On complex structure of local free volume in bond fluctuation model of polymer matrix

Radosz, Wojciech; Orlik, Rafal; Pawlik, Grzegorz; Mituś, Antoni C.

doi:10.1016/j.polymer.2019.05.068

Cited by 3 publications

(22 citation statements)

References 36 publications

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“…The distribution in space of local free volume, characterized by local void parameter V , displays complex fractal-like structure [ 157 ] and leads to a quasi binary physical picture of the structure of an instantaneous configuration: about half of cells are blocked by monomers, while approximately one third of them have their neighbourhood nearly free of monomers. Cells with

form scale-free clusters with fractal dimension dependent on the size of the cluster.…”

Section: Resultsmentioning

confidence: 99%

“…The correspondence between the size of the cube and the corresponding scale in real polymeric materials can be roughly estimated using the length of the Kuhn segment which corresponds to the averaged bond length in BFM. For example, the Kuhn’s length for PMMA is

nm [ 158 ] leading to the conclusion that the volume of the cube used to calculate V is approximately

[ 157 ].…”

Section: Methodsmentioning

confidence: 99%

“… Scheme for calculation of local parameters V ( a ) and C ( b )—see text for more details. Based on [ 157 ]. …”

Section: Figurementioning

confidence: 99%

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Modeling of Nonlinear Optical Phenomena in Host-Guest Systems Using Bond Fluctuation Monte Carlo Model: A Review

et al. 2021

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We review the results of Monte Carlo studies of chosen nonlinear optical effects in host-guest systems, using methods based on the bond-fluctuation model (BFM) for a polymer matrix. In particular, we simulate the inscription of various types of diffraction gratings in degenerate two wave mixing (DTWM) experiments (surface relief gratings (SRG), gratings in polymers doped with azo-dye molecules and gratings in biopolymers), poling effects (electric field poling of dipolar molecules and all-optical poling) and photomechanical effect. All these processes are characterized in terms of parameters measured in experiments, such as diffraction efficiency, nonlinear susceptibilities, density profiles or loading parameters. Local free volume in the BFM matrix, characterized by probabilistic distributions and correlation functions, displays a complex mosaic-like structure of scale-free clusters, which are thought to be responsible for heterogeneous dynamics of nonlinear optical processes. The photoinduced dynamics of single azopolymer chains, studied in two and three dimensions, displays complex sub-diffusive, diffusive and super-diffusive dynamical regimes. A directly related mathematical model of SRG inscription, based on the continuous time random walk (CTRW) formalism, is formulated and studied. Theoretical part of the review is devoted to the justification of the a priori assumptions made in the BFM modeling of photoinduced motion of the azo-polymer chains.

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form scale-free clusters with fractal dimension dependent on the size of the cluster.…”

Section: Resultsmentioning

confidence: 99%

nm [ 158 ] leading to the conclusion that the volume of the cube used to calculate V is approximately

[ 157 ].…”

Section: Methodsmentioning

confidence: 99%

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Modeling of Nonlinear Optical Phenomena in Host-Guest Systems Using Bond Fluctuation Monte Carlo Model: A Review

et al. 2021

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“…This leads, in general, to a complex dynamics of guest molecules with sufficiently small spatial dimensions 48 , since some of them occupy voids and display the dynamics of an unconstrained molecule. The characteristic linear sizes of voids were roughly estimated as 6-9 nm for PMA matrix 47 , thus enabling the unconstrained poling scenario presented in this paper. The only difference between high- and low temperature scenarios for small guest molecules is that the dynamical evolution of local polymer environment of an octupole is present in the former and absent in the latter case.…”

Section: Summary and Discussionmentioning

confidence: 98%

“…It takes into account the local inhomogeneity of the polymer matrix and the relation between characteristic spatial scales of local voids and of guest molecules. This topic was recently studied by one of us using Monte Carlo simulations 47 , leading to the conclusion that voids form scale-free clusters with power-law distribution of sizes and complex fractal structure, with fractal dimension dependent on the size of a cluster. This leads, in general, to a complex dynamics of guest molecules with sufficiently small spatial dimensions 48 , since some of them occupy voids and display the dynamics of an unconstrained molecule.…”

Section: Summary and Discussionmentioning

confidence: 99%

Nanoscale ordering of planar octupolar molecules for nonlinear optics at higher temperatures

Jarema

Mituś

Zyss

2021

Sci Rep

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We develop scenarios for orientational ordering of an in-plane system of small flat octupolar molecules at the low-concentration limit, aiming towards nonlinear-optical (NLO) applications at room temperatures. The octupoles interact with external electric poling fields and intermolecular interactions are neglected. Simple statistical-mechanics models are used to analyze the orientational order in the very weak poling limit, sufficient for retrieving the NLO signals owing to the high sensitivity of NLO detectors and measurement chains. Two scenarios are discussed. Firstly, the octupolar poling field is imparted by a system of point charges; the setup is subject to cell-related constraints imposed by mechanical strength and dielectric breakdown limit. The very weak octupolar order of benchmarking TATB molecules is shown to emerge at Helium temperatures. The second scenario addresses the dipoling of octupolar molecules with a small admixture of electric dipolar component. It requires a strong field regime to become effective at Nitrogen temperature range. An estimation of the nonlinear susceptibility coefficient matrix for both scenarios is done in the high-temperature (weak interaction) limit formalism. We argue that moderate modifications of the system like, e.g., an increase of the size of the octupole, accompanied by dipole-assisted octupoling, can increase the poling temperature above Nitrogen temperatures.

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Characterization of Monte Carlo Dynamic/Kinetic Properties of Local Structure in Bond Fluctuation Model of Polymer System

2021

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We report the results of the characterization of local Monte Carlo (MC) dynamics of an equilibrium bond fluctuation model polymer matrix (BFM), in time interval typical for MC simulations of non-linear optical phenomena in host-guest systems. The study contributes to the physical picture of the dynamical aspects of quasi-binary mosaic states characterized previously in the static regime. The polymer dynamics was studied at three temperatures (below, above and close to the glass transition), using time-dependent generalization of the static parameters which characterize local free volume and local mobility of the matrix. Those parameters play the central role in the kinetic MC model of host-guest systems. The analysis was done in terms of the probability distributions of instantaneous and time-averaged local parameters. The main result is the characterization of time scales characteristic of various local structural processes. Slowing down effects close to the glass transition are clearly marked. The approach yields an elegant geometric criterion for the glass transition temperature. A simplified quantitative physical picture of the dynamics of guest molecules dispersed in BFM matrix at low temperatures offers a starting point for stochastic modeling of host-guest systems.

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On complex structure of local free volume in bond fluctuation model of polymer matrix

Cited by 3 publications

References 36 publications

Modeling of Nonlinear Optical Phenomena in Host-Guest Systems Using Bond Fluctuation Monte Carlo Model: A Review

Modeling of Nonlinear Optical Phenomena in Host-Guest Systems Using Bond Fluctuation Monte Carlo Model: A Review

Nanoscale ordering of planar octupolar molecules for nonlinear optics at higher temperatures

Characterization of Monte Carlo Dynamic/Kinetic Properties of Local Structure in Bond Fluctuation Model of Polymer System

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