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L. DOLGOV, O. YAROSHCHUK, and M. LEBOVKA
«Structure and Electrooptical Response of Liquid Crystal with Negative Dielectric Anisotropy Doped by Carbon Nanotubes»
625–633 (2008)

PACS numbers: 61.30.Gd, 61.30.Jf, 61.46.+w, 64.75.+g, 77.84.Nh, 78.20.Jq, 82.70.Kj

The microstructure and electrooptical response of n-(n-ethoxybenzylidene)- n-butylaniline (EBBA) liquid crystal (LC) with negative dielectric anisotropy doped with the multiwall carbon nanotubes are investigated. The concentration of the nanotubes in LC is small enough (CCNT < 0.5 wt.%) to avoid essential disturbance of LC orientation. The electric-field application results in reorientation of LC from the initial homeotropic state to planar one. As revealed, in contrast to the pure liquid crystal, in the LC doped with nanotubes,the planar state, which is achieved under electric-field action, remains after the field is off. It is accompanied by residual light transmittance or memory. The efficiency of such memory depends non-monotonically on the nanotubes concentration with the maximum at concentrations CCNT = 0.02—0.05 wt.%, which corresponds to the percolation transition from non-conductive state to conductive one. The model of electrooptical memory is proposed. According to this model, the nanotubes form the aggregates’ network in LC, which maintains a certain orientation state. During LC reorientation in the electric field, the network of aggregates rebuilds and stabilizes the planar state. The formation of nanotubes’ network is confirmed by additional experiments.