Page 541 - Book Hosokawa Nanoparticle Technology Handbook

23 LIQUID-CRYSTALLINE INORGANIC NANO AND FINE PARTICLES APPLICATIONS

F
F R

PL1: R = OPO H ;
3 2
77 M 129 S 193 N 194 Iso
G-50 M 1 2 A
PL2: R = H;
Cr 41 S 45 N 121 Iso
B
NC O
OPO H
( ) 6 3 2
PL3: G -4 M 57 S 146 Iso
A
Figure 23.5
Structures of thermotropic LCs PL1–PL3 for
hybridization with -Fe O particles. G: glass; Cr: crystal;
3
2
M: mesomorphic; S : smectic A; N: nematic; Iso:
A
isotropic phases. The figures in between are transition
temperatures in C.
[29, 30], were used in our study. All particles were
thoroughly washed with 1 M NH and water by cen-
3
trifugation to completely remove impurities and
freeze dried. The resulting powders H1–H6 were con-
firmed as -Fe O by X-ray diffraction analysis, and
2
3
no difference in their surface conditions was observed
by X-ray photoelectron spectroscopy.
Also, we designed and synthesized PL1 and PL3
with a phosphate moiety as shown in Fig. 23.5.
Phosphate group-free PL2 was also prepared. The
phase transition temperatures and LC phases of
PL1–PL3 were determined by POM with a hot stage,
DSC, and X-ray diffraction. The monodispersed spin-
dle-type H1–H3 are expected to adsorb the phosphate
moiety of PL1, because they were obtained with
PO 3 ions as a shape controller [32, 33].
4
Hybridization of PL1 and H1–H6 or PL2–PL3 and Figure 23.6
H2 was carried out as follows. Twenty milligrams of Optical photomicrographs of thermotropic hybrid LC
PL and the same weight or 40 mg of H (PL/H 1/1 phases of 1/2 hybrids (i) PL1/H2, (ii) PL1/H5, and
or 1/2) were mixed together and dispersed in 2 ml of (iii) PL1/H6 at 90 C (a) with a polarizer; (i)-(a) and
methanol and 2 ml of CHCl by ultrasonication for (b) insets: sheared monodomain.
3
30 min followed by removal of the solvents at 60 C
under Ar flowing. Fig. 23.6 exhibits optical micro-
scopic images of 1/2 hybrids of PL1/H2, PL1/H5,
and PL1/H6 at 90 C in the presence of a cross polar- behavior was also seen for 1/2 hybrids of PL1/H1,H3
izer (a) and its absence (b). For the PL1/H2 hybrid, a and 1/1 hybrids of PL1/H1–H3. However, the further
marbled texture as a characteristic of an N phase with increase of the PL1 component resulted in the partial
strong birefringence and fluidity was observed. The phase separation of PL1 with H1–H3. On the other
mesomorphic phase was readily transformed to a uni- hand, 1/2 as well as 1/1 hybrids of PL1/H5 also
axially aligned monodomain by shearing (Fig. 23.6i-a formed a uniform fluidized material without phase
inset). DSC measurement on the second heating scan segregation of PL1 with H5 (Fig. 23.6ii-b), however
revealed that the hybrid showed the glass–mesophase no birefringence was found and formed an optically
transition at 35 C. After an endothermic peak at isotropic state. The PL1/H4 1/2 and 1/1 hybrids,
148 C, the hybrid showed a highly fluidized state with consisted from monodispersed cuboidal -Fe O par-
3
2
strong birefringence observed by POM. The birefrin- ticles, also showed an optically isotropic state with
gence was kept up to 250 C. Similar mesomorphic fluidity. Thus, the aspect ratio of the -Fe O particles
2
3
513