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5.7
4.5
4.8
5.1
5.4
(a)
4.2
3.9
2.4
2.7
3.0
3.3
3.6
1.8
2.1
1.5
d
(ms)
10
5
0
-5
PPM
13
12
11
10
(b)
9
8
7
6
5
4
3
2
1
d
(ms)
50
-5
PPM
Figure 4.7
NMR diffusion experiment in cubic phases showing peak attenuation as
duration of fi eld gradient pulse (δ) is increased. Sample compositions: (a) MonooleinO/
D
2
O 70 : 30 wt/wt and (b) monoolein/DOPC/D
2
O 42.5 : 42.5 : 15 wt/wt (Eriksson and
Lindblom, 1993 ).
was added to the system (Fig. 4.7), which has important implications when
considering multicomponent biological membranes.
4.2.5
Positron Annihilation Lifetime Spectroscopy
PALS is a well-established technique used for investigating chain packing and
nanostructure in polymer (Ata et al., 2009; Misheva et al., 2000) high-viscosity
liquid (Jain, 1995) and recently lyotropic liquid crystals (Dong et al., 2009). It
is used to provide an atomic-scale probe of the dimensions of free volume
within materials, based on the lifetime of orthopositronimum (oPs) localized
in inter- and intramolecular spaces.
PALS has promising potential as a novel technique for characterizing the
phase behavior of lyotropic liquid crystals. However, there is a lack of system-
atic correlation of PALS parameters with molecular structure.
Dong et al. (2009) have compared the relationship between the oPs lifetime
and rheology of mesophases summarized in Figure 4.8. They found that
the oPs lifetime is correlated with rheological properties, lipid chain packing
(
d
spacing), and mobility in various mesophases.
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