Stiffness Tomography of Ultra-Soft Nanogels by Atomic Force Microscopy

The softness of nanohydrogels results in unique properties and recently attracted tremendous interest due to the multi-functionalization of interfaces. Herein, we study extremely soft temperature-sensitive ultra-low cross-linked (ULC) nanogels adsorbed to the solid/water interface by atomic force microscopy (AFM). The ultra-soft nanogels seem to disappear in classical imaging modes since a sharp tip fully penetrates these porous networks with very low forces in the range of steric interactions (ca. 100 pN). However, the detailed evaluation of Force Volume mode measurements allows us to resolve their overall shape and at the same time their internal structure in all three dimensions. The nanogels exhibit an extraordinary disk-like and entirely homogeneous but extremely soft structure-even softer than polymer brushes. Moreover, the temperature-sensitive nanogels can be switched on demand between the ultra-soft and a very stiff state.

Automated summary

This study investigates extremely soft temperature-sensitive ultra-low cross-linked nanogels adsorbed to the solid/water interface using atomic force microscopy. The nanogels exhibit extraordinary disk-like and homogeneous structure, softer than polymer brushes, and can be switched between ultra-soft and very stiff states on demand. Force Volume mode measurements provide detailed evaluation of their overall shape and internal structure in three dimensions.