Reversing-Pulse Electric Birefringence of Montmorillonite K10 in Aqueous Media: Electric Moments, Field Orientation, and Changes in Sign and Profile of Signals Observed in the Low-Field Region

✍ Scribed by Kiwamu Yamaoka; Ryo Sasai

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 207 KB
• Volume: 209
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1998.5909

✦ Synopsis

The reversing-pulse electric birefringence (RPEB) of a montmorillonite K10 (MK-10) sample was measured at 25°C and 633 nm in aqueous suspensions in the concentration range 0.005-0.145 g/L in the 0 -200 V/cm region. The sign of the RPEB signals was negative and the profile was associated with a deep dip in the reverse process in all cases at weak fields lower than the signinversion point, E si . Above E si , the sign became positive, whereas the signal profile usually showed a hump in the buildup process and a larger hump in the reverse process. A complex signal pattern appeared at the highest MK-10 concentration (0.145 g/L). For the multicomponent equilibrium system, theoretical RPEB expressions were derived in terms of three electric dipole moments: the permanent moment, the fluctuating counterion polarizability ( 3 ) with ionic relaxation time ( I ) along the symmetry axis, and the covalent polarizability anisotropy (⌬␣). Analysis of profiles of the observed RPEB signals showed that the MK-10 particle possesses no permanent dipole moment. The ratio 3 /⌬␣ was less than ؊1, and 1 was comparable with the overall rotational relaxation time of the disklike MK-10 particle. RPEB signals at 0.145 g/L were analyzed with the two-state equilibrium theory and the MK-10 particle was found to form thin platelike aggregates with partially overlapping surfaces. The field-strength dependence of the steadystate birefringence was fitted with SUSID orientation functions. The field orientation mechanism of MK-10 particles in aqueous media was discussed.