Link between morphology, structure and interactions of composite microgels

TL;DR

This study combines experiments and simulations to explore how the internal structure and morphology of composite PNIPAM-PEG microgels influence their interactions and phase behavior, revealing tunable properties through morphological control.

Contribution

It provides new insights into how PEG chain placement within microgels affects their internal structure and interparticle interactions, enabling tailored design of microgel properties.

Findings

Internal structure transitions with temperature, from loose to core-embedded PEG.

PEG placement alters interparticle attractions and phase behavior.

Morphological tuning enables control over microgel collective properties.

Abstract

We combine small angle scattering experiments and simulations to investigate the internal structure and interactions of composite Poly(N-isopropylacrylamide)-Poly(ethylene glycol) (PNIPAM-PEG) microgels. At low temperatures the experimentally determined form factors and the simulated density profiles indicate a loose internal particle structure with an extended corona, that can be modeled as a star-like object. Increasing temperature across the volumetric phase transition, the form factor develops an inflection which, using simulations, is interpreted as arising from a configuration in which PEG chains are incorporated in the interior of the PNIPAM network. In this configuration a peculiar density profile characterized by two dense, separate regions is observed, at odds with configurations in which the PEG chains reside on the surface of the PNIPAM core. The conformation of the PEG chains have also profound effects on the interparticle interactions: While chains on the surface reduce the solvophobic attractions typically experienced by PNIPAM particles at high temperatures, PEG chains inside the PNIPAM network shift the onset of attractive interaction at even lower temperatures. Our results show that by tuning the morphology of the composite microgels we can qualitatively change both their structure and their mutual interactions, opening the way to explore new collective behaviors of these objects.