Liquid Heterostructures: Generation of Liquid-Liquid Interfaces in Free-Flowing Liquid Sheets

TL;DR

This paper introduces a microfluidic method to create large-area, thin liquid-liquid interfaces within free-flowing sheets, enabling detailed spectroscopic and scattering studies of these interfaces.

Contribution

It presents a novel technique for generating and characterizing tunable, multilayered liquid heterostructures with well-defined interfaces suitable for advanced spectroscopic analysis.

Findings

Liquid-liquid interfaces can be generated within free-flowing sheets.

The inner layer thickness can be tuned below 100 nm.

The method allows for spectroscopic access to the interfaces.

Abstract

Chemical reactions and biological processes are often governed by the structure and transport dynamics of the interface between two liquid phases. Despite their importance, our microscopic understanding of liquid-liquid interfaces has been severely hindered by difficulty in accessing the interface through the bulk liquid. Here we demonstrate a method for generating large-area liquid-liquid interfaces within free-flowing liquid sheets, which we call liquid heterostructures. These sheets can be made thin enough to transmit photons from across the spectrum, which also minimizes the amount of bulk liquid relative to the interface and makes them ideal targets for a wide range of spectroscopies and scattering experiments. The sheets are produced with a microfluidic nozzle that impinges two converging jets of one liquid onto two sides of a third jet of another liquid. The hydrodynamic forces provided by the colliding jets both produce a multilayered laminar liquid sheet with the central jet is flattened in the middle. Infrared microscopy, white light reflectivity, and imaging ellipsometry measurements demonstrate that the buried layer has a tunable thickness and displays well-defined liquid-liquid interfaces, and that the inner layer can be thinner than 100 nm.