Dynamic Behavior of the Minority Phase of Photoaddressable Block Copolymers

Walker

Kador

et al. 2011

Chemistry A European J

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This paper reports on the synthesis and the thermal and optical properties of photochromic low-molecular-weight compounds, especially with respect to the formation of holographic volume gratings in the pure materials and in binary blends with polystyrene. Its aim is to provide a basic understanding of the holographic response with regard to the molecular structure, and thus to show a way to obtain suitable rewritable materials with high sensitivity for holographic data storage. The photoactive low-molecular-weight compounds consist of a central core with three or four azobenzene-based arms attached through esterification. Four different cores were investigated that influence the glass transition temperature and the glass-forming properties. Additional structural variations were introduced by the polar terminal substituent at the azobenzene chromophore to fine-tune the optical properties and the holographic response. Films of the neat compounds were investigated in holographic experiments, especially with regard to the material sensitivity. In binary blends of the low-molecular-weight compounds with polystyrene, the influence of a polymer matrix on the behavior in holographic experiments was studied. The most promising material combination was also investigated at elevated temperatures, at which the holographic recording sensitivity is even higher.

Section: Resultscontrasting

confidence: 56%

“…This value is smaller than the activation energies obtained for azobenzene-containing block copolymers. [41]…”

Section: Photophysical Properties Of the Azobenzene-containing Lowmolmentioning

confidence: 99%

Holographic Investigations of Azobenzene‐Containing Low‐Molecular‐Weight Compounds in Pure Materials and Binary Blends with Polystyrene

Walker

Kador

et al. 2011

Chemistry A European J

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“…The crossover from constant amplitudes at low temperatures to the strong decrease indicates the structural relaxation of the material which we have described in a similar way for photoaddressable polymers. [32] The crossover temperature of 338 K is significantly lower (by 35 8C) than the glass transition temperature as measured by DSC (372 K). One of the reasons for this difference is the light-induced increase of the local temperature by the writing laser which is discussed later.…”

Section: Temperature-dependent Growth and Decay Of Srgsmentioning

confidence: 99%

Synthesis and Structure–Property Relations of a Series of Photochromic Molecular Glasses for Controlled and Efficient Formation of Surface Relief Nanostructures

Walker

Kador

et al. 2009

Adv Funct Materials

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This paper reports on the synthesis and properties of a new series of photochromic molecular glasses and their structure–property relations with respect to a controlled and efficient formation of surface relief nanostructures. The aim of the paper is to establish a correlation between molecular structure, optical susceptibility, and the achievable surface relief heights. The molecular glasses consist of a triphenylamine core and three azobenzene side groups attached via an ester linkage. Structural variations are performed with respect to the substitution at the azobenzene moiety in order to promote a formation of a stable amorphous phase and to tune absorption properties and molecular dynamics. Surface relief gratings (SRGs) and complex surface patterns can easily be inscribed via holographic techniques. The modulation heights are determined with an equation adapted from the theory for thin gratings, and the values are confirmed with AFM measurements. Temperature‐dependent holographic measurements allow for monitoring of SRG build‐up and decay and the stability at elevated temperatures, as well as determination of the glass transition temperature. SRG modulation heights of above 600 nm are achieved. These are the highest values reported for molecular glasses to date. The surface patterns of the molecular glasses are stable enough to be copied in a replica molding process. It is demonstrated that the replica can be used to transfer the surface pattern onto a common thermoplastic polymer.

“…An additional effect of the molecular glass, especially at higher concentrations, is that the reproducibility of the holographic performance is further improved, as can be seen by the smaller error bars. However, a drawback is that holographic gratings in similar block copolymers (without molecular glass) are not long‐term stable …”

Section: Introductionmentioning

confidence: 99%

Improving holographic writing performance of photo-orientable azobenzene polymers by molecular glasses

Probst

Meichner

J. Polym. Sci. Part B: Polym. Phys.

et al. 2016

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Long‐term stable holographic volume gratings in azobenzene‐containing films have potential applications as forgery‐proof security features or in holographic data storage. However, azobenzene‐based polymer systems often lack sufficiently high writing speeds. Here, an approach to improve the holographic writing performance of photo‐orientable azobenzene‐containing polymers by blending with azobenzene molecular glasses is presented. The molecular glass enhances the photo‐plastification effect and, consequently, the writing speed. This concept of improving the holographic performance of photo‐orientable azobenzene polymers with azobenzene molecular glasses is demonstrated with a homopolymer and two block copolymers. In the azobenzene homopolymer, an addition of 10 wt % of the molecular glass leads to a doubling of the writing speed. Simultaneously, the long‐term stability of inscribed gratings is maintained. In case of the block copolymers, the molecular glass is present in the polystyrene matrix and accumulates in the azobenzene minority phase. Adding 5–10 wt % of molecular glass improves the writing speed of the azobenzene block copolymer by a factor of 3–4. An addition of 15 wt % of molecular glass to the block copolymer containing azobenzene and nonphotoactive mesogenic side groups reduces the writing time by a factor of 15 and the long‐term stability of the gratings is retained. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2110–2117