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Figure 1.6
Schematics of the fundamental concepts used in the H-bonding SCFT
treatment. [Reproduced with permission from Lee et al. (2007).]
the drawback to introduce a number of unknowns, which complicates the
numerical simulations (e.g., the binging energy
F
b
, the two head - to - tail Flory -
Huggins parameters
χ
OFF
).
Nonetheless, this approach clearly allows an unprecedented physical descrip-
tion of the self-assembly process. Figure 1.6 summarizes the main physical
ingredients used for the hydrogen-bonding SCFT treatment.
An insight into the model results show that some remarkable predictions
can be made by implementing hydrogen bonding into SCFT. Figure 1.7a shows
the predicted phase diagram and compares it to the experimental one estab-
lished by Qiu and Caffrey (2000) shown in Figure 1.7b. An effective tempera-
ture is used in the phase diagram, expressed by the inverse of the energy gain
for hydrogen bonding (
χ
ON
and
χ
OFF
, and the two head - to - solvent
χ
ON
and
′
′
1/
F
b
): When the temperature increases, hydrogen
bonds are progressively broken, with a progressive reduction of the energy
gain (e.g.,
−
1/
F
b
increases).
The anomalous transition sequence—isotropic fl uid
−
L
α
— is now
correctly predicted, which represents a breakthrough in the lyotropic behavior
interpretation. The theory is even capable of predicting thermodynamic coex-
istence regions such as the L
α
→
Ia3d
→
+
Ia3d. Additionally, the thermotropic sequence,
isotropic fl uid, is also well predicted. The exact
location of the phase boundaries depends on the amount of complexity added
to the model. For example, implementing multiple water molecule-polar head
binding sites for hydrogen bonds and handling the multiple hydrogen bonds
in a procedure similar to that discussed by the groups of Tanaka and Pincus
(Bekiranov et al., 1997; Matsyama and Tanaka, 1990) is anticipated to lead to
afi ner agreement between the experiments and the theory. Therefore, SCFT
implementing reversible H bonds clearly settles a new direction for the physi-
cal description of phase diagrams in lipid-water systems.
L
α
→
Ia3d
→
hexagonal
→
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