Capillary sorting of fiber suspensions by dip coating

TL;DR

This paper introduces a capillary dip coating method to selectively sort fibers in suspensions by length or diameter, improving sorting control and efficiency over traditional filtration techniques.

Contribution

It demonstrates a novel capillary filtration technique using dip coating to achieve controlled fiber sorting by size, with practical guidelines for implementation.

Findings

Fibers are primarily sorted by diameter during substrate withdrawal.

Sorting by length is achieved with cylindrical substrates under specific conditions.

Guidelines for designing efficient capillary sorting processes are provided.

Abstract

Sorting elongated anisotropic particles, such as fibers, dispersed in suspensions poses significant challenges as they present two characteristic dimensions: length and diameter. Fibers in suspension usually align with the flow, leading to diameter-based filtration when passing through a sieve. Modifying the flow conditions by introducing more mixing so that fibers are arbitrarily oriented can lead to sorting by diameter and length simultaneously, resulting in a lower filtration quality. In this paper, we demonstrate that capillary filtration by dip coating can be utilized to selectively sort fibers by length or by diameter in a controlled manner. Using the withdrawal of a flat substrate from a fiber suspension, we demonstrate that fibers are primarily sorted by their diameters. When considering cylindrical substrates, fibers can be sorted by length under appropriate conditions due to the orientation adopted by the fibers during their entrainment. We report guidelines for designing this filtration process and obtaining good sorting efficiency.