Research ArticleMATERIALS ENGINEERING

Programmable colloidal molecules from sequential capillarity-assisted particle assembly

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Science Advances  01 Apr 2016:
Vol. 2, no. 4, e1501779
DOI: 10.1126/sciadv.1501779
  • Fig. 1 Working principle of depositing a single particle in a large trap.

    (A) Scheme of the assembly in rectangular traps (1.2 × 2.2 μm2), with the trap depth d approximately equal to the particle radius r (d = 510 nm, r = 500 nm). The zoom shows the front particle (particle 1) experiencing a downward capillary force Fc perpendicular to the meniscus. The force Fc partly transmits to the rear particle (particle 2), leading to an upward force Fc in the presence of a small vertical displacement, which pushes particle 2 out of the trap. Eventually, only particle 1 is assembled in the trap. (B and C) Trapping only a single particle is also found in 10-μm-long traps (B) and in triangular traps (C). The insets to (B) and (C) are the corresponding scanning electron microscopy (SEM) images. Scale bars, 5 μm (B and C) and 2 μm (insets to B and C).

  • Fig. 2 One-dimensional linear colloidal chains assembled by sCAPA.

    (A) Scheme illustrating the stepwise sequence for fabricating multicomponent colloidal chains. (B to E) One-dimensional linear PS colloidal chains assembled using different particles and sequences, resembling bar-code chains (B and C), block copolymers (D), and surfactants (E) (merged fluorescence images). The insets show the specific assembly sequence and directions in each case. Note that in the assembly of surfactant-like colloidal chains, the assembly direction was rotated by ~80° for the second step (inset to E). Scale bars, 5 μm (B and C) and 10 μm (D and E).

  • Fig. 3 Polydispersity in the tail length of surfactant-like colloidal chains.

    (A) Fluorescence image of the second assembly step for the formation of surfactant-like chains, demonstrating the variability of the local assembly direction caused by the curvature of the moving droplet. The inset shows the orientation of the traps. Scale bar, 200 μm. (B to E) Merged fluorescence images taken at different positions along the contact line. The arrows in the insets schematically represent the local assembly direction relative to the traps. Scale bars, 5 μm. (F) Histograms of the distribution of tail lengths, that is, the number of particles in the tail corresponding to cases 1, 2, and 3 shown in (B) to (D). For each histogram, 140 colloidal molecules were analyzed. (E) There is no tail-length count for position 4 because, in that case, most tails are pushed to the opposite end of the trap, leaving a gap between the “head” and the “tail” particles.

  • Fig. 4 Two-dimensional and 3D PS colloidal molecules assembled by sCAPA.

    (A) Scheme showing local sequential assembly directions. (B and C) Yield of colloidal trimers with three different lobes (B) in traps of different sizes (C). The numbers on top of the columns in (B) correspond to the numbers assigned to the traps in (C). D indicates the diameter of the circle inscribed to the triangular trap. (D and E) Merged fluorescence images of close-packed (D) and separated (E) colloidal trimers with three different lobes. Insets depict the corresponding SEM micrographs. (F to H) Three-dimensional chiral clusters with four different lobes. (F) Scheme of assembly steps and directions. (G) Overlay of fluorescence and bright-field images. (H) SEM micrograph with a 45° incident angle. Scale bars, 5 μm.

  • Fig. 5 Multimaterial linear and nonlinear clusters.

    (A and B) Asymmetric dumbbells assembled from carboxylate PS/amine PS (merged fluorescence image) (A) and from PS and SiO2 (overlay of fluorescence and bright-field image) (B). (C and D) Three-particle colloidal chains with a magnetic SiO2 particle (left), a PS particle (middle), and a nonfunctionalized SiO2 particle (right) [energy-dispersive x-ray (EDX) spectroscopy; see fig. S4]. Overlay of a fluorescence image with a bright-field image on the template (C) and SEM image after the printing of the particles onto a silicon substrate (D). (E and F) Surfactant-like colloidal chains with a magnetic SiO2 particle followed by a tail of PS particles. Overlay of a fluorescence image with a bright-field image on the template (E) and SEM image after the printing of the particles onto a silicon substrate (F). (G and H) Trimers with a magnetic particle and two different PS particles. Overlay of a fluorescence image with a bright-field image on the template (G) and SEM image after the printing of the particles onto a silicon substrate (H). Scale bars, 5 μm.

  • Fig. 6 Scheme of the harvesting process.

    The SEM image shows a linked PS-PS dumbbell in a trap on the template. Scale bar, 1 μm. The micrograph shows the frozen water droplet attached to a micropipette tip.

  • Fig. 7 Harvested clusters.

    (A to C) Merged fluorescence images of harvested and dried R-G PS dumbbells (A), R-B-G PS three-particle chains (B), and R-G-B PS three-particle trimers (C) on silicon substrates. (D) Snapshots of colloidal surfactants with PS tails that are one particle (left), three particles (middle), and seven particles (right) long and have a magnetic head. The clusters are in solution and undergo Brownian motion. The images were captured by combining the fluorescence and transmission channels. Scale bars, 5 μm.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/4/e1501779/DC1

    Technical details of the assembly of linear colloidal chains.

    Technical details of the assembly of nonlinear colloidal clusters (trimers and 3D clusters).

    Fig. S1. SEM images of different colloidal chains on the template.

    Fig. S2. Effect of trap size on the assembly yield of R-G-B PS trimers.

    Fig. S3. Yield of assembled carboxylate PS and amine PS dumbbells on an area of 5 × 12 mm2.

    Fig. S4. EDX spectroscopy of three-particle chains with plain SiO2, PS, and magnetic SiO2.

    Fig. S5. Linking of clusters by thermal sintering.

    Fig. S6. Harvesting of clusters.

    Fig. S7. Harvesting of clusters at extremely low temperatures.

    Fig. S8. Effects of varying lateral trap dimensions on the structure of 3D clusters.

    Fig. S9. Effects of local assembly direction on the first sCAPA step of colloidal trimers.

    Fig. S10. Effects of local assembly direction on the assembly of open colloidal trimers with three different lobes.

    Movie S1. The first assembly step for the fabrication of surfactant-like colloidal chains.

    Movie S2. The second assembly step for the fabrication of surfactant-like colloidal chains.

    Movie S3. Brownian motion of a dumbbell with a magnetic head and a PS lobe dispersed in water after harvesting.

    Movie S4. Brownian motion of a four-particle chain with a magnetic head and a PS tail dispersed in water after harvesting.

    Movie S5. Brownian motion of an eight-particle chain with a magnetic head and a PS tail dispersed in water after harvesting.

    Movie S6. Rotation of colloidal chains with a magnetic head in an external rotating magnetic field.

    Movie S7. Oscillation of colloidal chains with a magnetic head in an external oscillating magnetic field.

    Movie S8. Translation of a colloidal chain with a magnetic head by a permanent magnet.

    Movie S9. The third assembly step for the fabrication of open PS trimers with three different lobes.

  • Supplementary Materials

    This PDF file includes:

    • Technical details of the assembly of linear colloidal chains.
    • Technical details of the assembly of nonlinear colloidal clusters (trimers and 3D clusters).
    • Fig. S1. SEM images of different colloidal chains on the template.
    • Fig. S2. Effect of trap size on the assembly yield of R-G-B PS trimers.
    • Fig. S3. Yield of assembled carboxylate PS and amine PS dumbbells on an area of 5 × 12 mm2.
    • Fig. S4. EDX spectroscopy of three-particle chains with plain SiO2, PS, and magnetic SiO2.
    • Fig. S5. Linking of clusters by thermal sintering.
    • Fig. S6. Harvesting of clusters.
    • Fig. S7. Harvesting of clusters at extremely low temperatures.
    • Fig. S8. Effects of varying lateral trap dimensions on the structure of 3D clusters.
    • Fig. S9. Effects of local assembly direction on the first sCAPA step of colloidal trimers.
    • Fig. S10. Effects of local assembly direction on the assembly of open colloidal trimers with three different lobes.
    • Legends for movies S1 to S9

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.avi format). The first assembly step for the fabrication of surfactant-like colloidal chains.
    • Movie S2 (.avi format). The second assembly step for the fabrication of surfactant-like colloidal chains.
    • Movie S3 (.avi format). Brownian motion of a dumbbell with a magnetic head and a PS lobe dispersed in water after harvesting.
    • Movie S4 (.avi format). Brownian motion of a four-particle chain with a magnetic head and a PS tail dispersed in water after harvesting.
    • Movie S5 (.avi format). Brownian motion of an eight-particle chain with a magnetic head and a PS tail dispersed in water after harvesting.
    • Movie S6 (.avi format). Rotation of colloidal chains with a magnetic head in an external rotating magnetic field.
    • Movie S7 (.avi format). Oscillation of colloidal chains with a magnetic head in an external oscillating magnetic field.
    • Movie S8 (.avi format). Translation of a colloidal chain with a magnetic head by a permanent magnet.
    • Movie S9 (.avi format). The third assembly step for the fabrication of open PS trimers with three different lobes.

    Files in this Data Supplement:

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