Unveiling the Layered Structure of Sulfobetaine Polymer Brushes through Bimodal Atomic Force Microscopy

Evan Angelo Quimada Mondarte, Yuchen Shi, Xue Qi Koh, Xueyu Feng, Dan Daniel, Xin-Xing Zhang, Jing Yu

Research output: Contribution to journalArticlepeer-review


Many zwitterionic polymer brushes exhibit highly stimuli-responsive properties stemming from the strong dipole and electrostatic interaction of their building blocks. Here, we showed how a combination of two atomic force microscopy (AFM) modes can reveal the layered structure of poly(sulfobetaine methacrylate) brushes synthesized by surface-initiated atom-transfer radical polymerization. Due to polydispersity and anti-polyelectrolyte effect, a diffused layer emerges on top of a condensed layer of the brush as a function of salt concentration. The amplitude-modulation mode of the AFM, owing to the tip’s dynamic motion, can only probe the more stable condensed layer near the substrate, whereas the force-spectroscopic mode with its high sensitivity can accurately detect the diffused layer and hence determine the total brush thickness. Infrared spectroscopy and quartz crystal microbalance monitoring revealed the strong ion-screening effect and higher brush hydration propensity of multivalent ions. Different cation valencies also showed subtle effects on the dimensionality of the layered structure. Our results highlight the usefulness of AFM in revealing various contextual phenomena that arise from the unique properties of zwitterionic polymers.
Original languageEnglish (US)
StatePublished - Jun 23 2023

Bibliographical note

KAUST Repository Item: Exported on 2023-07-13
Acknowledgements: This work is supported by the Singapore National Research Fellowship (NRF-NRFF11-2019-0004) and the Singapore Ministry of Education (MOE) Tier 2 Grant (MOE-T2EP30220-0006). X.-X.Z. acknowledges the support from Fundamental Research Funds for the Central Universities (DUT21RC(3)030).

ASJC Scopus subject areas

  • Materials Chemistry
  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry


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