Computer simulations of asymmetric block copolymers

Hoffmann, Alexander; Sommer, Jens‐Uwe; Blumen, A.

doi:10.1063/1.474994

Cited by 56 publications

(53 citation statements)

References 67 publications

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“…Previous simulations using periodic boundary conditions have also investigate the phase-segregated structure in copolymer systems [74][75][76][77][78][79] and polymer blend systems 80-90 by calculating the structure factor.…”

Section: Resultsmentioning

confidence: 99%

Nanophase-Segregation and Transport in Nafion 117 from Molecular Dynamics Simulations: Effect of Monomeric Sequence

et al. 2004

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Nafion polyelectrolyte is widely used in polymer electrolyte membrane fuel cells (PEMFC) due to its high proton conductivity. The properties of hydrated Nafion are attributed to its nanophase-segregated structure in which hydrophilic clusters are embedded in a hydrophobic matrix. However, there has been little characterization of how the monomeric sequence of the Nafion chain affects the nanophase-segregation structure and transport in hydrated Nafion. To study such properties, we carried out molecular dynamics (MD) simulations of Nafion 117 using two extreme monomeric sequences: one very blocky and other very dispersed. Both produce a nanophase-segregated structure with hydrophilic and hydrophobic domains. However, the blocky Nafion leads to a characteristic dimension of phase-segregation that is ∼60% larger than for the dispersed system. We find that the water-polymer interface is heterogeneous, consisting of hydrophilic patches (water contacting sulfonate groups of Nafion) and hydrophobic patches (water contacting fluorocarbon group). The distribution of the hydrophilic and the hydrophobic patches at the interface (i.e., the heterogeneity of interface) is much more segregated for blocky Nafion. This leads to a water diffusion coefficient for the dispersed case that is ∼25% smaller than for the blocky case (0.46 × 10 -5 vs 0.59 × 10 -5 cm 2 /s at 300 K). The experimental value (0.50 × 10 -5 cm 2 /s) is within the calculated range. On the other hand, we find that the vehicular diffusion of hydronium is not affected significantly by the monomeric sequence. These results should be useful in optimizing the properties of Nafion and as targets for developing other membranes to replace Nafion in PEMFC and other applications.

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Section: Resultsmentioning

confidence: 99%

Nanophase-Segregation and Transport in Nafion 117 from Molecular Dynamics Simulations: Effect of Monomeric Sequence

et al. 2004

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“…Moreover, polymers align parallel to the wall. The latter effect is partially captured in the self-consistent field calculations and favors a perpendicular arrangement of the lamellae [17,18]. The aim of our paper to present a quantitative comparison between the Monte Carlo simulations and self-consistent field calculations and to quantify the effects discussed above in the framework of a well-studied model.…”

Section: Introductionmentioning

confidence: 99%

Symmetric diblock copolymers in thin films. II. Comparison of profiles between self-consistent field calculations and Monte Carlo simulations

Geisinger

Mueller

Binder

1999

The Journal of Chemical Physics

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The structure of lamellar phases of symmetric AB diblock copolymers in a thin film is investigated. We quantitatively compare the composition profiles and profiles of individual segments in self-consistent field calculations with Monte Carlo simulations in the bond fluctuation model for chain length N = 32 and χN = 30. Three film thicknesses are investigated, corresponding to parallel oriented lamellae with 2 and 4 interfaces and a perpendicular oriented morphology. Taking account of capillary waves, we find good quantitative agreement between the Monte Carlo simulations and the self-consistent field calculations. However, the fluctuations of the local interfacial position are strongly suppressed by confinement and mutual interactions between lamellae.

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“…Differences in the required energy for layer breaking (i.e., glide) may play a role in the observed difference in domain coarsening. We understand the origin for such an energy difference by noting that in the cylindrical striped pattern it is possible to glide without traversing a cylindrical domain, as molecules can diffuse or rotate around cylinder cores [23] (with the favorable D par ). In lamellar striped patterns, glide necessarily involves molecular diffusion across domains with the slower D perp .…”

mentioning

confidence: 99%

“…Striped patterns form from parallel oriented cylindrical-phase films and perpendicular lamellar domain orientations. Considerable previous theoretical work has described both the formation and evolution of generalized striped patterns [16][17][18] as well as two-dimensional lamellar block copolymers, [19][20][21][22][23] with predictions for f ranging from 0.2 to 0.5. Experimentally, Harrison et al first measured the time evolution of n(t) in cylindrical phase PS-b-PI diblock copolymer thin-films, [24] finding a value for f of 0.25.…”

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confidence: 99%

Induced Orientational Order in Symmetric Diblock Copolymer Thin Films

Sandstrom²,

2007

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Block-copolymer self-assembly has proven to be an attractive fabrication method for nanotechnology applications because of its ability to precisely define regular patterns with dimensions in the range of 10 to 100 nm. [1,2] Thin films of cylindrical and spherical patterns have been successfully used as lithographic templates in electronics applications [3][4][5][6][7][8] that require an optimal mask profile along with a minimum number of defects. Thin films of lamellar diblock copolymers have an advantageous profile for lithographic applications involving striped patterns; [2,9,10] however, their coarsening dynamics (i.e., pattern-forming properties) have not been as fully characterized as those of their asymmetric counterparts, [11][12][13] and their utility is not yet demonstrated.In this Communication we present a new polymer multilayer fabrication method -analogous to heteroepitaxial film growth -employing thin films of lamellar polystyrene-blockpoly(methyl methacrylate) (PS-b-PMMA). We also demonstrate the effectiveness of the technique by patterning silicon wire arrays with a 20 nm width and a 35 nm center-to-center spacing. In understanding the pattern-formation properties of lamellar-phase PS-b-PMMA, we find that orientational correlations in symmetric (lamellar) thin films evolve much more slowly with time than in asymmetric (cylindrical) films, limiting their use in applications that require long-range orientational order. To overcome this limitation, we demonstrate a multilayer pattern-formation process that features defect-free lamellar pattern formation.Diblock copolymer thin films of cylindrical and lamellar phases both form striped patterns that coarsen with annealing time (t) according to the power law n(t) ∼ t f , [14,15] where n is a correlation length associated with grain size, and f is termed the growth exponent. Striped patterns form from parallel oriented cylindrical-phase films and perpendicular lamellar domain orientations. Considerable previous theoretical work has described both the formation and evolution of generalized striped patterns [16][17][18] as well as two-dimensional lamellar block copolymers, [19][20][21][22][23] with predictions for f ranging from 0.2 to 0.5. Experimentally, Harrison et al. first measured the time evolution of n(t) in cylindrical phase PS-b-PI diblock copolymer thin-films, [24] finding a value for f of 0.25. Earlier experimental work by Garetz et al. [25] measured n in bulk lamellar diblock copolymers. From their data, one can estimate a value for f in the range of 0.066-0.131, i.e., significantly lower than f = 0.25. Despite their relevance in lithographic applications, correlations on thin films of symmetric diblock copolymers have been studied less. We prepared thin-film striped patterns of both parallel PSb-PMMA cylinders (Fig. 1a) and perpendicular PS-b-PMMA lamellae (Fig. 1b and c) to compare the time evolution of n. We spin-casted thin films of cylindrical and lamellar materials, and annealed them (195°C in vacuum) for times ranging from 5 to 4000 min...

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Computer simulations of asymmetric block copolymers

Cited by 56 publications

References 67 publications

Nanophase-Segregation and Transport in Nafion 117 from Molecular Dynamics Simulations: Effect of Monomeric Sequence

Nanophase-Segregation and Transport in Nafion 117 from Molecular Dynamics Simulations: Effect of Monomeric Sequence

Symmetric diblock copolymers in thin films. II. Comparison of profiles between self-consistent field calculations and Monte Carlo simulations

Induced Orientational Order in Symmetric Diblock Copolymer Thin Films

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