Two-dimensional liquid-like order in a confined population of swimming Eudorina colonies
Abstract
Swimming microorganisms accumulate at boundaries, but the spatial statistics of the resulting layers are rarely measured. We report a population of colonial green algae, of order 71 μm across, that accumulates against the rigid upper wall of a closed 1-2 mm chamber and holds a two-dimensional non-contacting arrangement for about 105 min. The pair correlation function has a first shell at r/D̅ = 1.73, g = 4.8; a hard-disc null at the same area fraction reaches only g = 2.1, so the ordering is not excluded volume alone. Nearest-neighbour separation is 1.80 ± 0.13 diameters. The bond-orientational order parameter is ⟨|ψ6|⟩ = 0.456 against 0.385 for the null, only 36% of interior colonies are six-coordinated, and the orientational correlation g6(r) decays over 1.5 diameters with η6 = 1.31 against the hexatic bound of 1/4: the arrangement is a two-dimensional liquid, not a crystal or a hexatic. Colonies execute a persistent random walk with reorientation time 1.4-1.7 s at Reynolds number ∼ 9× 10−4. Breakup begins at 127 min. Thermal convection is excluded on Rayleigh-number grounds. Caveats: the length calibration is nominal rather than metrological, and this is a single population observed once. All data and code are deposited.
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BibTeX
@misc{tufillaro2026twodimensional,
title = {{Two-dimensional liquid-like order in a confined population of swimming Eudorina colonies}},
author = {Nicholas Tufillaro},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.09946},
eprint = {2611.09946},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.09946},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Two-dimensional liquid-like order in a confined population of swimming Eudorina colonies
AU - Nicholas Tufillaro
PY - 2026
DA - 2026/11/01
PB - arXiv
DO - 10.48550/arxiv.2611.09946
UR - https://arxiv.org/abs/2611.09946
AB - Swimming microorganisms accumulate at boundaries, but the spatial statistics of the resulting layers are rarely measured. We report a population of colonial green algae, of order 71 μm across, that accumulates against the rigid upper wall of a closed 1-2 mm chamber and holds a two-dimensional non-contacting arrangement for about 105 min. The pair correlation function has a first shell at r/D̅ = 1.73, g = 4.8; a hard-disc null at the same area fraction reaches only g = 2.1, so the ordering is not excluded volume alone. Nearest-neighbour separation is 1.80 ± 0.13 diameters. The bond-orientational order parameter is ⟨|ψ_6|⟩ = 0.456 against 0.385 for the null, only 36% of interior colonies are six-coordinated, and the orientational correlation g_6(r) decays over 1.5 diameters with η_6 = 1.31 against the hexatic bound of 1/4: the arrangement is a two-dimensional liquid, not a crystal or a hexatic. Colonies execute a persistent random walk with reorientation time 1.4-1.7 s at Reynolds number ∼ 9× 10^−4. Breakup begins at 127 min. Thermal convection is excluded on Rayleigh-number grounds. Caveats: the length calibration is nominal rather than metrological, and this is a single population observed once. All data and code are deposited.
ER -