Buckling and Interfacial Deformation of Fluorescent Poly(N-isopropylacrylamide) Microgel Capsules

Abstract

Hollow microgels are fascinating model systems at the crossover between polymer vesicles, emulsions, and colloids as they deform, interpenetrate, and eventually shrink at higher volume fraction or when subjected to an external stress. Here, we introduce a system consisting of microgels with a micrometer-sized cavity enabling a straightforward characterization in situ using fluorescence microscopy techniques. Similarly to elastic capsules, these systems are found to reversibly buckle above a critical osmotic pressure, conversely to smaller hollow microgels, which were previously reported to deswell at high volume fraction. Simulations performed on monomer-resolved in silico hollow microgels confirm the buckling transition and show that the presented microgels can be described with a thin shell model theory. When brought to an interface, these microgels, that we define as microgel capsules, strongly deform and we thus propose to utilize them to locally probe interfacial properties within a theoretical framework adapted from the Johnson–Kendall–Roberts (JKR) theory. Besides their capability to sense their environment and to address fundamental questions on the elasticity and permeability of microgel systems, microgel capsules can be further envisioned as model systems mimicking anisotropic responsive biological systems such as red blood and epithelial cells thanks to the possibility offered by microgels to be synthesized with custom-designed properties.

Thermoresponsive Dendronized Microgels through In Situ Cross-Linking Polymerization to Exhibit Enhanced Confinement for Solvatochromic Dyes

“…An increase in the proportion of EGDMA from 2 to 5% resulted in microgels with an increased size of 729 from 199 nm (comparing MG 2.5 ‑ 5 ‑ 400/65 and MG 2.5 ‑ 2 ‑ 400/65 with MG 2.5 ‑ 3 ‑ 400/65 ). It is necessary to point out that the microgels shown through AFM measurements should have flattened upon absorption on the substrate, similarly as revealed in the literature. − The deformation became even more pronounced when microgels were closely packed as shown in Figure b, and spherical microgels transformed into hexagonal arrays. − …”

Influence of Architecture on the Interfacial Properties of Polymers: Linear Chains, Stars, and Microgels

“…Furthermore, the second increase between ∼600 to 400 cm 2 mg –1 and ∼32 to 34 mN m –1 is more shallow. This can be understood when considering the elasticity of the entire microgel; changing the microgels’ internal architecture, i.e., replacing the denser core by a solvent-filled cavity, allows for a larger deformation at interfaces. ,, …”

Exploring the 3D Conformation of Hard‐Core Soft‐Shell Particles Adsorbed at a Fluid Interface

“…The same procedure was also exploited in Refs. [ 8 , 50 ] for the assembly of hollow microgel particles. Subsequently, the core with the grafted polymer chains were inserted in the cavity of the hollow polymer network and bonds were created between chains and polymer network, thus forming a core‐shell microgel.…”