Formation of Surface Relief Gratings:  Effect of the Density of the Host Material

Teboul, Victor; Accary, J. B.

doi:10.1021/jp3053423

Cited by 6 publications

(9 citation statements)

References 23 publications

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“…We simulate the photoisomerization of one dispersed red (DR1) molecule (C 16 works [8,[13][14][15]. The main differences are that: i) The concentration of probe molecules is here much smaller and the size of the box larger.…”

Section: Calculationsmentioning

confidence: 99%

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Induced cooperative motions in a medium driven at the nanoscale: Searching for an optimum excitation period

Teboul

Accary

2014

Phys. Rev. E

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Recent results have shown the appearance of induced cooperative motions called dynamic heterogeneity during the isomerization of diluted azobenzene molecules in a host glass-former. In this paper we raise the issue of the coupling between these "artificial" heterogeneities and the isomerization period. How do these induced heterogeneities differ in the saturation regime and in the linear response regime ? Is there a maximum of the heterogeneous motion versus isomerization rate and why ? Are the heterogeneity evolution with the isomerization rate connected with the diffusion or relaxation time evolution ? We use out of equilibrium molecular dynamics simulations to answer these questions. We find that the heterogeneity increases in the linear response regime for large isomerization periods and small perturbations. In contrast the heterogeneity decreases in the saturation regime, i.e. when the isomerization half-period (τp/2) is smaller than the relaxation time of the material (τα). This result makes possible a test of the effect of cooperative motions on the dynamics using the chromophores as Maxwell demons that destroy or stimulate the cooperative motions. Because the heterogeneities increase in the linear regime and then decrease in the saturation regime, we find a maximum for τp/2 ≈ τα. The induced excitations concentration follows a power law evolution versus the isomerization rate and then saturates. As a consequence the α relaxation time is related to the excitation concentration with a power law, a result in qualitative agreement with recent findings in constrained models. This result supports a common origin for the heterogeneities with constrained models and a similar relation to the excitation concentration. Published in Phys. Rev. E 89, 012303 (2014).

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Section: Calculationsmentioning

confidence: 99%

“…works [8,[13][14][15]. The main differences are that: i) The concentration of probe molecules is here much smaller and the size of the box larger.…”

Section: Calculationsmentioning

confidence: 99%

Induced cooperative motions in a medium driven at the nanoscale: Searching for an optimum excitation period

Teboul

Accary

2014

Phys. Rev. E

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“…Dynamic simulation models implementing cyclic trans-cis-trans photoisomerization of azobenzene have been developed for coarse-grained [79,80] and fully atomistic simulation studies [43][44][45][46]81] as well as combinations of such approaches [82]. As a starting point, the present investigation adapts the so-called cyclic photoisomerization model (CPM) in close agreement with the protocol of Ref.…”

Section: Modeling the Collective Photoisomerization Kinetics: The Cyclic Photoisomerization Modelmentioning

confidence: 80%

Cyclic Photoisomerization of Azobenzene in Atomistic Simulations: Modeling the Effect of Light on Columnar Aggregates of Azo Stars

2021

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This computational study investigates the influence of light on supramolecular aggregates of three-arm azobenzene stars. Every star contains three azobenzene (azo) moieties, each able to undergo reversible photoisomerization. In solution, the azo stars build column-shaped supramolecular aggregates. Previous experimental works report severe morphological changes of these aggregates under UV–Vis light. However, the underlying molecular mechanisms are still debated. Here we aim to elucidate how light affects the structure and stability of the columnar stacks on the molecular scale. The system is investigated using fully atomistic molecular dynamics (MD) simulations. To implement the effects of light, we first developed a stochastic model of the cyclic photoisomerization of azobenzene. This model reproduces the collective photoisomerization kinetics of the azo stars in good agreement with theory and previous experiments. We then apply light of various intensities and wavelengths on an equilibrated columnar stack of azo stars in water. The simulations indicate that the aggregate does not break into separate fragments upon light irradiation. Instead, the stack develops defects in the form of molecular shifts and reorientations and, as a result, it eventually loses its columnar shape. The mechanism and driving forces behind this order–disorder structural transition are clarified based on the simulations. In the end, we provide a new interpretation of the experimentally observed morphological changes.

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“…3. 12,37,38 from molecular dynamics simulations in several papers. Then below 200 K the exponential evolution slows down tending to a constant low temperature limit hSi E 1.5 mm 2 .…”

Section: Resultsmentioning

confidence: 99%

“…From room temperature to T E 200 K the mean surface of the aligned pattern zones follows an exponential evolution with temperature (green dashed line). 12,37,38 When the material is not illuminated the diffusion coefficient D follows a similar Arrhenius law to the inverse of the viscosity Z as these two quantities are related to the Stokes-Einstein law: D = k B T/6pZa. This evolution upon exposure to light is reminiscent of the diffusion coefficient evolution with temperature when the material is illuminated reported = 73 K, right).…”

Section: Resultsmentioning

confidence: 99%

Light mediated emergence of surface patterns in azopolymers at low temperatures

et al. 2015

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Polymer thin films doped with azobenzene molecules do have the ability to organize themselves in spontaneous surface relief gratings (SRG) under irradiation using a single polarized beam. To shed some light on this still unexplained phenomenon, we use a new method that permits us to access experimentally the very first steps of the pattern formation process. By decreasing the temperature, we slow down the formation and organization of patterns, due to the large increase in the viscosity and relaxation time of the azopolymer. As a result, decreasing the temperature allows us to access and study much shorter time scales, in the physical mechanisms underlying the pattern formation, than those previously reported. We find that the patterns organize themselves in sub-structures which size increases with the temperature, following the diffusion coefficient evolution of the material. This result suggests that the pattern formation and organization are mainly governed by diffusive processes, in agreement with some theories of SRG formation. Upon decreasing the temperature further, we observe the emergence of small voids located at the junction of the sub-structures.

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Formation of Surface Relief Gratings: Effect of the Density of the Host Material

Cited by 6 publications

References 23 publications

Induced cooperative motions in a medium driven at the nanoscale: Searching for an optimum excitation period

Induced cooperative motions in a medium driven at the nanoscale: Searching for an optimum excitation period

Cyclic Photoisomerization of Azobenzene in Atomistic Simulations: Modeling the Effect of Light on Columnar Aggregates of Azo Stars

Light mediated emergence of surface patterns in azopolymers at low temperatures

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