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A Unified Material Description for Light Induced Deformation in Azobenzene Polymers.

Bin J, Oates WS - Sci Rep (2015)

Bottom Line: It is shown that dipole forces strongly respond to polarized light in contrast to higher order quadrupole forces that are often used to describe surface relief grating deformation through a field gradient constitutive law.The modeling results and comparisons with a broad range of photomechanical data in the literature suggest that the molecular structure of the azobenzene monomers dramatically influences the photostrictive behavior.The results provide important insight for designing azobenzene monomers within a polymer network to achieve enhanced photo-responsive deformation.

View Article: PubMed Central - PubMed

Affiliation: Florida Center for Advanced Aero Propulsion (FCAAP), Department of Mechanical Engineering, Florida State University. Tallahassee, FL, 32310, USA.

ABSTRACT
Complex light-matter interactions in azobenzene polymers have limited our understanding of how photoisomerization induces deformation as a function of the underlying polymer network and form of the light excitation. A unified modeling framework is formulated to advance the understanding of surface deformation and bulk deformation of polymer films that are controlled by linear or circularly polarized light or vortex beams. It is shown that dipole forces strongly respond to polarized light in contrast to higher order quadrupole forces that are often used to describe surface relief grating deformation through a field gradient constitutive law. The modeling results and comparisons with a broad range of photomechanical data in the literature suggest that the molecular structure of the azobenzene monomers dramatically influences the photostrictive behavior. The results provide important insight for designing azobenzene monomers within a polymer network to achieve enhanced photo-responsive deformation.

No MeSH data available.


Simulation results in the case of a linearly polarized vortex laser beam.(a) The spatial distribution of the trans vector (The color denotes the magnitude of the trans vector, . The region of  where the photoisomerization is negligible was filtered out). (b) Shape deformation (A color denotes the variation in the z direction). The positive vortex topological charge ξ = +10 is used.
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f7: Simulation results in the case of a linearly polarized vortex laser beam.(a) The spatial distribution of the trans vector (The color denotes the magnitude of the trans vector, . The region of where the photoisomerization is negligible was filtered out). (b) Shape deformation (A color denotes the variation in the z direction). The positive vortex topological charge ξ = +10 is used.

Mentions: Figure 7 illustrates the spatial distribution of the trans vector due to the illumination of the linearly polarized vortex laser beam when ξ = +10 and the resultant surface deformation of the polymer. This is the case where the deformation is relatively large and clearly observed experimentally15. Figure 7(a) illustrates the trans vectors superimposed on the time averaged magnitude of the trans state. The results illustrate where the light-induced trans-cis-trans isomerization of the azobenzene most strongly occurs. The trans vectors are found to be approximately aligned with the rotation direction of the vortex field. Note also the reduction of the trans order in regions associated with larger light intensity. These regions contain a larger concentration of the randomly ordered cis as illustrated in the supplementary text. Such effects contribute to the deformation as the trans vector order parameter in (5) is reduced. Photoisomerization becomes negligible at the core of the vortex for higher topological charge as expected due to a lack of an optical field at the beam core. Along the beam’s perimeter, the microstructure evolves asymmetrically due to the light intensity and phase induced by the topological charge. This case is more complicated than linearly or circularly polarized light since the vortex beam contains electric field components in all three Cartesian directions as it propagates in the z direction48. Figure 7(b) illustrates the resultant surface relief pattern. The double-arm spiral structure pattern in the clockwise (or left-handed) direction due to the positive ξ is clearly observed. Although not shown, we also verify that the direction of surface relief changes to the counter-clockwise direction if ξ = −10 (see the supplemental material).


A Unified Material Description for Light Induced Deformation in Azobenzene Polymers.

Bin J, Oates WS - Sci Rep (2015)

Simulation results in the case of a linearly polarized vortex laser beam.(a) The spatial distribution of the trans vector (The color denotes the magnitude of the trans vector, . The region of  where the photoisomerization is negligible was filtered out). (b) Shape deformation (A color denotes the variation in the z direction). The positive vortex topological charge ξ = +10 is used.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4594130&req=5

f7: Simulation results in the case of a linearly polarized vortex laser beam.(a) The spatial distribution of the trans vector (The color denotes the magnitude of the trans vector, . The region of where the photoisomerization is negligible was filtered out). (b) Shape deformation (A color denotes the variation in the z direction). The positive vortex topological charge ξ = +10 is used.
Mentions: Figure 7 illustrates the spatial distribution of the trans vector due to the illumination of the linearly polarized vortex laser beam when ξ = +10 and the resultant surface deformation of the polymer. This is the case where the deformation is relatively large and clearly observed experimentally15. Figure 7(a) illustrates the trans vectors superimposed on the time averaged magnitude of the trans state. The results illustrate where the light-induced trans-cis-trans isomerization of the azobenzene most strongly occurs. The trans vectors are found to be approximately aligned with the rotation direction of the vortex field. Note also the reduction of the trans order in regions associated with larger light intensity. These regions contain a larger concentration of the randomly ordered cis as illustrated in the supplementary text. Such effects contribute to the deformation as the trans vector order parameter in (5) is reduced. Photoisomerization becomes negligible at the core of the vortex for higher topological charge as expected due to a lack of an optical field at the beam core. Along the beam’s perimeter, the microstructure evolves asymmetrically due to the light intensity and phase induced by the topological charge. This case is more complicated than linearly or circularly polarized light since the vortex beam contains electric field components in all three Cartesian directions as it propagates in the z direction48. Figure 7(b) illustrates the resultant surface relief pattern. The double-arm spiral structure pattern in the clockwise (or left-handed) direction due to the positive ξ is clearly observed. Although not shown, we also verify that the direction of surface relief changes to the counter-clockwise direction if ξ = −10 (see the supplemental material).

Bottom Line: It is shown that dipole forces strongly respond to polarized light in contrast to higher order quadrupole forces that are often used to describe surface relief grating deformation through a field gradient constitutive law.The modeling results and comparisons with a broad range of photomechanical data in the literature suggest that the molecular structure of the azobenzene monomers dramatically influences the photostrictive behavior.The results provide important insight for designing azobenzene monomers within a polymer network to achieve enhanced photo-responsive deformation.

View Article: PubMed Central - PubMed

Affiliation: Florida Center for Advanced Aero Propulsion (FCAAP), Department of Mechanical Engineering, Florida State University. Tallahassee, FL, 32310, USA.

ABSTRACT
Complex light-matter interactions in azobenzene polymers have limited our understanding of how photoisomerization induces deformation as a function of the underlying polymer network and form of the light excitation. A unified modeling framework is formulated to advance the understanding of surface deformation and bulk deformation of polymer films that are controlled by linear or circularly polarized light or vortex beams. It is shown that dipole forces strongly respond to polarized light in contrast to higher order quadrupole forces that are often used to describe surface relief grating deformation through a field gradient constitutive law. The modeling results and comparisons with a broad range of photomechanical data in the literature suggest that the molecular structure of the azobenzene monomers dramatically influences the photostrictive behavior. The results provide important insight for designing azobenzene monomers within a polymer network to achieve enhanced photo-responsive deformation.

No MeSH data available.