Self-Assembling Anti-Freezing Lamellar Nanostructures in Subzero Temperatures.

The requirement for cryogenic supramolecular self-assembly of amphiphiles in subzero environments is a challenging topic. Here, the self-assembly of lamellar lyotropic liquid crystals (LLCs) are presented to a subzero temperature of -70 °C. These lamellar nanostructures are assembled from specifically tailored ultra-long-chain surfactant stearyl diethanolamine (SDA) in water/glycerol binary solvent. As the temperature falls below zero, LLCs with a liquid-crystalline Lα phase, a tilted Lß phase, and a new folded configuration are obtained consecutively. A comprehensive experimental and computational study is performed to uncover the precise microstructure and formation mechanism. Both the ultra-long alkyl chain and head group of SDA play a crucial role in the formation of lamellar nanostructures. SDA head group is prone to forming hydrogen bonds with water, rather than glycerol. Glycerol cannot penetrate the lipid layer, which mixes with water arranging outside of the lipid bilayer, providing an ideal anti-freezing environment for SDA self-assembly. Based on these nanostructures and the ultra-low freezing point of the system, a series of novel cryogenic materials are created with potential applications in extremely cold environments. These findings would contribute to enriching the theory and research methodology of supramolecular self-assembly in extreme conditions and to developing novel anti-freezing materials.

Supramolecular self-assembly of robust, ultra-stable, and high-temperature-resistant viscoelastic worm-like micelles.

HYPOTHESIS: Worm-like micelles are susceptible to heating owing to the fast dynamic exchange of molecules between micelles. Inhibition of such exchange could afford robust worm-like micelles, which is expected to largely improve rheology properties at high temperatures. EXPERIMENTS: A cationic surfactant docosyl(trimethyl)azanium chloride (DCTAC) and a strongly hydrophobic organic counterion 3-hydroxy naphthalene-2-carboxylate (SHNC) were used for the worm-like micelles fabrication. The microstructure was characterized using cryogenic transmission electron microscopy and small-angle neutron scattering, and the interactions between DCTAC and SHNC were characterized using nuclear magnetic resonance spectroscopy. Rheometer was employed to measure the rheological properties of the solution. FINDINGS: SHNC/DCTAC at the molar ration of 1:2 forms ultra-stable worm-like micelles, whose viscosity remain stable at temperature up to 130 °C. SHNC is found to strongly adsorbs on DCTAC micelle with the orientation on the surface of micelle, keeping the naphthalene backbone entire penetration into the palisade layer while both carboxylic and hydroxyl groups protrude out of the micelle. With temperature increasing, this adsorption further strengthens, resulting in the growth contour length and accompanying the enhancement of rheological properties. One SHNC molecule and two DCTAC molecules are speculated to form a stable complex via multiple interactions including hydrophobic, cationic-π, and π-π interactions, which decreases the dynamic exchange of them between micelles. These findings are helpful to understand surfactant aggregates stability and assist the development of novel stable supramolecular nanostructures. Additionally, the excellent thermal stability of this worm-like micellar fluid makes it a potential high-temperature resistant clean fracturing fluid for deep oil reservoirs.