Extended Data Fig. 8: Dynamics of the interfacial structure on mica surface in 20 mM MgCl2 at various pH values.
From: How charge frustration causes ion ordering and microphase separation at surfaces
a, b, Before pH 10, there is very weak adsorption observed on the mica surface, as shown in (a) at pH 3.4 and (b) at pH 6.9. c,d, Once the pH is raised to 10, where Mg(OH)2 becomes supersaturated, monolayered Mg(OH)2 films start to form on the mica surface. The thickness of the film is around 0.5 nm, which is close to the thickness of a layer of brucite, but the film is not well-crystalline, as shown in (d). e, A high-resolution AFM image of the mica surface in 20 mM MgCl2, where some contrasts are observed, but no obvious interfacial structure due to ion adsorption is seen, unlike in trivalent ion electrolytes. f, A time averaged image of over 100 frames (shown in Movie S5). It is likely that the brighter spots correspond to regions with a higher probability of Mg2+ adsorption. g, A space-correlated averaged image showing the mica lattice structure. h-l, A time series of the nucleation of the Mg(OH)2 films on mica in 20 mM MgCl2 at pH 10. Combined with the AFM data showing the growth kinetics in Fig. 4, the formation of these films is consistent with the prediction of classical nucleation theory for two-dimensional systems.
