Polymer azobenzene LCs

As another approach to fast I-N phase transition, the optical switching behavior of LMW and polymer azobenzene LCs has been explored by means of reflection-mode analysis (Figure 10). 45 On laser-pulse irradiation, it is possible to switch the... 

A unique feature of polymer azobenzene LCs as optical image storage materials has been demonstrated. In nematic glasses (solid state azobenzene LC films retaining an N... 

The stability of the induced I phase at the irradiated site of polymer azobenzene LC strongly depends on temperature. At temperatures above the induced I phase disappeared and the N phase was restored after some time, which depended on temperature. At high temperatures such as 140°C, the I phase disappeared in seconds. At temperatures just above Tg the induced I phase remained fairly stable for some time, but disappeared after a prolonged time. On the other hand, at temperature below Tg the induced I phase remained unchanged even after 1 year and 6 months. The cis-trans back-isomerization took place thermally even at room temperature, and the trans-ioun was restored almost completely in 1 day. Polarized absorption spectroscopy showed that even though the trans-iorm was restored in 1 day at room temperature, orientation of the /ra 5-azobenzene mesogens was different from that of the initial state. Before photoirradiation, the azobenzenes were aligned in one direction to form uniaxial monodomain, but after photoirradiation the cw-form was produced, and N—I phase transition was induced. However, after the trans-ioim was restored thermally, the orientation... 

A new system has been developed in which every mesogen in the LC or LC polymer is photosensitive (Ikeda, 2001 Tsutsumi et al., 1998b Tsutsumi et al., 1997 Ikeda and Tsutsumi, 1995). For example, the azobenzene moiety could play roles as both a mesogen and a photosensitive moiety (Fig. 3.20) in azobenzene derivatives that form LC phases. These azobenzene LCs show a stable LC phase only when the azobenzene moiety is in the trans form, but do not show an LC phase when all the azobenzene moieties are in the cis form. Examination of these azobenzene LCs revealed that a nematic-isotropic phase transition is induced in the azobenzene LC polymers within 200 ns over a wide temperature range imder optimized conditions (Ikeda, 2001). 

In all the studies discussed, the grating is transmission-type, with the grating vector lying in the sample plane. Using azobenzene-containing polymer-stabilized and polymer-dispersed LCs (PSLCs and PDLCs), Running and coworkers... 

ITO-coated cell (8- to 10- tm gap) is subjected to holographically induced photopolymerization, grating can be formed with alternating regions of polymer and LC droplets. Figure 11.29 is a schematic illustration of the optical switching mechanism based on the reversible photoisomerization of azobenzene dopant mixed with the LC host (in droplets) as well as the supporting experimental data. 

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