Study of phase-separation dynamics by use of cell dynamical systems. I. Modeling

Oono, Yoshitsugu; Puri, Sanjay

doi:10.1103/physreva.38.434

Cited by 588 publications

(331 citation statements)

References 56 publications

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“…In analogy to pattern formation and phase separation in diblock copolymers (35,36,(47)(48)(49), a conventional CDS model approach was chosen to reproduce the experimentally observed light-induced patterns. The local concentration c is identified with the order parameter ψ of the system ðc = ψÞ.…”

Section: Methodsmentioning

confidence: 99%

Instability-induced pattern formation of photoactivated functional polymers

Galinski

Ambrosio

Maddalena

et al. 2014

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

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Since the pioneering work of Turing on the formation principles of animal coat patterns [Turing AM (1952) Phil Trans R Soc Lond B 237(641):37-72], such as the stripes of a tiger, great effort has been made to understand and explain various phenomena of selfassembly and pattern formation. Prominent examples are the spontaneous demixing in emulsions, such as mixtures of water and oil [Herzig EM, et al. (2007) Nat Mater 6:966-971]; the distribution of matter in the universe [Kibble TWB (1976 A zobenzenes, which belong to photochromic materials, are switchable two-state systems with distinct optical, electronic, magnetic, and/or electrochemical properties that can be reversibly converted by irradiation. Since the discovery of the unique photochemical properties of azobenzene in 1937 (1), azobenzenes have been mainly used in the chemical industry. Only recently, after studies of the molecular physics of the photoisomerization of azo dyes have revealed that the photoisomerization reaction occurs on the timescale of a few picoseconds (2, 3), azobenzenes came back into focus as potential photoswitchable materials (4, 5). Azobenzenes have been investigated in terms of ultrafast spectroscopy (4, 6, 7), mechanoisomerization (8), the effect of slow photons (9), two-photon absorption (10) and laser-induced periodic surface structuring (11-17). The latter describes the phenomenon of Turing pattern formation on the surface of an azopolymer film upon exposure to UV or visible light. The outstanding feature of this photoactivated pattern formation is its dependence on both the light's intensity and polarization, which allows for the formation of a large variety of Turing patterns, such as hexagonal cells, parallel stripes, or turbulent structures. Several attempts have been made to understand the underlying physics that controls these various forms of pattern formation (18-23), but a sound picture is still lacking.In this paper, we demonstrate that the photoactivated pattern formation on azopolymer films can be entirely explained by the physical concept of phase separation of two coexistent immiscible phases in the polymer. A phase separation can be briefly characterized as follows: A (meta)stable configuration subjected to an external perturbation (temperature, light) becomes unstable. The unstable system tends to equilibrate by the formation of two immiscible phases. These two phases tend to separate leading to a spatial reorganization of the system.In the case of azopolymers, the instability is caused by the random optical excitation of the isomers in the polymer film. Excited by a photon of suitable energy (λ = 200-550 nm), the azobenzene isomer undergoes a structural transition by inversion or rotation (3), called photoisomerization, and relaxes either in the trans or cis ground state. The symmetry of the system is broken. The principle of the photoisomerization reaction for one azobenzene isomer is illustrated in Fig. 1A. The ground-state energy is characterized by an asymmetric double-well potential (Fig. 1A), containing...

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Section: Methodsmentioning

confidence: 99%

Instability-induced pattern formation of photoactivated functional polymers

Galinski

Ambrosio

Maddalena

et al. 2014

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

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“…The traditional tanh mapping 29 is not used. Rather we use the mapping directly derived from the free energy functional (2)-(4), 30,31 which is essential for studying the subtle nature of nucleation and growth when one phase is metastable and the other is stable.…”

Section: Numerical Resultsmentioning

confidence: 99%

“…We do not solve the time-dependent Ginzburg-Landau (TDGL) equation directly. Instead, we use the cell dynamics method 29 to solve TDGL approximately. In a previous study we 20,30 have already shown that the cell dynamics method is accurate enough and numerically very efficient to study the general feature of the dynamics of various first order phase transformations.…”

Section: Numerical Resultsmentioning

confidence: 99%

Cell Dynamics Simulation of Droplet and Bridge Formation within Striped Nanocapillaries

Iwamatsu

2007

Langmuir

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The kinetics of droplet and bridge formation within striped nano-capillaries is studied when the wetting film grows via interface-limited growth. The phenomenological time-dependent Ginzburg-Landau (TDGL)-type model with thermal noise is used and numerically solved using the cell dynamics method.The model is two-dimensional and consists of undersaturated vapor confined within a nano-capillary made of two infinitely wide flat substrates. The surface of the substrate is chemically heterogeneous with a single stripe of lyophilic domain that exerts long-range attractive potential to the vapor molecule.The dynamics of nucleation and subsequent growth of droplet and bridge can be simulated and visualized. In particular, the evolution of the morphology from droplet or bump to bridge is clearly identified. Crucial role played by the substrate potential on the morphology of bridge of nanoscopic size is clarified. Nearly temperature-independent evolution of capillary condensation is predicted when the interface-limited growth dominates. In addition, it is shown that the dynamics of capillary 2 condensation follows the scenario of capillary condensation proposed by Everett and Haynes three decades ago.

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“…Although their degrees of simplification of the dynamics differ, it is often the case that discretization for pattern generation is discussed under the same framework [2]. One of the models that rather faithfully discretizes the dynamics of a continuous system is that of Markus and Hess [3] which uses a complex rule configuration.…”

Section: Modelmentioning

confidence: 99%

A reaction‐diffusion model performing stripe‐ and spot‐image restoration and its LSI implementation

Suzuki

Takayama

Motoike

et al. 2006

Electron Comm Jpn Pt III

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SUMMARYThis paper is intended to develop an LSI that restores in real time an image pattern with defects and contamination. To this end, based on the principle of shape formation in biological bodies, a reaction-diffusion model that can generate and repair Turing patterns, such as stripes and spots seen in fingerprint and body marks, is proposed. A parallel architecture of the reaction-diffusion chips incorporating this model is presented. By means of circuit simulation, it is shown that this LSI can restore stripe (spot) patterns

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Study of phase-separation dynamics by use of cell dynamical systems. I. Modeling

Cited by 588 publications

References 56 publications

Instability-induced pattern formation of photoactivated functional polymers

Instability-induced pattern formation of photoactivated functional polymers

Cell Dynamics Simulation of Droplet and Bridge Formation within Striped Nanocapillaries

A reaction‐diffusion model performing stripe‐ and spot‐image restoration and its LSI implementation

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