Hunter Harry C, Ray Asit K
Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506-0045, USA.
Phys Chem Chem Phys. 2009 Aug 7;11(29):6156-65. doi: 10.1039/b820457h. Epub 2009 May 20.
The charge level at which a drop undergoes a Coulombic fission is given by the Rayleigh limit. The charge and mass losses from the drop during the fission and the characteristics of resulting progeny droplets, however, remain unpredictable. The charge of a dielectric drop arises from ions, and we have examined the effects of ions on fission-related charge and mass emissions from single levitated microdrops. The ion concentration in a drop was varied through addition of appropriate amounts of an ionophore or ionic liquid. The results show that the mass loss from a drop decreases, while the charge-to-mass ratio of progeny droplets increases as the ion concentration in the drop increases. From these observations we establish that nonuniform ion distributions that exist in a charged dielectric drop play a dominant role in the fission process by influencing the electrical conductivity at the drop surface. We show that the charge-to-mass ratio of progeny droplets is proportional to the conductivity at the surface of the mother drop, which has been calculated from the mobilities of ions and ion concentrations at the surface of the mother drop. By minimizing the Gibbs free energy change associated with a Coulombic fission we deduce that a progeny droplet carries 50% of the Rayleigh limit charge, and from the experimental data we establish that the progeny droplet size varies inversely to the surface conductivity raised to the power of 2/3.
液滴发生库仑裂变时的电荷水平由瑞利极限给出。然而，裂变过程中液滴的电荷和质量损失以及产生的子液滴的特性仍然无法预测。介电液滴的电荷来自离子，我们研究了离子对单个悬浮微滴裂变相关的电荷和质量发射的影响。通过添加适量的离子载体或离子液体来改变液滴中的离子浓度。结果表明，随着液滴中离子浓度的增加，液滴的质量损失减少，而子液滴的电荷质量比增加。从这些观察结果中我们确定，带电介电液滴中存在的不均匀离子分布通过影响液滴表面的电导率在裂变过程中起主导作用。我们表明，子液滴的电荷质量比与母液滴表面的电导率成正比，该电导率是根据母液滴表面离子的迁移率和离子浓度计算得出的。通过最小化与库仑裂变相关的吉布斯自由能变化，我们推断子液滴携带瑞利极限电荷的50%，并且从实验数据中我们确定子液滴尺寸与表面电导率的2/3次方成反比。
