Structure and Conformation of Stereoregular Poly(methyl methacrylate) Chains Adsorbed on Graphene Oxide and Reduced Graphene Oxide via Atomistic Simulations

Behbahani, Alireza F.; Motlagh, Ghodratollah Hashemi; Allaei, S. Mehdi Vaez; Harmandaris, Vagelis

doi:10.1021/acs.macromol.9b00574

Cited by 26 publications

(40 citation statements)

References 66 publications

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“…For both RGO and GO, concentrations of epoxied groups and hydroxyl groups are equal. The details of the generation of the RGO and GO model structures are provided elsewhere [ 35 ]. To describe PG and sp

carbon atoms of GO and RGO, a modified Dreiding force field has been used [ 21 , 36 , 37 ].…”

Section: Model and Methodsmentioning

confidence: 99%

“…The equilibrated configurations at higher temperatures were used as the initial configurations for the lower temperatures. The length of the production runs were from around

s up to

s. More details about the model and simulation procedure are reported in the previous work [ 35 ].…”

Section: Model and Methodsmentioning

confidence: 99%

“…The structural properties of the model interfacial systems have been extensively discussed elsewhere [ 35 ]. Here, we only review some of the key results.…”

Section: Structural Propertiesmentioning

confidence: 99%

“…Recently, we studied the interfacial structure and conformation of i-, a-, s-PMMA chains close to pristine graphene (PG), RGO, and GO [ 35 ]. Here, we extend the previous work and investigate the interfacial segmental dynamical properties of these systems at different temperatures (well above T g ).…”

Section: Introductionmentioning

confidence: 99%

“…The model nanosheets have practical importance in the synthesis of polymer nanocomposites; furthermore, they allow for the study of the effects of surface roughness and polymer/surface interactions on the interfacial polymer dynamics. In addition, PMMA chains form tacticity-dependent interfacial structures [ 35 ], and investigating the segmental dynamics of PMMA chains of different tacticities allows for an investigation of the correlation between interfacial structure and segmental dynamics. In the current work, the interfacial segmental dynamics are studied in detail at various temperatures.…”

Section: Introductionmentioning

confidence: 99%

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Gradient of Segmental Dynamics in Stereoregular Poly(methyl methacrylate) Melts Confined between Pristine or Oxidized Graphene Sheets

Behbahani

Harmandaris

2021

Polymers

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Segmental dynamics in unentangled isotactic, syndiotactic, and atactic poly(methyl methacrylate) (i-, a-, and s-PMMA) melts confined between pristine graphene, reduced graphene oxide, RGO, or graphene oxide, GO, sheets is studied at various temperatures, well above glass transition temperature, via atomistic molecular dynamics simulations. The model RGO and GO sheets have different degrees of oxidization. The segmental dynamics is studied through the analysis of backbone torsional motions. In the vicinity of the model nanosheets (distances less than ≈2 nm), the dynamics slows down; the effect becomes significantly stronger with increasing the concentration of the surface functional groups, and hence increasing polymer/surface specific interactions. Upon decreasing temperature, the ratios of the interfacial segmental relaxation times to the respective bulk relaxation times increase, revealing the stronger temperature dependence of the interfacial segmental dynamics relative to the bulk dynamics. This heterogeneity in temperature dependence leads to the shortcoming of the time-temperature superposition principle for describing the segmental dynamics of the model confined melts. The alteration of the segmental dynamics at different distances, d, from the surfaces is described by a temperature shift, ΔTseg(d) (roughly speaking, shift of a characteristic temperature). Next, to a given nanosheet, i-PMMA has a larger value of ΔTseg than a-PMMA and s-PMMA. This trend correlates with the better interfacial packing and longer trains of i-PMMA chains. The backbone torsional autocorrelation functions are shown in the frequency domain and are qualitatively compared to the experimental dielectric loss spectra for the segmental α-relaxation in polymer nanocomposites. The εT′′(f) (analogous of dielectric loss, ε′′(f), for torsional motion) curves of the model confined melts are broader (toward lower frequencies) and have lower amplitudes relative to the corresponding bulk curves; however, the peak frequencies of the εT′′(f) curves are only slightly affected.

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carbon atoms of GO and RGO, a modified Dreiding force field has been used [ 21 , 36 , 37 ].…”

Section: Model and Methodsmentioning

confidence: 99%

“…The equilibrated configurations at higher temperatures were used as the initial configurations for the lower temperatures. The length of the production runs were from around

s up to

s. More details about the model and simulation procedure are reported in the previous work [ 35 ].…”

Section: Model and Methodsmentioning

confidence: 99%

“…The structural properties of the model interfacial systems have been extensively discussed elsewhere [ 35 ]. Here, we only review some of the key results.…”

Section: Structural Propertiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Gradient of Segmental Dynamics in Stereoregular Poly(methyl methacrylate) Melts Confined between Pristine or Oxidized Graphene Sheets

Behbahani

Harmandaris

2021

Polymers

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Modeling the Interface Between Phases in Dense Polymer‐Carbon Black Nanoparticle Composites by Dielectric Spectroscopy: Where Are We Now and What are the Opportunities?

Brosseau

2024

Macro Theory & Simulations

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The macroscopic properties of polymer nanocomposites (PNC) rely largely on the interphase between the polymer chains and the filler particles. One significant difficulty to solve this issue is to quantitatively model the structure‐property correlations due to the interfacial region in these complex materials. While dielectric spectroscopy (DS) measurements are routinely used to characterize the effective permittivity of filled polymers, fitting standard effective medium models and mixing equations to these data remains notoriously difficult to interpret. This is due to the absence of explicit reference to internal length scales characterizing the interfaces in the PNC. As an illustrative example, a two‐level homogenization framework is proposed which enables the extraction of useful information on the impact of a thin interphase confined on a nanometer length scale based on broadband DS data. This model leads to new ways of tuning the interphase so as to optimize the material's response to electric field, a situation relevant for electromagnetic shielding. This approach provides guidance on how to observe directly and experimentally the actual properties of the interface between the phases (as opposed to model‐based inference). Aside from its secure physical foundation in the theory of effective medium, a significant advantage of this approach is that a genetic algorithm (GA) technique applied to this physics‐based model enables the uniqueness of the fit parameters to be considered, as the GA method is robust in terms of finding globally optimum solutions, therefore placing confidence in non‐universal values of the percolation exponents. Recent work in physics‐informed machine learning indicates that the effective dielectric properties of PNC with many degrees of freedom due to their complex morphology can be described by considering only a few degrees of freedom describing the interface features between the phases in these composites.

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Functionalized graphenes as nanofillers for polylactide: Molecular dynamics simulation study

Prasitnok

In‐noi

2019

Polymer Composites

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This simulation studied graphene functionalized with methyl (CH3), hydroxyl (OH), carboxyl (COOH), and amine (NH2) groups as potential nanofillers for polylactide (PLA) biodegradable polymers. Key properties including the structure and dynamics of polymer chains, interaction energy and interfacial shear force between the polymer matrix and the filler, and glass transition temperature (Tg) of the nanocomposites were investigated. Results indicated that graphene functional groups play important roles in the interfacial bonding characteristics between polymer matrix and the filler. Among the fillers studied, graphene modified by COOH groups provided the strongest enhancement of interfacial interaction and shear force between the PLA matrix and the filler. The presence of nanofillers resulted in a moderate shift of the composite Tg compared to the unfilled polymer. The system with stronger interfacial interaction possessed higher Tg due to lower mobility of chain segments induced by the interaction strength between the polymer and the filler.

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Structure and Conformation of Stereoregular Poly(methyl methacrylate) Chains Adsorbed on Graphene Oxide and Reduced Graphene Oxide via Atomistic Simulations

Cited by 26 publications

References 66 publications

Gradient of Segmental Dynamics in Stereoregular Poly(methyl methacrylate) Melts Confined between Pristine or Oxidized Graphene Sheets

Gradient of Segmental Dynamics in Stereoregular Poly(methyl methacrylate) Melts Confined between Pristine or Oxidized Graphene Sheets

Modeling the Interface Between Phases in Dense Polymer‐Carbon Black Nanoparticle Composites by Dielectric Spectroscopy: Where Are We Now and What are the Opportunities?

Functionalized graphenes as nanofillers for polylactide: Molecular dynamics simulation study

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