Research ArticleCOLLOIDS

Opto-thermophoretic assembly of colloidal matter

See allHide authors and affiliations

Science Advances  08 Sep 2017:
Vol. 3, no. 9, e1700458
DOI: 10.1126/sciadv.1700458
  • Fig. 1 Schematic illustration of the concept of OTA.

    (A) Dispersion of colloidal atoms in solvents. (B) CTAC surfactants adsorbed on the surface of the colloidal particles form molecular double layers, generating a positive and hydrophilic surface. Meanwhile, the CTAC molecules self-assemble into CTAC micelles with high surface charge density. (C) Manipulation of the colloidal atoms with the light-directed dynamic temperature field, and bonding of the closely positioned colloidal atoms with depletion attraction. (D) Construction of colloidal atoms into one-dimensional (1D) and 2D assemblies.

  • Fig. 2 Colloidal manipulation with a light-directed thermoelectric field.

    (A) Working principle of colloidal trapping. The black arrows indicate the trapping force. The temperature gradient field along the z axis is calculated when a laser beam with a diameter of 2 μm and an optical power of 0.253 mW is incident onto the substrate. (B) Top: Optical images of the parallel trapping of polystyrene (PS) beads of different sizes. Scale bar, 10 μm. Bottom: Schematic of colloidal trapping with a light-controlled temperature field. (C to E) Measured escape velocities of the trapped colloidal atoms as a function of optical intensity at variable CTAC concentrations. The diameters of the PS colloidal atoms are 2 μm (C), 0.96 μm (D), and 500 nm (E), respectively. The purple lines indicate the maximum temperature gradient along the r axis [as shown in (A)] as a function of optical intensity.

  • Fig. 3 Physical principle of bonding in OTA.

    (A) Schematics of the depletion attraction between two colloidal atoms, which is enhanced by the light-controlled temperature field. Middle: The green arrows indicate that thermophoresis drives the CTAC micelles from hot to cold regions. FT is the trapping force, Fvdw is the van der Waals force, and Fe is the electrostatic repulsive force. Right: Embedded Image is the depletion volume, which is indicated with dashed circles, and ΔΠ is the osmotic pressure difference between the bulk region (cold region) and the depletion region (hot region). In all panels, the gray rings around the micelles indicate an effective depletion size. (B to D) Calculated interaction potential between two PS beads and optical images of colloidal superstructures of beads of different diameters: 2 μm (B), 0.96 μm (C), and 500 nm (D). In (C), the optical images (from left to right) are recorded, where the distances between the focus plane of the 100× objective [numerical aperture (NA), 0.9] and the substrate are 12.275, 13.125, and 13.950 μm, respectively. Scale bars, 5 μm (B) and 2 μm (C and D).

  • Fig. 4 General applicability of the OTA strategy.

    (A) 1D hybrid assembly of 2- and 0.96-μm PS beads. The assembly was achieved by adding the 2- and 0.96-μm PS beads alternatively. (B) 2D hybrid square assembly of 2- and 0.96-μm PS beads. Each 0.96-μm PS bead was added at the interface between two 2-μm PS beads and then confined by two other 2-μm PS beads. (C) 2D hybrid assembly of a double-layer Saturn-ring structure with 2- and 0.96-μm PS beads. The structure was built layer by layer from the inside out. (D) 2D hybrid assembly of 2-μm PS beads and anisotropic PS particles. The anisotropic particles were aligned with a 1D optical image and inserted into the heptamer. (E) 3D assembly and manipulation of four 500-nm PS beads. (F) 2D hybrid superlattice of 2-μm PS, 0.96-μm PS, 2-μm silica, and 1-μm silica beads. The assembly process is similar to (B), whereas half of the PS beads were replaced with silica beads. (G) 2D assembly of a star pattern of 2-μm silica beads. The structure was built layer by layer from top to bottom. (H) A heterogeneous dimer consisted of a 500-nm PS bead and a 200-nm Au nanosphere. (I) 2D assembly of a Saturn-ring structure with 2- and 0.96-μm PS beads. The 0.96-μm PS beads were added around the 2-μm PS bead to obtain the structure. (J) 2D assembly of a 0.96-μm PS with three 500-nm PS beads as satellites. The three 500-nm PS beads were added around the 0.96-μm PS at the specific location with a rotation angle of 120°. (K) An Au dimer consisted of two 200-nm Au nanospheres. (A to F, I, and J) Schematics and bright-field optical images of colloidal superstructures. (G) Bright-field and dark-field optical images of the superstructure. (H and K) Schematics and dark-field optical images of the colloidal atoms and dimers. Arrows in the optical images of (K) indicate the use of different incident light polarizations. Scale bars, 5 μm (A to D, F, and G) and 2 μm (E and H to K).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/9/e1700458/DC1

    fig. S1. ζ potential of 2-μm PS beads dispersed in a 10 mM CTAC solution.

    fig. S2. Parallel trapping and dynamic manipulation of PS beads by the light-controlled temperature field.

    fig. S3. Scanning electron micrograph of the anisotropic PS particles fabricated with microsphere lithography.

    fig. S4. Rotation of a single anisotropic PS particle using a 1D optical image.

    fig. S5. Size dependency of the escape velocity of the trapped PS beads.

    fig. S6. Trapping, rotation, and bonding of a 1D chain of colloidal atoms.

    fig. S7. Assembly of a chiral structure of 2-μm PS beads.

    fig. S8. Time response of a heptamer of 2-μm PS beads at different CTAC concentrations.

    fig. S9. Time response of a plus pattern of 2-μm PS beads at a CTAC concentration of 20 mM.

    fig. S10. Multiple experiments on the assembly of the plus pattern with 2-μm PS beads at a CTAC concentration of 20 mM.

    fig. S11. Assembly of heterogeneous 1D chains of 2- and 0.96-μm PS beads.

    fig. S12. Hybrid assembly of 2-μm PS beads and anisotropic PS particles.

    fig. S13. 3D reconfiguration and manipulation of colloidal assemblies of six 500-nm PS beads.

    fig. S14. Assembly of the Saturn-ring structure with 0.96-μm and 500-nm PS beads.

    fig. S15. Interaction potential of silica particles.

    fig. S16. Electrostatic interaction potential between the CTAC micelle and the PS bead as a function of the micelle-particle distance.

    fig. S17. Light manipulation by a heptamer assembled from seven 0.96-μm PS beads.

    fig. S18. 3D reconfiguration and manipulation of colloidal assemblies.

    note S1. Calculation of the interaction potential.

    note S2. Exclusion of other bonding mechanisms in CTAC surfactants.

    note S3. Light manipulation with designed colloidal assembly.

    note S4. 3D reconfiguration and manipulation of colloidal assemblies.

    movie S1. Repelling of PS beads in SDS solution and thermal convection of PS beads in Triton X-100 solution.

    movie S2. Dynamic rotation of eight 0.96-μm PS beads.

    movie S3. Dynamic rotation of a hybrid pattern of 2- and 0.96-μm PS beads.

    movie S4. Assembly process of a 2D thermodynamically stable structure with 2-μm PS beads.

    movie S5. Manipulation of the 2D assembly of 2-μm PS beads.

    movie S6. Trapping, rotation, and bonding of the 1D assembly of 2-μm PS beads.

    movie S7. Assembly of anisotropic PS particles.

    movie S8. Manipulation of the 3D assembly of 500-nm PS beads.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. ζ potential of 2-μm PS beads dispersed in a 10 mM CTAC solution.
    • fig. S2. Parallel trapping and dynamic manipulation of PS beads by the light-controlled temperature field.
    • fig. S3. Scanning electron micrograph of the anisotropic PS particles fabricated with microsphere lithography.
    • fig. S4. Rotation of a single anisotropic PS particle using a 1D optical image.
    • fig. S5. Size dependency of the escape velocity of the trapped PS beads.
    • fig. S6. Trapping, rotation, and bonding of a 1D chain of colloidal atoms.
    • fig. S7. Assembly of a chiral structure of 2-μm PS beads.
    • fig. S8. Time response of a heptamer of 2-μm PS beads at different CTAC concentrations.
    • fig. S9. Time response of a plus pattern of 2-μm PS beads at a CTAC concentration of 20 mM.
    • fig. S10. Multiple experiments on the assembly of the plus pattern with 2-μm PS beads at a CTAC concentration of 20 mM.
    • fig. S11. Assembly of heterogeneous 1D chains of 2- and 0.96-μm PS beads.
    • fig. S12. Hybrid assembly of 2-μm PS beads and anisotropic PS particles.
    • fig. S13. 3D reconfiguration and manipulation of colloidal assemblies of six 500-nm PS beads.
    • fig. S14. Assembly of the Saturn-ring structure with 0.96-μm and 500-nm PS beads.
    • fig. S15. Interaction potential of silica particles.
    • fig. S16. Electrostatic interaction potential between the CTAC micelle and the PS bead as a function of the micelle-particle distance.
    • fig. S17. Light manipulation by a heptamer assembled from seven 0.96-μm PS beads.
    • fig. S18. 3D reconfiguration and manipulation of colloidal assemblies.
    • note S1. Calculation of the interaction potential.
    • note S2. Exclusion of other bonding mechanisms in CTAC surfactants.
    • note S3. Light manipulation with designed colloidal assembly.
    • note S4. 3D reconfiguration and manipulation of colloidal assemblies.
    • Legends for movies S1 to S8

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Repelling of PS beads in SDS solution and thermal convection of PS beads in Triton X-100 solution.
    • movie S2 (.mp4 format). Dynamic rotation of eight 0.96-μm PS beads.
    • movie S3 (.mp4 format). Dynamic rotation of a hybrid pattern of 2- and 0.96-μm PS beads.
    • movie S4 (.mp4 format). Assembly process of a 2D thermodynamically stable structure with 2-μm PS beads.
    • movie S5 (.mp4 format). Manipulation of the 2D assembly of 2-μm PS beads.
    • movie S6 (.mp4 format). Trapping, rotation, and bonding of the 1D assembly of 2-μm PS beads.
    • movie S7 (.mp4 format). Assembly of anisotropic PS particles.
    • movie S8 (.mp4 format). Manipulation of the 3D assembly of 500-nm PS beads.

    Files in this Data Supplement: