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Colloidal molecules in microgravity assembled by critical Casimir forces

P. J. M. Swinkels

P. J. M. Swinkels

Institute of Physics, University of AmsterdamThe Netherlands
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Swinkels, P. J. M.
, 
Z. Gong

Z. Gong

Molecular Design Institute, Department of Chemistry, New York UniversityUSA
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Gong, Z.
, 
S. Sacanna

S. Sacanna

Molecular Design Institute, Department of Chemistry, New York UniversityUSA
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Sacanna, S.
, 
W. V. Meyer

W. V. Meyer

Universities Space Research Association, with GEARS at NASA GRC
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Meyer, W. V.
 y 
P. Schall

P. Schall

Institute of Physics, University of AmsterdamThe Netherlands
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Schall, P.
  
14 mar 2025
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Categoría del artículo: Research Note
Publicado en línea: 14 mar 2025
Páginas: 21 - 29
DOI: https://doi.org/10.2478/gsr-2025-0001
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© 2025 P. J. M. Swinkels et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Figure 1.

Assembly of equilibrium and out-of-equilibrium structures by critical Casimir forces. (a–d) Confocal microscopy images of particles in equilibrium gas (a), liquid (b) and crystal (c) phases, and out-of-equilibrium, fractal aggregate (d). Temperature offsets DT=Tc-T are indicated. (e) Corresponding equilibrium phase diagram computed using Monte Carlo simulations with effective critical Casimir interactions as input. Experimental data: black dots and error bars; gas-liquid critical point is indicated by a star. Reprinted from [22] with the permission of AiP Publishing. (f) Space measurements of fully grown aggregates in microgravity. The compactness b=RH/Rg is plotted as a function of the fractal dimension df. Lines indicate relation for unit-step (solid), Gaussian (dashed) exponential (dotted) density–density correlation function of the aggregates. Insets show holographic reconstructions of aggregates grown at highest (top) and lowest (bottom) attraction. Reprinted with permission from [24].
Assembly of equilibrium and out-of-equilibrium structures by critical Casimir forces. (a–d) Confocal microscopy images of particles in equilibrium gas (a), liquid (b) and crystal (c) phases, and out-of-equilibrium, fractal aggregate (d). Temperature offsets DT=Tc-T are indicated. (e) Corresponding equilibrium phase diagram computed using Monte Carlo simulations with effective critical Casimir interactions as input. Experimental data: black dots and error bars; gas-liquid critical point is indicated by a star. Reprinted from [22] with the permission of AiP Publishing. (f) Space measurements of fully grown aggregates in microgravity. The compactness b=RH/Rg is plotted as a function of the fractal dimension df. Lines indicate relation for unit-step (solid), Gaussian (dashed) exponential (dotted) density–density correlation function of the aggregates. Insets show holographic reconstructions of aggregates grown at highest (top) and lowest (bottom) attraction. Reprinted with permission from [24].

Figure 2.

Directional bonding by critical Casimir forces. (a) Illustration of patchy colloids binding via their patches. The attraction is mediated by solvent fluctuations, localized between the patches by their hydrophobic affinity. (b–d) Possible structures formed by di-patch (b), mixtures of di- and tetra-patch (c) and pure tetra-patch particles (right).
Directional bonding by critical Casimir forces. (a) Illustration of patchy colloids binding via their patches. The attraction is mediated by solvent fluctuations, localized between the patches by their hydrophobic affinity. (b–d) Possible structures formed by di-patch (b), mixtures of di- and tetra-patch (c) and pure tetra-patch particles (right).

Figure 3.

Equilibrium polymerization of di-patch particles. (a) Fluorescence image showing a chain of particles bonded by critical Casimir forces via their patches (bright dots). Scale bar is 3μm (b–d) Microscope images of di-patch particle chains at increasing attractive strength (decreasing ΔT) at a surface coverage of f= 0.28. Colors mark connected chains. Scale bar is 20μm. (e) Corresponding chain length distributions for the different ΔT (see legend). Lines are exponential fits. (f) Chain network obtained with addition of a small fraction (10%) of tetra-patch particles. (g) Cluster size distributions after different growth times (see legend). Dotted lines indicate power-law fits with exponent T ~ −1.5 and exponential cutoff x̅ = 4, 11, 68 (dotted). (h) Confocal microscope image of three-dimensional network of di- and tetra-patch particles achieved with smaller (1μm) particles having larger gravitational height. Scale bar is 10μm. Panels (d)–(g) reprinted with permission from [29]. Copyright (2021) by the American Physical Society.
Equilibrium polymerization of di-patch particles. (a) Fluorescence image showing a chain of particles bonded by critical Casimir forces via their patches (bright dots). Scale bar is 3μm (b–d) Microscope images of di-patch particle chains at increasing attractive strength (decreasing ΔT) at a surface coverage of f= 0.28. Colors mark connected chains. Scale bar is 20μm. (e) Corresponding chain length distributions for the different ΔT (see legend). Lines are exponential fits. (f) Chain network obtained with addition of a small fraction (10%) of tetra-patch particles. (g) Cluster size distributions after different growth times (see legend). Dotted lines indicate power-law fits with exponent T ~ −1.5 and exponential cutoff x̅ = 4, 11, 68 (dotted). (h) Confocal microscope image of three-dimensional network of di- and tetra-patch particles achieved with smaller (1μm) particles having larger gravitational height. Scale bar is 10μm. Panels (d)–(g) reprinted with permission from [29]. Copyright (2021) by the American Physical Society.

Figure 4.

Assembly of colloidal organic molecules. Backbones of colloidal organic-molecule analogues (“colloidal alkanes”), assembled from tetra-patch particles: Colloidal butane (a), 2-butyne (b), cyclobutane (c), cyclopentane (d) and methylcyclohexane (e), microscopy image (left) reconstruction (center) and chemical symbol (right). Reproduced with adaptation from [39].
Assembly of colloidal organic molecules. Backbones of colloidal organic-molecule analogues (“colloidal alkanes”), assembled from tetra-patch particles: Colloidal butane (a), 2-butyne (b), cyclobutane (c), cyclopentane (d) and methylcyclohexane (e), microscopy image (left) reconstruction (center) and chemical symbol (right). Reproduced with adaptation from [39].

Figure 5.

Conformations and pseudorotation of colloidal cyclopentane. (a) Three-dimensional reconstructions of typical conformations of colloidal cyclopentane: Planar conformation (top), twist (or ‘half-chair’) conformation (bottom left), and envelope (or ‘bend’) conformation (bottom right). (b) Time series of three-dimensional configurations showing pseudo-rotation of colloidal cyclopentane. Snapshots are t = 12s apart. The typical relaxation time of a conformation is 24s, allowing for convenient observation. Symbols + and − indicate particles above and below the average plane, respectively, and arrows indicate particle movement towards the next time step. (c) Transition states in polar space during pseudorotation of three colloidal cyclopentane rings. Black trajectory: numbers correspond to snapshots in (b). Reproduced with adaptation from [39].
Conformations and pseudorotation of colloidal cyclopentane. (a) Three-dimensional reconstructions of typical conformations of colloidal cyclopentane: Planar conformation (top), twist (or ‘half-chair’) conformation (bottom left), and envelope (or ‘bend’) conformation (bottom right). (b) Time series of three-dimensional configurations showing pseudo-rotation of colloidal cyclopentane. Snapshots are t = 12s apart. The typical relaxation time of a conformation is 24s, allowing for convenient observation. Symbols + and − indicate particles above and below the average plane, respectively, and arrows indicate particle movement towards the next time step. (c) Transition states in polar space during pseudorotation of three colloidal cyclopentane rings. Black trajectory: numbers correspond to snapshots in (b). Reproduced with adaptation from [39].

Figure 6.

Assembly of patchy particles in microgravity. (a,b) Preliminary results of assembled di- and tetra-patch particles, obtained during the ACE-T2 experiments. The pictures show confocal microscope images of the assembled particles with overlays indicating a few of the assembled structures. (c) Characteristic motifs: chains formed from di-patch particles (I), kinks (II) and branching points (III) due to tetra-patch particles. (d) Bright-field image of a ground experiment performed under similar conditions (DT~0.05°C) showing the same basic motifs.
Assembly of patchy particles in microgravity. (a,b) Preliminary results of assembled di- and tetra-patch particles, obtained during the ACE-T2 experiments. The pictures show confocal microscope images of the assembled particles with overlays indicating a few of the assembled structures. (c) Characteristic motifs: chains formed from di-patch particles (I), kinks (II) and branching points (III) due to tetra-patch particles. (d) Bright-field image of a ground experiment performed under similar conditions (DT~0.05°C) showing the same basic motifs.
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