Effects of Ligand vs. Linker on Phase Behavior and Mechanical Properties of Nanoparticle Gels

TL;DR

This study uses simulations to compare how ligand and linker roles influence the phase behavior and mechanical properties of nanoparticle gels, revealing that structural arrangements significantly affect stretchability and network rigidity.

Contribution

It provides a systematic comparison of ligand versus linker roles in nanoparticle gels, highlighting how their structural differences influence phase separation and mechanical responses.

Findings

Rigid ligands limit phase separation at low nanoparticle volume fractions.

Linked nanoparticle networks are less stretchable than ligand-grafted gels.

Structural arrangements explain differences in mechanical properties.

Abstract

Nanoparticle gels have attracted considerable attention due to their highly tunable properties. One strategy for producing nanoparticle gels involves using strong local attractions between polymeric molecules, such as DNA hybridization or dynamic covalent chemistry, to form percolated nanoparticle networks. These molecules can be used in two distinct roles: as "ligands" with one end grafted to a nanoparticle or as "linkers" with both ends free. Here, we explore how these roles shape the phase behavior and mechanical properties of gel-like nanoparticle assemblies using coarse-grained simulations. We systematically vary the interaction strength and bending stiffness of both ligands and linkers. We find that phase separation can be limited to low nanoparticle volume fractions by making the ligands rigid, consistent with previous studies on linked nanoparticle gels. At fixed interaction strength and volume fraction, both ligand- and linker-mediated nanoparticle assemblies show similar mechanical responses as bending stiffness is varied. However, a comparison between the two association schemes reveals that the linked nanoparticles form rigid percolated networks that are less stretchable than the ligand-grafted gels, despite exhibiting similar tensile strength. We attribute these differences between ligands and linkers to the distinct structural arrangement of nanoparticles within the gel. Our findings highlight the potential to use different association schemes to tune specific mechanical properties.