The effect of nanometre-scale structure on interfacial energy

Abstract

Natural surfaces are often structured with nanometre-scale domains, yet a framework providing a quantitative understanding of how nanostructure affects interfacial energy, gamma(SL), is lacking. Conventional continuum thermodynamics treats gamma(SL) solely as a function of average composition, ignoring structure. Here we show that, when a surface has domains commensurate in size with solvent molecules, gamma(SL) is determined not only by its average composition but also by a structural component that causes gamma(SL) to deviate from the continuum prediction by a substantial amount, as much as 20% in our system. By contrasting surfaces coated with either molecular- (<2 nm) or larger-scale domains (>5 nm), we find that whereas the latter surfaces have the expected linear dependence of gamma(SL) on surface composition, the former show a markedly different non-monotonic trend. Molecular dynamics simulations show how the organization of the solvent molecules at the interface is controlled by the nanostructured surface, which in turn appreciably modifies gamma(SL).

Direct mapping of the solid–liquid adhesion energy with subnanometre resolution

“…It is apparent that there is good agreement in both water and DMSO for all of the samples studied. We have also found good agreement for mixed self-assembled monolayers on flat surfaces as well as on gold nanoparticles 31 . The linear regression plot illustrates the quality of the agreement and proves that the linear relationship between the two values is statistically significant.…”

In Situ Mapping of the Molecular Arrangement of Amphiphilic Dye Molecules at the TiO2 Surface of Dye-Sensitized Solar Cells

“…In these particular imaging conditions, the energy dissipated by the vibrating AFM tip is not sufficient to fully remove the liquid between the tip and the sample, and the tip mainly probes the properties of the interfacial liquid at the surface of the sample. 12,22,28 The phase contrast is then related to the local 'wetting' properties of 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 6 the sample, i.e. the local solvation free energy 12,22 or, at the macroscopic level, the solid-liquid work of adhesion.…”

“…12,22,28 The phase contrast is then related to the local 'wetting' properties of 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 6 the sample, i.e. the local solvation free energy 12,22 or, at the macroscopic level, the solid-liquid work of adhesion. In practice, imaging over the TiO 2 substrate provides a darker phase contrast than over the Z907 regions, indicating a higher affinity of the solvent for the substrate than for the dye-covered surface (Fig.…”

“…This phase contrast indicates a higher affinity of the solvent for the TiO 2 than for the dye, and could be consistently used throughout this study to identify dye-covered (light) and uncovered (dark) regions. 12,22 At 30 % mass coverage, the dye layer exhibits dark spots in the phase, suggesting that uniform gaps exist between the adsorbed Z907 molecules. These gaps give the apparent sponge-like appearance to the dye layer topography.…”

Water-induced correlation between single ions imaged at the solid–liquid interface

“…When operated in liquid, AFM is able to investigate solid-liquid interfaces locally, often with atomic-or molecular-level resolution [22][23][24][25][26][27][28][29][30][31] and in the presence of ions [32][33][34][35][36] . Studies allowing a clear and unequivocal identification of single ions within a Stern layer are however still sparse, with little information about the formation, stability and dynamics of adsorbed ions at the nanoscale.…”