Gaddam Prudhvidhar, Ducker William
Department of Chemical Engineering and Center for Soft Matter, Biological Physics , Virginia Tech , Blacksburg , Virginia 24061 , United States.
Langmuir. 2019 Apr 30;35(17):5719-5727. doi: 10.1021/acs.langmuir.9b00375. Epub 2019 Apr 17.
Thin films (0-30 nm) of very concentrated aqueous monovalent salt solutions (2-10 M of LiCl, NaCl, and CsCl) were examined to determine how ionic strength affects the screening length of the electrostatic potential. Measurements were consistent with a screening length in the range of 3-12 nm. The screening length increased monotonically as a function of salt concentration, and the rate of increase was a function of the monovalent salt type. The results were incompatible with the Debye length of Poisson-Boltzmann theory but consistent with previous measurements of surface forces. The screening length was determined from the surface excess of fluorescein, a dianion under basic conditions, which was present in trace amounts in the thin film and detected via its fluorescence emission. That is, we directly observed that the ion concentration in very concentrated solutions is perturbed far from an interface.
研究了非常浓的单价盐溶液（2 - 10 M的LiCl、NaCl和CsCl）的薄膜（0 - 30 nm），以确定离子强度如何影响静电势的屏蔽长度。测量结果与3 - 12 nm范围内的屏蔽长度一致。屏蔽长度随盐浓度单调增加，且增加速率是单价盐类型的函数。结果与泊松 - 玻尔兹曼理论的德拜长度不相符，但与先前的表面力测量结果一致。屏蔽长度由荧光素的表面过量确定，荧光素在碱性条件下为二价阴离子，在薄膜中以痕量存在，并通过其荧光发射进行检测。也就是说，我们直接观察到在非常浓的溶液中离子浓度在远离界面处受到扰动。
