Conformational Properties of Semiflexible Chains at Nematic Ordering Transitions in Thin Films: A Monte Carlo Simulation

Иванов, В. А.; Rodionova, A. S.; Martemyanova, Julia A.; Stukan, M. R.; Müller, Marcus; Paul, Wolfgang; Binder, Kurt

doi:10.1021/ma402138c

Cited by 32 publications

(38 citation statements)

References 75 publications

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“…The MD does not allow simulating minute-long crystallization processes, but yet enables us to register the atomic-scale polymer ordering near the nanoller surface. 30,31 This was shown for a R-BAPB and CNT composite in our previous study, and may be considered as a pre-crystallization effect. 32 In the present paper we consider two types of nanollers with extreme curvatures: a at graphene sheet which has been here simulated ab ovo and a high-curvature small radius CNT and a pure polymer melt without any ller which we previously simulated.…”

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confidence: 51%

Influence of the carbon nanofiller surface curvature on the initiation of crystallization in thermoplastic polymers

et al. 2014

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Experimental results have shown that graphitizated carbon nanofibers initiate crystallization in R-BAPB polyimides twice as fast as single-wall carbon nanotubes (CNT) leading to the hypothesis that nanofiller curvature influences polyimide crystallization. Therefore, atomistic molecular-dynamics simulations have been performed for R-BAPB in the presence of a flat graphene sheet and the results were compared with those obtained in the presence of a small-radius CNT. The polyimide chain segments tend to lie parallel to the nanofiller surface and this tendency is stronger and the segments are closer to the graphene surface than to the CNT one. Moreover, the density of the polyimide in the near-surface layer is higher for composites filled with graphene than with CNT. This confirms the assumption that the nanofiller surface curvature is indeed a factor influencing the polymer patterning structure, and that a smaller curvature (i.e. flat surface) provides an enhanced initiation of polymer ordering. A IntroductionOne of the most promising ways to improve the performance of polymeric materials consists of developing polymer composites.1-3 Signicant changes aer addition of a ller are inuenced by the polymer and ller properties, but also by the interface interactions between both components. The use of nanoscalereinforcing llers leading to a considerable increase in the interaction area between the composite components has driven the interest of researchers in last years.4-11 Allotropic carbon compounds (carbon black, fullerenes, single-and multiwall nanotubes, nanobers and graphene sheets) are among the popular nanollers. 4,7,9,[11][12][13][14][15][16][17] Polymers with a relatively simple or complicated molecular structure have been and are currently used as matrices in nanocomposite materials. 4,[17][18][19] By combining different types of matrices and nanollers, it is possible to obtain composites with a wide range of physical properties. In some cases, a nanoller can initiate the crystallization of the polymer matrix, 18,20-25 signicantly accelerating the formation of crystallites, or even initiating their formation in the polymer under conditions which do not normally favor the crystallization, as in the case of ODPA-P3 polyimide.26 Crystallization of a polymer matrix in a nanocomposite may signicantly impact its mechanical and thermophysical properties, which should be taken into account when developing new composite materials.18,27,28 The advantage of using nanoparticles for initiation of crystallization is that the formation of a large number of nanoscale crystallites improves the strength of the nanocomposite preventing the typical failure on the boundary area between crystalline regions, thus improving the performance of the material. Therefore, the question arises on how the physical properties of carbon nanollers affect the initiation of crystallization in semicrystalline thermoplastic matrices.Yudin et al. 17,[23][24][25]29 investigated the crystallization initiation of the semicrystalline ther...

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confidence: 51%

Influence of the carbon nanofiller surface curvature on the initiation of crystallization in thermoplastic polymers

et al. 2014

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“…Prefreezing is expected for strongly attractive surfaces or epitaxial systems for which the lattices of the substrate and the crystallizing materials match well (9)(10)(11)(12). In the case of polymers, prefreezing can also manifest itself in the conformational degrees of freedom, leading to an interfacial layer with nematic order, which was recently shown in simulations (13). Because of the difficult accessibility of the buried interface between a melt and a solid, direct observation of crystallization of molecular systems at the interface is lacking, and there is only limited, indirect evidence that, in some cases, prefreezing at the solid interface exists (e.g., for the growth of aluminum crystals on TiB 2 particles) (14,15).…”

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confidence: 76%

Direct observation of prefreezing at the interface melt–solid in polymer crystallization

Löhmann

Henze

Thurn‐Albrecht

2014

Proc. Natl. Acad. Sci. U.S.A.

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Crystallization is almost always initiated at an interface to a solid. This observation is classically explained by the assumption of a reduced barrier for crystal nucleation at the interface. However, an interface can also induce crystallization by prefreezing (i.e., the formation of a crystalline layer that is already stable above the bulk melting temperature). We present an atomic force microscopy (AFM)-based in situ observation of a prefreezing process at the interface of a polymeric model system and a crystalline solid. Explicitly, we show an interfacial ordered layer that forms well above the bulk melting temperature with thickness that increases on approaching melt-solid coexistence. Below the melting temperature, the ordered layer initiates crystal growth into the bulk, leading to an oriented, homogeneous semicrystalline structure.semicrystalline polymers | AFM | thin films | epitaxy T he fundamental process of crystallization from the liquid or gaseous state is of importance in many areas of condensed matter physics and materials science. In practice, crystallization is, in most cases, initiated at an interface to a solid. Crystal growth on solid substrates from the gaseous state has been studied in depth, and detailed understanding of different growth modes as well as interfacial thermodynamics has been achieved (1-3). Much less experimental data are available for crystallization occurring at the interface from the solid to the melt. Generally, crystallization can be initiated at the solid-melt interface by two processes: heterogeneous nucleation or formation of a crystalline wetting layer (so-called prefreezing) (4-6). In terms of thermodynamics, these processes are very different. Whereas nucleation takes place under nonequilibrium conditions at finite supercooling below the melting temperature T m of the bulk material, the formation of a wetting layer is an equilibrium phenomenon taking place above T m (4). It is often assumed that heterogeneous nucleation is the more relevant process (7), but in simulations, nucleation as well as prefreezing have been shown to occur (4,8). Prefreezing is expected for strongly attractive surfaces or epitaxial systems for which the lattices of the substrate and the crystallizing materials match well (9-12). In the case of polymers, prefreezing can also manifest itself in the conformational degrees of freedom, leading to an interfacial layer with nematic order, which was recently shown in simulations (13). Because of the difficult accessibility of the buried interface between a melt and a solid, direct observation of crystallization of molecular systems at the interface is lacking, and there is only limited, indirect evidence that, in some cases, prefreezing at the solid interface exists (e.g., for the growth of aluminum crystals on TiB 2 particles) (14, 15). Recently, it has been suggested that prefreezing also plays a role during epitaxial crystallization in some polymeric systems (16). It is well-known, however, that one or sometimes several ordered layers of organ...

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“…For

ρ = 0.3

both the snapshot of the local order parameter orientation, Figure , and the large value , S ( z ) > 0.7, of the local order throughout the slit, Figure , suggest that one encounters a well ordered nematic state: the order is clearly more pronounced than in a corresponding bulk system at this density. This is clearly an effect due to “capillary nematization,” as previously studied by SCFT as well as by simulations of lattice models of semiflexible polymers …”

Section: Selected MD Resultsmentioning

confidence: 60%

“…This “capillary nematization,” well known for hard rod fluids (e.g., ref and by lattice model Monte Carlo methods . However, as stated above, lattice Monte Carlo models do not include effects related to the deflection length, and SCFT approach does not describe the monomer packing effects near the walls.…”

Section: Introductionmentioning

confidence: 94%

“…In the context of such applications, the interaction of the semiflexible macromolecules with confining walls clearly is of great importance. Thus, the effect of confining walls on the semiflexible polymers in solutions and melts has been studied theoretically by various computational and analytical approaches . However, this work suffers from certain limitations.…”

Section: Introductionmentioning

confidence: 99%

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Capillary Nematization of Semiflexible Polymers

Егоров

Milchev

Binder

2016

Macro Theory & Simulations

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Semiflexible polymers under good solvent conditions confined by two planar parallel repulsive walls are investigated for a wide range of monomer concentrations and distances between the walls, for a case where persistence length and contour length of the macromolecules are almost equal. Chain conformations and local nematic ordering near the walls are studied by both molecular dynamics methods and density functional theory, putting it in perspective with the recent work where the isotropic phase of semiflexible polymer solutions in the vicinity of a single repulsive wall in semi‐infinite geometry is considered. Profiles of the total density of monomers as well as densities of end‐ and middle‐monomers and also the local orientational order parameter across the slit are computed. For small distances between the walls, the increase of monomer density causes a gradual onset of nematic order without a sharp transition while for large distances between the walls a first‐order “capillary nematization” transition is found at a monomer concentration somewhat smaller than needed for the onset of nematic order in the bulk. A brief comparison with related treatments for other models is made.

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Conformational Properties of Semiflexible Chains at Nematic Ordering Transitions in Thin Films: A Monte Carlo Simulation

Cited by 32 publications

References 75 publications

Influence of the carbon nanofiller surface curvature on the initiation of crystallization in thermoplastic polymers

Influence of the carbon nanofiller surface curvature on the initiation of crystallization in thermoplastic polymers

Direct observation of prefreezing at the interface melt–solid in polymer crystallization

Capillary Nematization of Semiflexible Polymers

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