Speaker
Description
Poly(N-isopropylacrylamide), commonly known as PNIPAM, is a synthetic polymer mostly exploited for its thermo-responsive nature, but it is also of interest because of its affinity with proteins in terms of energy landscape and amphiphilic chemical composition. Depending on the specific synthesis protocol, different molecular architecture can be originated, such as linear chains or microgels, i.e. polymer network particles with a colloidal size. In this talk I will discuss two studies on the behavior of this synthetic soft material where atomistic molecular dynamics simulations are combined to elastic incoherent neutron scattering experiments.
In the first part I will discuss the behavior of concentrated PNIPAM microgel suspensions across the volume phase transition temperature, where particles go from a swollen state at low temperature to a collapsed state at high temperature. I will show that the volume phase transition in PNIPAM-based systems can be detected at different time- and length-scales as well as in overcrowded conditions [1].
In the second part I will focus on the low temperature behavior of PNIPAM microgels, providing evidence of the occurrence of a dynamical transition akin to that observed in proteins [2,3]. This study is based on a nanoscale model of a microgel network in water, which quantitatively reproduces neutron scattering experiments. By correlating the information extracted from the analysis of the polymer relaxations times, water self-diffusion coefficients and hydrogen bonding interactions I will show that water-polymer coupling plays a driving role in the phenomenon. I will also report the observation of a low temperature dynamical transition in PNIPAM linear chains, which suggest a wide generality of the phenomenon, independently on the macromolecular architecture [4].
References
[1] Zanatta M. et al. “Atomic scale investigation of the volume phase transition in concentrated PNIPAM Microgels” J. Chem. Phys., 2020, 152, 204904.
[2] Zanatta M. et al. “Evidence of a low-temperature dynamical transition in concentrated microgels” Science advances 2018, 4, eaat5895.
[3] Tavagnacco L. et al. “Water-polymer coupling induces a dynamical transition in microgels” The journal of physical chemistry letters, 2019, 10, 870-876.
[4] Tavagnacco L. et al. “Protein-like dynamical transition of hydrated polymer chains” submitted arXiv:2007.11860.
