A molecular dynamics simulation scenario for studying solvent-mediated interactions of polymers and application to thermoresponse of poly(N-isopropylacrylamide) in water

García, Edder J.; Bhandary, Debdip; Horsch, Martin; Hasse, Hans

doi:10.1016/j.molliq.2018.07.025

Cited by 16 publications

(18 citation statements)

References 45 publications

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“…To keep up with the large number of experimental and theoretical results, the role of numerical simulations has recently become more and more crucial for a better understanding of microgels behavior [35]. In particular atomistic simulations have helped evaluating the molecular features that affect the lower critical solution temperature of the polymer and thus the related VPT of microgels [36][37][38][39][40][41][42][43][44][45][46][47] and they provided useful insights into the molecular mechanism that drives the process [48][49][50][51].…”

Section: Introductionmentioning

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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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: 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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“…For all simulations, the temperature was set to 295 K. A low temperature was preferred as it enhances the sampling problems that we want to study. Furthermore, for low temperatures, previous simulations of NIPAM chains with the force field that was applied in the present work have yielded mixed results regarding the prevailing configuration [7,13,25]. For distinctly higher temperatures, the NIPAM chain collapses quickly independently of the chosen initial configuration and then remains in the globule state.…”

Section: Simulationsmentioning

confidence: 63%

“…These doubts are strengthened by the fact that in most of these simulations only very few transitions between the globule and coil states were observed, if any were observed at all. Even the results of the longest available simulations [4,7,13,25] are not entirely conclusive regarding the equilibrium conformation of PNIPAM in water. The authors of [7] and [13] have explicitly mentioned the problems of sampling the equilibrium state in their studies.…”

Section: Introductionmentioning

confidence: 95%

Studying equilibria of polymers in solution by direct molecular dynamics simulations: poly(N-isopropylacrylamide) in water as a test case

García

Hasse

2019

Eur. Phys. J. Spec. Top.

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It is well known that studying equilibria of polymers in solution by atomistic simulations is computationally demanding as a large phase space has to be adequately sampled. Nevertheless, direct molecular dynamics (MD) simulations are often used for this purpose in the literature. To assess whether such approach is adequate, we have conducted a case study for a polymer + solvent system that has been commonly studied with direct MD simulations by many authors: poly(nisopropylacrylamide) (PNIPAM) in water. The total simulation time of the present study is much longer than that typically used in MD simulations of that system. A NIPAM chain of 30 monomers was studied in explicit water at 295 K. Three initial configurations were used. For each configuration, five replicas were run for 1000 ns. The statistical analysis of our data shows that the equilibration time is of the order of 600 -700 ns and that the remaining time for the production run is not sufficient to sample the equilibrium state adequately. These results underpin the well-known difficulty of sampling equilibrium states of polymers in solution with direct MD simulations and the need for a careful interpretation of results of such studies. The problem with the unsatisfactory sampling persists despite the increasing available computing power. Therefore, enhanced sampling techniques and workarounds, such as simplified scenarios or coarse-graining, remain important.

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“…Recently, Garcìa et al [48] pointed out that standard MD simulation might not be able to provide an adequate sampling of PNIPAM chain conformation in solution, because of the high number of involved degrees of freedom and the intrinsic time scale limitations. Indeed, in order to collect suitable statistics from a simulation, coil-to-globule transition should be observed several times, and this can require very long simulations, up to microsecond time scale.…”

Section: Applicationsmentioning

confidence: 99%

Section: Figurementioning

confidence: 99%

From Microscale to Macroscale: Nine Orders of Magnitude for a Comprehensive Modeling of Hydrogels for Controlled Drug Delivery

Casalini

Perale

2019

Gels

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Because of their inherent biocompatibility and tailorable network design, hydrogels meet an increasing interest as biomaterials for the fabrication of controlled drug delivery devices. In this regard, mathematical modeling can highlight release mechanisms and governing phenomena, thus gaining a key role as complementary tool for experimental activity. Starting from the seminal contribution given by Flory–Rehner equation back in 1943 for the determination of matrix structural properties, over more than 70 years, hydrogel modeling has not only taken advantage of new theories and the increasing computational power, but also of the methods offered by computational chemistry, which provide details at the fundamental molecular level. Simulation techniques such as molecular dynamics act as a “computational microscope” and allow for obtaining a new and deeper understanding of the specific interactions between the solute and the polymer, opening new exciting possibilities for an in silico network design at the molecular scale. Moreover, system modeling constitutes an essential step within the “safety by design” paradigm that is becoming one of the new regulatory standard requirements also in the field-controlled release devices. This review aims at providing a summary of the most frequently used modeling approaches (molecular dynamics, coarse-grained models, Brownian dynamics, dissipative particle dynamics, Monte Carlo simulations, and mass conservation equations), which are here classified according to the characteristic length scale. The outcomes and the opportunities of each approach are compared and discussed with selected examples from literature.

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A molecular dynamics simulation scenario for studying solvent-mediated interactions of polymers and application to thermoresponse of poly(N-isopropylacrylamide) in water

Cited by 16 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

Studying equilibria of polymers in solution by direct molecular dynamics simulations: poly(N-isopropylacrylamide) in water as a test case

From Microscale to Macroscale: Nine Orders of Magnitude for a Comprehensive Modeling of Hydrogels for Controlled Drug Delivery

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