Self-Healing of Charged Microgels in Neutral and Charged Environments

The softness of microgels depends on many aspects, suchas particlecharacteristic lengths, sample concentration, chemical compositionof the sample, and elastic moduli of the particle. Here, the responseto crowding of ionic microgels is studied. Charged and uncharged ionicmicrogels are studied in concentrated suspensions of both neutraland ionic microgels with the same swollen size. The combination ofsmall-angle X-ray and neutron scattering with contrast variation allowsus to probe both the particle-to-particle arrangement and the responseof individual ionic microgels to crowding. When the ionic microgelsare uncharged, initial isotropic deswelling followed by faceting isobserved. Therefore, the ionizable groups in the polymeric networkdo not affect the response of the ionic microgel to crowding, whichis similar to what has been reported for neutral microgels. In contrast,the kind of microgels composing the matrix plays a key role once theionic microgels are charged. If the matrix is composed of neutralmicrogels, a pronounced faceting and negligible deswelling is observed.When only charged ionic microgels are present in the suspension, isotropicdeswelling without faceting is dominant.