Research ArticlePHYSICAL SCIENCE

Belousov-Zhabotinsky autonomic hydrogel composites: Regulating waves via asymmetry

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Science Advances  23 Sep 2016:
Vol. 2, no. 9, e1600813
DOI: 10.1126/sciadv.1600813
  • Fig. 1 Oxidation wave direction is dependent on embedment symmetry.

    (A) Schematic of reflection symmetry about the horizontal (H-H) and vertical (V-V) axes and the definition of the orientation angle, θ. (B) Asymmetric embedment conditions with one or more broken reflection symmetries generate oriented waves. (C) Symmetric embedment conditions with reflection symmetries intact show no preferential wave orientation. Mean orientation angle was averaged over a minimum of 50 oscillations after t > 100 min. Data are means ± SD across n ≥ 10 specimens.

  • Fig. 2 Oxidation wave direction is diffusion-dependent.

    (A) Diffusion barrier case study. Oxidation waves initiate in the corner node exposed to the BZ solution and propagate toward the embedded corner when placed in contact with the glass boundary. Scale bar, 1 mm. (B) Bromide sequester case study. BZ gels placed in contact with the PDMS boundary initiate oxidation waves at the embedded corner and propagate toward the corner node exposed to the BZ solution. Data are means ± SD across 15 specimens. Line cuts parallel (a-a′) to wave direction over 10 min demonstrate the difference in wave direction. Scale bar, 1 mm.

  • Fig. 3 Oxidation wave direction in non-unity AR gels is dependent on embedment.

    (A and B) Schematic indicating wave direction in a (A) nonembedded and (B) embedded rectangular gel. Line plot of signal intensity along the gel centerline versus time for a nonembedded and embedded gel. Scale bars, 1 mm.

  • Fig. 4 Surface and bulk-embedded specimens have preferential wave orientations.

    (A) Waves remain along the long dimension of the gel even when asymmetrically embedded. Left or right directionality is dependent on secondary effects, such as geometric irregularities and local BZ reactant concentrations. (B) Waves travel toward the gel edge if the direction aligns with the long dimension of the gel. Scale bars, 1 mm.

  • Fig. 5 Wave direction switches in bulk-embedded specimens.

    (A) Representative plot of wave initiation point along the catalyzed gel as a function of time. Initiation of the BZ wave transitions from solution edge to embedded edge at approximately 100 min. Inset: Image of bulk-embedded gel and line cut a-a′. (B) Line plots of BZ gel (I) before, (II) during, and (III) after the transition. Scale bar, 1 mm. A movie file of the wave switch behavior is included in the Supplementary Materials (movie S7).

  • Fig. 6 T-specimen geometry indicates preference of interior node wave initiation.

    (A to C) Schematic of T-specimen geometry, top view image of the sample, and return map of Ru oxidation cycle shown for specimens with (A) ls/lb = 0.6, (B) ls/lb = 1.3, and (C) ls/lb = 2.1. The return map correlates the catalyst oxidation state between the three nodes (I, II, and III) denoted in the schematic. Nodes I and II transition from in-phase oxidation to antiphase with increasing ls/lb (blue dots). Nodes I and III are consistently out of phase because node III drives node I for ls/lb = 0.6 and 1.3 or node I drives node III for ls/lb = 2.1. Scale bars, 1 mm. Movie files of these gels are included in the Supplementary Materials (movies S8, S9, and S10).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/9/e1600813/DC1

    fig. S1. Initial gel shrinkage is not correlated with wave reversal.

    fig. S2. Custom cutting jig for sectioning of composite hydrogels.

    fig. S3. Quantification of orientation angle.

    movie S1. Glass notch study (speed, 4×; scale bar, 1 mm).

    movie S2. PDMS notch study (speed, 4×; scale bar, 1 mm).

    movie S3. Nonembedded rectangular strip (speed, 4×; scale bar, 1 mm).

    movie S4. Fully embedded rectangular strip (speed 4×; scale bar, 1 mm).

    movie S5. Surface-embedded rectangular strip (speed, 4×; scale bar, 1 mm).

    movie S6. Bulk-embedded rectangular strip (speed, 4×; scale bar, 1 mm).

    movie S7. Bulk-embedded wave switch (speed, 8×; scale bar, 1 mm).

    movie S8. T-shaped specimen (ls/lb = 0.6; speed, 4×; scale bar, 1 mm).

    movie S9. T-shaped specimen (ls/lb = 1.3; speed, 4×; scale bar, 1 mm).

    movie S10. T-shaped specimen (ls/lb = 2.1; speed, 4×; scale bar, 1 mm).

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Initial gel shrinkage is not correlated with wave reversal.
    • fig. S2. Custom cutting jig for sectioning of composite hydrogels.
    • fig. S3. Quantification of orientation angle.
    • Legends for movies S1 to S10

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.avi format). Glass notch study (speed, 4x; scale bar, 1 mm).
    • movie S2 (.avi format). PDMS notch study (speed, 4x; scale bar, 1 mm).
    • movie S3 (.mpg format). Nonembedded rectangular strip (speed, 4x; scale bar, 1 mm).
    • movie S4 (.mpg format). Fully embedded rectangular strip (speed 4x; scale bar, 1 mm).
    • movie S5 (.mpg format). Surface-embedded rectangular strip (speed, 4x; scale bar, 1 mm).
    • movie S6 (.mpg format). Bulk-embedded rectangular strip (speed, 4x; scale bar, 1 mm).
    • movie S7 (.mpg format). Bulk-embedded wave switch (speed, 8x; scale bar, 1 mm).
    • movie S8 (.mpg format). T-shaped specimen (ls/lb = 0.6; speed, 4x; scale bar, 1 mm).
    • movie S9 (.mpg format). T-shaped specimen (ls/lb = 1.3; speed, 4x; scale bar, 1 mm).
    • movie S10 (.mpg format). T-shaped specimen (ls/lb = 2.1; speed, 4x; scale bar, 1 mm).

    Files in this Data Supplement:

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