Biomedical Engineering Reference
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O
O
O
H
N
H
N
H
N
H
N
C
C
11
H
23
C
10
H
20
N(CH
3
)
3
+
Br
−
C
11
H
23
C
C
H
N
N
H
C
C
11
H
23
C
10
H
20
N(CH
3
)
3
+
Br
−
N
H
N
H
C
C
C
11
H
23
O
O
O
1
trans
(1
R
,2
R
)
2
trans
(1
R
,2
R
)
5
trans
(1
R
,2
R
)
O
O
O
H
N
H
N
H
N
H
N
C
11
H
23
C
C
10
H
20
N(CH
3
)
3
+
Br
−
C
C
C
11
H
23
H
N
N
H
C
C
11
H
23
C
10
H
20
N(CH
3
)
3
+
Br
−
N
H
C
N
H
C
C
11
H
23
O
O
O
3
trans
(1
S
,2
S
)
4
trans
(1
S
,2
S
)
6
trans
(1
S
,2
S
)
(a)
OH
RO
O
HO
HO
O
N
OH
N
1
: R = H
O
CC
3
H
7
(b)
2
: R = H
Scheme 5.1
Molecular structures of some gelators used to prepare silica fibers, (a)
cyclohexanediamine-based gelators and (b) sugar-based gelator.
used to fabricate silica nanotubes or fibers [16]. Interestingly, double-twisted
helical silica fibrils were obtained by sol-gel transcription of chiral aggregates
of gemini surfactants [17], and double silica nanotubes were obtained with
crown-appended cholesterol nanotubes in gels as templates [18]. In another study,
fibers of a fluorescent gelator were coated with silica, creating a type of fluorescent
composite fiber with good mechanical strength, which may find applications in
optoelectronic devices [19].
5.2.2
Silica Nanoparticles
Silica nanoparticles are generally prepared in solutions. Although granular silica
particles can be prepared in the bulk gel phase, it is still hard to control the size
of the particles. Interestingly, highly monodisperse small silica nanoparticles were
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