Nonlamellar Lipid Liquid Crystalline Structures at Interfaces - Self-Assembled Supramolecular Architectures: Lyotropic Liquid Crystals - page 292

be extracted. For techniques that probe internal structure and morphology of
LCNP in solution or bulk, such as small-angle X-ray scattering (SAXS), small-
angle neutron scattering (SANS), cryogenic transmission electron microscopy
(cryo-TEM), shear rheology, and nuclear magnetic resonance (NMR), we refer
the reader to existing reviews (Binks, 1999; Boyd et al., 2009; Sagalowicz et al.,
2006b,c ).

10.3.1 Neutron Refl ectometry

Neutron refl ectometry (NR) is a relatively young, but fast growing, technique
for the study of soft matter at an interface, as it can provide quantitative
structural and compositional information of the interfacial layer at molecular
length scales. The neutron is very sensitive to the nuclear composition as it is
scattered by the nucleus of a molecule. Neutrons can distinguish the difference
between hydrogen isotopes, 1 H and 2 H (deuterium, D), which makes it an ideal
tool to elucidate the composition of multicomponent systems via selective
deuteration (Wacklin, 2010). Furthermore, neutrons can penetrate through
many materials, allowing it to be used to study buried layers. In NR, a well-
collimated beam of neutrons is directed at the sample and refl ected from the
interface. The intensity of the refl ected beam relative the incidence beam
(refl ectivity) allows information to be gained on the structure normal to the
interface as the scattering vector is perpendicular to the surface (Binks, 1999;
Thomas, 2004). For specular neutron refl ection, where angle of incidence is the
same as angle of refl ection, the ratio of the intensity of the refl ected beam to
the incident beam ( R = I / I 0 ) is measured as a function of the momentum

transfer vector q :

4 πθ

λ

sin

q =

with the wavelength. Standard optics and scat-

tering theory can be used to obtain layer thickness, interfacial roughness, and
scattering length density of the layer normal to the surface from the NR
profi le. The scattering length density,

θ the angle of incidence and λ

, is the sum of the coherent nuclear
scattering length, b i , of the atoms in volume V :

ρ

ρ= ∑ i b
V

From the scattering length density, it will then be possible to interpret the
physical and compositional structure of the interface. More detailed reviews
on the use of neutron refl ection to investigate lipid membranes can be found
in the literature (Nylander et al., 2008; Thomas, 2004; Wacklin, 2010).