Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200, Australia.
Phys Chem Chem Phys. 2011 Jul 21;13(27):12352-67. doi: 10.1039/c1cp20538b. Epub 2011 Jun 14.
The classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloids, and corresponding theories of electrolytes, are unable to explain ion specific forces between colloidal particles quantitatively. The same is true generally, for surfactant aggregates, lipids, proteins, for zeta and membrane potentials and in adsorption phenomena. Even with fitting parameters the theory is not predictive. The classical theories of interactions begin with continuum solvent electrostatic (double layer) forces. Extensions to include surface hydration are taken care of with concepts like inner and outer Helmholtz planes, and "dressed" ion sizes. The opposing quantum mechanical attractive forces (variously termed van der Waals, Hamaker, Lifshitz, dispersion, nonelectrostatic forces) are treated separately from electrostatic forces. The ansatz that separates electrostatic and quantum forces can be shown to be thermodynamically inconsistent. Hofmeister or specific ion effects usually show up above ≈10(-2) molar salt. Parameters to accommodate these in terms of hydration and ion size had to be invoked, specific to each case. Ionic dispersion forces, between ions and solvent, for ion-ion and ion-surface interactions are not explicit in classical theories that use "effective" potentials. It can be shown that the missing ionic quantum fluctuation forces have a large role to play in specific ion effects, and in hydration. In a consistent predictive theory they have to be included at the same level as the nonlinear electrostatic forces that form the skeletal framework of standard theory. This poses a challenge. The challenges go further than academic theory and have implications for the interpretation and meaning of concepts like pH, buffers and membrane potentials, and for their experimental interpretation. In this article we overview recent quantitative developments in our evolving understanding of the theoretical origins of specific ion, or Hofmeister effects. These are demonstrated through an analysis that incorporates nonelectrostatic ion-surface and ion-ion dispersion interactions. This is based on ab initio ionic polarisabilities, and finite ion sizes quantified through recent ab initio work. We underline the central role of ionic polarisabilities and of ion size in the nonelectrostatic interactions that involve ions, solvent molecules and interfaces. Examples of mechanisms through which they operate are discussed in detail. An ab initio hydration model that accounts for polarisabilities of the tightly held hydration shell of "cosmotropic" ions is introduced. It is shown how Hofmeister effects depend on an interplay between specific surface chemistry, surface charge density, pH, buffer, and counterion with polarisabilities and ion size. We also discuss how the most recent theories on surface hydration combined with hydrated nonelectrostatic potentials may predict experimental zeta potentials and hydration forces.
胶体的经典德贾古林-兰德弗韦尔-奥弗贝克（DLVO）理论以及相应的电解质理论，都无法定量解释胶体颗粒之间的离子特异性力。对于表面活性剂聚集体、脂质、蛋白质、zeta 和膜电位以及吸附现象，通常也是如此。即使使用拟合参数，该理论也没有预测能力。经典的相互作用理论始于连续溶剂静电（双电层）力。通过内和外亥姆霍兹平面以及“修饰”离子大小等概念来处理包括表面水合作用在内的扩展。相反的量子力学吸引力（各种称为范德华、哈马克、利夫希茨、分散、非静电相互作用）与静电力分开处理。将静电和量子力分开的假设可以证明在热力学上是不一致的。Hofmeister 或特定离子效应通常出现在 ≈10(-2)摩尔盐以上。必须根据水合作用和离子大小来调用这些参数，每个案例都是特定的。在使用“有效”势的经典理论中，离子-离子和离子-表面相互作用之间的离子溶剂色散力不明确。可以证明，缺失的离子量子涨落力在特定离子效应和水合作用中起着重要作用。在一致的预测性理论中，它们必须与形成标准理论骨架框架的非线性静电力处于同一水平。这带来了挑战。挑战不仅限于学术理论，还涉及 pH 值、缓冲液和膜电位等概念的解释和意义，以及它们的实验解释。在本文中，我们概述了我们对特定离子或 Hofmeister 效应理论起源的不断发展的理解的最新定量发展。通过分析，这些得到了证明，该分析纳入了非静电离子-表面和离子-离子色散相互作用。这是基于从头算离子极化率以及最近从头算工作量化的有限离子大小。我们强调了离子极化率和离子大小在涉及离子、溶剂分子和界面的非静电相互作用中的核心作用。详细讨论了它们运作的机制示例。引入了一种从头算水化模型，该模型考虑了“亲溶”离子紧密保持的水化壳的极化率。结果表明，Hofmeister 效应取决于特定表面化学、表面电荷密度、pH 值、缓冲液和与极化率和离子大小有关的抗衡离子之间的相互作用。我们还讨论了最近关于表面水合作用的理论如何与水合非静电势结合以预测实验 zeta 电位和水合力。
