Macroscopically anisotropic hydrogels were synthesized by hybridization of poly(N-isopropylacrylamide) with liquid crystalline inorganic nanosheets; their anisotropies in the structure and properties are demonstrated.
The drying process of clear precursor solutions for fabricating highly porous titania films was observed by CLSM. Further, we succeeded in detecting the formation of micelles in the precursor solution containing high-molecular-weight PS-b-PEO diblock copolymers at the initial stage of the drying process as the direct evidence that this synthesis consisted of the EISA process.
Inorganic layered materials can be
converted to colloidal liquid
crystals through exfoliation into inorganic nanosheets, and binary
nanosheet colloids exhibit rich phase behavior characterized by multiphase
coexistence. In particular, niobate–clay binary nanosheet colloids
are characterized by phase separation at a mesoscopic (∼several
tens of micrometers) scale whereas they are apparently homogeneous
at a macroscopic scale. Although the mesoscopic structure of the niobate–clay
binary colloid is advantageous to realize unusual photochemical functions,
the structure itself has not been clearly demonstrated in real space.
The present study investigated the structure of niobate–clay
binary nanosheet colloids in detail. Four clay nanosheets (hectorite,
saponite, fluorohectorite, and tetrasilisic mica) with different lateral
sizes were compared. Small-angle X-ray scattering (SAXS) indicated
lamellar ordering of niobate nanosheets in the binary colloid. The
basal spacing of the lamellar phase was reduced by increasing the
concentration of clay nanosheets, indicating the compression of the
liquid crystalline niobate phase by the isotropic clay phase. Scattering
and fluorescence microscope observations using confocal laser scanning
microscopy (CLSM) demonstrated the phase separation of niobate and
clay nanosheets in real space. Niobate nanosheets assembled into domains
of several tens of micrometers whereas clay nanosheets were located
in voids between the niobate domains. The results clearly confirmed
the spatial separation of two nanosheets and the phase separation
at a mesoscopic scale. Distribution of clay nanosheets is dependent
on the employed clay nanosheets; the nanosheets with large lateral
length are more localized or assembled. This is in harmony with larger
basal spacings of niobate lamellar phase for large clay particles.
Although three-dimensional compression of the niobate phase by the
coexisting clay phase was observed at low clay concentrations, the
basal spacing of niobate phase was almost constant irrespective of
niobate concentrations at high clay concentrations, which was ascribed
to competition of compression by clay phase and restoring of the niobate
phase.
Anisotropic chemical wave propagation of self-oscillating Belousov-Zhabotinsky (BZ) reaction was demonstrated in the poly( N-isopropylacrylamide) gel films embedded with macroscopically aligned liquid crystalline inorganic nanosheets. Although the average propagation rate of chemical wave v̅ was 3.56 mm min in the gels without nanosheets, the propagation was retarded in the gels with 1 wt % of nanosheets: [Formula: see text] = 1.89 mm min and [Formula: see text] = 1.33 mm min along the direction parallel and perpendicular to the nanosheet planes, respectively. Thus, the wave propagation is anisotropic with the anisotropy ratio [Formula: see text] = 1.42 in these gels and the periodic patterns formed by the BZ reaction were concentric ellipses, different from circles seen in isotropic gels. Furthermore, the propagation rate and degree of anisotropy were controllable by nanosheet concentration. These phenomena can be explained that the diffusion of molecules inside the gel is effectively hindered along the direction perpendicular to the nanosheet planes due to the very large aspect ratio of the aligned nanosheets. The present systems will be applicable for anisotropic self-oscillating soft actuators with one-dimensional motions as well as for ideal model system of BZ reactions.
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