International Journal of Molecular Sciences Article Glass and Jamming Rheology in Soft Particles Made of PNIPAM and Polyacrylic Acid Silvia Franco 1,2 , Elena Buratti 2 , Valentina Nigro 2,3 , Emanuela Zaccarelli 2,4 , Barbara Ruzicka 2,4,* and Roberta Angelini 2,4,* 1 Dipartimento di Scienze di Base e Applicate per l’Ingegneria (SBAI), Sapienza Università di Roma, 00185 Roma, Italy;
[email protected] 2 Istituto dei Sistemi Complessi del Consiglio Nazionale delle Ricerche (ISC-CNR), Sede Sapienza, 00185 Roma, Italy;
[email protected] (E.B.);
[email protected] (V.N.);
[email protected] (E.Z.) 3 ENEA Centro Ricerche Frascati, FSN-TECFIS-MNF Photonics Micro and Nanostructures Laboratory, 00044 Frascati, Rome, Italy 4 Dipartimento di Fisica, Sapienza Università di Roma, 00185 Roma, Italy * Correspondence:
[email protected] (B.R.);
[email protected] (R.A.) Abstract: The phase behaviour of soft colloids has attracted great attention due to the large variety of new phenomenologies emerging from their ability to pack at very high volume fractions. Here we report rheological measurements on interpenetrated polymer network microgels composed of poly(N- isopropylacrylamide) (PNIPAM) and polyacrylic acid (PAAc) at fixed PAAc content as a function of weight concentration. We found three different rheological regimes characteristic of three different states: a Newtonian shear-thinning fluid, an attractive glass characterized by a yield stress, and a jamming state. We discuss the possible molecular mechanisms driving the formation of these states. Citation: Franco, S.; Buratti, E.; Keywords: rheology; microgel; shear-thinning; glass; jamming; soft colloids; PNIPAM Nigro, V.; Zaccarelli, E.; Ruzicka, B.; Angelini, R.