Azobenzene-polymer-stabilized ferroelectric liquid crystals: photoalignment and morphology

Photoinduced Alignment of Ferroelectric Liquid Crystals Using Azobenzene Polymer Networks of Chiral Polyacrylates and Polymethacrylates

“…Two significant differences are emerged between chiral and achiral azobenzene polymers investigated for the photoalignment of FLC. First, in the case of the achiral polymer network, , there is an enhanced segregation of the polymer network from aligned FLC in the S C * phase, which results in the appearance of thick polymer threads (∼ several micrometers in width) running parallel to the aligned smectic domains. No such increased phase separation was observed for aligned FLC with the chiral azobenzene polymer networks.…”

“…Polymerization of the monomer Azo1, which is most effective in inducing photoalignment, results in a polymer network formed by strings of colloidal particles with diameters in the range of 250 nm. Experimental evidence suggests that the photoinduced bulk alignment of FLC related to the chiral azobenzene polymer networks may be achieved through a different mechanism as compared with achiral azobenzene polymers. − Instead of the anisotropic polymer network observed in the latter case, which serves as a framework for the induction and stabilization of FLC, the network from chiral Azo1 may be isotropic, and it is the photoinduced orientation of the large number of azobenzene moieties on the surface of the network, i.e., at the interface with the FLC, that is responsible for the alignment of FLC. This mechanism accounts for the observed reorientation of FLC by changing the polarization of irradiation light as well as the absence of the orientational memory effect characteristic of an anisotropic network.…”

“…In recent years, azobenzene-containing polymers, including amorphous, , liquid crystalline, − and elastomers, − have attracted a great deal of attention due to their potential utility in holographic storage as well as other optical and photonic applications. Being motivated by this, our group has been exploiting a new type of PSLC, in which the polymer network bears the azobenzene chromophore. − We showed that the presence of an azobenzene polymer in PSLC made possible the use of the reversible trans−cis photoisomerization as well as the related photoalignement of azobenzene to affect or induce the LC orientation. − Indeed, when a diacrylate monomer containing an azobenzene moiety is polymerized under linearly polarized irradiation, either in the nematic 15 or isotropic phase, the azobenzene network formed can be anisotropic and induce a stable bulk alignment of the LC in the nematic phase in the absence of rubbed surfaces. More recently, we reported that azobenzene polymer networks could also be used to optically align FLC. , In the latter case, however, an increased segregation of the polymer network from the FLC host was observed in aligned samples in the ferroelectric chiral smectic-C (S* C ) phase, giving rise to the formation of thick polymer threads parallel to the FLC alignment direction.…”

“…Being motivated by this, our group has been exploiting a new type of PSLC, in which the polymer network bears the azobenzene chromophore. [14][15][16][17][18] We showed that the presence of an azobenzene polymer in PSLC made possible the use of the reversible trans-cis photoisomerization as well as the related photoalignement of azobenzene to affect or induce the LC orientation. [14][15][16][17][18] Indeed, when a diacrylate monomer containing an azobenzene moiety is polymerized under linearly polarized irradiation, either in the nematic 15 or isotropic phase, 16 the azobenzene network formed can be anisotropic and induce a stable bulk alignment of the LC in the nematic phase in the absence of rubbed surfaces.…”

“…More recently, we reported that azobenzene polymer networks could also be used to optically align FLC. 17,18 In the latter case, however, an increased segregation of the polymer network from the FLC host was observed in aligned samples in the ferroelectric chiral smectic-C (S* C ) phase, 18 giving rise to the formation of thick polymer threads parallel to the FLC alignment direction. Although the bulk alignment of FLC remains, such a large-scale phase separation is not desirable because of the resulting inhomogeneity.…”