Chemistry Reference
In-Depth Information
expansion of the lattice on heating and cooling (the “breathing mode”) was
accompanied by concurrent expulsion and uptake of water from the matrix to
satisfy the changes in lattice dimension.
In the case of higher concentrations of GNR, the 5-s on pulse for both the
1.5- and 3-nM systems did induce a phase change to the H
2
and L
2
phase
structures. At 3 nM, complete transformation to the L
2
phase occurred by the
end of the 5-s irradiation, while the lower 1.5-nM concentration resulted in a
mixed H
2
L
2
phase, indicating a reduced heating effect (Fig. 8.16). Again,
when the laser was switched off, the system ultimately returned to the initial
v
2
(Pn3m) phase structure. Interestingly, on conversion from the L
2
or L
2
+
H
2
state back to the v
2
structure, the “gyroid” bicontinuous cubic phase with Ia3d
space group was encountered. The gyroid phase coexisted with the H
2
phase
initially and then with the v
2
(Pn3m) phase for approximately 5-6 s after the
laser was switched off.
In addition, Fig. 8.16 clearly demonstrated that in the case where no GNRs
were added to the matrix, there was no signifi cant change in apparent sample
temperature (
T
app
) upon laser irradiation. The reversibility of the heating effect
in the presence of the GNR is evident from the
T
app
profi les for the three
samples containing the nanorods. The sample containing 0.3 nM GNR is
heated to approximately 50°C, just below the transition above which the coex-
isting H
2
phase occurs. Increasing the nanorod concentration to 1.5 nM induces
heating to approx 70°C, while 3 nM GNR heated the matrix to an apparent
temperature of 75°C. The repeat irradiation provided the same peak tempera-
ture within 1-2°C and reproducible kinetics of heating and cooling. The heating
effect observed in these experiments is clearly a function of nanorod concen-
tration, although the relationship between concentration and maximum tem-
perature at differing irradiation conditions requires further investigation and
is likely complicated by concurrent cooling. The “breaking wave” shape of the
profi les indicates nonlinear heating/cooling gradients in the material.
The authors (Fong et al., 2010) concluded that GNRs embedded in liquid
crystalline matrices produce localized plasmonic heating of the hybrid matrix,
enabling fi ne control over the nanostructure. The phase transitions resulting
from photothermal heating were fully reversible and specifi c to the GNR/laser
wavelength combination. Localized plasmonic heating of the liquid crystal did
not compromise the integrity of the lipid molecules in any of the mesophases.
Undoubtedly, this research represented a signifi cant advance toward effective,
light-activated drug delivery systems with potential to solve unmet medical
needs.
The most straightforward stimulus, which can be exploited for in vivo con-
trolled release, is certainly pH because of the large pH changes occurring
spontaneously within the mouth-stomach-intestine tract.
In this context Negrini and Mezzenga (2011) presented a pH-responsive
lipid-based LLC, which has a number of signifi cant advantages for real oral-
administration - controlled delivery. First, the system is based on a simple for-
mulation of monolinolein and linoleic acid, which maintains it entirely food
+
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