Collapsed Structure of Hydrophobically Modified Polyacrylamide Adsorbed at the Air-Water Interface: The Polymer Surface Excess and the Gibbs Equation

Neutron reflection and the thermodynamics of the air-water interface

By means of isotopic substitution, measurements of the neutron reflectivity (NR) from a flat water surface generally give model independent measurements of the amount of a chosen solute at the surface irrespective of whether the layer is a mixture or whether there is any aggregation in the bulk solution. Previously, adsorption at air-water interfaces has been determined by applying the Gibbs equation to surface tension (ST) measurements, which requires assumptions about the composition of the surface and about the activity of the solute in the bulk, which, in turn, means that in practice the surface is assumed to consist of the pure solute or of a mixture of pure solutes, and that the activity of the solute in the bulk solution is known. The use of NR in combination with ST-Gibbs measurements makes it possible to (i) avoid these assumptions and hence understand several patterns of ST behaviour previously considered to be anomalous and (ii) to start to analyse quantitatively the behaviour of mixed surfactants both below and above the critical micelle concentration. These two developments in our understanding of the thermodynamics of the air-water interface are described with recent examples.

Liquid Metal Interfacial Growth and Exfoliation to Form Mesoporous Metallic Nanosheets for Alkaline Methanol Electroreforming

Two-dimensional (2D) materials have spurred great interest in the field of catalysis due to their fascinating electronic and thermal transport properties. However, adding uniform mesopores to 2D metallic materials has remained a great challenge owing to the inherent high surface energy. Here, we introduce a generic liquid metal interfacial growth and exfoliation strategy to synthesize a library of penetrating mesoporous metallic nanosheets. The formation of liquid-metal/water interface promotes the adsorption of metal ion-encapsulated copolymer micelles, induces the self-limiting galvanic replacement reaction, and enables the exfoliation of products under mechanical agitation. These 2D mesoporous metallic nanosheets with large lateral size, narrow thickness distribution, and uniform perforated structure provide facilitated channels and abundant active sites for catalysis. Typically, the generated mesoporous PtRh nanosheets (mPtRh NSs) exhibit superior electroactivity and durability in hydrogen evolution reaction as well as methanol electrooxidation in alkaline media. Moreover, the constructed symmetric mPtRh NSs cell requires only a relative low electrolysis voltage to achieve methanol-assisted hydrogen production compared with traditional overall water electrolysis. The work reveals a specific growth pattern of noble metals at the liquid-metal/water interface and thus introduces a versatile strategy to form 2D penetrating mesoporous metallic nanomaterials with extensive high-performance applications.