Nanoscale capillary freezing of ionic liquids confined between metallic interfaces and the role of electronic screening

Abstract

Room temperature Ionic liquids (RTIL) are new materials with fundamental importance for energy storage and active lubrication. They are unsual liquids, which challenge the classical frameworks of electrolytes, whose behavior at electrified interfaces remains elusive with exotic responses relevant to their electrochemical activity. By means of tuning fork based AFM nanorheological measurements, we explore here the properties of confined RTIL, unveiling a dramatic change of the RTIL towards a solid-like phase below a threshold thickness, pointing to capillary freezing in confinement. This threshold is related to the metallic nature of the confining materials, with more metallic surfaces facilitating freezing. This is interpreted in terms of the shift of freezing transition, taking into account the influence of the electronic screening on RTIL wetting of the confining surfaces. Our findings provide fresh views on the properties of confined RTIL with implications for their properties inside nanoporous metallic structures and suggests applications to tune nanoscale lubrication with phase-changing RTIL, by varying the nature and patterning of the substrate, and application of active polarisation.

Solidification and superlubricity with molecular alkane films

“…T he dynamics of nano-confined liquids are central to processes such as filtration, energy storage, lubrication, cell membrane pumps and channels, and a multitude of other technological and biological scenarios. When the confinement lengthscale is comparable to the molecular size of the contained liquid a spectrum of dynamic phenomena are possible depending on the detailed intermolecular and surface interactions at play (1)(2)(3)(4)(5)(6). In light of such strong relevance it is surprising that one of the simplest model systems of confined fluid -a non-polar molecular liquid confined between two atomically smooth surfaces -still evades full explanation.…”

Substrate-Induced Liquid Layering: A New Insight into the Heterogeneous Nucleation of Liquid Metals

“…It is necessary to explore the factors that might contribute to these differences. The surface roughness of the substrate is a vital factor that greatly influences the behaviors of the nearsurface layering or the self-assembly of atoms (or molecules) [8,53,54]. In this work, we focus on the atomically smooth surfaces, and our results show that when liquid Al is in contact with the atomically smooth surfaces of (0001) sapphire and (0001) TiB2, stratified liquid structures develop spontaneously.…”

“…These ordered structures may manifest as clusters with unique symmetry (such as the well-assumed icosahedral structure [3]) or quasi-layers [4][5][6][7][8][9]. The former mainly occur in the systems absence of inoculation [3] and the latter have frequently been observed near the atomically smooth surfaces [10][11][12][13].…”

“…The former mainly occur in the systems absence of inoculation [3] and the latter have frequently been observed near the atomically smooth surfaces [10][11][12][13]. In this work, we focus on the substrate-induced liquid layers, which have been extensively studied in the field of lubrication, epitaxial growth, superhydrophobic materials [6], energy-storage materials [8,14], etc. Apart from the aforementioned applications, the liquid layers have also been interpreted as pre-nucleation structures [15,16], which can enhance or weaken the nucleation process [7,17] and dictate their structural features.…”

Tracer diffusion in crowded narrow channels

“…(26) (with the factor 1/4 replaced by 1/(2d)) and with P (r|0; z) given in eq. (27) in case of two-dimensional strips, and by a bit more complicated expression describing the propagator of a random walk in case of threedimensional capillaries (see Ref. [137] for more details).…”