Limits...
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.


A description of the azobenzene liquid crystal polymer model used to simulate optically active microstructure and coupling with a homogenized polymer network.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4594130&req=5

f1: A description of the azobenzene liquid crystal polymer model used to simulate optically active microstructure and coupling with a homogenized polymer network.

Mentions: Azobenzene undergoes trans-cis photoisomerization from UV light (~365 nm) and a reverse cis-trans reaction when exposed to visible light (~450–500 nm) which affords unique polymer deformation control from polarized light excitation6252627. UV exposure results in a rod shaped azobenzene molecule with length approximately 10 Å transforming into a “kinked” shape with length of ~5.5 Å27; see Fig. 1. The higher energy cis state can be transformed back to its original rod shape (trans state) upon exposure to visible light or heat. Alternatively, exposure to blue-green light results in simultaneous trans-cis and cis-trans photochemical reactions due to the overlap in the optical absorption spectra. This process is known as trans-cis-trans photoisomerization. If the light is polarized, it can lead to what is known as the Weigert effect where the molecules in the trans state reorient to a plane orthogonal to the polarization direction18282930. When the azobenzene molecules are polymerized (pendent or cross-linked), free standing polymer films undergo significant bending or twisting that can be controlled by the polarization orientation of the light source4671331. Given the large shape anisotropy in the trans state, it is often assumed that azo-LCNs exhibit prolate behavior which predicts the majority of polarized induced free bending and twisting behavior73233; however, direct extensions of such behavior to surface relief deformation has not been possible.


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

Bin J, Oates WS - Sci Rep (2015)

A description of the azobenzene liquid crystal polymer model used to simulate optically active microstructure and coupling with a homogenized polymer network.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: A description of the azobenzene liquid crystal polymer model used to simulate optically active microstructure and coupling with a homogenized polymer network.
Mentions: Azobenzene undergoes trans-cis photoisomerization from UV light (~365 nm) and a reverse cis-trans reaction when exposed to visible light (~450–500 nm) which affords unique polymer deformation control from polarized light excitation6252627. UV exposure results in a rod shaped azobenzene molecule with length approximately 10 Å transforming into a “kinked” shape with length of ~5.5 Å27; see Fig. 1. The higher energy cis state can be transformed back to its original rod shape (trans state) upon exposure to visible light or heat. Alternatively, exposure to blue-green light results in simultaneous trans-cis and cis-trans photochemical reactions due to the overlap in the optical absorption spectra. This process is known as trans-cis-trans photoisomerization. If the light is polarized, it can lead to what is known as the Weigert effect where the molecules in the trans state reorient to a plane orthogonal to the polarization direction18282930. When the azobenzene molecules are polymerized (pendent or cross-linked), free standing polymer films undergo significant bending or twisting that can be controlled by the polarization orientation of the light source4671331. Given the large shape anisotropy in the trans state, it is often assumed that azo-LCNs exhibit prolate behavior which predicts the majority of polarized induced free bending and twisting behavior73233; however, direct extensions of such behavior to surface relief deformation has not been possible.

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.