Flow of thin liquid films on chemically structured substrates

TL;DR

This paper explores the fundamental differences in liquid flow behavior on chemically patterned substrates when transitioning from micron-scale to nanometer-scale, emphasizing molecular interactions and thermal fluctuations.

Contribution

It identifies key conceptual differences and formulates design issues for nanofluidic devices based on these scale-dependent effects.

Findings

Differences in triple line structure at nanoscale

Impact of molecular interactions on flow behavior

Design considerations for nanofluidic channels

Abstract

Chemically patterned surfaces are of significant interest in the context of microfluidic applications. Miniaturization of such devices will eventually lead to structures on the nano-scale. Whereas on the micron scale purely macroscopic descriptions of liquid flow are valid, on the nanometer scale long-ranged inter-molecular interactions, thermal fluctuations such as capillary waves, and finally the molecular structure of the liquid become important. We discuss the most important conceptual differences between flow on chemically patterned substrates on the micron scale and on the nanometer scale. These concern the structure of the triple line, the type of interactions between neighboring liquid flows, and the influence of the molecular structure of the liquid on the flow. We formulate four design issues for nanofluidics related to channel width, channel separation, and channel bending radius, and conclude with a discussion of the relevance of the conceptual differences between the micron scale and the nanometer scale for these issues.