Matsumoto Mitsuhiro, Koibuchi Sae, Hayashi Naoki
Department of Chemistry, Faculty of Integrated Arts and Sciences, University of Tokushima, 1 Minamijousanjima, Tokushima 770-8502, Japan.
Colloids Surf B Biointerfaces. 2007 Apr 15;56(1-2):107-13. doi: 10.1016/j.colsurfb.2006.11.035. Epub 2006 Dec 6.
Imogolite synthesized from sodium orthosilicate and aluminum trichloride was fractionated into four fractions by centrifuging at 12,000 x g (1h). The supernatant, which did not deposit by three times centrifugations, was used for all measurements. The signal of birefringence under a reversing electric pulse showed that the permanent dipole moment is negligibly small at low fields. The electric birefringence under a rectangular electric pulse is positive. The saturated value is proportional to the concentration of imogolite in the range of 0-0.1mg/ml and decreases rapidly with an increase of added salt concentration for NaCl and AgNO(3). It slightly depends on the pH of solution and is biggest in pure water. Then we have determined the anisotropy of electric polarizability (Deltaalpha) for imogolite in pure water at 0.05 mg/ml. Deltaalpha we obtained from the method decreases rapidly at low fields and slowly at high fields as shown in references [M. Matsumoto, Colloids Surf. A 148 (1999) 75, M. Matsumoto, Biophys. Chem. 58 (1996) 173]. It is approximately shown by the following expression, Deltaalpha=Deltaalpha(infinity)+(Deltaalpha(0)-Deltaalpha(infinity))/(1+KE), (Deltaalpha(0):Deltaalpha at E=0, Deltaalpha(infinity):Deltaalpha at E=infinity). Using this relation we can draw the curve of electric birefringence as a function of electric field and compare it with experimental values. The results, when Deltaalpha(0)=1.17x10(-28)Fm(2), Deltaalpha(infinity)=0.005x10(-28)Fm(2) and K=0.00031 m/V, are in good agreement with each other. In order to explain the reason why the anisotropy of electric polarizability rapidly decreases with an increase of electric field we propose that the difference of electrophoretic mobility between parts of colloidal particle causes the orientation of a rod like particle. The theoretical electric birefringence as a function of electric field we obtained is considerably in good agreement with the experimental values.
由原硅酸钠和三氯化铝合成的伊莫戈石通过在12,000×g（1小时）下离心分离为四个级分。经过三次离心仍未沉淀的上清液用于所有测量。反向电脉冲下的双折射信号表明，在低场下永久偶极矩小到可以忽略不计。矩形电脉冲下的电双折射为正。饱和值在0 - 0.1mg/ml范围内与伊莫戈石的浓度成正比，并且随着NaCl和AgNO₃添加盐浓度的增加而迅速降低。它略微依赖于溶液的pH值，在纯水中最大。然后我们测定了0.05mg/ml纯水中伊莫戈石的电极化率各向异性（Δα）。我们从该方法获得的Δα在低场下迅速降低，在高场下缓慢降低，如参考文献[M. Matsumoto, Colloids Surf. A 148 (1999) 75, M. Matsumoto, Biophys. Chem. 58 (1996) 173]所示。它大约由以下表达式表示，Δα = Δα(∞)+(Δα(0) - Δα(∞))/(1 + KE)，（Δα(0)：E = 0时的Δα，Δα(∞)：E = ∞时的Δα）。使用此关系我们可以绘制电双折射随电场变化的曲线，并将其与实验值进行比较。当Δα(0)=1.17×10⁻²⁸Fm²，Δα(∞)=0.005×10⁻²⁸Fm²和K = 0.00031 m/V时，结果彼此非常吻合。为了解释电极化率各向异性随电场增加而迅速降低的原因，我们提出胶体颗粒各部分之间电泳迁移率的差异导致棒状颗粒的取向。我们获得的作为电场函数的理论电双折射与实验值相当吻合。
