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Measuring elastic properties of granular hydrogels: Effects of capillary interaction and ionic conditions

Jiayin Zhao, Haiyi Zhong, Yixiang Gan

Abstract

The elastic properties of granular hydrogels are commonly characterised under wet conditions, yet the influence of capillary interactions remains unclear. In practical applications, hydrogels operate in aqueous environments containing dissolved ionic species, where swelling and elastic behaviour depend sensitively on ionic conditions. In this study, an experimental setup is developed to measure elastic responses of granular hydrogels under wet conditions. This setup directly observes liquid bridges formation and its evolution during compression. Our results show that neglecting capillary contributions leads to a systematic underestimation of the Young's modulus of hydrogels. Such an underestimation due to the capillary interaction increases as the sample size or its intrinsic stiffness decreases. In addition to the swelling ratio, the tested samples were also prepared under controlled salinity levels. The experimentally observed dependence of stiffness on swelling and salinity conditions is well captured by a modified constitutive model. The development of this study offers a robust testing protocol for measuring elastic properties of hydrogels under various environmental conditions.

Measuring elastic properties of granular hydrogels: Effects of capillary interaction and ionic conditions

Abstract

The elastic properties of granular hydrogels are commonly characterised under wet conditions, yet the influence of capillary interactions remains unclear. In practical applications, hydrogels operate in aqueous environments containing dissolved ionic species, where swelling and elastic behaviour depend sensitively on ionic conditions. In this study, an experimental setup is developed to measure elastic responses of granular hydrogels under wet conditions. This setup directly observes liquid bridges formation and its evolution during compression. Our results show that neglecting capillary contributions leads to a systematic underestimation of the Young's modulus of hydrogels. Such an underestimation due to the capillary interaction increases as the sample size or its intrinsic stiffness decreases. In addition to the swelling ratio, the tested samples were also prepared under controlled salinity levels. The experimentally observed dependence of stiffness on swelling and salinity conditions is well captured by a modified constitutive model. The development of this study offers a robust testing protocol for measuring elastic properties of hydrogels under various environmental conditions.
Paper Structure (12 sections, 5 equations, 6 figures, 2 tables)

This paper contains 12 sections, 5 equations, 6 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Methodology
  3. Materials
  4. Experimental setup
  5. Test procedures
  6. Image processing
  7. Results and Discussion
  8. Effects of capillary interactions
  9. Effective Young's modulus
  10. Constitutive model for effective modulus
  11. Discussion
  12. Conclusions

Figures (6)

  • Figure 1: Temporal evolution of hydrogel water content under varying ionic conditions.
  • Figure 2: Experimental setup: (a) Overview of the custom-developed test setup (side view); (b) A typical experimental image captured by the camera.
  • Figure 3: Image processing for extracting principal radii from the captured liquid bridge.
  • Figure 4: Effects of capillary interactions. (a) Typical force--displacement curves from replicate tests under purified water condition; (b) Measured capillary force versus particle radius.
  • Figure 5: Size-dependent capillary effects. (a) Relative deviation of Young’s modulus versus the effective Young’s modulus; (b) Effective Young’s modulus as a function of particle radius; (c) Size-dependence of relative Young’s modulus.
  • ...and 1 more figures