Azobenzene Polymers for Photonic Applications

Yager, Kevin G.; Barrett, Christopher J.

doi:10.1002/9780470439098.ch1

Cited by 36 publications

(36 citation statements)

References 364 publications

(337 reference statements)

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“…For the ratio of quantum efficiencies η we use an estimated value of 3 from ref. 31. Now one can calculate α, β, and d t by comparing the calculated and measured transmitted light intensity for different source intensities.…”

Section: Resultsmentioning

confidence: 99%

Reverse switching of surface roughness in a self-organized polydomain liquid crystal coating

Liu

Onck

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

124

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In this work we propose randomly ordered polydomain nematic liquid crystal polymer networks to reversibly generate notable jagged relief patterns at a polymer coating surface by light illumination. The domain size is controlled by the addition of traces of partly insoluble fluorinated acrylate. The photoresponse of the coating is induced by a small amount of copolymerized azobenzene monomers. Upon exposure to UV light, azobenzene undergoes trans to cis isomerization, resulting in a change in molecular order and packing within each domain. The extent of this effect and its directionality depends on the domain orientation. Localized to domain level, this morphological change forms large 3D spikes at the surface with a modulation amplitude of more than 20% of the initial thickness. The process is reversible; the surface topographical patterns erase within 10 s by stopping the light exposure. A finite element model is applied to simulate the surface topography changes of the polydomain coating. The simulations describe the formation of the topographic features in terms of light absorption and isomerization process as a function of the director orientation. The random director distribution leads to surface structures which were found to be in close agreement with the ones measured by interference microscopy. The effect of domain size on surface roughness and depth modulation was explored and related to the internal mechanical constraints. The use of nematic liquid crystal polydomains confined in a polymer network largely simplifies the fabrication of smart coatings with a prominent triggered topographic response.surface dynamics | self-organization | switchable jagged surfaces | polydomain liquid crystal polymer | light activation I n nature, living creatures have developed a series of motion and surviving strategies based on unique topographic patterns on their surfaces. The surface topographies range from static patterns as, for instance, found on the leaves of the lotus flower, repelling water and dirt particles, to the dynamic structures that appear under certain conditions as found in many mammals. An example is the pilomotor reflex at the skin of mammals which creates insulation in cold conditions and provides protection by scaring away predators when the body appears larger. To date, many studies have been devoted to the use of static surface topographies fabricated by wrinkling (1, 2), embossing (3), or lithography. However, there is an increasing demand to make these surface structures switchable in modern applications, such as adjustable gas and water flow behavior at corrugated surfaces (4), autonomously adjusting lenses (5), controlled wettability (6), and modulated optics such as scattering, diffraction, or reflection (7-9). Also, the mechanical properties can be altered by the appearance or disappearance of protrusions at the surface (10, 11), such as friction, stick, and adhesion which manifest themselves in, e.g., haptic applications (12).Our focus here is to develop dynamic topographic patterns at su...

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Section: Resultsmentioning

confidence: 99%

Reverse switching of surface roughness in a self-organized polydomain liquid crystal coating

Liu

Onck

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

124

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“…The mechanism of photo-induced reorientation is detailed in a recent review [9]. A hallmark of reorientation is photo-induced birefringence and dichroism [31]. The absorption of azobenzene-based alignment layers is maximized when the electric field vector of polarized interrogation light is parallel to the alignment direction of the long molecular axis of the trans azobenzene isomer (i.e., interrogation light polarizer angle defined at 0° in this work (see Figure 5a)).…”

Section: Effect Of the Polarization State Of Light On Photosensitive mentioning

confidence: 82%

“…Exposure of the photoalignment layer to linearly polarized light of a suitable wavelength (blue/green light) promoted alignment of the long axes of the chromophores in the substrate plane orthogonal to the polarization state of the light (Figure 5a) due to repeated trans-cis-trans cycling [31]. The mechanism of photo-induced reorientation is detailed in a recent review [9].…”

Section: Effect Of the Polarization State Of Light On Photosensitive mentioning

confidence: 99%

“…Sinusoidal variation of the magnitude of absorbance was observed in the case of preferred alignment after exposure to linearly polarized light. Specifically, after irradiation with linearly (y-direction) polarized 488 nm light the long molecular axis showed preferred orientation (i.e., in the x-direction) perpendicular to the polarization state of the laser light (Figure 5a Unpolarized and circularly polarized light have been reported to randomize chromophore orientations [31]. The average decrease in absorbance is attributed to some preferential alignment along the radiation propagation axis (i.e., out-of-plane or along z-axis) [31].…”

Section: Effect Of the Polarization State Of Light On Photosensitive mentioning

confidence: 99%

“…Specifically, after irradiation with linearly (y-direction) polarized 488 nm light the long molecular axis showed preferred orientation (i.e., in the x-direction) perpendicular to the polarization state of the laser light (Figure 5a Unpolarized and circularly polarized light have been reported to randomize chromophore orientations [31]. The average decrease in absorbance is attributed to some preferential alignment along the radiation propagation axis (i.e., out-of-plane or along z-axis) [31]. Three of the unexposed absorbance spectra and three spectra obtained after counterpropagating LHCP light exposure absorbance spectra are presented in Figure 5c, showing a decrease in absorption for the entire peak and a peak blue-shift after exposure.…”

Section: Effect Of the Polarization State Of Light On Photosensitive mentioning

confidence: 99%

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Generation of Light Scattering States in Cholesteric Liquid Crystals by Optically Controlled Boundary Conditions

et al. 2013

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Circularly polarized light was previously employed to stimulate the reversible and reconfigurable writing of scattering states in cholesteric liquid crystal (CLC) cells constructed with a photosensitive layer. Such dynamic photodriven responses have utility in remotely triggering changes in optical constructs responsive to optical stimulus and applications where complex spatial patterning is required. Writing of scattering regions required the handedness of incoming radiation to match the handedness of the CLC and the reflection bandwidth of the CLC to envelop the wavelength of the incoming radiation. In this paper, the mechanism of transforming the CLC into a light scattering state via the influence of light on the photosensitive alignment layer is detailed. Specifically, the effects of: (i) the polarization state of light on the photosensitive alignment layer; (ii) the exposure time; and (iii) the incidence angle of radiation on domain formation are reported. The photogenerated light-scattering domains are shown to be similar in appearance between crossed polarizers to a defect structure that occurs at a CLC/air interface (i.e., a free CLC surface). This observation provides strong indication that exposure of the photosensitive alignment layer to the circularly polarized light of appropriate wavelength and handedness generates an out-of-plane orientation leading to a periodic distortion of the original planar structure. OPEN ACCESSCrystals 2013, 3 235

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Multi‐stimuli‐responsive Polymers Based on Calix[4]arenes and Dibenzo‐18‐crown‐6‐ethers

Wiktorowicz

Tenhu

Aseyev

2018

Temperature‐Responsive Polymers

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Azobenzene Polymers for Photonic Applications

Cited by 36 publications

References 364 publications

Reverse switching of surface roughness in a self-organized polydomain liquid crystal coating

Reverse switching of surface roughness in a self-organized polydomain liquid crystal coating

Generation of Light Scattering States in Cholesteric Liquid Crystals by Optically Controlled Boundary Conditions

Multi‐stimuli‐responsive Polymers Based on Calix[4]arenes and Dibenzo‐18‐crown‐6‐ethers

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