Kiyoharu Nakatani

In situ measurements of ion-exchange processes in single polymer particles : laser trapping microspectroscopy and confocal fluorescence microspectroscopy

Ion-exchange processes of a cationic dye (Rhodamine B; RhB) were studied for individual polymer particles (diameter of 16-20 μm) by laser trapping microspectroscopy and confocal fluorescence laser microspectroscopy. The absorbance of RhB at 565 nm adsorbed on a cation-exchange particle increased linearly with the concentration of RhB in the aqueous phase, while it was independent of the particle diameter. Fluorescence intensity profile measurements of RhB along the particle diameter by confocal fluorescence microspectroscopy directly proved that ion exchange took place in the surface layer (∼2-μm thickness) of the particle in the initial stage (1 h). Diffusion of RhB in the particle was very slow, and ion exchange proceeded gradually to the inner volume in the order of days. The ion-exchange processes were analyzed on the basis of simulation of the time course of the concentration profile of RhB in the particle, and the diffusion coefficient of RhB was determined to be (2-4) × 10(-11) cm(2)·s(-1).

Droplet-size dependence of the electron transfer rate across the single-microdroplet/water interface

Abstract Electron transfer between ferrocene in a single oil droplet and hexacyanoferrate(III) in the surrounding water phase was studied by laser trapping, spectroscopic, and electrochemical techniques. We determined the rate of interfacial electron transfer for an individual droplet and found for the first time that the rate increased with a decreased in the droplet diameter. This particular micrometer size dependence was discussed on the basis of kinetic analysis of the electron transfer rate.

Laser trapping and electrochemistry of a single oil droplet in water: Electron transfer across the oil-droplet | electrode interface

Abstract The electrochemistry of ferrocene (FeCp) in a single micrometer-sized nitrobenzene droplet dispersed in water was studied by laser trapping and microelectrochemical techniques. Mass transfer of FeCp, ferrocenium ion, and tetra-n-butylammonium ion between the droplet and water phases accompanied by oxidation of FeCp proceeded across the droplet | water interface. The peak potential of a cyclic voltammogram of FeCp was highly dependent on the potential sweep rate. The potential shift was analyzed by thin-layer electrolysis and the results are discussed in terms of the irreversible electron transfer of FeCp across the droplet | electrode interface and in terms of mass transfer of ion species across the droplet | water interface.

Transfer and adsorption of 1-pyrene sulfonate at the water 1,2-dichloroethane interface studied by potential modulated fluorescence spectroscopy

The transfer mechanism of 1-pyrene sulfonate anion (PSA−) across the polarized water 1,2-dichloroethane (DCE) interface was investigated by a combination of electrochemical techniques and potential modulated fluorescence (PMF) spectroscopy under total internal-reflection. The dependence of the cyclic voltammogram and the ac voltammogram on the PSA− concentration showed an apparent reversible ion transfer process. However, the PMF responses exhibited a complex dependence on the PSA− concentration, revealing adsorption and dimerization processes taking place at the interface. Analysis of the dynamic spectroelectrochemical responses suggests that PSA− is adsorbed at the interface prior to the transfer step. Upon transferring to the organic phase, PSA− appears to accumulate at the interface undergoing a dimerization reaction.

Spectroscopic and electrochemical analyses of electron transfer and mass transfer across the microdroplet/solution interface

A laser trapping - spectroscopy - electrochemistry method has been applied to study electron transfer and mass transfer across the microdropletlwater interface. Electron transfer from Fe(III) produced electrochemically at an optically transparent Sn02 electrode in water to ferrocene (FeCp) in an oil droplet was directly measured by both fluorometric and coulometric methods. The rate determining step of the FeCp oxidation was the electron transfer process across the dropletlwater interface and the relevant rate constant was determined for individual micrometer droplets. As a model of color developing reactions in photographic emulsions, cyan dye formation reaction in a single oil droplet was also investigated. Mass transfer of a reagent across the dropletlwater interface and subsequent dye formation reaction in the droplet were demonstrated. The yield and the rate constant of the dye formation reaction in single droplets were also discussed.

A mechanistic study on ion pair extraction using single microdroplet injection and microelectrochemical techniques

Ion pair extraction from water into oil in a (ferrocenylmethyl)trimethylammonium bromide (FcTMABr)–sodium hexafluorophosphate (NaPF6) system was studied kinetically by injection and manipulation of a single oil droplet of 10−8 cm3 and electrochemistry of the single droplet contacting a microelectrode. The FcTMA+ concentration extracted into the oil phase at the distribution equilibrium was dependent on the FcTMABr, NaPF6, and NaCl concentrations in the water phase. The initial rate of the ion pair extraction was directly proportional to the FcTMABr concentration in water, while it was independent of the NaPF6 and NaCl concentrations in water. These results indicate that the ion pair extraction rate is governed by the ion transfer of FcTMA+ from water into the droplet, maintaining the electroneutrality in the droplet by the PF6− transfer.

Dissolution characteristics of resist polymers studied by quartz crystal microbalance transmission-line analysis and pKa acidity analysis

The development process is very important in determining the resist resolution of lithography. Polymer dissolution during development was studied based on resonance frequency and impedance measured by the quartz crystal microbalance (QCM) method. A transmission-line analysis of QCM data was then carried out. The dissolution characteristics were also evaluated from the standpoint of molecular structures and polymer acidity measured by potentiometric titration. Fluoropolymers showed dissolution characteristics which reflect large fluorine effects in addition to acidity effects. The fluorine effects retarded the dissolution rates and formed a swelling layer. Poly(methacrylate)s had a complicated swelling behavior during development owing to the hydrophobic components in the polymers. The fluorine and hydrophobic effects rather than polymer acidity play the dominant role in forming the swelling layer during development.

External and Intraparticle Diffusion of Coumarin 102 with Surfactant in the ODS-silica Gel/water System by Single Microparticle Injection and Confocal Fluorescence Microspectroscopy

The release mechanism of coumarin 102 from a single ODS-silica gel microparticle into the water phase in the presence of Triton X-100 was investigated by confocal fluorescence microspectroscopy combined with the single microparticle injection technique. The release rate significantly depended on the Triton X-100 concentration in the water phase and was not limited by diffusion in the pores of the microparticle. The release rate constant was inversely proportional to the microparticle radius squared, indicating that the rate-determining step is the external diffusion between the microparticle and the water phase.

Analysis of Distribution and Intraparticle Diffusion of a Fluorescent Dye in Mesoporous Silica Gel by Confocal Fluorescence Microspectroscopy

A micrometer-sized spherical silica gel microparticle (pore diameter, ∼7 nm) was injected into an aqueous rhodamine 6G solution using microcapillary manipulation-injection technique, and the dye distribution in the single microparticle was measured as the fluorescence depth profile by confocal fluorescence microspectroscopy. The fluorescence depth profile was simulated by the convolution and deconvolution methods to correct the contribution of the spatial resolution of the experimental system. The dye homogeneously or heterogeneously distributed in the microparticle at the adsorption equilibrium, dependent on the type of silica gel. The intraparticle diffusion coefficient of the dye distributed homogeneously in the silica gel was analyzed by the simulations of the time dependence of the fluorescence depth profile based on the external and intraparticle diffusion model. The results indicated that the intraparticle diffusion of the dye in the silica gel is governed by the pore diffusion.

Three-dimensional Representation Method Using Pressure, Time, and Number of Theoretical Plates to Analyze Separation Conditions in HPLC Columns

There has been considerable discussion of the speed performance of HPLC separation, especially regarding the relationship between theoretical plates and hold-up time. The fundamental discussion focuses on the optimal velocity, u0,opt, which gives a minimal height equivalent to a theoretical plate of the van Deemter plot. On the other hand, Desmets method, using the kinetic performance limit (KPL), calculates the highest performance with a constant pressure drop, without focusing solely on the optimal velocity. In this paper, a precise method based on the KPL is proposed, to understand how increasing pressure enhances both theoretical plates and hold-up time. A three-dimensional representation method that combines the pressure drop with two axes of time and theoretical plates will be useful for discussing the effect of pressure in pressure-driven chromatography. Using three dimensions, the methods based on u0,opt and the KPL can be combined, because u0,opt can be visualized three-dimensionally, including the neighbor of u0,opt; and the question of whether the KPL is an asymptotic or effective limit can be investigated. Three performances of high resolution, high speed, and low pressure can be understood on different packing supports at a glance.