Interface characteristics of polystyrene melts in free-standing thin films and on graphite surface from molecular dynamics simulations

Lee, Shanghun; Lyulin, Alexey V.; Frank, Curtis W.; Yoon, Do Y.

doi:10.1016/j.polymer.2017.02.078

Cited by 23 publications

(21 citation statements)

References 73 publications

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“…The density in the present united-atom simulations also compares well with that obtained using the fully atomistic models. 73 We find that for linear polymers the glass transition temperature decreases strongly with film thickness below 10 nm. This decrease must be due to the presence of free surfaces, as the interfacial properties, dynamics as well as static structure, differ from those of the bulk-like middle regions.…”

Section: Discussionmentioning

confidence: 72%

“…3,17,18 All these effects have also been observed in fully atomistic simulations of PS. 73 In order to test which of the two mechanisms, increase in the fraction of end groups versus weakening of phenyl-phenyl aromatic (π−π) interactions, is predominant, we compared the films comprised of linear and cyclic PS chains. For both polymers, the glass transition depends strongly on the film thickness, albeit this dependence is slightly weaker for cyclic PS.…”

Section: Discussionmentioning

confidence: 99%

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Interfacial and topological effects on the glass transition in free-standing polystyrene films

Lyulin

Балабаев

Baljon

et al. 2017

The Journal of Chemical Physics

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United-atom molecular-dynamics computer simulations of atactic polystyrene (PS) were performed for the bulk and free-standing films of 2 nm-20 nm thickness, for both linear and cyclic polymers comprised of 80 monomers. Simulated volumetric glass-transition temperatures (T) show a strong dependence on the film thickness below 10 nm. The glass-transition temperature of linear PS is 13% lower than that of the bulk for 2.5 nm-thick films, as compared to less than 1% lower for 20 nm films. Our studies reveal that the fraction of the chain-end groups is larger in the interfacial layer with its outermost region approximately 1 nm below the surface than it is in the bulk. The enhanced population of the end groups is expected to result in a more mobile interfacial layer and the consequent dependence of T on the film thickness. In addition, the simulations show an enrichment of backbone aliphatic carbons and concomitant deficit of phenyl aromatic carbons in the interfacial film layer. This deficit would weaken the strong phenyl-phenyl aromatic (π-π) interactions and, hence, lead to a lower film-averaged T in thin films, as compared to the bulk sample. To investigate the relative importance of the two possible mechanisms (increased chain ends at the surface or weakened π-π interactions in the interfacial region), the data for linear PS are compared with those for cyclic PS. For the cyclic PS, the reduction of the glass-transition temperature is also significant in thin films, albeit not as much as for linear PS. Moreover, the deficit of phenyl carbons in the film interface is comparable to that observed for linear PS. Therefore, chain-end effects alone cannot explain the observed pronounced T dependence on the thickness of thin PS films; the weakened phenyl-phenyl interactions in the interfacial region seems to be an important cause as well.

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Section: Discussionmentioning

confidence: 72%

Section: Discussionmentioning

confidence: 99%

Interfacial and topological effects on the glass transition in free-standing polystyrene films

Lyulin

Балабаев

Baljon

et al. 2017

The Journal of Chemical Physics

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“…L-J potential parameters between different crossed atoms were calculated using the Lorentz-Berthelot combining rules. In the short-range homogeneous flat potential model, the parameters were taken from the literature [23][24][25] and the atoms were frozen for stability as recommended.…”

Section: Methodsmentioning

confidence: 99%

Elucidating esterification reaction during deposition of cutin monomers from classical molecular dynamics simulations

2020

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The structural behavior of some cutin monomers, when deposited on mica support, was extensively investigated by our research group. However, other events, such as esterification reaction (ER), are still a way to explore. In this paper, we explore possible ER that could occur when these monomers adsorb on support. Although classical molecular dynamics simulations are not able to capture reactive effects, here, we show that they become valuable strategies to analyze the initial structural configurations to predict the most favorable reaction routes. Thus, when depositing aleuritic acid (ALE), it is observed that the loss of capacity to form self-assembled (SA) systems favors different routes to occur ER. In pure ALE bilayers systems, an ER is given exclusively through the -COOH and primary -OH groups. In pure ALE monolayers systems, the ER does not happen when the system is self-assembled. However, for disorganized systems, it is able to occur by two possible routes: -COOH and primary -OH (route 1) and -COOH and secondary -OH (route 2). When palmitic acid (PAL) is added in small quantities, ALE SAMs can now form an ER. In this case, ER occurs mostly through the -COOH and secondary -OH groups. However, when the presence of PAL is dominant, ER can occur with either of both possibilities, that is, routes 1 and 2.

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“…Various simulation studies have been conducted to clarify the thermomechanical properties of polymers [21][22][23][24], reinforcements [25,26], and composites [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] using MD simulations. For composites of thermosetting polymers and carbon-nanotubes (CNT), Alien et al and Park et al conducted pullout tests to investigate the effect of the atomisticscale mechanism on the interfacial shear modulus [27,28].…”

Section: Introductionmentioning

confidence: 99%

Effect of Electrostatic Interactions on the Interfacial Energy between Thermoplastic Polymers and Graphene Oxide: A Molecular Dynamics Study

Morita

Oya

Kato³

et al. 2022

Polymers

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In this study, the atomistic-scale mechanisms affecting the interfacial stability of a thermoplastic polymer/graphene oxide interface are investigated using molecular dynamics simulations. Different combinations of thermoplastic polymers (polyethersulfone (PES) and polyetherimide (PEI)) and graphene oxides modified with –O–, –OH, and –COOH are prepared. PES is found to be more strongly stabilized with modified/functionalized graphene oxide in the order of –COOH, –OH, –O–, which is opposite to the stability order of PEI. Our results suggest that these orders of stability are governed by a balance between the following two factors resulting from electrostatic interactions: (1) atoms with a strong charge bias attract each other, thereby stabilizing the interface; (2) the excluded-volume effect of the functional groups on graphene oxide destabilizes the interface by preventing - stacking of aromatic rings.

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Interface characteristics of polystyrene melts in free-standing thin films and on graphite surface from molecular dynamics simulations

Cited by 23 publications

References 73 publications

Interfacial and topological effects on the glass transition in free-standing polystyrene films

Interfacial and topological effects on the glass transition in free-standing polystyrene films

Elucidating esterification reaction during deposition of cutin monomers from classical molecular dynamics simulations

Effect of Electrostatic Interactions on the Interfacial Energy between Thermoplastic Polymers and Graphene Oxide: A Molecular Dynamics Study

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