Motohiro Kasuya

Two types of two-component gels formed from pseudoenantiomeric ethynylhelicene oligomers.

Two-component gels formed from pseudoenantiomeric ethynylhelicene oligomers in toluene exhibited two different properties depending on difference in numbers of helicenes in the two components. The combinations (M)-5/(P)-4, (M)-6/(P)-4, and (M)-7/(P)-4, which contained oligomers with comparable numbers of helicenes, formed transparent gels (Type I gels). The combinations (M)-6/(P)-3, (M)-7/(P)-3, and (M)-8/(P)-3, which contained oligomers with considerably different numbers of helicenes, formed turbid gels (Type II gels). Negative Cotton effects were observed for the Type I gels in the region between 350 and 450 nm, and were positive for the Type II gels, despite the use of (M)-oligomers for the longer components. UV/vis exhibited absorption maxima at 350 nm for the Type I gels and at 338 nm for the Type II gels. Different behaviors in gel formation processes were observed by fluorescence studies. Atomic force microscopy analysis showed fiber structures of 25-50 nm diameter for Type I gels and bundles of 100-150 nm diameter for Type II gels. The stoichiometry in gel formation also differed: The Type I gels showed 1:1 stoichiometry of the two components; the Type II gels showed no 1:1 stoichiometry, likely 1:2 stoichiometry. Using the Type I and II gels, two-layer gel systems were constructed.

Characterization of Ferrocene-Modified Electrode Using Electrochemical Surface Forces Apparatus

A electrochemical surface forces apparatus (EC-SFA) was employed to measure the interactions between gold electrodes modified with self-assembled monolayers of ferrocene alkyl thiol (Fc-SAM) and oxidized ferrocene (ferrocenium cation, Fc(+)-SAM) in a 1 mM aqueous electrolyte. The double-layer repulsion in both cases of the Fc-SAM and Fc(+)-SAM electrodes was observed. The surface charge density (σ) evaluated from the double-layer repulsions between the Fc(+)-SAM electrodes in 1 mM aqueous KClO4 was 0.0027 C/m(2), which was 2.5 times greater than that of the Fc-SAM, at 0.0011 C/m(2). The σ values of the Fc(+)-SAM were evaluated for various counteranions using the same method, which were 0.0048, 0.0040, and 0.0104 C/m(2) for NO3(-), SO4(2-), and CF3SO3(-), respectively. The degrees of dissociation (αd) between the ferrocenium cation and these counteranions were obtained from σ and the density of the ferrocenium on the electrode. The αd value of CF3SO3(-), 4.1%, was the highest, followed in the order, SO4(2-) > NO3(-) > ClO4(-), indicating that most of the positive charges of the ferrocenium cation were compensated by formation of an ion pair with counteranions.

Surface Structuring Using Photo-Polymerization at the Interface between Vinyl-Modified Quartz and a Dynamic Phase Separating Solution

Spinodal phase separation was initiated using a nanosecond infrared laser temperature-jump at the interface between a modified quartz surface and a 2-butoxyethanol-water solution. The evolving phase domains formed spatial distributions of solvents and solutes at the interface. Radical photo-polymerization was induced in this solution using pulsed UV laser irradiation. Various polymer patterns formed at the quartz surface, depending on the UV pulse delay time after the initiation of phase separation, the fluence, and the number of pulses. Patterns which formed at earlier delay times were smaller and more spatially regular than those which formed later.

Nanotribological Characterization of Lubricants between Smooth Iron Surfaces

We performed the resonance shear measurement (RSM) for evaluating the nanorheological and tribological properties of model lubricants, hexadecane and poly(α-olefin) (PAO), confined between iron surfaces. The twin-path surface forces apparatus (SFA) was used for determining the distance between the surfaces. The obtained resonance curves for the confined lubricants showed that the viscosity of the confined hexadecane and PAO increased due to liquid structuring when the surface separation (D) decreased to a value less than 24 and 20 nm, respectively. It was also determined that the iron surfaces were lubricated by the hexadecane when normal load (L) was less than 1.1 mN, while the confined hexadecane behaved almost solid-like and showed poor lubricity when L was greater than 1.1 mN. In contrast, PAO between the iron surfaces showed high lubricity even under the high load (L > 2 mN). The surface separation of hexadecane and PAO at a hard wall contact between the iron surfaces was determined to be 4.6 ± 0.5 and 5.0 ± 0.4 nm by applying the fringes of equal chromatic order (FECO) for half-transparent iron films deposited on mica surfaces as substrates. We also characterized hexadecane and PAO confined between mica surfaces for studying the effect of substrates on the confined lubricants.

Dynamics of Volume Expansion of De-Mixing Liquids after Pulsed IR Heating

Triethylamine (TEA)–water mixtures have a critical-temperature (Tc). Below Tc the mixture exists as one phase and above Tc it exists in two phases. The de-mixed volume is different to the mixed volume. A nanosecond pulsed-laser heated a TEA–water mixture so that it de-mixed. The resulting dynamics of volume expansion were monitored using interferometry. For T-jumps within the one phase region the dynamics of volume change were limited by the speed of sound. However, T-jumps between the one and two phase regions also manifested a slower volume change associated with the de-mixing process. After 150 ns, the volume of the de-mixed TEA–water was consistent with the equilibrium volume change. This suggests that, within 150 ns, the system had split into phase-domains having equilibrium compositions of TEA and water. Subsequently the phase domains would simply merge and grow resulting in no further volume change to reduce surface tension between the phases.

Nanometer-Resolved Fluidity of an Oleophilic Monomer between Silica Surfaces Modified with Fluorinated Monolayers for Nanoimprinting

Ultraviolet (UV) nanoimprinting has the potential to fabricate sub-15 nm resin patterns, but the interfacial fluidity of organic monomers near monomer liquid/mold solid interfaces related to filling nanoscale mold recesses with UV-curable resins still remains unclear. In this study, we demonstrated that surface forces and resonance shear measurements were helpful to select a surface modifier appropriate for silica mold surfaces for UV nanoimprinting with the low-viscosity monomer 1,10-decanediol diacrylate. Surface forces between silica surfaces mediated with the diacrylate monomer and fluidities of the monomer were investigated with nanometer resolution. Chemical vapor surface modification of silica surfaces with chlorodimethyl(3,3,3-trifluoropropyl)silane (FAS3-Cl) and tridecafluoro-1,1,2,2-tetrahydrooctyltrimethoxysilane (FAS13) gave fluorinated silica surfaces with root-mean-square roughness of less than 0.24 nm suitable for the measurements. When the distance D between two silica surfaces was decreased stepwise in the range of 0-30 nm, monomer viscosity between cleaned silica surfaces increased markedly at D < 6 nm. Surface modification with FAS3-Cl suppressed this increase of interfacial monomer viscosity. In contrast, FAS13-modified silica surfaces caused a jump-in phenomenon at approximately D = 7-9 nm, suddenly decreasing to D = 1 nm as the monomer fluid layer was squeezed out. We concluded that FAS3-Cl was appropriate as a fluorinated surface modifier for silica molds used in UV nanoimprinting with an oleophilic low-viscosity monomer, because the chemisorbed monolayer maintained low monomer viscosity near the surface/monomer interface, in addition to its low surface free energy and short CF3CH2CH2- group.

Low-Temperature Surface Forces Apparatus to Determine the Interactions between Ice and Silica Surfaces

We have developed a low-temperature surface forces apparatus (SFA) using a thermoelectric Peltier module inserted below the bottom surface of the lower sample holder, giving easy access to the samples and allowing quick temperature changes. In air, the temperature can be decreased to ca. -20 °C. To demonstrate the performance of the apparatus, we measured the interactions between ice and a silica surface at -11.5 ± 0.5 °C. An exponentially decaying repulsion of the decay length, 11.2 ± 1.0 nm, was observed, and attributed to the electric double layer (EDL) repulsion. The surface potential of the ice was calculated to be -35 mV by fitting the data to the EDL model.

Selection of Diacrylate Monomers for Sub-15 nm Ultraviolet Nanoimprinting by Resonance Shear Measurement

In UV nanoimprinting, the selection of monomers suitable for sub-15 nm patterning is difficult because the filling behavior of resin at this scale still remains scientifically unclear. We demonstrate sub-15 nm patterning by UV nanoimprinting using silica molds with 20, 15, and 7 nm diameter holes; however, the 7 nm diameter pillar patterns were not fabricated using hydroxy-containing monomers. The filling behavior into silica holes of around 10 nm depended on the chemical structure of the monomers. Resonance shear measurements revealed the following: (1) The viscosities of hydroxy-containing monomers confined between chlorodimethyl(3,3,3-trifluoropropyl)silane (FAS3-Cl)-modified surfaces began to increase at distances shorter than those of the monomers between unmodified surfaces. (2) The monomers confined between tridecafluoro-1,1,2,2-tetrahydrooctyltrimethoxysilane-modified surfaces were squeezed out when the surface-surface distance decreased at less than 7 nm. The measured viscosities between the FAS3-Cl-modified silica surfaces were correlated with the insufficient filling behavior into the silica holes of around 10 nm in UV nanoimprinting. Contact angle measurements provided an additional insight that a higher wettability of the monomers onto the antisticking chemisorbed monolayers resulted in imprinted patterns with higher aspect ratios. Considering the increase in the monomer viscosity in the nanospace and the wettability of monomers onto chemisorbed monolayers, we concluded that the monomer showing low viscosity under confinement and high wettability onto the mold surface was suitable for single-digit nanometer UV nanoimprinting.

Surface forces between hydrophilic silica surfaces in a moisture-sensitive oleophilic diacrylate monomer liquid

We measured the surface forces generated between fused silica surfaces in a low-viscosity oleophilic diacrylate monomer for reliably repeated ultraviolet (UV) nanoimprinting, and studied the influence of water in monomer liquids on the forces. Fused silica surfaces, with a static contact angle of 52.6 ± 1.7° for water, owing to the low degree of hydroxylation, hardly showed reproducible surface forces with repeated scan cycles, comprising approach and separation, even in an identical liquid monomer medium with both of low and high water content. The monomer liquid with a high water content of approximately 420 ppm showed a greater tendency to increase the surface forces at longer surface-surface distances compared with the monomer liquid with a low water content of approximately 60 ppm. On the other hand, silica surfaces with a water contact angle of < 5° after exposure to vacuum UV (VUV) light under a reduced air pressure showed reproducible profiles of surfaces forces using the monomer with a low water ...