Consta Styliani
Department of Chemistry, The University of Western Ontario, London, Ontario, CanadaN6A 5B7.
Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EWUnited Kingdom.
J Phys Chem B. 2022 Oct 20;126(41):8350-8357. doi: 10.1021/acs.jpcb.2c05849. Epub 2022 Oct 6.
The first atomistic simulations that reveal the mechanism of Rayleigh fission are presented. It is demonstrated that simple ion or macroion ejection takes place through droplet deformation from a spherical into a distinct "tear" shape that contains a conical protrusion. We assert that the latter state is a free-energy minimum along an order parameter that measures the degree of droplet asphericity. The charged droplet's long-time evolution proceeds by alternating between the two minima above and below the critical value that are reached through solvent evaporation and ion ejection, respectively. For the first time, this mechanism allows one to explain the nature of the progeny droplets and the percentage of charge lost during fission. The cone half angle is estimated and found to be in good agreement with the value predicted from the solution of the electrostatic equation for the dielectric liquid. It is found that the conical deformation is independent of the effect of electrohydrodynamic forces reported in experiments. Contrary to the experimental observations of two diametrically opposite jets for droplets suspended in the electric field, we find that a single jet is formed at the Rayleigh limit. The study provides insight into the mechanism of capture of a macroion in jets appearing in electrospray ionization mass spectrometry (ESI-MS) experiments and may explain the tolerance of the ESI-MS spectrum to salt contamination of the sample.
本文展示了首批揭示瑞利裂变机制的原子模拟。结果表明，简单离子或大离子的喷射是通过液滴从球形变形为独特的“泪滴”形状来实现的，该形状包含一个锥形突起。我们断言，后一种状态是沿着一个测量液滴非球形程度的序参量的自由能最小值。带电液滴的长期演化是通过分别通过溶剂蒸发和离子喷射达到的临界值上下的两个最小值之间交替进行的。首次，这种机制使人们能够解释子代液滴的性质以及裂变过程中损失的电荷百分比。估计了锥半角，发现与介电液体静电方程解预测的值非常吻合。发现锥形变形与实验中报道的电流体动力效应无关。与电场中悬浮液滴的两个直径相反的射流的实验观察结果相反，我们发现在瑞利极限处形成单个射流。该研究深入了解了电喷雾电离质谱（ESI-MS）实验中出现的射流中大离子的捕获机制，并可能解释ESI-MS谱对样品盐污染的耐受性。
