Volumetric and Rheological Properties of Vitrimers: A Hybrid Molecular Dynamics and Monte Carlo Simulation Study

Perego, Alessandro; Khabaz, Fardin

doi:10.1021/acs.macromol.0c01423

Cited by 51 publications

(98 citation statements)

References 62 publications

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“…Now we turn our attention to the timescale of the bond exchanges, and to better understand the impact of the lifetime of the exchangeable bonds on the dynamic and mechanical properties of the vitrimer, we compute the following autocorrelation function:

C ((), \overset{true˜}{t}) = \frac{〈H (\overset{true˜}{t} + {\overset{t}{true}}_{0}) H ({\overset{true˜}{t}}_{0})〉}{〈H {((), {\overset{t}{true}}_{0})}^{2}〉},

where

H ((), \overset{true˜}{t})

represents a binary function. If two pairs of crosslinking beads are connected at a time interval

t

, then

H ((), \overset{true˜}{t}) = 1

, otherwise

H ((), \overset{true˜}{t}) = 0

53,70 . This correlation function represents the lifetime of the exchangeable bonds that corresponds to the elementary exchange time inside the vitrimer melt 53 …”

Section: Resultsmentioning

confidence: 99%

Effect of bond exchange rate on dynamics and mechanics of vitrimers

Perego

Khabaz

2021

Journal of Polymer Science

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Thermoset polymers are classified amongst the most challenging materials to recycle due to the permanent crosslinks that increase their strength and stiffness compared to their thermoplastic counterparts. Vitrimers provide a promising route to achieve the recyclability of thermosets by implementing dynamic covalent bonds within the network. In this study, a hybrid molecular dynamics (MD)‐Monte Carlo (MC) technique is used to simulate these adaptive networks constructed by a coarse‐grained model. The model proposed in this work describes the dynamic nature of the covalent bonds while maintaining a constant crosslink density. As this framework also shows flexibility in accommodating various exchange reaction activation energy via adjusting the energy difference in MC step, the dynamic and mechanical properties of the vitrimer system are intensely affected by the number of successful bond exchanges happening at every step. In both rubbery and glassy regimes, lowering the energy barrier of the bond exchange reaction results in enhanced motion for the vitrimer segments. This enhanced mobility, in turn, directly affects the stress–strain relationship of these networks, where a higher number of exchanges results in larger deformation before fracture even at low temperatures. Furthermore, the stress distribution in vitrimers shows more homogenous distribution before failure than in the thermoset network.

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C ((), \overset{true˜}{t}) = \frac{〈H (\overset{true˜}{t} + {\overset{t}{true}}_{0}) H ({\overset{true˜}{t}}_{0})〉}{〈H {((), {\overset{t}{true}}_{0})}^{2}〉},

where

H ((), \overset{true˜}{t})

represents a binary function. If two pairs of crosslinking beads are connected at a time interval

t

, then

H ((), \overset{true˜}{t}) = 1

, otherwise

H ((), \overset{true˜}{t}) = 0

53,70 . This correlation function represents the lifetime of the exchangeable bonds that corresponds to the elementary exchange time inside the vitrimer melt 53 …”

Section: Resultsmentioning

confidence: 99%

Effect of bond exchange rate on dynamics and mechanics of vitrimers

Perego

Khabaz

2021

Journal of Polymer Science

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“…Furthermore, understanding of the rheological features is essential because these are related to the materials processing, which is currently underway in conjunction with theoretical points of view [32][33][34] .…”

Section: Discussionmentioning

confidence: 99%

Rheological Characteristics of Cross-Linked Materials with Associative Bond Exchange Mechanisms

Hayashi

2022

J. Soc. Rheol., Jpn

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Vitrimers are a new class of sustainable cross-linked materials with an associative bond exchange mechanism. Bond exchange in vitrimers functions in an addition/elimination pathway, where bond dissociation and reassociation appear to occur simultaneously, as opposed to traditional dynamic covalent bonds that act with discrete distinct, separated steps of bond dissociation and reassociation. Because of these characteristics, network disconnection never occurs in vitrimers, and network topology alternation proceeds with maintaining the constant cross-link density at a temperature greater than the activation temperature of the bond exchange. Some unique rheological properties of vitrimers are highlighted in this review article. The first section summarizes the general relaxation features of vitrimer networks based on temperature-ramp creep test, stress-relaxation test, and temperature-sweep viscoelasticity. The applicability or inapplicability of the time-temperature superposition concept is examined in the latter section, which is vital for understanding the thermorheological simplicity (or complexity) of vitrimer materials.

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“…Although the wide range of timescales in vitrimer systems makes it difficult to use standard atomistic molecular simulations, Perego and Khabaz overcame this barrier by employing hybrid MD/MC simulations to study expansion and chain diffusivity around T v . 69 Using coarse-grained MD, Sciortino et al found that the macroscopic vitrimer viscosity is a reflection of both network topology and cross-linker exchange kinetics. [70][71][72] Coarse-grained slip link modeling also offers a pathway to interrogate the interactions between backbone relaxations and transient cross-linking.…”

Section: Introductionmentioning

confidence: 99%

Unentangled Vitrimer Melts: Interplay between Chain Relaxation and Cross-link Exchange Controls Linear Rheology

Ricarte

Shanbhag

2021

Macromolecules

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Vitrimers are polymer networks that engage in dynamic associative exchange reactions.Their covalent cross-links preserve network connectivity but permit topology fluctuations, making them both insoluble and processable. Here, we use a sticky Rouse model approach to elucidate structure-viscoelasticity relationships for unentangled vitrimer melts. Two different versions of the sticky Rouse model are explored: the simplified sticky Rouse (SSR) and the inhomogeneous Rouse (IHR). Unlike the SSR, the IHR model accounts for interactions between slow modes that arise due to cross-linking and fast Rouse modes of the underlying polymer chain. First, we identify the conditions where the SSR sufficiently approximates the IHR. Then, we use the IHR to explore the influence of structure and temperature on the zeroshear viscosity (η 0 ) and characteristic relaxation time (τ * ). Vitrimers with uniform and random cross-link distributions exhibit larger η 0 and τ * than gradient and blocky types. Polydimethylsiloxane vitrimer (which has a flexible backbone) shows an Arrhenius temperature dependence for η 0 , while polystyrene vitrimer (which has a rigid backbone) is only Arrhenius at high temperatures. For stress relaxation measurements, the short time dynamics represent monomer friction, while the long time dynamics encompass a combination of network strand relaxation and cross-link exchange. Due to the different temperature dependences of the processes, timetemperature superposition fails. The effective rheological activation energy can be estimated a priori from the cross-link exchange activation energy and backbone Williams-Landel-Ferry parameters. Finally, we discuss the utility and limitations of the sticky Rouse approach for studying vitrimer viscoelasticity, and best practices for measuring η 0 and τ * .

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Volumetric and Rheological Properties of Vitrimers: A Hybrid Molecular Dynamics and Monte Carlo Simulation Study

Cited by 51 publications

References 62 publications

Effect of bond exchange rate on dynamics and mechanics of vitrimers

Effect of bond exchange rate on dynamics and mechanics of vitrimers

Rheological Characteristics of Cross-Linked Materials with Associative Bond Exchange Mechanisms

Unentangled Vitrimer Melts: Interplay between Chain Relaxation and Cross-link Exchange Controls Linear Rheology

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