The viscoelasticity of a fluid was tuned with the Faradaic reaction of (11-ferrocenylundecyl)trimethylammonium bromide (FTMA), a "redox-switchable" surfactant. An aqueous solution of the reduced form of FTMA exhibited a remarkable viscoelasticity in the presence of sodium salicylate (NaSal) because of the formation of three-dimensional entanglement of wormlike micelles. Electrolytic oxidation of FTMA caused the viscosity of the system to dramatically decrease and the elasticity to disappear. This drastic decrease in viscoelasticity arose from the disruption of wormlike micelles. This novel electrorheological phenomenon is expected to be applicable to ink for inkjet printers, the electrochemically controlled release of substances entrapped in wormlike micelles of FTMA, and fluid flow rate control using electric signals.

In this study, we demonstrate a novel method for preparing crystallized mesoporous titania by using a low-temperature synthesis technique in the presence of cationic surfactant. XRD patterns showed that the titania particles obtained had both hexagonal structure and a wall with anatase crystalline structure. Transmission electron microscopy (TEM) observation and corresponding electron diffraction pattern confirmed that the calcined particles are crystallized mesoporous titania.

Core/shell-type titania nanocapsules containing a single Ag nanoparticle were prepared. Ag nanoparticles were prepared using the reduction of silver nitrate with hydrazine in the presence of cetyltrimethylammonium bromide (CTAB) as protective agent. The sol-gel reaction of titanium tetraisopropoxide (TTIP) was used to prepare core/shell-type titania nanocapsules with CTAB-coated Ag nanoparticles as the core. TEM observations revealed that the size of the core (Ag particle) and the thickness of the shell (titania) of the core/shell particles obtained are about 10 nm and 5-10 nm, respectively. In addition, the nanocapsules were found to be dispersed in the medium as individual particles without aggregation. Moreover, titania coating caused the surface plasmon absorption of Ag nanoparticles to shift toward the longer wavelength side.

We report a reversible photoinduced fluid viscosity change. A small amount of a "photoswitchable" azobenzene-modified cationic surfactant (4-butylazobenzene-4'-(oxyethyl)trimethylammonium bromide, AZTMA) was added to a wormlike micellar solution of cetyltrimethylammonium bromide (CTAB) containing sodium salicylate (NaSal). The trans-AZTMA solution had a remarkably high viscosity as a result of the entangled network of wormlike micelles. UV light irradiation on the trans-AZTMA solution remarkably decreased the viscosity of the solution because the bulky structure of cis-AZTMA is likely to disrupt the network structure of wormlike micelles. This photoinduced viscosity change is perfectly reversible between the trans- and cis-AZTMA solutions.

The pore-wall chemistry of activated carbon fiber (ACF) was controlled by heating in Ar and H2. The ACF structures were characterized from various levels, and interaction of water vapor with the micropores of ACF was directly measured by calorimetry. Two kinds of pitch-based ACFs with different pore widths (w) (P5, w = 0.7 nm, and P20, w = 1.0 nm) were used. P20 was treated at 1273 K in a gas flow of Ar or H2 for 1 h to modify its surface properties. Adsorption isotherms of water on the two ACFs at 303 K showed different features, which are possibly caused by the pore width difference. The surface modification by the heat treatment of P20 changed its pore structure, leading to different water adsorption behavior. The mechanisms of water adsorption and desorption can be discussed through the differential or integral heat of water adsorption or desorption. Water adsorbs on the functional groups located at the surface of P20 with an adsorption heat comparable to the heat of condensation at relatively low P/P 0, causing the cluster formation of water molecules. The removal of such functional groups by heat treatment decreases the adsorption heat at low pressure. The differential heat abruptly increases at filling in all cases, indicating a structural formation of water from a clustered form to a highly ordered form.