Evidence of a low-temperature dynamical transition in concentrated microgels

Zanatta, M.; Tavagnacco, Letizia; Buratti, Elena; Bertoldo, Monica; Natali, Francesca; Chiessi, Ester; Orecchini, A.; Zaccarelli, Emanuela

doi:10.1126/sciadv.aat5895

Cited by 35 publications

(86 citation statements)

References 45 publications

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“…For such very dense regime, we recently reported an investigation of the dynamical behavior of PNIPAM microgels at low temperatures, well below room temperature. By means of neutron scattering experiments and numerical simulations, it was found that the low-temperature evolution of the mean square displacement (MSD) of the polymer atoms shows a slope change at a temperature T C 250 K, due to the onset of anharmonic motions [23]. This phenomenon in microgels is similar to the known dynamical transition observed in proteins [24,25] and appears to be strongly driven by PNIPAM-water interactions [26].…”

Section: Introductionmentioning

confidence: 85%

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

Zanatta

Tavagnacco

Buratti

et al. 2020

The Journal of Chemical Physics

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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.

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Section: Introductionmentioning

confidence: 85%

“…For c ≥ 43 wt%, data were normalized to 1 at T = 0 K using the low-temperature measurements reported in Ref. [23]. Upon heating, the integrated elastic intensity of the hy -FIG.…”

Section: All-atom Molecular Dynamics Simulationsmentioning

confidence: 99%

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

Zanatta

Tavagnacco

Buratti

et al. 2020

The Journal of Chemical Physics

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“…Swelled PNIPAM microgels synthesized with the original method [6] have a diameter of hundreds of nanometers and display a heterogeneous structure, with a dense core and a looser external region of the particle. The internal nano-structure is suitable to confine molecular entities, such as enzymes or reactants, to promote chemical processes in a selective modality [7] and also to prevent ice nucleation [8,9]. By exploiting the temperature sensitivity of the polymer chain conformation across the volume phase transition temperature (VPTT), the architecture of the network can be reversibly adapted.…”

Section: Introductionmentioning

confidence: 99%

Molecular description of the coil-to-globule transition of Poly(N-isopropylacrylamide) in water/ethanol mixture at low alcohol concentration

Tavagnacco

Zaccarelli

Chiessi

2020

Journal of Molecular Liquids

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Poly(N-isopropylacrylamide), PNIPAM, is a widely studied polymer, which serves as a key constituent of nanostructured soft materials with responsive properties. Upon increasing temperature the PNIPAM polymer chain undergoes a reversible coil-to-globule transition at T ∼305K, which is reflected by a volume phase transition in cross-linked architectures, such as microgels, valuable for many practical applications. The addition of a cosolvent is a simple method to tune the transition temperature according to the specific purpose. In this study, we use atomistic molecular dynamics simulations to explore the solution behavior of a PNIPAM chain in a mixture of water and ethanol, acting as cosolvent, at low alcohol concentration. Our simulations reproduce the occurrence of the coil-to-globule transition of the polymer chain at 289 K, a temperature lower than that measured in water, in full agreement with experimental findings. By monitoring the temperature evolution of structural and dynamical properties of the PNIPAM-water-ethanol ternary system, we detect a localization of ethanol molecules at the polymer interface, mainly due to interactions between isopropyl and ethyl groups. We observe that the transition occurs without a release of adsorbed ethanol molecules, but with a loss of water molecules from the surrounding of PNIPAM hydrophobic moieties that favours the aggregation of ethanol molecules close to the polymer. Our results support the idea that both the decreased chemical potential of water in the bulk of the mixture and the competition between water and ethanol molecules in the interactions with the polymer play a driving role in the transition.

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“…Very recently, a regular dynamical transition was observed for the first time in a nonbiological macromolecule. 319 This offers the possibility to study a wider array of pressure-vitrified macromolecule solutions. If a low temperature dynamical transition would be observed independently of the chemical nature of the macromolecule this transition is highly likely related to the unique behavior of water alone.…”

Section: Discussionmentioning

confidence: 99%

Glass polymorphism and liquid–liquid phase transition in aqueous solutions: experiments and computer simulations

Bachler

Handle

Giovambattista

et al. 2019

Phys. Chem. Chem. Phys.

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Evidence of a low-temperature dynamical transition in concentrated microgels

Abstract: The dynamical transition of hydrated proteins also occurs in nonbiological macromolecules, such as colloidal microgels.

Cited by 35 publications

References 45 publications

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

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

Molecular description of the coil-to-globule transition of Poly(N-isopropylacrylamide) in water/ethanol mixture at low alcohol concentration

Glass polymorphism and liquid–liquid phase transition in aqueous solutions: experiments and computer simulations

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