Extending the timescale of molecular simulations by using time–temperature superposition: rheology of ionic liquids

Balogun, A L B; Lazarenko, Daria; Khabaz, Fardin; Khare, Rajesh

doi:10.1039/d1sm00701g

Cited by 12 publications

(18 citation statements)

References 54 publications

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“…Figure C shows that it is possible to derive the TTS shift factors of the viscoelastic moduli and local displacements from the characteristic decay time of the intermediate scattering function. In order to evaluate the generality of this result, we have revisited atomistically detailed MD simulations for an imidazolium-based ionic liquid . This ionic liquid consists of the 1-(cyclohexylmethyl)-3-methylimidazolium cation ([CyhmC 1 im] + ) and the bistriflimide anion ( [NTf 2 ] − ).…”

Section: Discussionsupporting

confidence: 79%

“…The detailed chemical structure and a description of the simulation procedure are given in the Supporting Information (Figure S3 and section SI2). We have previously reported that the simulated volumetric and linear viscoelastic properties of this ionic liquid are in a good agreement with experiments . In Figure C, we observe that the shift factors obtained from the master MSD curves both for the cation ([CyhmC 1 im] + ) and anion ([NTf 2 ] − ) at different temperatures are collapsed on the same line a T = a T ′ = τ r when they are plotted against the rescaled ISF decay time.…”

Section: Discussionsupporting

confidence: 74%

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Microscopic Dynamics and Viscoelasticity of Vitrimers

et al. 2022

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We implement a hybrid molecular dynamics/Monte Carlo simulation to study the microscopic dynamics and the macroscopic rheology of vitrimers with a fast bond exchange rate. We show that the linear viscoelastic properties and mean squared displacement of the vitrimers collapse onto master curves by applying the same shift factors that follow the Williams−Landel−Ferry equation at low temperatures and Arrhenius-like behavior at high temperatures. The linkage between the microscopic dynamics and the linear rheology of vitrimers is established using the generalized Stokes−Einstein relationship, which efficiently extends the timescale of simulations and predicts the viscoelasticity. The values of the shift factors are related to the characteristic decay time of the intermediate scattering function, which is accessible in scattering experiments. The same results hold in the case of an all-atom model of an ionic liquid. Our methodology provides a microscopic basis for the time-superposition principle and predicts the macroscopic rheology of thermo-rheologically simple vitrimers.

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Section: Discussionsupporting

confidence: 79%

Section: Discussionsupporting

confidence: 74%

Microscopic Dynamics and Viscoelasticity of Vitrimers

et al. 2022

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“…We note that the implementation of the SLLOD equation, when SAOS flows are used, is only valid when the deformation frequency is above 2 × 10 −9 s −1 in our simulations. 43,50,52 For lower frequencies where the propagation of the shear forces are slow in the material, this method is not suitable. The second regime is found at intermediate temperatures (120 ≤ T ≤ 380 K) and exhibits a rapid increase of α corresponding to the glass transition of the system.…”

Section: Model and Simulation Detailsmentioning

confidence: 99%

“…The SBR modeled in this study has a T g of 274 ± 5 K, which is higher than the reported experimental value of 227 K. 72 The higher cooling rate used in simulations compared to experiments causes this apparent disagreement between experimental and simulation glass transition temperature, and it has been reported in previous literature works for linear and cross-linked polymers, ionic liquids, and asphalt. 43,49,61,73 In addition, the transition regime is broader than that in experiments. The divergence is also seen in the density close to the T g of the simulation and below that in the glassy state.…”

Section: Model and Simulation Detailsmentioning

confidence: 99%

“…Additionally, taking the WLF equation into account for the discrepancy of T g values between simulations and experiments, 49 they were able to shift the universal curves obtained in simulations and match them with the experimental ones, where they showed a remarkable agreement between the two sets of data. In this study, we follow a similar procedure to the one reported by Balogun et al 43 and apply it to a model SBR polymer.…”

Section: Introductionmentioning

confidence: 99%

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Rheology of Styrene–Butadiene Rubber: Bridging the Gap between Timescales of Atomistically-Detailed Molecular Simulations and Experiments

Perego

Mani

Khabaz

2022

ACS Appl. Polym. Mater.

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We present an atomistically-detailed molecular dynamics (MD) simulation study of the rheology and dynamics of a single styrene−butadiene rubber (SBR) chain. The density and coefficient of thermal expansion of the simulated system are consistent with the experimental observations. Nonequilibrium molecular dynamics (NEMD) is used to characterize the storage and loss moduli of SBR. Both rheological and dynamic (mean squared displacement) properties of SBR successfully collapse onto universal curves using a set of shift factors with the help of the time−temperature superposition (TTS) principle. The mismatch in the timescale of MD simulations and experiments is resolved by rescaling the shift factors to accommodate the influence of the fast cooling rate present in MD simulations. Both storage and loss moduli show an excellent agreement between simulations and experimental results. As rheology simulations are performed under nonequilibrium conditions, they are often computationally expensive; thus being able to determine the shift factors from simulations under equilibrium conditions has the potential to significantly reduce the computational cost of these simulations. Furthermore, the ability to bridge the timescale difference between experiments and simulations allows MD simulations to predict the rheology of polymers such as SBR at a wide range of frequencies.

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