Chemistry Reference
In-Depth Information
pH (Vandoolaeghe et al., 2009b). It was suggested that the adsorption is con-
trolled by an interplay between two competing processes: the faster adsorption
of excess free Pluronic stabilizer and the slower binding of the LCNP in the
gaps. The adsorption of free block copolymers at the surface can hinder
the adsorption of LCNP by steric repulsion and thus limit the adsorption of
the particles. The interaction mechanism is therefore dictated by interplays
between the particle stabilizer, the lipid matrix, and the substrate surface.
Figure 10.4 shows the effect of surface chemistry and solvent condition on the
adsorption of LCNP. The slightly negatively charged LCNP adsorbed signifi -
cantly more on the cationic surface.
A recent study has utilized the layer-by-layer (LbL) adsorption technique
to embed CPNPs in the capsule shell wall (Driever et al., 2011). Oppositely
charged polyelectrolytes are assembled layer by layer onto a surface, with the
layers forming due to electrostatic attraction. The study demonstrated CPNP
incorporation within a multilayer assembly of oppositely charged polyelectro-
lytes on planar silica substrate as well as on silica microparticles. The SAXS
measurements confi rm the preservation of the cubic phase embedded within
the polyelectrolyte matrix. Confocal microscopy of the microparticles shows
the presence of fl uorescent CPNP within the polymer shell of silica particles
both before and after silica core removal. This study demonstrates that the
LbL adsorption technique can be used to embed LCNP to form a surface layer
of liquid crystalline structure.
10.5.2
Forming from Components
The deposition of LCNP can be achieved by depositing the components from
a solvent. Such a process occurs, for example, when constructing a calibration
curve for an ATR-FTIR experiment. For ATR-FTIR, a calibration curve of
known LCNP mass on the surface is needed to accurately quantify the adsorbed
mass. To construct such a calibration curve, the components of LCNP can be
dissolved in chloroform and applied to the surface (Dong et al., 2011). The
chloroform solvent is then evaporated to leave a known mass deposited on
the crystal surface. The layer prepared in this way only contains the substances
that make up the LCNP, which may retain internal crystalline structure once
the layer is rehydrated.
Another possible mechanism of depositing LCNP is through the applica-
tion of dry powder precursors on a surface. Dry powder precursors of CPNP
have been produced using the spray - drying technique from starch - encapsulated
dispersion as well as dextran-encapsulated emulsion (Spicer et al., 2002). These
spray-dried precursors of CPNP have been shown to form the cubic crystalline
structure upon hydration in water. This new formulation technique may allow
the formation of a crystalline surface through deposition and then rehydration
from powdered CPNP precursors on the surface. Such an application still
requires an understanding of means to control the adhesion strength between
the CPNP and the supporting surface.
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