Research ArticleMOLECULAR CHEMISTRY

Reorganization of hydrogen bond network makes strong polyelectrolyte brushes pH-responsive

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Science Advances  05 Aug 2016:
Vol. 2, no. 8, e1600579
DOI: 10.1126/sciadv.1600579
  • Fig. 1 Macroscopic pH-responsive properties of PMETAC brushes.

    The dry thickness of PMETAC brushes used here is ~26 ± 4 nm. (A) Shifts in frequency (Δf) and dissipation (ΔD) of PMETAC brushes as a function of pH at the overtone number (n) of 3. (B) Measured WCA and OCA on the surface of PMETAC brushes as a function of pH. (C) Lubrication tests on the surface of PMETAC brushes at different pH values. (D) The adhesive force between an oil (1,2-dichloroethane) droplet and the PMETAC brushes as a function of pH. Inset: A series of photos taken of the PMETAC brushes approaching and retracting from the oil droplet at pH 2 and 12 during measurements of the adhesive force. (E) The mass of adsorbed lysozyme on the PMETAC brushes as a function of pH. The mass was calculated from the frequency change induced by the lysozyme adsorption according to the Sauerbrey equation. Error bars are obtained from repeated measurements.

  • Fig. 2 Microscopic mechanism of pH response of PMETAC brushes.

    (A) Changes in surface charge density (σ) and wet thickness (dwet) of the PMETAC brushes as a function of pH. (B) Change in mole fraction of OH (Embedded Image) in the outer part of the PMETAC brushes as a function of pH obtained from XPS measurements. The dashed line is a fit to the experimental data by the Langmuir-type adsorption isotherm. The equilibrium constant Embedded Image is determined by the ratio of the adsorption constant to the desorption constant of OH. (C) The ssp SFG spectra of PMETAC brushes in the frequency range of 3000 to 3800 cm−1 as a function of pH. (D) The ssp SFG spectra of PMETAC brushes in the frequency range of 1100 to 1400 cm−1 as a function of pH. Error bars are obtained from repeated measurements.

  • Fig. 3 Schematic illustration of the pH-mediated reorganization of the interchain hydrogen bond network of the PMETAC brushes.

    As pH increases, the interchain hydrogen bonds are formed between the grafted chains due to the adsorption of hydroxide onto the PMETAC brushes. For clarity, the K+, H3O+, and excess free Cl and OH within the PMETAC brushes are not depicted in this figure.

  • Fig. 4 Schematic illustration of the pH-mediated reorganization of the interchain hydrogen bond network of the PSPMA brushes.

    As pH increases, the interchain hydrogen bonds are broken between the grafted chains due to the desorption of hydronium from the PSPMA brushes. For clarity, the Cl, OH, and excess free K+ and H3O+ within the PSPMA brushes are not depicted in this figure.

  • Fig. 5 pH response of PSPMA brushes.

    The dry thickness of the PSPMA brushes used here is ~26 ± 4 nm. (A) The ppp SFG spectra of PSPMA brushes in the frequency range of 1100 to 1400 cm−1 as a function of pH. (B) The ssp SFG spectra of PSPMA brushes in the frequency range of 3000 to 3800 cm−1 as a function of pH. (C) Change in mole fraction of H3O+ (Embedded Image) in the outer part of the PSPMA brushes as a function of pH obtained from XPS measurements. The dashed line is a fit to the experimental data by the Langmuir-type adsorption isotherm. The equilibrium constant Embedded Image is determined by the ratio of the adsorption constant to the desorption constant of H3O+. (D) Shifts in frequency (Δf) and dissipation (ΔD) of the PSPMA brushes as a function of pH at the overtone number (n) of 3. (E) The adhesive force between an oil (1,2-dichloroethane) droplet and the PSPMA brushes as a function of pH. Inset: A series of photos taken at pH 2 and 12 during measurements of the adhesive force. (F) Changes in surface charge density (σ) and wet thickness (dwet) of the PSPMA brushes as a function of pH. Error bars are obtained from repeated measurements.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/8/e1600579/DC1

    fig. S1. The time scale for the pH-responsive behavior of the PMETAC brushes in QCM-D experiments, where the overtone number (n) is 3.

    fig. S2. Δf and ΔD as a function of pH of the blank gold-coated resonator, where the overtone number (n) is 3.

    fig. S3. Shifts in frequency (Δf) and dissipation (ΔD) as a function of pH of the gold-coated resonator grafted with PEMA brushes, where the overtone number (n) is 3.

    fig. S4. Δf and ΔD as a function of pH of the gold-coated resonator grafted with PMETAC brushes at the overtone number (n) of 3, 5, and 7.

    fig. S5. WCA on the surface of PMETAC brushes as a function of pH obtained from the pendant bubble contact angle measurements under the relevant pH solutions.

    fig. S6. Measured oil (hexadecane) contact angle (OCA) on the surface of PMETAC brushes as a function of pH.

    fig. S7. A series of photos taken of the PMETAC brushes approaching and retracting from an oil (1,2-dichloroethane) droplet at different pH values during measurements of the adhesive force.

    fig. S8. Δf and ΔD induced by protein adsorption on the surface of PMETAC brushes as a function of pH.

    fig. S9. In situ AFM measurements of the wet thickness of the PMETAC brushes with pH.

    fig. S10. XPS measurements of the PMETAC brushes as a function of pH.

    fig. S11. Change in fitting strength of the 3200 cm−1 peak of the PMETAC brushes as a function of pH in the ssp SFG spectra.

    fig. S12. The ppp SFG spectra of PMETAC brushes in the frequency range of 3000 to 3800 cm−1 as a function of pH.

    fig. S13. The ppp SFG spectra of PMETAC brushes in the frequency range of 1100 to 1400 cm−1 as a function of pH.

    fig. S14. Change in frequency of the C–O stretching peak of the PMETAC brushes as a function of pH in the ssp SFG spectra.

    fig. S15. Change in fitting strength of the 1220 cm−1 peak of the PMETAC brushes as a function of pH in the ssp SFG spectra.

    fig. S16. The ssp SFG spectra of the PMETAC brushes in the frequency range of 2750 to 3100 cm−1 as a function of pH.

    fig. S17. The ppp SFG spectra of the PMETAC brushes in the frequency range of 1600 to 1800 cm−1 as a function of pH.

    fig. S18. The ssp SFG spectra of the PMETAC brushes in the frequency range of 1600 to 1800 cm−1 as a function of pH.

    fig. S19. Change in frequency of the C–O stretching peak of the PSPMA brushes as a function of pH in the ppp SFG spectra.

    fig. S20. The ssp SFG spectra of the PSPMA brushes in the frequency range of 1100 to 1400 cm−1 as a function of pH.

    fig. S21. Change in fitting strength of the 1220 cm−1 peak of the PSPMA brushes as a function of pH in the ppp SFG spectra.

    fig. S22. The ppp SFG spectra of the PSPMA brushes in the frequency range of 1400 to 1800 cm−1 as a function of pH.

    fig. S23. Change in fitting strength of the 3200 cm−1 peak of the PSPMA brushes as a function of pH in the ssp SFG spectra.

    fig. S24. The ppp SFG spectra of PSPMA brushes in the frequency range of 3000 to 3800 cm−1 as a function of pH.

    fig. S25. XPS measurements of the PSPMA brushes as a function of pH.

    fig. S26. Δf and ΔD as a function of pH of the gold-coated resonator grafted with PSPMA brushes at the overtone number (n) of 3, 5, and 7.

    fig. S27. In situ AFM measurements of the wet thickness of the PSPMA brushes with pH.

    fig. S28. Water contact angle (WCA) on the surface of PSPMA brushes as a function of pH obtained from the contact angle measurements in air.

    fig. S29. WCA on the surface of PSPMA brushes as a function of pH obtained from the pendant bubble contact angle measurements under the relevant pH solutions.

    fig. S30. OCA on the surface of PSPMA brushes as a function of pH.

    fig. S31. Lubrication tests on the surface of PSPMA brushes at different pH values.

    fig. S32. Surface ζ potential and surface charge density (s) as a function of pH for the blank substrate and the quartz substrates grafted with PMETAC, PSPMA, PDMAEMA, and PMA brushes.

    fig. S33. Δf and ΔD of the gold-coated resonator grafted with PMA brushes as a function of pH, where the overtone number (n) is 3.

    fig. S34. Wet thickness of the PMA brushes as a function of pH obtained from ellipsometric measurements.

    fig. S35. Δf and ΔD of the gold-coated resonator grafted with PDMAEMA brushes as a function of pH, where the overtone number (n) is 3.

    fig. S36. Wet thickness of the PDMAEMA brushes as a function of pH obtained from ellipsometric measurements.

    fig. S37. Response of the PMETAC brushes as a function of the concentration of OH or Br.

    fig. S38. Response of the PMETAC and PVBTMA brushes as a function of pH.

    fig. S39. Molar conductivity (∧m) of free strong polyelectrolytes as a function of pH at different polymer concentrations.

    fig. S40. XPS spectra of the PMETAC and PSPMA brushes as a function of pH.

    movie S1. Lubrication tests on the surface of PMETAC brushes at different pH values.

    movie S2. Lubrication tests on the surface of PSPMA brushes at different pH values.

    References (4150)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. The time scale for the pH-responsive behavior of the PMETAC brushes in QCM-D experiments, where the overtone number (n) is 3.
    • fig. S2. Δf and ΔD as a function of pH of the blank gold-coated resonator, where the overtone number (n) is 3.
    • Shifts in frequency (Δf) and dissipation (ΔD) as a function of pH of the gold-coated resonator grafted with PEMA brushes, where the overtone number (n) is 3.
    • fig. S4. Δf and ΔD as a function of pH of the gold-coated resonator grafted with PMETAC brushes at the overtone number (n) of 3, 5, and 7.
    • fig. S5. WCA on the surface of PMETAC brushes as a function of pH obtained from the pendant bubble contact angle measurements under the relevant pH solutions.
    • fig. S6. Measured oil (hexadecane) contact angle (OCA) on the surface of PMETAC brushes as a function of pH.
    • fig. S7. A series of photos taken of the PMETAC brushes approaching and retracting from an oil (1,2-dichloroethane) droplet at different pH values during measurements of the adhesive force.
    • fig. S8. Δf and ΔD induced by protein adsorption on the surface of PMETAC brushes as a function of pH.
    • fig. S9. In situ AFM measurements of the wet thickness of the PMETAC brushes with pH.
    • fig. S10. XPS measurements of the PMETAC brushes as a function of pH.
    • fig. S11. Change in fitting strength of the 3200 cm−1 peak of the PMETAC brushes as a function of pH in the ssp SFG spectra.
    • fig. S12. The ppp SFG spectra of PMETAC brushes in the frequency range of 3000 to 3800 cm−1 as a function of pH.
    • ig. S13. The ppp SFG spectra of PMETAC brushes in the frequency range of 1100 to 1400 cm−1 as a function of pH.
    • fig. S14. Change in frequency of the C–O stretching peak of the PMETAC brushes as a function of pH in the ssp SFG spectra.
    • fig. S15. Change in fitting strength of the 1220 cm−1 peak of the PMETAC brushes as a function of pH in the ssp SFG spectra.
    • fig. S16. The ssp SFG spectra of the PMETAC brushes in the frequency range of 2750 to 3100 cm−1 as a function of pH.
    • fig. S17. The ppp SFG spectra of the PMETAC brushes in the frequency range of 1600 to 1800 cm−1 as a function of pH.
    • fig. S18. The ssp SFG spectra of the PMETAC brushes in the frequency range of 1600 to 1800 cm−1 as a function of pH.
    • fig. S19. Change in frequency of the C–O stretching peak of the PSPMA brushes as a function of pH in the ppp SFG spectra.
    • fig. S20. The ssp SFG spectra of the PSPMA brushes in the frequency range of 1100 to 1400 cm−1 as a function of pH.
    • fig. S21. Change in fitting strength of the 1220 cm−1 peak of the PSPMA brushes as a function of pH in the ppp SFG spectra.
    • fig. S22. The ppp SFG spectra of the PSPMA brushes in the frequency range of 1400 to 1800 cm−1 as a function of pH.
    • fig. S23. Change in fitting strength of the 3200 cm−1 peak of the PSPMA brushes as a function of pH in the ssp SFG spectra.
    • fig. S24. The ppp SFG spectra of PSPMA brushes in the frequency range of 3000 to 3800 cm−1 as a function of pH.
    • fig. S25. XPS measurements of the PSPMA brushes as a function of pH.
    • fig. S26. Δf and ΔD as a function of pH of the gold-coated resonator grafted with PSPMA brushes at the overtone number (n) of 3, 5, and 7.
    • fig. S27. In situ AFM measurements of the wet thickness of the PSPMA brushes with pH.
    • fig. S28. Water contact angle (WCA) on the surface of PSPMA brushes as a function of pH obtained from the contact angle measurements in air.
    • fig. S29. WCA on the surface of PSPMA brushes as a function of pH obtained from the pendant bubble contact angle measurements under the relevant pH solutions.
    • fig. S30. OCA on the surface of PSPMA brushes as a function of pH.
    • fig. S31. Lubrication tests on the surface of PSPMA brushes at different pH values.
    • fig. S32. Surface ε potential and surface charge density (s) as a function of pH for the blank substrate and the quartz substrates grafted with PMETAC, PSPMA, PDMAEMA, and PMA brushes.
    • fig. S33. Δf and ΔD of the gold-coated resonator grafted with PMA brushes as a function of pH, where the overtone number (n) is 3.
    • fig. S34. Wet thickness of the PMA brushes as a function of pH obtained from ellipsometric measurements.
    • fig. S35. Δf and ΔD of the gold-coated resonator grafted with PDMAEMA brushes as a function of pH, where the overtone number (n) is 3.
    • fig. S36. Wet thickness of the PDMAEMA brushes as a function of pH obtained from ellipsometric measurements.
    • fig. S37. Response of the PMETAC brushes as a function of the concentration of OH or Br.
    • fig. S38. Response of the PMETAC and PVBTMA brushes as a function of pH.
    • fig. S39. Molar conductivity (Λm) of free strong polyelectrolytes as a function of pH at different polymer concentrations.
    • fig. S40. XPS spectra of the PMETAC and PSPMA brushes as a function of pH.
    • Legends for movies S1 and S2
    • References (4150)

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mov format). Lubrication tests on the surface of PMETAC brushes at different pH values.
    • movie S2 (.mov format). Lubrication tests on the surface of PSPMA brushes at different pH values.

    Files in this Data Supplement:

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