Blends of Poly(methacrylate) Block Copolymers with Photoaddressable Segments

Breiner, Thomas; Kreger, Klaus; Hagen, Rainer; Häckel, Michael; Kador, Lothar; Müller, Axel H. E.; Krämer, Edward J.; Schmidt, Hans‐Werner

doi:10.1021/ma0624907

Cited by 58 publications

(39 citation statements)

References 71 publications

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“…Transmission electron microscopy on similar polymer blends revealed that the domain size of the minority phase is maintained while the spacing between the domains increases upon dilution. [12] The cooperative effect in the reorientation of the azobenzene and mesogenic side groups, which is also important for the stability of the inscribed information, is therefore still present. The polymer blend can be processed by injection-molding, the most common polymer processing technique, to prepare samples of any desired shape.…”

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confidence: 99%

Polymer Blends with Azobenzene‐ Containing Block Copolymers as Stable Rewritable Volume Holographic Media

et al. 2007

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Volume holography is a promising technology for high-capacity optical data storage. [1,2] When utilizing the entire volume of a medium instead of only its surface, capacities above one terabyte on a memory medium the size of a compact disc are theoretically possible. Recent developments in the field of holographic storage materials and advances in storage techniques and technology are summarized in review articles by Ashley et al. [3] and Hesselink et al. [4] Although there are still material challenges, write-once media seem to be fairly advanced. In search of rewritable media, many studies have been performed on photorefractive crystals and organic glasses. [1,4] Manufacturing single crystals of the required size is very expensive, and a major drawback of the organic photorefractive materials is the requirement of very high electric field strengths. With increasing material thickness, the voltage necessary for creating the field becomes difficult to handle. A different potential class of rewritable media are polymers containing photoaddressable azobenzene chromophores.[5] Many studies have been performed on azobenzene-containing polymer films with thicknesses in the range of 0.5-10 lm. [3,6] However, the preparation of the thick samples required for multiplexing with sufficiently low optical density remains difficult to achieve. Because the absorption coefficient depends on the wavelength, it is in principle possible to tune a laser with an adjustable wavelength (e.g., a dye laser) to the very edge of the absorption band. [7] If writing is to be performed at a wavelength where fixed-wavelength, solid-state lasers are available (515 or 532 nm), however, a concept that allows for diluting the chromophores is required. So far, the best results have been reported by Minabe et al. with a homogeneous polymer blend based on an azobenzene-containing polymer and a similar but nonabsorbing polymer. [8] In a sample of 250 lm thickness, a set of 20 data pages were successfully inscribed; yet, the individual holograms were not completely spatially overlapping. The important issues of stabilizing the inscribed data and rewritability were not addressed. We use a different concept of controlling the optical density, by using block copolymers that contain azobenzene side groups in one block. Block copolymers with less than 15 vol % of one component form spherical microphases with typical diameters in the range of 10-20 nm. Thus, we can macroscopically dilute the chromophores while, at the same time, keeping them in a local confinement. The latter is important for the stability of the inscribed information. In an earlier paper, we have already reported the formation of individual holographic gratings in 10 lm thick films of a material that contained azobenzene and nonabsorbing three-ring mesogenic side groups in the minority phase.[9] In the confined geometry, the presence of a cooperative effect of the side groups was demonstrated. The mesogenic side groups were reoriented together with the chromophores; furthermore, in materia...

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Polymer Blends with Azobenzene‐ Containing Block Copolymers as Stable Rewritable Volume Holographic Media

et al. 2007

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“…In order to further decrease the optical density, the same authors blended a polystyrene-block-poly(hydroxyethyl methacrylate), PS-b-PHEMA, where the HEMA block is partially grafted with azobenzenes and biphenyl mesogens, with polystyrene. [82] The chemical structure of the block copolymer is shown in Figure 24. The blend of this diblock (5 wt.-%) with PS (95 wt.-%) was processed by injectionmolding in order to obtain a film with a diameter of 25 mm and a thickness of 1.1 mm [ Figure 24(b)].…”

Section: Holographic Gratingsmentioning

confidence: 99%

Light‐Responsive Block Copolymers

Schumers

Fustin

Gohy

2010

Macromol. Rapid Commun.

303

255

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Stimuli-responsive polymers are the subject of intense research because they are able to show responses to various environmental changes. Among those stimuli, light has attracted much attention since it can be localized in time and space and it can also be triggered from outside of the system. In this paper, we review light-responsive block copolymers (LRBCs) that combine characteristic features of block copolymers, e.g., self-assembly behavior, and light-responsive systems. The different photo-responsive moieties that have been incorporated so far in block copolymers as well as the proposed applications are discussed.

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“…Larger changes in refractive index need to be induced even at a lower content of the azobenzene. To solve these problems, Schmidt's group 32,71,72 designed polymer blends of block copolymers and polystyrene to obtain thick films and generate Bragg holograms with high angular multiplicity. Minabe et al 31 used blends of an azobenzene-containing polyester and a polyester with a photoinactive moiety to prepare transparent thick films.…”

Section: Bragg Holograms Of Liquid-crystalline Polymersmentioning

confidence: 99%

“…Several approaches to obtain high performance parameters of the Bragg holograms are introduced. 8,9,31,32,[71][72][73][74][75] …”

Section: Introductionmentioning

confidence: 99%

Rewritable holograms based on azobenzene-containing liquid-crystalline polymers

Shishido

2010

Polym J

160

108

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The design and preparation of azobenzene-containing polymers showing a large photoinduced change in refractive index, and their applications to rewritable Raman-Nath and Bragg holograms are reviewed. Optically transparent films with a thickness of 4200 lm have been prepared with random copolymers, which contain photoresponsive and amplifying components in the side chain. Various azobenzene chromophores are used as the photoresponsive component. Cyanobiphenyl and tolane moieties are incorporated as the amplifying component, which enhances the change in refractive index triggered by the azobenzene. When two writing beams are made to overlap in the film, a periodic change in refractive index is induced, and an incident probe beam is diffracted at B100% diffraction efficiency. The recorded holograms can be erased by thermal treatment or by photoirradiation with a single writing beam. Angular multiplicity is discussed from the viewpoint of high-density information storage. Keywords: azobenzene; grating; hologram; liquid crystal; refractive index INTRODUCTION Holograms, in which we can observe natural three-dimensional (3D) images without eyeglasses, have been of great interest from the viewpoint of 3D television. [1][2][3] In addition, other photonic applications such as holographic memory, optical switch and waveguide have been proposed. [3][4][5][6][7][8][9] The holograms can be categorized into two types: (1) Raman-Nath type and (2) Bragg type. The Raman-Nath hologram recorded in a thin film causes multiple diffraction of an incident beam, leading to low diffraction efficiency (o34%). On the other hand, the Bragg hologram shows a single diffraction, which enables 100% diffraction efficiency. Furthermore, angular multiplicity can be used in the Bragg hologram. Therefore, thick films are suitable for holograms with high diffraction efficiency. The diffraction efficiency also depends on a photoinduced change in refractive index of the film. If materials in which a large change in refractive index can be induced by light can be prepared, the performances parameters such as diffraction efficiency, response and multiplicity of the holograms can be enhanced. How can we induce the change in refractive index efficiently? In an isotropic material, the change in refractive index by photoirradiation is rather small and the efficiency is not high. In addition, the material is theoretically polarization inactive. On the other hand, an anisotropic material could show birefringence. By controlling their molecular alignment by photoirradiation, a large change in refractive index and high diffraction efficiency can be obtained. Furthermore, an anisotropic material shows polarization activity. Therefore, we can expect the fabrication of high-performance holograms by photoinduced alignment of anisotropic molecules.

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Blends of Poly(methacrylate) Block Copolymers with Photoaddressable Segments

Cited by 58 publications

References 71 publications

Polymer Blends with Azobenzene‐ Containing Block Copolymers as Stable Rewritable Volume Holographic Media

Polymer Blends with Azobenzene‐ Containing Block Copolymers as Stable Rewritable Volume Holographic Media

Light‐Responsive Block Copolymers

Rewritable holograms based on azobenzene-containing liquid-crystalline polymers

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