Photodynamics of stress in clamped nematic elastomers

Knežević, Miloš; Warner, Mark; Čopič, Martin; Sánchez‐Ferrer, Antoni

doi:10.1103/physreve.87.062503

Cited by 28 publications

(33 citation statements)

References 18 publications

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“…At the beginning of the illumination with the UV intensity pattern, the photoisomerization reaction takes place only in a few micrometers thick surface layer of the film, but later on, photobleaching of the azobenzene dye molecules allows UV light to penetrate deeper and deeper into the sample depth . The associated periodic refractive index modulation causes optical diffraction of the probe beam.…”

Section: Resultsmentioning

confidence: 99%

Light‐Induced Refractive Index Modulation in Photoactive Liquid‐Crystalline Elastomers

Tašič

Sánchez‐Ferrer

et al. 2013

Macro Chemistry & Physics

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A comparative study of UV‐irradiation‐induced refractive index modulation in two analogous monodomain nematic side‐chain liquid‐crystalline elastomer materials is conveyed. In one of them, mesogenic azobenzene derivatives are incorporated as pendant co‐monomers, and in the other as crosslinking units. The dependence of the optical diffraction properties on the polarization state of the probe beam reveals that diffraction is predominantly of a bulk origin for both materials. For prolonged UV exposures, the material with pendant azobenzene derivatives exhibits practically constant diffraction properties, while the material with cross‐linking azobenzene units shows a profound decrease of diffraction efficiency with increasing exposure time. The difference is attributed to photoinduced alignment of the azobenzene molecules, which is much stronger in the material with the crosslinking azobenzene units.

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Section: Resultsmentioning

confidence: 99%

Light‐Induced Refractive Index Modulation in Photoactive Liquid‐Crystalline Elastomers

Tašič

Sánchez‐Ferrer

et al. 2013

Macro Chemistry & Physics

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“…[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] In these numerous efforts, azobenzene has been used as a molecular switch to convert input light energy into conformational change which subsequently generates strain in the polymeric materials. Light is potentially a "smart" stimulus that can uniquely allow for wireless (remote) spatio-temporal control of the force or shape change.…”

mentioning

confidence: 99%

“…[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] In these numerous efforts, azobenzene has been used as a molecular switch to convert input light energy into conformational change which subsequently generates strain in the polymeric materials. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] In these numerous efforts, azobenzene has been used as a molecular switch to convert input light energy into conformational change which subsequently generates strain in the polymeric materials.…”

mentioning

confidence: 99%

Photoinduced Topographical Feature Development in Blueprinted Azobenzene‐Functionalized Liquid Crystalline Elastomers

Ahn

Ware

Lee

et al. 2016

Adv Funct Materials

151

137

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5819wileyonlinelibrary.com or shape (topography). Light is potentially a "smart" stimulus that can uniquely allow for wireless (remote) spatio-temporal control of the force or shape change.A considerable volume of recent research has focused on photomechanical effects in azobenzene-functionalized liquid crystalline polymer networks (azo-LCNs) and elastomers (azo-LCEs) both experimetnally and theoretically. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] In these numerous efforts, azobenzene has been used as a molecular switch to convert input light energy into conformational change which subsequently generates strain in the polymeric materials. Two related but distinguished photochemical processes have been employed including (i) transcis photoisomerization of azobenzene typically initiated with UV irradiation [ 28 ] and (ii) trans-cis-trans reorientation of azobenzene initiated with blue-green irradiation. [ 12,14,29,30 ] These photoinduced conformational changes convert input photonic energy into a mechanical output by distorting the local polymer network. Trans-cis-trans reorientation has recently been subject to intense fundamental studies focused on the athermal softening of the material at the molecular and macromolecular level. [ 30,31 ] The photogenerated strain has correspondingly been demonstrated to induce motion including bending, oscillation, and torsion. [ 19,32,33 ] For aligned azo-LCNs and azo-LCEs, the strain is anisotropic and oriented parallel to the nematic director. For example, the photogenerated strain in a monodomain (nematic) LCN results in in-plane deformation [ 29,34 ] while offsetting the orientation of the director profi le to the sample geometry results in out-of-plane deformation yielding twisting. [ 15,16,32,35,36 ] Spatial variation in the orientation (programming) of liquid crystalline monomers using surface alignment techniques such as photoalignment has many potential benefi ts. [ 32,37,38 ] In the work presented here, we employ a commercial photoalignment material also based on azobenzene. This material is formulated in solution and applied to glass substrates by spin coating, subsequently evaporating solvent, and then subjecting the surface layer to patterned linearly polarized light. The azobenzene molecules on the surface layer orient orthogonal to the electric fi eld vector of the incident linearly polarized light. Upon fi lling the cell after photoalignment, the LC monomer orients to the local surface and retains this alignment during polymerization. ). The azo-LCEs are synthesized via an orthogonal, two-step reaction between commercially available LC monomers and n -butylamine. By employing surface alignment, the local orientation of the nematic director is spatially complex ("blueprinted"). Exposing the blueprinted LCE fi lms to light as an actinic stimulus generates a photomechanical response which yields reversible shape changes between 2D and 3D shapes. The deformation of azo-LCEs strongly depends on the azobenzene concentration as well as the networ...

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“…Photomechanical response.-In many previous theoretical studies, the photoinduced strain was commonly assumed to be linearly proportional to the cis volume fraction [8,11,12], or nonlinear but monotonically increasing [10,21]. However, the measured density decrease [14] ( Fig.…”

Section: -2mentioning

confidence: 99%

“…This actuation can be reversed by exposing the material to visible (VIS) light or heat, which accelerate the cis azobenzenes to fall back to the trans state. The current consensus in experimental [5,[7][8][9] and theoretical studies [10][11][12][13] is that the amplitude of the photoinduced deformation is related to the statistical building up of molecules in the cis state. However, a recent experimental study [14] has revealed that this is only one side of the story.…”

mentioning

confidence: 99%

Enhanced Deformation of Azobenzene-Modified Liquid Crystal Polymers under Dual Wavelength Exposure: A Photophysical Model

Liu

Onck

2017

Phys. Rev. Lett.

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Azobenzene-embedded liquid crystal polymers can undergo mechanical deformation in response to ultraviolet (UV) light. The natural rodlike trans state azobenzene absorbs UV light and isomerizes to a bentlike cis state, which disturbs the order of the polymer network, leading to an anisotropic deformation. The current consensus is that the magnitude of the photoinduced deformation is related to the statistical building up of molecules in the cis state. However, a recent experimental study [Liu and Broer, Nat. Commun. 6 8334 (2015).] shows that a drastic (fourfold) increase of the photoinduced deformation can be generated by exposing the samples simultaneously to 365 nm (UV) and 455 nm (visible) light. To elucidate the physical mechanism that drives this increase, we develop a two-light attenuation model and an optomechanical constitutive relation that not only accounts for the statistical accumulation of cis azobenzenes, but also for the dynamic trans-cis-trans oscillatory isomerization process. Our experimentally calibrated model predicts that the optimal single-wavelength exposure is 395 nm light, a pronounced shift towards the visible spectrum. In addition, we identify a range of optimal combinations of twowavelength lights that generate a favorable response for a given amount of injected energy. Our model provides mechanistic insight into the different (multi)wavelength exposures used in experiments and, at the same time, opens new avenues towards enhanced, multiwavelength optomechanical behavior.

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Photodynamics of stress in clamped nematic elastomers

Cited by 28 publications

References 18 publications

Light‐Induced Refractive Index Modulation in Photoactive Liquid‐Crystalline Elastomers

Light‐Induced Refractive Index Modulation in Photoactive Liquid‐Crystalline Elastomers

Photoinduced Topographical Feature Development in Blueprinted Azobenzene‐Functionalized Liquid Crystalline Elastomers

Enhanced Deformation of Azobenzene-Modified Liquid Crystal Polymers under Dual Wavelength Exposure: A Photophysical Model

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