Complex dewetting scenarios captured by thin-film models

Becker, Jürgen C.; Grün, Günther; Seemann, Ralf; Mantz, Hubert; Jacobs, Karin; Mecke, Klaus; Blossey, Ralf

doi:10.1038/nmat788

Cited by 382 publications

(469 citation statements)

References 32 publications

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“…In two dimensions, the Minkowski functionals m n are surface descriptors, which capture morphological quantities such as the covered area m 0 , the boundary length m 1 , the number of isolated (cylindrical) domains, and the number of connected components (valleys), the Euler number m 2 . Minkowski functionals are capable of detecting higher orders of spatial correlation and are suited to testing spatial structures for non-Gaussian behavior or features (38,51). To do so, a given dataset is split into a set of binary data with different threshold levels.…”

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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“…This is a surprising phenomenon since intermolecular forces were considered to stabilize a film. 7 For low molecular weight polymers, the rupture and subsequent dewetting of very thin films, the size of a few nanometers, have actually been simulated and well explained. This is based on the thin film equation, 7 within intermolecular force theory, as low molecular weight polymers behave as Newtonian liquids.…”

Section: Introductionmentioning

confidence: 93%

“…7 For low molecular weight polymers, the rupture and subsequent dewetting of very thin films, the size of a few nanometers, have actually been simulated and well explained. This is based on the thin film equation, 7 within intermolecular force theory, as low molecular weight polymers behave as Newtonian liquids. However, these polymers are usually not applied technologically due to their brittle nature in the solid state.…”

Section: Introductionmentioning

confidence: 93%

Mechanism of spontaneous hole formation in thin polymeric films

Rasmussen

Marín

et al. 2012

Phys. Rev. B

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“…We have mentioned that physical experiments have shown that a nearly uniform layer of a thin film will break up due to instabilities [2,6]. Our first step will be to try to model this dewetting.…”

Section: Formulation Of the Thin Film Problemmentioning

confidence: 99%

“…This particular phenomenon is called dewetting, and it occurs frequently in dynamic mechanical systems. For example, experiments on different polymer solutions [2,6] have attempted to pin down the peculiar nature of dewetting. More simply however, this behavior is also exhibited in everyday materials such as printing ink, paint, and lubricant.…”

Section: Introductionmentioning

confidence: 99%

Statistical Analysis of Simulations of Coarsening Droplets Coating a Hydrophobic Surface

Semko¹

2010

SIURO

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Thin layers of slow-moving, viscous fluid which coat hydrophobic surfaces are shaped by the competing forces of disjoining pressure and surface tension. These forces form the fluid layer into an array of discrete droplets separated by an ultra thin layer. However, the droplet array is unstable, and the droplets will interact with one another. To determine the structure and properties of steady droplets, we use the Reynolds' PDE in one dimension and phase-plane methods. We can then analyze the unstable droplet system by utilizing paired ODEs. Numerical solutions show how the droplets interact to produce movement and mass exchange, giving rise to coarsening events which reduce the number of droplets in the system. These events occur when a droplet collapses into the ultra thin layer or when two droplets collide, and thus, merge. Using numerical simulations and analysis of their results, we aim to gain a better understanding of the dynamics of this system including the factors that influence coarsening events such as system parameters and initial conditions.

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Complex dewetting scenarios captured by thin-film models

Cited by 382 publications

References 32 publications

Instability-induced pattern formation of photoactivated functional polymers

Instability-induced pattern formation of photoactivated functional polymers

Mechanism of spontaneous hole formation in thin polymeric films

Statistical Analysis of Simulations of Coarsening Droplets Coating a Hydrophobic Surface

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