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1981). Lipase and water must be free to diffuse through the phases formed
by the lipolysis products, surrounding the diminishing fat droplet. Thus, the
bicontinuity as well as the incorporation properties of the cubic monoglyc-
eride phases are thought to be important features for the lipolysis process
(Patton et al., 1985).
So far lipolysis has not been used for the surface modifi cation of oil fi lm.
One reason might be that it can be hard to stop the lipolytic activity at the
requested liquid crystalline structure. Recent interfacial studies of lipase activ-
ities on monolayers have provided some leads on how to control the lipase
activity by modulating the lipid composition (Reis et al., 2009). Another obsta-
cle is to prepare well-defi ned oil fi lms. The recently developed spin-freeze-
thaw technique has opened up the possibility of forming stable, uniform oil
fi lms with thicknesses of
m by spin coating the oil onto hydrophobically
modifi ed silicon substrates (Zarbakhsh et al., 2005). We are convinced that this
technique has a so far unexploited potential for the future.
∼
2
μ
10.6
STRUCTURAL CHARACTERISTICS
10.6.1
Internal Structure of the Layer
The internal crystalline structure of the dispersed LCNP can be characterized
with SAXS and cryo-TEM. These two techniques have been the most popular
because they provide information on the internal crystalline structure and
particle morphology (Boyd et al., 2009). In SAXS, the periodic crystalline
structure gives rise to characteristic diffraction patterns. Indexing the peaks in
the diffraction pattern to a specifi c space group allows identifi cation of the
crystalline phase. Cryo-TEM is a way to directly visualize the morphology and
structure of the LCNP in the equilibrium state with minimal disruption to the
morphology. The nanoparticles are frozen before imaging. The internal crystal-
line structure can be deduced from the cryo-TEM micrograph and can be
further processed by Fourier transformation to reveal the crystalline phases.
Cryo-TEM reveals the structure of individual particles, while SAXS measures
on an assembly of particles with higher accuracy, which makes it less sensitive
to individual variations. These complementary techniques have been widely
utilized to investigate the internal structure of dispersed particles (Barauskas
and Landh, 2003; Barauskas et al., 2005a,b, 2006a); however, they cannot easily
provide the corresponding information on the internal structure of a crystal-
line layer on a surface.
Neutron refl ectometry can provide some quantitative information on the
internal structure of the layer at an interface. The wavelength of neutrons,
∼
5 Å, is similar to that of molecular length scales, providing enough resolution
to detect crystalline structures at the interface (Nylander et al., 2008). Uniform
thin fi lms on surfaces can exhibit pronounced fringes in the NR curve, and
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