Nanotribology of hydrogels with similar stiffness but different polymer and crosslinker concentrations

Hua Li; Yu Suk Choi; Mark W Rutland; Rob Atkin

doi:10.1016/j.jcis.2019.12.045

Nanotribology of hydrogels with similar stiffness but different polymer and crosslinker concentrations

J Colloid Interface Sci. 2020 Mar 15:563:347-353. doi: 10.1016/j.jcis.2019.12.045. Epub 2019 Dec 13.

Authors

Hua Li¹, Yu Suk Choi², Mark W Rutland³, Rob Atkin⁴

Affiliations

¹ School of Molecular Sciences, The University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia; Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Perth, WA 6009, Australia. Electronic address: hua.li@uwa.edu.au.
² School of Human Sciences, The University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia.
³ School of Chemical Science and Engineering, KTH Royal Institute of Technology, SE100 44, Sweden; Surfaces, Processes and Formulation, RISE Research Institutes of Sweden, SE114 86 Stockholm, Sweden.
⁴ School of Molecular Sciences, The University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia.

PMID: 31887698
DOI: 10.1016/j.jcis.2019.12.045

Abstract

Hypothesis: The stiffness has been found to regulate hydrogel performances and applications. However, the key interfacial properties of hydrogels, like friction and adhesion are not controlled by the stiffness, but are altered by the structure and composition of hydrogels, like polymer volume fraction and crosslinking degree.

Experiments: Colloidal probe atomic force microscopy has been use to investigate the relationship between tribological properties (friction and adhesion) and composition of hydrogels with similar stiffness, but different polymer volume fractions and crosslinking degrees.

Findings: The interfacial normal and lateral (friction) forces of hydrogels are not directly correlated to the stiffness, but altered by the hydrogel structure and composition. For normal force measurements, the adhesion increases with polymer volume fraction but decreases with crosslinking degree. For lateral force measurements, friction increases with polymer volume fraction, but decreases with crosslinking degree. In the low normal force regime, friction is mainly adhesion-controlled and increases significantly with the adhesion and polymer volume fraction. In the high normal force regime, friction is predominantly load-controlled and shows slow increase with normal force.

Keywords: Adhesion; Colloidal probe atomic force microscopy; Friction; Hydrogel.