Microgel structure-driven linear and non-linear mechanical properties of self-assembled microgel films

Soft self-supported cohesive films were formed by self-assembly of pH- and thermo-responsive P(MEO(2)MA-co-OEGMA-co-MAA) microgels without any preparation and/or post-treatments. Linear and non-linear mechanical properties of those films were characterized respectively by dynamic mechanical measurements at low strain and uniaxial extensional tests at high deformation. A relationship between the microstructure of microgels and the mechanical strength of microgel-based films was successfully established. Compared to microgels crosslinked with Oligo(ethylene glycol) diacrylate (OEGDA), microgels with N,N-methylenebisacrylamide (MBA) demonstrate a less crosslinked structure but especially a looser shell which enables the particles to better interpenetrate between one another and resist to higher deformation. Novel films were also designed by controlled mixing microgels and the synthesis side-product, namely water-soluble polymer, WSP, in a ratio with WSP content till 100 %. Those films demonstrated promising mechanical properties due to the structural characteristics of the later. The later act as a lever to tune the elastic modulus of films without diminishing their resistance at strain thanks to its high molar mass and crosslinked structure revealed by Steric Exclusion Chromatography (SEC) measurements.