Tomonori Nomoto

Optically excited near-surface phonons of TiO2 (110) observed by fourth-order coherent Raman spectroscopy

We observed the fourth-order and third-order optical responses in the time domain on a TiO(2) (110) surface covered with trimethyl acetates. Coherent vibrations assignable to near-surface phonon modes were present at 179, 191, 359, 440, 507, 609, and 823 cm(-1) in the fourth-order responses. The amplitude and phase of each mode were determined with different azimuths and polarizations of pump and probe light pulses. Vibrational assignments and possible mechanisms to excite the vibrations were discussed.

Fourth-order coherent Raman spectroscopy in a time domain: applications to buried interfaces

A Raman-based, nonlinear optical spectroscopy is a promising method for observing vibrational modes localized at buried interfaces. The principles of Raman excitation and interface-selective detection of coherent vibrations are described. Applications to air-liquid, liquid-liquid, air-solid, liquid-solid, and solid-solid interfaces are reviewed.

Delayed Response of Interfacial Tension in Propagating Chemical Waves of the Belousov–Zhabotinsky Reaction without Stirring

Time-resolved measurements of the interfacial tension of propagating chemical waves of the Belousov-Zhabotinsky reaction based on the iron complex catalysts were carried out without stirring by monitoring the frequency of capillary waves with the quasi-elastic laser scattering method. A delayed response of the interfacial tension with respect to absorption was found with the delay being ligand-dependent when the reaction was conducted at a liquid/liquid interface. This behavior is attributed to differences in adsorption activity of the hydrophobic metal catalyst. The delay time and the increase in interfacial tension were also reproduced by a model considering the rate constants of equilibrium adsorption.

Fourth-order coherent Raman spectroscopy of liquid-solid interfaces: near-surface phonons of TiO2 (110) in liquids.

The fourth-order coherent Raman response of a TiO2 (110) surface covered by HCl aqueous solution, neat octanol, acetic acid, or carbon tetrachloride layers is acquired. Four fourth-order optical responses were identified at 837–826, 452–448, 371–362, and 184–183 cm−1 and assigned to near-surface phonons of TiO2. A third-order response produced in the bulk liquid layer was superimposed on the fourth-order response, when coherent vibrations are efficiently excited in the layer.

Experimental investigation of the self-propelled motion of a sodium oleate tablet and boat at an oil-water interface

The self-propelled behaviors of macroscopic inanimate objects at surfaces and interfaces are ubiquitous phenomena of fundamental interest in interface science. However, given the existence of a large variety of systems with their own inherent chemical properties, the kinematics of the self-propelled motion and the dynamics of the forces driving these systems often remain largely unknown. Here, we experimentally investigate the spontaneous motion of a sodium oleate tablet at a water-nitrobenzene interface, under nonequilibrium and global isothermal conditions, through measurements of the interfacial tension with the noninvasive, quasi-elastic laser scattering method. The sodium oleate tablet was self-propelled due to an imbalance in the interfacial tension induced by the inhomogeneous adsorption of oleate/oleic acid molecules. The kinetics of the self-propelled motion of a boat-shaped plastic sheet bearing sodium oleate tablets at a sodium oleate aqueous solution-nitrobenzene interface was also studied. The interfacial tension difference between the front and rear of the boat was quantitatively identified as the force pushing the boat forward, although the Marangoni flow due to the uneven distribution of the interfacial tension behind the boat tended to decelerate the motion.

Motion modes of two self-propelled camphor boats on the surface of a surfactant-containing solution

HYPOTHESIS The existence of a surface tension difference and a surface flow around self-propelled objects, such as camphor boats, has been confirmed by many studies. However, the interactions in the collective motion of several camphor boats have not been explicitly discussed. Here, a model system of two camphor boats was investigated for the first time from the viewpoint of surface tension and surface flow. EXPERIMENTS The behavior of one fixed boat and one movable boat on a sodium dodecylsulfate aqueous solution in an oval track has been studied as a model system of two-body interactions. The surface tension around the movable boat was measured using the non-invasive, double-beam quasi-elastic laser scattering method. The Marangoni surface flow was quantitatively estimated using a mock boat in order to evaluate the net repulsive interaction between the two boats. FINDINGS We succeeded in controlling the motion of the two camphor boats by varying the boat characteristics and the surfactant concentration. The balance/unbalance between the surface tension distribution and the surface flow around the boats was found to drive two different behavior modes: stationary and oscillatory. These results allow us to gain further insight into the dynamics of the interactions in the collective behavior of autonomous inanimate objects.

Effects of halide ions on the acceptor phase in spontaneous chemical oscillations in donor/membrane/acceptor systems.

The effects of halide ions on the acceptor phase in the chemical oscillation in donor/membrane/acceptor systems were examined. The transfer of cetyltrimethylammonium (CTA(+)) ions from the donor phase and their adsorption and desorption at the membrane/acceptor interface led to spontaneous, nonlinear oscillations of the electric potential. Chloride ions stabilized the adsorption of CTA(+) ions and gave rise to a large-amplitude, long-interval, and a long relaxation-time constant. On the contrary, iodide ions, which are more hydrophobic than chloride ions, demonstrated opposite results. This mechanism was proposed based on the simultaneous time-resolved measurements of the interfacial tensions at both the donor/membrane and membrane/acceptor interfaces and observation of the convective flow due to Marangoni instability.

Changes in Interfacial Tension of a Lipid Membrane Formed at the Water/Chloroform Interface upon DNA Complex Formation

Changes in the interfacial tension of a lipid monolayer membrane formed at the water/chloroform interface upon DNA addition were measured using the quasi-elastic laser scattering (QELS) method. A cationic lipid, N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTAP), as well as zwitterionic lipids, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), were used to form lipid monolayer membranes at different calcium ion concentrations. A rapid decrease of the interfacial tension resulting from electrostatic interactions between DOTAP and DNA was observed within 10 s. However, such rapid decreases were not observed for DOPE or DOPC. A decrease in the interfacial tension was exhibited by DOPE after 1000 s from the addition of DNA, which may be due to an overall structural change in the DOPE membrane. A DOTAP/DOPE complex system showed behaviors attributable to both DOTAP and DOPE, whereas the behavior of the DOTAP/DOPC system resembled that of DOPC alone. The current results provide a model for the so-called lipoplex carriers used in gene therapy.

Surface vibrations of TiO 2 in liquids observed by fourth-order Raman spectroscopy

We present fourth-order Raman spectra of a TiO2 surface immersed in different liquids. Although an undesired optical process occurs in some liquids covering the interface, phonon modes localized at the liquid-TiO2 interfaces were observed by fourth-order Raman spectroscopy.