Mean-Field Theory of Photoinduced Formation of Surface Reliefs in Side-Chain Azobenzene Polymers

Pedersen, Thomas Garm; Johansen, Per Michael; Holme, N.C.R.; Ramanujam, P. S.; Hvilsted, Søren

doi:10.1103/physrevlett.80.89

Cited by 329 publications

(235 citation statements)

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“…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)(19)(20)(21)(22)(23), but a sound picture is still lacking.…”

mentioning

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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mentioning

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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“…10,11,[26][27][28] The photoisomerization of the molecules in glassy state creates a mobile heterogeneity inside the film. 29 A similar discussion should be applicable to SR formation in the P1 film; the interferometric beam pattern must contain periodic linear polarization in a direction parallel to the grating vector for a sufficient SR structure.…”

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confidence: 99%

Photoinduced reorientation and polarization holography in a new photopolymer with 4-methoxy-N-benzylideneaniline side groups

Kawatsuki¹,

Matsushita²,

Kondo³

et al. 2013

Apl Materials

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The photoinduced reorientation and surface relief (SR) formation behaviors of a novel photosensitive polymer, which was transparent in visible region, were investigated using linearly polarized-313-nm light and holographic exposure with a 325-nm He-Cd laser. The polymer was comprised of photosensitive 4-methoxy-N-benzylideneaniline side groups, and exhibited a sufficient photoinduced molecular reorientation with a birefringence of 0.11. Holographic exposure generated a SR structure, which had a periodical molecular reorientation that depended on the polarization of the interference beams. The generated SR height was ∼212 nm, and the inscription of a double holographic exposure yielded a two-dimensional SR structure

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“…When illuminated, azobenzene doped materials are subject to intriguing macroscopic transport that in some conditions lead to the formation of surface relief gratings (SRG) [49]. While the exact physical mechanisms leading to that macroscopic transport is still a matter of debate [49][50][51][52][53][54][55][56][57], there is no doubt that it originates from the repeated foldings of the azobenzene molecule inside the material.…”

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confidence: 99%

Folding time dependence of the motions of a molecular motor in an amorphous medium

et al. 2017

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We investigate the dependence of the displacements of a molecular motor embedded inside a glassy material on its folding characteristic time τ f . We observe two different time regimes. For slow foldings (regime I) the diffusion evolves very slowly with τ f , while for rapid foldings (regime II) the diffusion increases strongly with τ f ( D ≈ τ −2 f ) suggesting two different physical mechanisms. We find that in regime I the motor's displacement during the folding process is counteracted by a reverse displacement during the unfolding, while in regime II this counteraction is much weaker. We notice that regime I behavior is reminiscent of the scallop theorem that holds for larger motors in a continuous medium. We find that the difference in the efficiency of the motor's motion explains most of the observed difference between the two regimes. For fast foldings the motor trajectories differ significantly from the opposite trajectories induced by the following unfolding process, resulting in a more efficient global motion than for slow foldings. This result agrees with the fluctuation theorems expectation for time reversal mechanisms. In agreement with the fluctuation theorems we find that the motors are unexpectedly more efficient when they are generating more entropy, a result that can be used to increase dramatically the motor's motion.

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Mean-Field Theory of Photoinduced Formation of Surface Reliefs in Side-Chain Azobenzene Polymers

Cited by 329 publications

References 12 publications

Instability-induced pattern formation of photoactivated functional polymers

Instability-induced pattern formation of photoactivated functional polymers

Photoinduced reorientation and polarization holography in a new photopolymer with 4-methoxy-N-benzylideneaniline side groups

Folding time dependence of the motions of a molecular motor in an amorphous medium

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