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Overcharging and reentrant condensation of thermoresponsive ionic microgels

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Abstract

We investigated the complexation of thermoresponsive anionic poly(N-isopropylacrylamide) (PNiPAM) microgels and cationic ε-polylysine (ε-PLL) chains. By combining electrophoresis, light scattering, transmission electron microscopy (TEM) and dielectric spectroscopy (DS) we studied the adsorption of ε-PLL onto microgel networks and its effect on the stability of suspensions. We show that the volume phase transition (VPT) of microgels triggers a large polyion adsorption. Two interesting phenomena with unique features occur: a temperature-dependent microgel overcharging and a complex reentrant condensation. The latter may occur at fixed polyion concentration, when temperature is raised above the VPT of microgels, or by increasing the number density of polycations at fixed temperature. TEM and DS measurements unambiguously show that short PLL chains adsorb onto microgels and act as electrostatic glue above the VPT. By performing thermal cycles, we further show that polyion-induced clustering is a quasi-reversible process: within the time of our experiments large clusters form above the VPT and partially re-dissolve as the mixtures are cooled down. Finally we give a proof that the observed phenomenology is purely electrostatic in nature: an increase of the ionic strength gives rise to polyion desorption from the microgel outer shell.

Graphical abstract: Overcharging and reentrant condensation of thermoresponsive ionic microgels

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Publication details

The article was received on 30 Nov 2017, accepted on 11 Mar 2018 and first published on 17 Apr 2018


Article type: Paper
DOI: 10.1039/C7SM02357J
Citation: Soft Matter, 2018, Advance Article
  • Open access: Creative Commons BY license
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    Overcharging and reentrant condensation of thermoresponsive ionic microgels

    D. Truzzolillo, S. Sennato, S. Sarti, S. Casciardi, C. Bazzoni and F. Bordi, Soft Matter, 2018, Advance Article , DOI: 10.1039/C7SM02357J

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