Research ArticleCHEMICAL PHYSICS

Time-resolved structural evolution during the collapse of responsive hydrogels: The microgel-to-particle transition

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Science Advances  06 Apr 2018:
Vol. 4, no. 4, eaao7086
DOI: 10.1126/sciadv.aao7086
  • Fig. 1 SAXS curves.

    (A) SAXS patterns of PNIPAM microgels for the solvent composition change from pure MeOH to xMeOH = 0.20 at different times. (B) Examples of form factor fits for two SAXS patterns obtained at 35 and 435 ms after mixing (for better visibility, the intensity of the SAXS pattern at 435 ms is shifted vertically by a factor of 0.3).

  • Fig. 2 Radial excess electron density profiles calculated from the form factor model.

    The structural change of PNIPAM microgels for a solvent composition change starting from pure MeOH to xMeOH = 0.2 in the MeOH/H2O mixture is presented for different times (5, 235, and 2083 ms).

  • Fig. 3 Microgel size and internal structure change from the form factor fit.

    The collapse transition of the PNIPAM microgel induced by the solvent composition change from pure MeOH to xMeOH = 0.20 is shown. The evolution of the microgel size RT, of the core region Wcore, and of the shell Wshell is represented in black, red, and blue, respectively.

  • Fig. 4 Simulation results of the time evolution of the microgel radius of gyration for systems with different quenching depths ε and different polymer lengths Nm.
  • Fig. 5 Simulation results of the time-dependent structural evolution of a microgel.

    (A) Radial monomer density distribution P(r) for a microgel with Nm = 20 and ε = 2.5. The various curves correspond to different times. The inset shows the time evolution of the outer radius RT, the shell thickness Wshell, and the core thickness Wcore, respectively. (B) The snapshots illustrate the full microgel structure. (Left) Two-dimensional (2D) projection of the 3D monomer density and (right) 2D projection of monomers within a thin slice containing the center of mass of the microgel at indicated times during the simulation.

  • Fig. 6 Scheme of a radial excess electron density profile for PNIPAM microgels in MeOH/H2O mixtures.

    The parameters characterizing the radial excess electron density in this form factor model are the core thickness Wcore, the shell thickness Wshell, the inner radius Rin, the outer radius Rout, and the total radius RT.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/4/eaao7086/DC1

    section S1. Experimental

    section S2. Computer simulation

    fig. S1. Hydrodynamic radius as a function of the methanol mole fraction at 10° and 21°C.

    fig. S2. Normalized scattering curves for PNIPAM microgel at 10°C measured by SLS in the small q range and SAXS in the high q range.

    fig. S3. Static SAXS curves for PNIPAM microgel in xMeOH = 0.20 at 10°C.

    fig. S4. Radially averaged SAXS pattern for PNIPAM in the solvent composition jump from pure MeOH to xMeOH = 0.20 at 5 ms after the mixture.

    fig. S5. Radially averaged SAXS and fit curves for PNIPAM microgel in the solvent composition jump from pure MeOH to xMeOH = 0.20.

    fig. S6. Radial excess electron density profiles calculated from the modeling procedure for PNIPAM microgels in the solvent composition jump from MeOH to xMeOH = 0.20 at 10°C.

    fig. S7. Radially averaged SAXS patterns of PNIPAM microgels for the solvent composition change from pure H2O to xMeOH = 0.20.

    fig. S8. Radially averaged SAXS patterns and fit curves for PNIPAM in the solvent composition jump from pure H2O to xMeOH = 0.20.

    fig. S9. Radial excess electron density profiles calculated from the modeling procedure for PNIPAM microgels in the solvent composition jump from H2O to xMeOH = 0.20 at 10°C.

    fig. S10. Fit results for the collapse transition of PNIPAM induced by the solvent composition jump from pure H2O to xMeOH = 0.20 at 10°C.

    fig. S11. SAXS curves of PNIPAM in xMeOH = 0.20 obtained by the static equilibrium measurements (squares), by the solvent composition change from MeOH (circles), and by the solvent composition change from H2O (triangles).

    fig. S12. Turbidity as a function of time for the collapse transition of PNIPAM microgel induced by changing the solvent composition from pure solvent (either H2O or MeOH) to xMeOH = 0.20 at 10°C.

    fig. S13. Effect of the temperature on the excess enthalpy HE of mixing H2O and MeOH.

    fig. S14. Schematic representation of the stopped-flow setup for the estimation of the increase of the temperature inside the TC-100/10T cuvette upon H2O/MeOH mixing.

    fig. S15. Increase of the temperature inside the TC-100/10T cuvette with time by mixing H2O and MeOH at 10°C to reach a final solvent composition of xMeOH = 0.20.

    fig. S16. Increase of the temperature inside the TC-100/10T cuvette during the H2O/MeOH mixing.

    fig. S17. Comparison of the temperature-dependent size of PNIPAM microgel.

    fig. S18. Simulation results of the time evolution of Formula for microgels with different quenching depths ε and different polymer lengths Nm.

    fig. S19. Results from simulations for evolution of the microgel size and collapse velocity.

    fig. S20. Results from simulations for monomer distribution and microgel conformations.

    table S1. Fit results for PNIPAM microgel in pure H2O, pure MeOH, and xMeOH = 0.20 at 10°C.

    movie S1. Animation of microgel conformational changes during collapse for ε = 2.5.

    References (6674)

  • Supplementary Materials

    This PDF file includes:

    • section S1. Experimental
    • section S2. Computer simulation
    • fig. S1. Hydrodynamic radius as a function of the methanol mole fraction at 10° and 21°C.
    • fig. S2. Normalized scattering curves for PNIPAM microgel at 10°C measured by SLS in the small q range and SAXS in the high q range.
    • fig. S3. Static SAXS curves for PNIPAM microgel in xMeOH = 0.20 at 10°C.
    • fig. S4. Radially averaged SAXS pattern for PNIPAM in the solvent composition jump from pure MeOH to xMeOH = 0.20 at 5 ms after the mixture.
    • fig. S5. Radially averaged SAXS and fit curves for PNIPAM microgel in the solvent composition jump from pure MeOH to xMeOH = 0.20.
    • fig. S6. Radial excess electron density profiles calculated from the modeling procedure for PNIPAM microgels in the solvent composition jump from MeOH to xMeOH = 0.20 at 10°C.
    • fig. S7. Radially averaged SAXS patterns of PNIPAM microgels for the solvent composition change from pure H2O to xMeOH = 0.20.
    • fig. S8. Radially averaged SAXS patterns and fit curves for PNIPAM in the solvent composition jump from pure H2O to xMeOH = 0.20.
    • fig. S9. Radial excess electron density profiles calculated from the modeling procedure for PNIPAM microgels in the solvent composition jump from H2O to xMeOH = 0.20 at 10°C.
    • fig. S10. Fit results for the collapse transition of PNIPAM induced by the solvent composition jump from pure H2O to xMeOH = 0.20 at 10°C.
    • fig. S11. SAXS curves of PNIPAM in xMeOH = 0.20 obtained by the static equilibrium measurements (squares), by the solvent composition change from MeOH (circles), and by the solvent composition change from H2O (triangles).
    • fig. S12. Turbidity as a function of time for the collapse transition of PNIPAM microgel induced by changing the solvent composition from pure solvent (either H2O or MeOH) to xMeOH = 0.20 at 10°C.
    • fig. S13. Effect of the temperature on the excess enthalpy HE of mixing H2O and MeOH.
    • fig. S14. Schematic representation of the stopped-flow setup for the estimation of the increase of the temperature inside the TC-100/10T cuvette upon H2O/MeOH mixing.
    • fig. S15. Increase of the temperature inside the TC-100/10T cuvette with time by mixing H2O and MeOH at 10°C to reach a final solvent composition of xMeOH = 0.20.
    • fig. S16. Increase of the temperature inside the TC-100/10T cuvette during the H2O/MeOH mixing.
    • fig. S17. Comparison of the temperature-dependent size of PNIPAM microgel.
    • fig. S18. Simulation results of the time evolution of ‹R2g (0) › − ‹R2g (t) › for microgels with different quenching depths ε and different polymer lengths Nm.
    • fig. S19. Results from simulations for evolution of the microgel size and collapse velocity.
    • fig. S20. Results from simulations for monomer distribution and microgel conformations.
    • table S1. Fit results for PNIPAM microgel in pure H2O, pure MeOH, and xMeOH = 0.20 at 10°C.
    • References (66–74)

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