Phase-sensitive optical coherence tomography reveals droplet penetration into a powder bed

Taye Tolu Mekonnen, Shaokoon Cheng, Hak-Kim Chan, Agisilaos Kourmatzis*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

Understanding the mixing behavior that unfolds when liquid droplets impact on powder beds requires a sub-surface dynamic imaging method that provides high spatial and temporal resolution. In this study, a high-resolution phase-sensitive optical coherence tomography (PhS-OCT) technique was introduced to provide in-depth insights into the interaction of droplets and powder beds. A theoretical model correlating changes in the optical path differences (OPD) of the OCT signal with physical properties of the powder bed was presented. Experiments were conducted on three powders with median particle diameters, i.e., the size corresponding to the 50th percentile of the cumulative volume distribution, of 3 µm (mannitol), 4 µm (mannitol) and 109 µm (SV010). Water and ethanol droplets were used to illustrate the technique. The results demonstrated that OPD maps can qualitatively resolve the liquid-powder mixture region, both temporally and spatially, as the droplet diffuses into the powder bed, allowing for a quantitative description of diffusion behavior. A comparison of lactose and mannitol powder samples revealed varying diffusion rates, potentially attributed to differences in porosity, particle size, and agglomeration. Additionally, water and ethanol droplets exhibited significantly different (p = 0.005) diffusion profiles for the same powder properties. In general, the findings indicate the potential of the proposed PhS-OCT technique for evaluating the mixing behavior of multi-phase mixtures, holding promise in applications such as pharmaceutical drug formulations and additive manufacturing.

Original languageEnglish
Article number108329
Pages (from-to)1-10
Number of pages10
JournalOptics and Lasers in Engineering
Volume180
DOIs
Publication statusPublished - Sept 2024

Bibliographical note

Copyright the Author(s) 2024. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

Keywords

  • Phase sensitive optical coherence tomographyPhase sensitive optical coherence tomography
  • Diffusion
  • Multiphase detection
  • Droplet
  • Powder bed
  • Optical path difference

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