Speaker
Description
Responsive polymers as poly-N-isopropylacrylamide (PNIPAM) are known as “smart”
materials due to their ability to respond to variations of parameters like temperature, pH,
pressure, and many others. PNIPAM phase behaviour results from a highly temperaturesensitive competition between hydrophobicity of methyl and methylene groups and the
ability of amide groups to make strong hydrogen bonds. When the temperature increases
above a critical value (lower critical solution temperature, LCST), molecular agitation
disrupts hydrogen bonds and leads to the breakdown of the local structure of water around
PNIPAM chains. PNIPAM can be arranged in 3-D networks in order to form microgel
particles which in correspondence of a critical temperature pass from a swollen, hydrated
phase to a collapsed, dehydrated one, giving rise to the so-called Volume Phase Transition
(VPT). Different environments can impact on this delicate balance between hydrophilic and
hydrophobic interactions and strongly affect the LCST [1]. It is interesting to look at the
transition of PNIPAM as an analogous to the cold denaturation of proteins: at high
temperature PNIPAM is in a globular, folded state, but it unfolds to a coil as it is cooled
below a critical temperature. It is known that changes of the environment by the addition of
cosolvents has an impact on the protein behaviour, as they can act as cryopreservant (e.g.,
DMSO), denaturant (e.g., ethanol), stabilizer (e.g. glycerol) [2]. Despite the great interest in
the understanding of the mechanisms underlying these effects, they are not yet completely
understood. In this context, we use a multi-technichal approach to study how different
solvent mixtures affect the PNIPAM hydration states and correlate with changes in the
structure of PNIPAM-based microgel particles across the VPT. We use UV-Raman and
neutron scattering measurements to get microscopic dynamical information to be correlated
to macroscopic structural information obtained by PCS.
[1] D. Mukherji, C. M. Marques, K. Kremer, Nat. Commun. 5, 4882 (2014)
[2] A. Paciaroni, E. Cornicchi, A. De Francesco, M. C. Marconi, G. Onori, Eur. Biophys. J.
35, 591 (2006)
[3] M. Zanatta, L. Tavagnacco, E. Buratti, M. Bertoldo, F. Natali, E. Chiessi, A. Orecchini, E.
Zaccarelli, Sci Adv 4, eeat5895 (2018)
| Topic | 1. Amorphous and soft matter |
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