Modeling of Water Evaporation in Hydrogels from Aspect of Mechanical Analytics

TL;DR

This paper presents a simplified mechanical model for water evaporation in hydrogels, linking stretching forces to vapor pressure and deformation, validated by experiments on common hydrogels.

Contribution

A novel mechanical model that predicts evaporation rates and deformation of hydrogels based solely on elastic stretching considerations.

Findings

Model accurately predicts vapor pressure and evaporation rates.

Hydrogels with higher modulus retain water better.

Good agreement with experimental data.

Abstract

Water evaporation is critically important for hydrogels in open-air applications, but theoretically modeling is difficult due to the complicated intermolecular interactions and sustained deformation. In this work, we construct a simplified model to describe the state of water inside the hydrogel by only considering mechanical stretching. We employ "negative pressure" to bridge the stretching force in water and elastic force generated by the polymer network. Combined with a constitutive equation of elasticity for hydrogels and classic diffusion equation, this model gives a universal solution to calculate the saturated vapor pressure, dynamic evaporation rates and real-time deformation of different hydrogels. The calculated results agree well with experiments results both in steady state and dynamic process for commonly used poly 2-hydroxyethyl methacrylate and polyacrylamide hydrogels with diverse components. In addition, the model predicts that, hydrogels with high modulus shows stronger ability to retain water in open environment.