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Ion distributions play a central role in various settings-from biology, where they mediate the electrostatic interactions between charged biomolecules in solution, to energy storage devices, where they influence the charging properties of supercapacitors. These distributions are determined by interactions dictated by the chemical properties of the ions and their environment as well as the long-range nature of the electrostatic force. Recent theoretical and computational studies have explored the role of correlations between ions, which have been suggested to underlie a number of counterintuitive results, such as like-charge attraction. However, the interdependency between ion correlations and other interactions that ions experience in solution complicates the connection between physical models of ion correlations and the experimental investigation of ion distributions. We exploit the properties of the liquid/liquid interface to vary the coupling strength Γ of ion-ion correlations from weak to strong while monitoring their influence on ion distributions at the nanometer scale with X-ray reflectivity and the macroscopic scale with interfacial tension measurements. These data are in agreement with the predictions of a parameterfree density functional theory that includes ion-ion correlations and ion-solvent interactions over the entire range of experimentally tunable correlation coupling strengths (from 0.8 to 3.7). This study provides evidence for a sharply defined electrical double layer for large coupling strengths in contrast to the diffuse distributions predicted by mean field theory, thereby confirming a common prediction of many ion correlation models. The reported findings represent a significant advance in elucidating the nature and role of ion correlations in charged soft matter.liquid surface scattering | ion density profile | surface excess charge | Poisson-Boltzmann | Debye-Hückel hole T he works by Gouy (1) and Chapman (2) introduced the Poisson-Boltzmann (PB) equation to describe the distribution of ions and the accompanying variation of electric potential at the interface between a charged planar electrode and an electrolyte solution (1, 2). This seminal theory considered point-like ions interacting through their mean electric field in a continuum solvent but neglected both chemically specific ion-solvent interactions and correlations between ions. Specific ion interactions are exemplified by the well-known Hofmeister series (3). The study of ion correlations has been motivated by observations of the reentrant condensation of DNA (4) and proteins (5) in solution, in which like-charged biomolecules aggregate in the presence of multivalent ions, and reports of charge reversal in colloidal suspensions, in which the sign of the screened charge on a colloid can be changed by varying the surrounding electrolyte solution (6, 7).Correlations between ions that are caused by their electrostatic interactions are expected to be important when the average electrostatic interaction energy between neighboring ions...

Scanning probe microscopy (SPM) techniques have opened the door to nanoscience and nanotechnology by enabling imaging and manipulation of the structure and functionality of matter at nanometer and atomic scales. Here, we analyze the scientific discovery process in SPM by following the information flow from the tip-surface junction, to knowledge adoption by the wider scientific community. We further discuss the challenges and opportunities offered by merging SPM with advanced data mining, visual analytics, and knowledge discovery technologies.

This document contains supporting information on experimental details, model-independent analyses of the RAXR data, analyses of ion uptake by RAXR, estimations on the distance between individual adsorbed Y 3+ species, and six figures (S1-S6).

The interface between minerals and aqueous solutions hosts globally important biogeochemical processes such as the growth and dissolution of carbonate minerals. Understanding such processes requires spatially and temporally resolved observations and experimental controls that precisely manipulate the interfacial thermodynamic state. Using the intense radiation fields of a focused synchrotron x-ray beam, we drove dissolution at the calcite/water interface and simultaneously probed the dynamics of the propagating reaction fronts using surface x-ray microscopy. Evolving surface structures were controlled by the time-dependent solution composition, as characterized by a kinetic reaction model. At extreme disequilibria, we observed the onset of reaction front instabilities with velocities of > 30 nanometers per second. These instabilities serve as a signature of transport-limited dissolution of calcite under extreme disequilibrium.