ABSTRACT
I. INTRODUCTION The solid-electrolyte interface takes a variety of geometrical expressions in the nanometer scale. Figure 1 illustrates some examples of these “solid”–electrolyte interfaces. The classical picture of Figure 1(a) is a charged planar rigid surface meeting a semi-infinite region of electrolyte solution. Induced by fixed charges of the solid surface, a differential distribution of ions forms in the solution layer adjacent to the interface. This electrochemical double layer has been a focus of investigations in electrochemistry and related fields such as colloids, materials science, and biology. Classical theories of Gouy-Chapman [1,2] and Stern [3] for the electrochemical double layer have formed the basis for intelligible interpretation of experiments and for useful applications in electrochemical and materials technologies. An electrolyte confined between two surfaces separated by nanometer dimensions behaves differently compared to the case of an open semi-infinite boundary. This confined situation can be found in colloids, as shown in Figure 1(b), or in a porous solid or membranes, as shown in Figure 1(c). The confining boundary or internal pores can be with or without fixed wall charges. Complexity increases with the dynamics of the fixed charges or solid structures in the molecular scale. In Figure 1(d), the dynamic surface structure of a polyelectrolyte (or macroion) has an interdependent relationship with other electrolyte and polyelectrolyte molecules in the solution. An important area is the study of protein folding, where, at the moment, consideration of interaction with explicit electrolyte molecules is rare. One class of these polyelectrolytes is ionic surfactants. Different levels of ordering in ionic or nonionic amphiphilic molecules can lead to a monolayer structure or a microemulsion, as shown in Figure 1(e), and a bilayer membrane with pores, as shown in Figure 1(f). Modern technology has exploited the nanoscopic domains, and important applications can be found in these nano-electrolyte interfaces in Figure 1. One example is the application of scanning probe microscopy in a solution environment. The scanning tip interacts closely with the solid surface and the electrolyte. The scanning tip can be that of an atomic force microscope (AFM), a scanning tunneling microscope (STM), or a near-field scanning optical microscope (NSOM).
