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.


Related in: MedlinePlus

Numerical result in the case of a circularly polarized Gaussian laser beam.(a) The spatial distribution of the trans vector due to the light exposure (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).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f6: Numerical result in the case of a circularly polarized Gaussian laser beam.(a) The spatial distribution of the trans vector due to the light exposure (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).

Mentions: Circularly polarized light is first considered where the electric field amplitudes E1 and E2 are equal and the phase angle is . The electric field of the circularly polarized Gaussian laser beam given by where is applied on the top plane of the domain, z = ztop. Figure 6 illustrates the spatial distribution of the trans vector due to the illumination of the circularly polarized Gaussian laser beam and the resultant deformation of the polymer. In a given z plane, the electric field vector rotates with constant angular velocity in the counter-clockwise direction. This field drives the trans state, initially randomly distributed, to reorient perpendicular to the electric field . Since the field aligned in the (x, y) plane rotates on the femtosecond time scale, slower trans-cis-trans photoisomerization results in trans alignment predominantly in the z direction along the perimeter of the beam as shown in Fig. 6(a). More trans-cis photochemical reactions occur in the center reducing deformation due to the loss of order near the beam center. This is illustrated in Fig. 6(a) by the magnitude of the trans state shown by the color bar. In the supplemental text, the complementary formation of the cis state is shown further illustrating the order-disorder behavior near the center of the beam. Figure 6(b) illustrates the deformation attributed to the stress in Eq. (5). To minimize any effects from the boundaries, the medium of a cylindrical shape is considered for the computation of the mechanical deformation. On the bottom of the azobenzene polymer domain, the model is fully clamped, whereas traction-free boundary conditions are applied to the remaining boundaries. This figure shows that the photo-induced surface deformation is axisymmetric along the z axis. The protrusion along the outer rim is qualitatively in agreement with experiments given in the literature20. This illustrates that time-dependent fields coupled to optically active microstructure evolution and coupling with polymer deformation are also driven by the dipole forces in Eq. (4).


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

Bin J, Oates WS - Sci Rep (2015)

Numerical result in the case of a circularly polarized Gaussian laser beam.(a) The spatial distribution of the trans vector due to the light exposure (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).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f6: Numerical result in the case of a circularly polarized Gaussian laser beam.(a) The spatial distribution of the trans vector due to the light exposure (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).
Mentions: Circularly polarized light is first considered where the electric field amplitudes E1 and E2 are equal and the phase angle is . The electric field of the circularly polarized Gaussian laser beam given by where is applied on the top plane of the domain, z = ztop. Figure 6 illustrates the spatial distribution of the trans vector due to the illumination of the circularly polarized Gaussian laser beam and the resultant deformation of the polymer. In a given z plane, the electric field vector rotates with constant angular velocity in the counter-clockwise direction. This field drives the trans state, initially randomly distributed, to reorient perpendicular to the electric field . Since the field aligned in the (x, y) plane rotates on the femtosecond time scale, slower trans-cis-trans photoisomerization results in trans alignment predominantly in the z direction along the perimeter of the beam as shown in Fig. 6(a). More trans-cis photochemical reactions occur in the center reducing deformation due to the loss of order near the beam center. This is illustrated in Fig. 6(a) by the magnitude of the trans state shown by the color bar. In the supplemental text, the complementary formation of the cis state is shown further illustrating the order-disorder behavior near the center of the beam. Figure 6(b) illustrates the deformation attributed to the stress in Eq. (5). To minimize any effects from the boundaries, the medium of a cylindrical shape is considered for the computation of the mechanical deformation. On the bottom of the azobenzene polymer domain, the model is fully clamped, whereas traction-free boundary conditions are applied to the remaining boundaries. This figure shows that the photo-induced surface deformation is axisymmetric along the z axis. The protrusion along the outer rim is qualitatively in agreement with experiments given in the literature20. This illustrates that time-dependent fields coupled to optically active microstructure evolution and coupling with polymer deformation are also driven by the dipole forces in Eq. (4).

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.


Related in: MedlinePlus