Link between Morphology, Structure, and Interactions of Composite Microgels

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 starlike object. With increasing temperature across the volumetric phase transition, the form factor develops an inflection that, using simulations, is interpreted as arising from a conformation in which PEG chains are incorporated in the interior of the PNIPAM network. This gives rise to a peculiar density profile characterized by two dense, separated regions, at odds with configurations in which the PEG chains reside on the surface of the PNIPAM core. The conformation of the PEG chains also have profound effects on the interparticle interactions: Although chains on the surface reduce the solvophobic attraction 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.

Probing Temperature Responsivity of Microgels and Its Interplay with a Solid Surface by Super-Resolution Microscopy and Numerical Simulations

“…We expect that dSTORM will be very useful to study different systems, such as copolymer microgels with more complex internal architectures, where different temperature behaviors of the forming polymers are at play. 13,47,48 Changing the Surface Affinity: the VPT of Microgels Close to a Hydrophobic Surface. We now discuss the case of microgels close to a hydrophobic surface.…”

“…Altogether, these results validate the adopted experimental procedure, indicating that they can clearly detect the changes in the internal structure of the particles at different temperatures. We expect that dSTORM will be very useful to study different systems, such as copolymer microgels with more complex internal architectures, where different temperature behaviors of the forming polymers are at play. ,, …”

“…8−11 Additionally, it is worth stressing that synthesis advances allow tuning of the microgel size and architecture, as well as decoration and functionalization, all of which in the end influence the responsiveness to external cues 9,12 and the mutual effective interactions between the particles. 13 All these features provide microgels with a richer behavior compared to standard "hard-sphere" colloids: in particular, the possibility to tune their properties in a controllable way makes them suitable as building blocks for designing materials that can be used for several purposes, from understanding fundamental problems in physics 9,14−17 to industrial applications such as, for example, viscosity modifiers, tunable optical scattering components, or carrier agents. 18−20 In this context, understanding how the internal complexity of microgels at the nanoscale translates into specific macroscopic material properties is one of the main goals of soft-matter physics.…”

“…Even more intriguing is their ability to respond to external stimuli: depending on the type of polymer employed in the synthesis, microgels can adjust their size in response to temperature, light, or pH changes, to name a few. − A well-known example is that of poly­( N -isopropylacrylamide) (pNIPAM)-based microgels that exhibit conformational changes in response to solvent composition or temperature. Specifically, they undergo a reversible volume phase transition (VPT) at a temperature of about 32 °C that leads to network shrinking and, consequently, to a change in the size of the particle. − Additionally, it is worth stressing that synthesis advances allow tuning of the microgel size and architecture, as well as decoration and functionalization, all of which in the end influence the responsiveness to external cues , and the mutual effective interactions between the particles …”

Deep learning potential of mean force between polymer grafted nanoparticles

“…The structure, morphology, and phase behaviour of these multicomponent systems such as colloidal suspension, composite microgels, protein crowding in a cell, and polymer composites are determined by the complex interplay between the packing entropy of nanoparticles with varying size and shape and interparticle interaction with varying strength and range. [1][2][3][4][5][6][7][8] In many of these systems, nonadsorbing macromolecules induce attractive forces between nanoparticles (NPs), which are known as depletion forces. [9][10][11] The depletion force has been exploited extensively to assemble nanoparticles into a variety of superstructures.…”