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).

No abstract

No abstract

Mass transfer processes of ferrocene derivatives (FeCp-X) across a single-nitrobenzene-microdroplet/water interface were studied by laser-trapping and microelectrochemical techniques. Substituent effects of FeCp-X on the mass transfer rate were discussed in terms of the distribution coefficient of FeCp-X between the nitrobenzene and water phases as well as of the adsorption rate of FeCp-X on the droplet/water interface. Interfacial mass transfer of ethylferrocene from water to a droplet was limited by diffusion of the molecule in the water phase, while that of 1-ferrocenylethanol or (N,N-dimethylamino)methylferrocene was governed by both adsorption on the droplet/water interface and diffusion in the water phase.

The dynamic anisotropy of Sulforhodamine 101 (SR101) at water/phthalate ester (PE, bis(2-ethylhexyl) phthalate, di-n-heptyl phthalate, di-n-butyl phthalate, or di-n-ethyl phthalate) interfaces was studied by using time-resolved total internal reflection (TIR) fluorometry. A magic-angle dependence of the TIR fluorescence dynamics revealed that rotational reorientation of SR101 at the water/PE interface was restricted in the X-Y plane (in-plane) of the interface. The results indicated that the interface was sharp with respect to the molecular size of SR101 (∼10 Å). In-plane rotational reorientation of SR101 at the interface showed two time constants (τ rot ). The fast component (τ 1 rot ) was similar to that in water irrespective of the nature of PE, while the slow one (τ 2 rot ) was affected by the viscosity of PE but not directly by the macroscopic viscosity. The two rotational reorientation times of SR101 characteristic to the water/PE interface were explained in terms of different adsorption modes of the dye on the interface and the chemical structure of PE itself: mobility of the alkyl chains in PE. Fluorescence dynamic anisotropy under the TIR conditions was shown to be a potential means to study molecular motion of a probe molecule at the water/PE interface as well as chemical/physical characteristics of the interface at a molecular level.

No abstract

No abstract

We explored optical trapping-spectrophotometry of ion-exchange polymer microparticles in water and, determined the dye (tris(2,2'-bipyridine)ruthenium(II) complex; Rue) concentration adsorbed on an individual particle (diameter (d)=20 -140 µm). The absorbance of Ru2+ on the particle increased with an increase of the dye concentration in the aqueous phase, while it was essentially independent of d. The results indicate that adsorption of the complex takes place in the surface layer of the particle, but not homogeneously in the entire particle. A possible role of the optical trappingspectrophotometry method in direct analyses of trace amounts of molecules concentrated on single microparticles in solution is discussed.