Looking inside Poly(N-isopropylacrylamide) Microgels: Nanomechanics and Dynamics at Solid–Liquid Interfaces

Abstract

The continuous improvement of synthesis leads to a great variety in the internal architecture and functionality of colloidal hydrogels. A majority of envisioned applications use microgels as colloidal building blocks for layer formation at solid substrates. In this context, a fundamental understanding of the influence of these substrates on the internal structure and physical properties is essential. Especially, the nanomechanical properties of adsorbed poly­(N-isopropylacrylamide) microgel particles are important for their application in cell cultivation, functional surface coatings, and others. Furthermore, these properties are closely related to the swelling behavior and the internal structure and dynamics of these microgels. However, the number of methods that are able to probe the viscoelasticity of adsorbed microgels over the entire vertical particle profile is limited. Grazing incidence neutron scattering techniques are suited to probe soft-matter samples with limited sample volumes at planar solid substrates and allow a resolution in the z-direction. We used neutron spin echo spectroscopy under grazing incidence to access fast thermal fluctuations (10–9 s) over the entire vertical particle profile. Atomic force microscopy nanoindentation was used to characterize the nanomechanical properties of adsorbed microgel particles prepared by batch and continuous monomer feeding methods. The resulting force maps revealed that batch microgels were “hard” and heterogeneous in their Young’s moduli, while the microgels from the continuous method were “soft” and homogeneous. Finally, neutron spin echo spectroscopy under grazing incidence revealed major differences in the vertical dynamic profile of both types of microgels.

Robust, anti-biofouling 2D nanogel films from poly(N-vinyl caprolactam-co-vinylimidazole) polymers

“…In conventional precipitation polymerization methods for preparing nanogels, bis-acrylamide is generally used as a crosslinker in a one-pot process. 37,38 Due to simultaneous initiation and cross-linking, the nanogel obtained by this method has a dense core, rather than being integrally soft. The one-pot method may also sacrifice precision in controlling the number of cross-linking sites and lacks the means to regulate the crosslink length.…”

A Combined Wetting and Scattering Study of the Near Surface Ordering in Sugar Surfactant Based Bicontinuous Microemulsions at Hydrophilic and Hydrophobic Surfaces

“…Furthermore, the relaxation of thermal fluctuations near solid interfaces was also investigated for other soft matter systems. In addition to phospholipid membranes Jaksch et al (2019), these also include adsorbed microgels, e.g., Witte et al (2021).…”

Nanoscale Mechanical Properties of Core–Shell-like Poly-NIPAm Microgel Particles: Effect of Temperature and Cross-Linking Density

“…In previous studies, the temperature effect on topography and nanomechanical properties , of semibatch and batch poly-NIPAm microgels have been studied with AFM. Other studies made on microgel and nanogel particles with AFM methods include investigations on poly­( N -isopropyl­acrylamide- co -acrylic acid) microgel particles where the cross-linking density effect and the two-step volume phase transition were evaluated , as well as investigations on poly-NIPAm microgels where either the combination of co-nonsolvency and temperature response or the internal dynamics of adsorbed batch and feeding microgels were studied. Finally, the nanomechanical properties of oligo­(ethylene glycol) side chain microgels and ultrasoft nanogels were also studied.…”