Magnetic-Field-Induced Orientational Phase Structure Transition

Magnetic field effect on the phase transition at high temperature (from 50 °C) inside the magnetic field has been found in C₁₄G₂ (<i>N</i>-tetradecyllactobionamide)/C₁₂EO₄ (tetraethylene glycol monododecyl ether)/D₂O system. The phase was transited quickly from lamellar phase to isotropic phases [bottom, micellar phase (L₁ phase) and top, sponge phase (L₃ phase)] induced by a magnetic field, which was demonstrated by ²H NMR and FF-TEM measurements. The isotropic phases induced by magnetic field were not stable, and the upper L₃ phase can recover to lamellar phase after being restored in a 55 °C thermostat outside the magnetic field for about one month. During the mechanism study, the C₁₂EO₄ molecule was proved to be the dominant component for the phase transition induced by the magnetic field, while the C₁₄G₂ molecule was the auxiliary and just affected the transition speed. The breaking and rebuilding of hydrogen bonds could play an important role in the phase transition and recovering. Moreover, the surfactant concentration had an effect on the speed of phase transiting and phase recovering. These observations could provide an understanding of the phase transition and also the applications for the controlled drug delivery system of bilayer membranes driving, induced by the magnetic field

Spontaneous Transformation of Lamellar Structures from Simple to More Complex States

Spontaneous transformation of lamellar structures, such as multilamellar vesicles from micelles or unilamellar vesicles, is an important challenge in the field of amphiphile molecules, which may serve as models to understand biologically relevant bilayer membranes. Herein, we report a progressive self-assembly progress of <i>N</i>-tetradecyllactobionamide (C₁₄G₂) and tetraethylene glycol monododecyl ether (C₁₂EO₄) mixtures in aqueous solution. Increasing temperature or surfactant compositions causes spontaneous transformation from simple to high-level aggregates, i.e., from unilamellar vesicles, to coexisting multilamellar vesicles, terraced planar bilayers, and finally terraced planar bilayers. Deuterium nuclear magnetic resonance (²H NMR), freeze-fracture transmission electron microscopy (FF-TEM), and small-angle X-ray scattering (SAXS) measurements clearly demonstrate the spontaneously progressive self-assembly process. The interlamellar spacing (<i>d</i>) of the bilayers decreases from unilamellar vesicles to the terraced planar bilayers with an increase of the temperature or surfactant compositions. Lamellar samples consisting of terraced planar bilayers at higher temperature still show viscoelastic properties, being Bingham fluids, and both the viscoelasticity and yield stress increase with the composition and decrease with the temperature. The spontaneous transformation of the progressive self-assembly progress of C₁₄G₂ and C₁₂EO₄ aqueous mixtures is due to a balance of three driving forces, hydrophobic interactions, hydrogen bonding, and steric effects