Spontaneous Transformation of Lamellar Structures
from Simple to More Complex States
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Abstract
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
(C<sub>14</sub>G<sub>2</sub>) and tetraethylene glycol monododecyl
ether (C<sub>12</sub>EO<sub>4</sub>) 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
(<sup>2</sup>H 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 C<sub>14</sub>G<sub>2</sub> and C<sub>12</sub>EO<sub>4</sub> aqueous mixtures is due to a balance of three driving forces, hydrophobic
interactions, hydrogen bonding, and steric effects