Unusual temperature-induced swelling of Q1 Q2 ionizable poly(N-isopropylacrylamide)-based microgels: experimental and theoretical insights into its molecular origin?

J.M. GIUSSI; M.I. VELASCO; G.S. LONGO; R.H. ACOSTA; O. AZZARONI

SOFT MATTER

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2015 vol. 11 p. 8879 - 8879

1744-683X

n the traditional view of temperature-driven volume phase transitions in PNIPAM-based microgel solutions,a monotonic and sharp decrease in the particle size occurs upon heating the solution to above the volumephase transition temperature (VPTT). However, at sufficiently high microgel concentrations and under lowsalt conditions, our dynamic light scattering experiments reveal an unexpected non-monotonic evolutionof the particle size when increasing the solution temperature. These findings show that poly(Nisopropylacrylamide-co-methacrylic acid) (P(NIPAM-co-MAA)) microgels swell upon heating the solution inthe temperature range where NIPAM is water-soluble (i.e., below the VPPT). Further heating the microgelsolution leads to microgel collapse as typically observed at temperatures above the VPTT. This novelbehavior depends on the particle and salt concentration. We have observed the expected monotonictemperature-response of P(NIPAm-co-MAA) microgel solutions at low particle density and h