Explaining the low-frequency shear elasticity of confined liquids

Experimental observations of unexpected shear rigidity in confined liquids, on very low frequency scales on the order of 0.01 to 0.1 Hz, call into question our basic understanding of the elasticity of liquids and have posed a challenge to theoretical models of the liquid state ever since. Here we combine the nonaffine theory of lattice dynamics valid for disordered condensed matter systems with the Frenkel theory of the liquid state. The emerging framework shows that applying confinement to a liquid can effectively suppress the low-frequency modes that are responsible for nonaffine soft mechanical response, thus leading to an effective increase of the liquid shear rigidity. The theory successfully predicts the scaling lawG′∼L−3for the low-frequency shear modulus of liquids as a function of the confinement length L, in agreement with experimental results, and provides the basis for a more general description of the elasticity of liquids across different time and length scales.

Hybrid nanocapsules for in situ TEM imaging of gas evolution reactions in confined liquids

Gold-coated liposome nanocapsules enable in situ TEM imaging and mixing of nanoscale reactions confined in zeptoliter volumes.

Surface forces measurement for materials science

This article reviews the surface forces measurement as a novel tool for materials science. The history of the measurement is briefly described in the Introduction. The general overview covers specific features of the surface forces measurement as a tool for studying the solid-liquid interface, confined liquids and soft matter. This measurement is a powerful way for understanding interaction forces, and for characterizing (sometime unknown) phenomena at solid-liquid interfaces and soft complex matters. The surface force apparatus (SFA) we developed for opaque samples can study not only opaque samples in various media, but also electrochemical processes under various electrochemical conditions. Electrochemical SFA enables us to determine the distribution of counterions between strongly bound ones in the Stern layer and those diffused in the Gouy-Chapman layer. The shear measurement is another active area of the SFA research. We introduced a resonance method, i.e. the resonance shear measurement (RSM), that is used to study the effective viscosity and lubricity of confined liquids in their thickness from μm to contact. Advantages of these measurements are discussed by describing examples of each measurement. These studies demonstrate how the forces measurement is used for characterizing solid-liquid interfaces, confined liquids and reveal unknown phenomena. The readers will be introduced to the broad applications of the forces measurement in the materials science field.