Core–Shell\nMicrogels with Switchable Elasticity\nat Constant Interfacial Interaction

Abstract

Hydrogels\nbased on poly­(<i>N</i>-isopropylacrylamide)\n(pNIPAAm) exhibit a thermo-reversible volume phase transition from\nswollen to deswollen states. This change of the hydrogel volume is\naccompanied by changes of the hydrogel elastic and Young’s\nmoduli and of the hydrogel interfacial interactions. To decouple these\nparameters from one another, we present a class of submillimeter sized\nhydrogel particles that consist of a thermosensitive pNIPAAm core\nwrapped by a nonthermosensitive polyacrylamide (pAAm) shell, each\ntemplated by droplet-based microfluidics. When the microgel core deswells\nupon increase of the temperature to above 34 °C, the shell is\nstretched and dragged to follow this deswelling into the microgel\ninterior, resulting in an increase of the microgel surficial Young’s\nmodulus. However, as the surface interactions of the pAAm shell are\nindependent of temperature at around 34 °C, they do not considerably\nchange during the pNIPAAm-core volume phase transition. This feature\nmakes these core–shell microgels a promising platform to be\nused as building blocks to assemble soft materials with rationally\nand independently tunable mechanics.