Nonlamellar Lipid Liquid Crystalline Structures at Interfaces - Self-Assembled Supramolecular Architectures: Lyotropic Liquid Crystals - page 296

Figure 10.5 Schematic illustration of factors that can control the adsorption of cubo-
some LCNP (CPNP) stabilized with the Pluronic F-127 molecule relative to adsorption
of small CPNP at steady state on silica surface at (a) pH 4 from 0.1 M NaCl aqueous
solution. (b) Removing salt increases repulsion between CPNP and surface and favor
adsorption of stabilizer; (c) larger particles give less extensive adsorption, while
(d) increasing the pH to 6 with smaller particles, leads to a decrease adsorption of free
F-127 and therefore increased adsorption of CPNP. [Reprinted with permission from
Vandoolaeghe et al. (2009b). Copyright 2009 by the American Chemical Society.]
illustrates the interaction mechanisms of CPNP with hydrophilic silica with
changing ionic strength, particle size, and pH.
The adsorption of LCNP on hydrophobic silica is dramatically different
from that on bare silica (Vandoolaeghe et al., 2006). On the hydrophobic
surface, the hydrophobic attraction results in structural transition from the
original particle morphology to a thin 3-nm monolayer coverage of lipid on
surface. In contrast, thick layers of lipid nanoparticles can be formed on
hydrophilic silica in the presence of electrolyte or at low pH. Figure 10.3
shows that the adsorption on hydrophilic silica is strongly dependent on the
pH. At high pH, no adsorption is observed. At low pH close to the isoelectric
point of silica, adsorption increases proportionally with time and reaches a
saturation value at approximately 10 mg/m 2 . The layer thickness decays ini-
tially but stabilizes quickly and plateaus at around 40 nm. The adsorption