Unlocking Cryogenic Self-Assembly of Lyotropic Liquid Crystals: A Molecular Perspective From Short-Range to Long-Range Scales.

Achieving the self-assembly of lamellar liquid crystals (LLCs) at sub-zero temperatures and elucidating their structure-assembly interplay are crucial for understanding cryobiological processes and facilitating cryogenic soft materials; however, this remains a formidable challenge. Herein, six alkyl alkanolamide amphiphiles are designed, and their self-assembly behavior in 1,2-propanediol/water cosolvent is investigated from 80 to -20 °C. The hydrocarbon chain length exerts a significant influence on self-assembly behavior at both short-range and long-range scales. Amphiphiles with hydrocarbon chains shorter than C16 (i.e., the number of carbon atom is 16) exhibit limited solubility and cannot form LLCs at low temperatures, while longer chains enhance cryo-solubility and self-assembly capabilities, contradicting conventional assumptions. Notably, amphiphiles with chains of C18 or longer require only 0.3 wt.% for LLCs formation. These LLCs exhibit intriguing temperature-dependent phase transitions, including a liquid-like lamellar phase, a tilted gel phase, and a distinct phase characterized by tighter alkyl chain packing. The hydrocarbon chain length directly governs the transition temperatures and further influences the long-range orientational ordering of lamellar sheets. Additionally, the tightly-packed configuration confers exceptional rheological properties, including ultra-high viscosity, shear-thinning behavior, and elasticity. These findings provide important insights for the design and engineering of high-performance soft materials used in extreme environments.