# Effect of Different Network Topologies on Swelling and Mechanical Properties of Polyelectrolyte Hydrogels

## TL;DR

This study explores how different network structures in polyelectrolyte hydrogels affect their mechanical and swelling properties, enabling better material design.

## Contribution

The paper introduces new hydrogel architectures that allow independent tuning of mechanical and swelling properties.

## Key findings

- Floating-chain gels exhibit higher moduli and swelling ratios compared to regular gels.
- Bottlebrush gels show lower moduli and swelling ratios than regular gels.
- Network topology significantly influences salt partitioning and mechanical behavior.

## Abstract

Elastic modulus, G, and equilibrium swelling ratio, Q
V, are two properties of hydrogels, which are
linked by the scaling law G ∼ Q
V
β, where
β = −1 and −9/4 in the low- and high-salt limits,
respectively. Tuning them independently would enable the optimization
of the material design for a wide variety of distinct applications.
In this work, we investigate several possibilities to achieve this
using various network heterogeneities. We employ implicit solvent
coarse-grained molecular dynamics simulations to explore mechanical,
structural, and thermodynamic properties of hydrogels with varying
topologies in comparison to a regular reference gel. We explore regular
gels with tetrafunctional cross-linkers arranged in a diamond-lattice
fashion, which we take as a reference gel, together with bottlebrush
gels, gels with dangling ends, and gels coexisting with floating chains.
We observe that incorporating dangling ends changes the swelling ratio
and bulk modulus following the relation obtained from the regular
reference gel, whereas the bottlebrush and floating-chain gels show
stronger deviations. Specifically, floating-chain gels resulted in
higher moduli and higher swelling ratios, while bottlebrush gels resulted
in lower moduli and lower swelling ratios than the regular counterparts.
Concomitantly, a clear change in salt partitioning was observed for
various hydrogel architectures. Our results show new ways to optimize
the elastic modulus of gels with respect to their swelling behavior
and allow for the optimization and on-demand design of hydrogels.