 30°C, the gel samples transformed into a lamellar liquid crystal phase at high temperatures (85°C) and a β-gel phase at low temperatures (5°C). Interestingly, following dilution by pure water, the viscosity of the gel samples decreased with increasing C ₁₈ OH content. We expect that the viscosity change affects the performance of the gel samples as hair conditioners.