Updates have been challenging with all of the cross-country move activities. However, I finally found a few minutes to at least post on the newest papers from the group. First comes a collaboration with the Fernandez-Nieves group and Urs Gasser at PSI that we published in JCP entitled “Form factor of pNIPAM microgels in overpacked states“. Actually, those two groups did most (all?) of the heavy lifting there, performing some very nice neutron scattering studies on mixed phases of pNIPAm and deuterated-pNIPAm microgels. However, I don’t mean to diminish the importance of all the dirty work Emily did on the synthesis side, preparing low polydispersity samples of both types of microgels in the same size range – not an easy task, to be sure. The take home message from the work is that microgels don’t start deswelling until they are actually touching – that is there is no “osmotic deswelling” effect in packed phases and the particles maintain their dilute solution hydrodynamic sizes until they start getting mechanically squeezed for space.
The second new paper (published in Langmuir) comes from former group member Dr. Ling Zhang and current grad student Mark Spears entitled “Tunable Swelling and Rolling of Microgel Membranes“. Here they have shown that when microgel-based multilayers are prepared under specific conditions, a pH-induced swelling event can cause the film to delaminate as a single, continuous sheet (see figure). When bilayer films composed of two different types of microgels (even just different size microgels) are prepared, the delamination event is accompanied by differential swelling, which drives rolling into a tube or scroll. The rolled films are cool looking, but we also think this work tells us a great deal about the fundamental interactions and swelling properties of microgel thin films.