Electrooptical properties of montmorillonite suspended in aqueous media 水分散系におけるモンモリロナイトの電気光学的性質

博士論文

To clarify the electrooptical property of clay particle suspended in aqueous media with a reversing-pulse electric birefringence (RPEB) method, the new RPEB transient theories and orientation function were derived, and the reversing pulse generator, which is also applicable to large particle such as clay, was newly constructed. The transient RPEB theory was derived on the basis of the interaction of applied electric pulse with two electric dipole moments of the macroion: one is due to the ion-atmosphere polarizability a, with a single relaxation time τ1, for the distortion of ion-atmosphere along the longitudinal axis and the other is due to the intrinsic molecular (instantaneously field-induced) polarizability anisotropy Δα' (= α33 - α11) between the longitudinal (3) and transverse (1) axes of the macroion. The new orientation function was derived for disklike model. It was assumed that the disklike particle possessed the following three electric dipole moments: (1) permanent dipole moment, (2) saturable induced dipole moment, which is induced in a finite time and saturated at an electric field strength, and (3) unsaturable induced dipole moment, which is instantaneously induced dipole moment by an external electric field. In the newly constructed reversing pulse generator, a field-effect transistor (MOS-FET) was used instead of a vacuum tube as the switching element. This pulse generator has the following characteristics: (1) a stable output voltage in the 5-300V range, (2) a widely variable output pulse duration in the 10 µs-l.2 s range, and (3) a very short time constant of electric pulse (in most cases, 150 ns for buildup and reverse and 50 ns for decay). Moreover, this generator could deliver a single rectangular pulse and/or a reversing pulse to high-ionic strength samples, e.g., 0.2 moldm-3 NaCI or MgCI2, because of a high electric current resistance of MOS-FET. The theories and reversing pulse generator newly developed were applied to study the effects of particle concentration, the ionic strength, and valence of electrolyte on the electrooptical and hydrodynamic properties of montmorillonite particles suspended in aqueous media. It was clear that both these theories and generator were very useful for the study of clay particle suspended in aqueous media. RPEB data of Na-montmorillonite particle indicated that the particle possesses no permanent dipole moment, but an ionic polarization makes a large contribution to the field orientation. Since the contribution of the ionic polarization increased with an increase of ionic strength, the distortion of sodium ions trapped on the cation-exchangeable sites may be responsible for this ionic polarization. The Na-montmorillonite particles form aggregates of card-house stnicture, which is an irregular structure, at increased concentrations of added sodium ions, since the optical anisotropy decreases and the diameter of particle increases with increasing ionic strength of added sodium ions. In contrast to the Na-montmorillonite particle, the RPEB signals of Mg-montmorillonite suspensions showed longer average rotational relaxation times, and the optical anisotropy of Mg-montmorillonite particle increased with an increase in concentrations of added magnesium ions. Moreover, the RPEB signals could not be analyzed theoretically. Therefore, Mg-montmorillonite particles form larger aggregates of hook-house structure, which is a regular structure. The present study has confirmed that the reversing-pulse electrooptical methods are very useful to characterize the structure and properties of clay particles. These findings give us some fundamental information for application of clay particles. In the future, the analysis methods of reversing-pulse electric birefringence newly developed in this study will be successfully extended to many colloidal particle systems other than clay particles.

Contents / p1 Abstract / p1 Chapter I.General Introduction / p1 　References / p5 Chapter II.Electrooptical Methods / p6 　II.1.Introduction / p6 　II.2.Reversing-Pulse Electric Birefringence Method / p9 　References / p13 Chapter III.Instrumentation / p14 　III.1.Introduction / p14 　III.2.Optical System / p15 　III.3.Reversing-Pulse Generator / p16 　III.4.Characterization of Reversing-Pulse Generator / p19 　References / p20 Chapter IV.Theory / p21 　IV.1.Introduction / p21 　IV.2.RPEB Transient Theory / p22 　IV.3.Orientation Function / p33 　IV.4.Rotational Relaxation / p51 　References / p53 Chapter V.Effect of Particle Concentration, Ionic Strength, and Valence of Electrolyte on Electrooptical Properties of Montmorillonite Particles in Aqueous Media / p55 　V.1.Introduction / p55 　V.2.Experimental / p56 　V.3.Na-montmorillonite Suspensions / p57 　V.4.Mg-montmorillonite Suspensions / p67 　References / p72 Chapter VI.Conclusions / p73 Acknowledgements / p75