Research ArticleMATERIALS SCIENCE

Experimental and theoretical evidence for molecular forces driving surface segregation in photonic colloidal assemblies

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Science Advances  20 Sep 2019:
Vol. 5, no. 9, eaax1254
DOI: 10.1126/sciadv.aax1254
  • Fig. 1 SEM images of the surface of supraballs made of binary particles with equal bulk volume fraction.

    (A) 139/137-nm SPs/SMPs, (B) 219/137-nm SPs/SMPs, (C) 299/137-nm SPs/SMPs, (D) 139/217-nm SPs/SMPs, (E) 219/217-nm SPs/SMPs, (F) 299/217-nm SPs/SMPs, (G) 139/298-nm SPs/SMPs, (H) 219/298-nm SPs/SMPs, and (I) 299/298-nm SPs/SMPs. SEM scale bars, 1 μm. All insets are dark-field optical images with scale bars of 50 μm.

  • Fig. 2 Supraballs and films from binary SPs.

    SEM images of the surfaces of supraballs (A to C) and films (D to F) made of binary SPs with different sizes and equal bulk volume fraction: (A and D) 139/219-nm SPs, (B and E) 139/299-nm SPs, and (C and F) 219/299-nm SPs. Insets (A to F) are dark-field optical images. SEM scale bars, 1 μm; inset scale bars, 50 μm. (G) Surface volume fractions of small SPs for supraballs and films.

  • Fig. 3 Supraballs and films assembled from binary 219/217nm SPs/SMPs.

    Supraballs made of 0.20 bulk volume fraction of SMPs (A to C) and 0.80 bulk volume fraction of SMPs (D to F). (A and D) SEM images on the supraball surfaces (scale bars, 1 μm), (B and E) TEM images on the supraball cross sections (scale bars, 500 nm), and (C and F) EDS elemental maps of the region of interest for the characteristic x-ray emission peaks for silicon (scale bars, 500 nm). SEM images on the surfaces of films made of 219/217-nm SPs/SMPs with varied bulk volume fractions of SMPs: (G) 0.20, (H) 0.50, and (I) 0.80. (G and H) Scale bars, 1 μm. Insets in (A), (D), and (G) to (I) are optical images of the supraballs and films with scale bars of 50 μm.

  • Fig. 4 Single-particle contact angle measurements.

    (A) Schematic diagram of single-nanoparticle contact angle measurement process using a gel trapping technique. SEM images of an SP (B) and an M-SP (C) embedded in PDMS for contact angle measurements (SP, ~78.4° ± 4.9°; M-SP, ~99.0° ± 3.6°). Scale bars, 200 nm.

  • Fig. 5 MD simulations of assembled binary films.

    (A to D) MD simulation snapshots for assembled films from similar-sized (~220 nm) SPs (yellow) and SMPs (blue) and mixtures of different sizes of SPs (~220 nm/~140 nm). The bulk volume fractions of SMPs are as follows: (A) 0.20, (B) 0.50, and (C) 0.80. (D) SPs (~220 nm; yellow): ~140-nm SPs (orange) at bulk volume fraction of small SP = 0.5. Particle-particle pair correlation functions, g(r), from experiments (circles) and simulations (lines) for (E to G) the film pictured in (B) and (H to J) the film pictured in (D).

  • Fig. 6 MD simulations of assembled binary supraballs.

    (A) Surface volume fractions of SMPs or small SPs at the supraball surface as a function of filling volume fraction (η) within the droplet and (B to F) simulation images for a 220/220-nm SPs/SMPs mixture of the equal bulk volume fractions with θSP = θSMP = 90° (B) (green solid line), 220/220-nm SPs/SMPs with θSP = 80° and θSMP = 100° (C) (light blue dashed line), 220/140-nm SPs/SPs with θSP = 80° (D) (orange dot-dashed line), 140/220-nm SPs/SMPs with θSP = 80° and θSMP = 100° (E) (thin black dashed line), and 140/300-nm SPs/SMPs with θSP = 80° and θSMP = 100° (F) (purple dotted line). The two left images in (B) to (D) show the entire emulsion droplet and a droplet cross section at the jammed surface layer state, and the two right images in (B) to (D) show the final assembled supraball and supraball cross section. SMPs are rendered in blue, and SPs are rendered in yellow in all panels except for (D), where 140-nm SPs are rendered in orange for visual contrast. The boxes surrounding (B) to (D) correspond to the line color and type in (A). The simulation images are not to scale.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/9/eaax1254/DC1

    CG-MD simulations model and methods

    Table S1. Zeta potentials and diameters of all six types of particles.

    Fig. S1. The workflow for preparing the binary supraballs.

    Fig. S2. Normal reflectance of nine types of supraballs in Fig. 1.

    Fig. S3. An SEM image of a typical broken film made of a mixture of 139- and 219-nm SPs.

    Fig. S4. Cross-sectional images of supraballs (interior) made of 219-nm SPs and 217-nm SMPs with varied mixing volume ratios.

    Fig. S5. Normal reflectance measurements of binary supraball and films.

    Fig. S6. The volume changes of different droplets over time during the pendant droplet measurements.

    Fig. S7. Surface and interfacial tension measurements.

    Fig. S8. TEM images of ~400-nm SPs and M-SPs.

    Fig. S9. Particle-particle pair correlation functions from experiment (circles) and simulations (lines) for films made of ~220-nm SP/SMPs mixtures.

    Fig. S10. Particle-particle pair correlation functions from simulations for a binary SP/SMP film with (solid lines) and without (dashed lines) a 17-nm Gaussian uncertainty in particle x-y positions.

    Fig. S11. Illustration of particle-interface potential for 220-nm SPs (yellow solid line) and 220-nm SMPs (blue dashed line).

    Fig. S12. Schematic of the later stages of supraball assembly.

    Fig. S13. Examples of particle position tracking analysis on SEM images.

    Fig. S14. Schematic of the simulation box geometry for film and supraball assembly.

    Fig. S15. Distributions of particle sizes and their effect on the particle-particle pair correlation function in simulations.

    Fig. S16. Pe effect on the simulations.

    Movie S1. A representative movie of the supraball assembly simulations.

    References (56, 57)

  • Supplementary Materials

    The PDF file includes:

    • CG-MD simulations model and methods
    • Table S1. Zeta potentials and diameters of all six types of particles.
    • Fig. S1. The workflow for preparing the binary supraballs.
    • Fig. S2. Normal reflectance of nine types of supraballs in Fig. 1.
    • Fig. S3. An SEM image of a typical broken film made of a mixture of 139- and 219-nm SPs.
    • Fig. S4. Cross-sectional images of supraballs (interior) made of 219-nm SPs and 217-nm SMPs with varied mixing volume ratios.
    • Fig. S5. Normal reflectance measurements of binary supraball and films.
    • Fig. S6. The volume changes of different droplets over time during the pendant droplet measurements.
    • Fig. S7. Surface and interfacial tension measurements.
    • Fig. S8. TEM images of ~400-nm SPs and M-SPs.
    • Fig. S9. Particle-particle pair correlation functions from experiment (circles) and simulations (lines) for films made of ~220-nm SP/SMPs mixtures.
    • Fig. S10. Particle-particle pair correlation functions from simulations for a binary SP/SMP film with (solid lines) and without (dashed lines) a 17-nm Gaussian uncertainty in particle x-y positions.
    • Fig. S11. Illustration of particle-interface potential for 220-nm SPs (yellow solid line) and 220-nm SMPs (blue dashed line).
    • Fig. S12. Schematic of the later stages of supraball assembly.
    • Fig. S13. Examples of particle position tracking analysis on SEM images.
    • Fig. S14. Schematic of the simulation box geometry for film and supraball assembly.
    • Fig. S15. Distributions of particle sizes and their effect on the particle-particle pair correlation function in simulations.
    • Fig. S16. Pe effect on the simulations.
    • References (56, 57)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). A representative movie of the supraball assembly simulations.

    Files in this Data Supplement:

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