Research ArticleNANOMATERIALS

Jamming and overpacking fuzzy microgels: Deformation, interpenetration, and compression

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Science Advances  20 Oct 2017:
Vol. 3, no. 10, e1700969
DOI: 10.1126/sciadv.1700969
  • Fig. 1 Superresolution microscopy of microgels under dilute conditions.

    (A) One-color microscopy. From left to right: Wide-field fluorescence image of individual microgels, single-molecule blinking frame, and final dSTORM image reconstructed from 60,000 blinking frames. In red, the smoothed contours correspond to particle sizes of 439 and 424 nm. (B) Two-color microscopy by spectral demixing. Two spatially equivalent but spectrally separated images are captured side by side on the camera, and the intensity ratio between long and short wavelength channels is used to identify different fluorescent dye species. From left to right: Wide-field fluorescence image of two microgels labeled with CF680R (orange) and AF647 (white), single-molecule frame showing different intensity split for the two dyes, and final reconstructed image obtained from single-molecule localizations on each side. Scale bars, 500 nm.

  • Fig. 2 MSD for dense microgel suspensions at different concentrations and example tracks (t ~ 20 s) centered in a circle of the same size as the particles (R = 470 nm).

    Particles go from simple diffusion at the lowest concentration of 7.4 wt % to complete arrest starting from 8.0 wt %.

  • Fig. 3 Small-angle light scattering from dense microgel suspensions.

    (A) Small-angle light scattering 2D plots from a thin h ~ 50 to 100 μm layer of densely packed pNIPAM microgels. As the concentration is increased, the diffraction rings become wider and the microgels are packed closer to each other. The image gets dimmer as the suspension becomes more homogeneous. Scale bar, r/D = 1 (where r is the radial distance and D is the sample to detector distance). (B) Radially averaged scattered intensity I(q). (C) Pair distance between microgels as a function of concentration obtained from light scattering as 2.2π/qmax (white squares) and from dSTORM images of adjacent microgel pairs (black squares). Dotted line indicates the swollen particle diameter 2Rtot = 940 nm, indicating that particles start touching for c ≥ 8 wt %. arb.u., arbitrary units.

  • Fig. 4 One- and two-color superresolution microscopy of densly packed microgels.

    Wide-field (A) and dSTORM (B) images at high concentration (23.8 wt %). The higher resolution of dSTORM reveals significant microgel deformations. In red, an example of a contour (solid line) and vertices (full circles) used for analysis. (C) 3D dSTORM visualization of microgel particles at high concentration (25.6 wt %). For clarity, the microgel visualizations have been placed closer to each other. An animated 3D rendering is shown in movie S1. (D) dSTORM images of individual microgels showing compression and deformation as the concentration is increased. (E) Two-color 2D dSTORM of microgel pairs revealing partial interpenetration besides compression and deformation. Contour lines are shown for the 23.8 wt % sample with a relative overlap area of 17.38%. Scale bars, 500 nm.

  • Fig. 5 Mechanisms involved in densely packed colloidal sized fuzzy microgels.

    (A) Reduction of effective radii. (B) Isoperimetric quotient. Horizontal dotted line is the measured value under dilute conditions. Each point is obtained from 30 to 50 microgels. (C) Increased overlap area as a function of concentration. Each point corresponds to a single pair. Vertical dashed lines separate the different compression-deformation stages identified in this work. (I) Weak compression and onset of interpenetration. (II) Shape deformation and interpenetration. (III) Isotropic compression of the microgel particles. The effective volume fraction ζeff is related to the mass concentration c via the swelling ratio k ~ 8, ζeff = k c.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/10/e1700969/DC1

    section S1. Static light scattering characterization

    section S2. Contour of microgel images

    section S3. Two-color superresolution microscopy—Calibration procedure

    fig. S1. Form factor of pNIPAM microgels in dilute conditions.

    fig. S2. Determination of microgel contours by using Fourier descriptors.

    fig. S3. Assessment of correlations between size and shape.

    fig. S4. Sample images of deformed microgels at 34 wt % with different values of IsoQ.

    fig. S5. Vertices detected as maxima of curvature for deformed particles at different concentrations.

    fig. S6. Distribution P(Lexp/Lth) at a concentration of 23.8 wt %.

    fig. S7. Principle of two-color imaging by spectral demixing.

    table S1. Average number of facets 〈n〉 as a function of concentration c in the final regime of isotropic compression.

    table S2. SD of the distribution P(Lexp/Lth) characterizing the shape variation in the 2D images of microgels via the fluctuations of Lexp/Lth.

    movie S1. Animated 3D visualization of deformed microgels within a densely packed suspension at 25.6 wt %.

  • Supplementary Materials

    This PDF file includes:

    • section S1. Static light scattering characterization
    • section S2. Contour of microgel images
    • section S3. Two-color superresolution microscopy—Calibration procedure
    • fig. S1. Form factor of pNIPAM microgels in dilute conditions.
    • fig. S2. Determination of microgel contours by using Fourier descriptors.
    • fig. S3. Assessment of correlations between size and shape.
    • fig. S4. Sample images of deformed microgels at 34 wt % with different values of IsoQ.
    • fig. S5. Vertices detected as maxima of curvature for deformed particles at different concentrations.
    • fig. S6. Distribution P(Lexp/Lth) at a concentration of 23.8 wt %.
    • fig. S7. Principle of two-color imaging by spectral demixing.
    • table S1. Average number of facets ‹n› as a function of concentration c in the final regime of isotropic compression.
    • table S2. SD of the distribution P(Lexp/Lth) characterizing the shape variation in the 2D images of microgels via the fluctuations of Lexp/Lth.

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Animated 3D visualization of deformed microgels within a densely packed suspension at 25.6 wt %.

    Files in this Data Supplement:

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