Combining elastic incoherent neutron scattering and differential scanning calorimetry, we investigate the occurrence of the volume phase transition (VPT) in very concentrated PNIPAM microgel suspensions, from a polymer weight fraction of 30 wt% up to dry conditions. Although samples are arrested at the macroscopic scale, atomic degrees of freedom are equilibrated and can be probed in a reproducible way. A clear signature of the VPT is present as a sharp drop of the mean square displacement of PNIPAM hydrogen atoms obtained by neutron scattering. As a function of concentration, the VPT gets smoother as dry conditions are approached whereas the VPT temperature shows a minimum at about 43 wt%. This behavior is qualitatively confirmed by calorimetry measurements. Molecular dynamics simulations are employed to complement experimental results and gain further insights into the nature of the VPT, confirming that it involves the formation of an attractive gel state between the microgels. Overall, these results provide evidence that the VPT in PNIPAM- based systems can be detected at different time- and length-scales as well as in overcrowded conditions.

Zanatta, M., Tavagnacco, L., Buratti, E., Chiessi, E., Natali, F., Bertoldo, M., et al. (2020). Atomic scale investigation of the volume phase transition in concentrated PNIPAM microgels. THE JOURNAL OF CHEMICAL PHYSICS, 152(20), 204904 [10.1063/5.0007112].

Atomic scale investigation of the volume phase transition in concentrated PNIPAM microgels

Chiessi, E.;
2020-01-01

Abstract

Combining elastic incoherent neutron scattering and differential scanning calorimetry, we investigate the occurrence of the volume phase transition (VPT) in very concentrated PNIPAM microgel suspensions, from a polymer weight fraction of 30 wt% up to dry conditions. Although samples are arrested at the macroscopic scale, atomic degrees of freedom are equilibrated and can be probed in a reproducible way. A clear signature of the VPT is present as a sharp drop of the mean square displacement of PNIPAM hydrogen atoms obtained by neutron scattering. As a function of concentration, the VPT gets smoother as dry conditions are approached whereas the VPT temperature shows a minimum at about 43 wt%. This behavior is qualitatively confirmed by calorimetry measurements. Molecular dynamics simulations are employed to complement experimental results and gain further insights into the nature of the VPT, confirming that it involves the formation of an attractive gel state between the microgels. Overall, these results provide evidence that the VPT in PNIPAM- based systems can be detected at different time- and length-scales as well as in overcrowded conditions.
Pubblicato
Rilevanza internazionale
Articolo
Esperti anonimi
Settore CHIM/02
English
Con Impact Factor ISI
https://doi.org/10.1063/5.0007112
Zanatta, M., Tavagnacco, L., Buratti, E., Chiessi, E., Natali, F., Bertoldo, M., et al. (2020). Atomic scale investigation of the volume phase transition in concentrated PNIPAM microgels. THE JOURNAL OF CHEMICAL PHYSICS, 152(20), 204904 [10.1063/5.0007112].
Zanatta, M; Tavagnacco, L; Buratti, E; Chiessi, E; Natali, F; Bertoldo, M; Orecchini, A; Zaccarelli, E
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/249006
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