Resumen:
n the traditional view of temperature-driven volume phase transitions in PNIPAm-based microgelsolutions, a monotonic and sharp decrease in particle size occurs upon heating the solution abovethe volume phase transition temperature (VPTT). However, at sufficiently high microgelconcentrations and low salt conditions, our dynamic light scattering experiments reveal anunexpected non-monotonic evolution of particle size when increasing the solution temperature.These findings show that poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAm-co-MAA))microgels swell upon heating the solution in the temperature range where NIPAM is water-soluble(i.e., below the VPPT). Further heating the microgel solution leads to microgel collapse as typicallyobserved at temperatures above the VPTT. This novel behavior depends on particle and saltconcentration. We have observed the expected monotonic temperature-response of P(NIPAm-co-MAA) microgel solutions at low particle density and high salt concentratio