Experimental Verification of "Electrodynamic" Interaction

我们提出了“电动力相互作用”作为胶体晶体形成的驱动力。为了阐明离子聚合物粒子间这种新作用力的机理，我们用超小角x射线散射（USAXS）进行了系统的实验。胶体晶体中的粒子间距离随着离子强度的增加而减小。然而，当添加盐浓度低于10^<-5>M时，它增加了。这一事实意味着胶体粒子之间的有效相互作用应该是一个有吸引力的相互作用，但它应该基于与已经提出的理论不同的机制。我们认为粒子周围的反离子对胶体晶体的形成起着重要的作用。作为第一个实验，我们将反离子从质子变为钠离子。随着质子与钠离子的交换，粒子间距离发生了变化。这一事实无疑意味着粒子间的相互作用受到反离子种的影响。其次，我们使用钾、锂和四甲基铵（TMA）离子作为反离子。USAXS评估的粒子间距离同样依赖于反离子种类。这些离子使吸引相互作用弱于质子，这种作用的强弱顺序为钾>钠>TMA=锂。这一顺序与阳离子的表面电荷密度即反离子的扩散常数的顺序是一致的。因此，我们可以得出如下结论：(1)当离子强度小于10^<-5>M时，“电动力相互作用”有效。(2)在此条件下，反离子气氛高度重叠。(3)大气中的反离子可以移动到胶体晶体的任何地方。(4)相互作用力取决于反扩散速度。(5)只有当反离子为质子时，才能观察到强吸引相互作用。因此，引力的来源应该是质子异常高的电导率。

We have proposed "Electrodynamic Interaction" as a driving force of colloidal crystal formation. To clarify the mechanism of this novel force between ionic polymer particles, we have performed the systematic experiment by ultra-small-angle X-ray scattering (USAXS). The interparticle distance in the colloidal crystal was believed to decrease with increasing ionic strength. However, we found that it increased when added salt concentration is below 10^<-5>M. This fact means the effective interaction between colloidal particles should be an attractive one, which should based on difference mechanism from the theory already proposed, however. We thought that the counterions around particles have an important role for colloidal crystal formation. As the first experiment, we changed counterion species from proton to sodium ion. With exchanging from proton to sodium ion, the interpaticle distance changed. This fact certainly means that the interpaticle interaction is affected by counterion species. Secondaly, we used potassium, lithium, and tetramethylammonium (TMA) ions as counterions. The interparticle distance evaluated by USAXS again depended on the counterions species. These ions made the attractive interaction weaker than proton, and this effect is stronger in the order of potassium>sodium>TMA=lithium. This order is in good agreement in that for surface charge density of these cations, i.e. diffusion constant of counterions. Hence, we can conclude as following;(1) "Electrodynamic Interaction" is effective when ionic strength is below 10^<-5>M.(2) At this condition, the counterion atmosphere is highly overlapped.(3) The counterions in atmosphere can move anywhere in the colloidal crystal.(4) The interaction force depends on speed of counterion diffusion.(5) The strong attractive interaction is observed only when counterion is proton. Hence, the origin of attraction should be anomalously high electric conductivity of protons.