A Study of the Evaporative Deposition Process: Pipes and Truncated Transport Dynamics

TL;DR

This paper models the contact line deposition process in evaporating drops using truncated transport dynamics, deriving deposit profiles, and predicting pattern formation consistent with empirical observations.

Contribution

It introduces 'pipe models' with shock front solutions to describe deposit formation, extending previous models and providing new analytical insights.

Findings

Deposit density near contact line follows a square root scaling law.

Maximal deposit occurs at about 2/3 of drying time for uniform evaporation.

Deposit profile exhibits power-law decay with radial distance.

Abstract

We consider contact line deposition and pattern formation of a pinned evaporating thin drop. We identify and focus on the transport dynamics truncated by the maximal concentration, proposed by Dupont, as the single deposition mechanism. The truncated process, formalized as "pipe models", admits a characteristic moving shock front solution that has a robust functional form and depends only on local conditions. By applying the models, we solve the deposition process and describe the deposit density profile in different asymptotic regimes. In particular, near the contact line the density profile follows a scaling law that is proportional to the square root of the concentration ratio, and the maximal deposit density/thickness occurs at about 2/3 of the total drying time for uniform evaporation and 1/2 for diffusion-controlled evaporation. Away from the contact line, we for the first time identify the power-law decay of the deposit profile with respect to the radial distance. In comparison, our work is consistent with and extends previous results. We also predict features of the depinning process and multiple-ring patterns within Dupont model, and our predictions are consistent with empirical evidence.