Improved Size Uniformity of Microcapillaries in Microcapillary Films by Separate Gas Injection

Abstract

Microcapillary films (MCFs) are microextrusion-processed plastic films containing an array of parallel microcapillaries, and have been widely utilized as microfluidic platforms. However, the nonuniform size distribution within a single MCF strip limits the application of MCFs in monodisperse droplet generation. In this paper, the mechanisms that lead to uneven microcapillary dimensions in conventional MCFs whose gas pressures in all channels are the same is first clarified. The effect of gas pressure in a single channel on the microcapillary dimensions in the film is then studied. Finally, the size uniformity of the microcapillaries is improved by separate gas injection in different channels, providing new possibilities for the generation of highly monodisperse microdroplets.

Precise Control of Microcapillary Size in Microcapillary Films by Liquid‐Assisted Extrusion

“…The structure of the die mold was reported in our previous work. [23] These needles served as channels for liquid. MCFs were produced by liquid-assisted extrusion for the first time.…”

“…Here, we focused on its effect on microcapillary size. The relationship between v d (unit: mm s −1 ) and F r was given by the literature, [23] which was as follows:…”

“…The CVs of MCFs produced by gas-assisted extrusion were ≈35.8% , [3] ≈13.1% (Hornung et al in 2010), [25] ≈16.3% (Gill et al in 2021), [11] and ≈14.8% (Our previous work in 2021). [23] These extrusion process were all gas-assisted and the numbers of microcapillary in the MCFs were 17, 19, 10, and 7. Therefore, we compared the size uniformity of MCFs by liquid-assisted extrusion with our previous work (CV value: 14.8%) for that they both had 7 microcapillaries.…”

“…The nonuniform size distribution of microcapillaries within an MCF strip limited MCFs' applications in microfluidics and biotechnologies because the generation of homogeneous droplets and the robust immunoassay performance needed the microcapillaries in an MCF strip to be uniform. [23] In the conventional extrusion process, gas was not only injected into the die mold by the gas supply, but also sucked into the channels to form the microcapillaries because when the polymer melt flowed through the inner die, there would be a pressure drop and the melt pressure in the front of the inner die could be lower than the atmospheric pressure, resulting in gas suction. [24] The shape and size of microcapillaries were different mainly due to the pressure and velocity fields distributions in the polymer melt.…”

“…[24] The shape and size of microcapillaries were different mainly due to the pressure and velocity fields distributions in the polymer melt. [23] The poor size uniformity was mainly caused by the compressibility of gas during the gas-assisted extrusion process.…”