Dispersibility and Electron Spin Resonance in the Colloidal System of Metal/ Organic Solvent Prepared by Means of Gas Evaporation Technique

Abstract

A highly pure colloidal system, composed of metal ultrafine particles and an organic solvent, was produced by means of modified gas evaporation method. This system is free from colloidal stbailizers and is good for the study of the interface of a simple colloidal system. The surface state of metal ultrafine particles dispersed in organic solvents and the dispersibility of the colloids thus prepared were examined as a function of kinds of metal species and solvents. A strong correlation between the state of the colloids and a dipole moment o f a. solvent was found. In a solvent with a large dipole moment, many metal particles were -well-dispersed. On the other hanel, none of metal particles was dispersed in the sol vent with a small dipole moment, resulting in coagulation. This was discussed in connection with the formation of the electric double layer on the surface of metal fine particles. Detailed studise of the dependence of particle dispersibility on the dipole moment of the solvent were made in lead colloidal systems.
Electron spin resonance ( E SR) was detected in the colloidal system of zinc particles in hexane (Zn/hexane) at 3 K. The Lorentzian ESR signal was observed at g=1.97. This line was reasonably attributed to the Zn⁺ ion localized in the surface layer of Zn ultrafine particles but not to the conduction electrons of Zn metal. The ESR signal was affected by the introduction of oxygen gas and it depended both on the type of solvent and on a state of colloid: In the Zn/hexane system, ESR signal disappeared after the introduction of O₂, but not in Zn/1-butanol system, indicating that the magnitude of the dipole moment of the solvents, hexane (0.085 D, 1 D=3.333×10^-30Cm) and 1-butanol (1.50 D), also affects ESR activity.
The ESR absorption intensity as a function of microwave power depended on the average size of the particles. With decreasing the particle size, ESR signal easily saturated at low power. This behavior was explained by the quantum size effect of phonon energy dispersion. When the particle size is reduced, a low energy phonon is cut off and the energy transfer from a spin system to a phonon system is prevented. This means that the longitudinal relaxation time becomes longer for small particles.