We report on the development of a dilute suspension of ferroelectric particles in a nematic liquid-crystal (LC) host. We found that the submicron particles do not disturb the LC alignment and the suspension macroscopically appears similar to a pure LC with no readily apparent evidence of dissolved particles. The suspension possesses enhanced dielectric anisotropy, and is sensitive to the sign of an applied electric field.

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Polymer multicomponent materials containing conjugated fragments (such as azo- or azomethine groups) have attracted significant attention due to their possible use in the efficient reversible stimuli-responsive, light-responsive devices. Light-responsive polyazomethines with azo groups in the backbone (Azo-Pams) are synthesized by polycondensation of tetrafluoro­benzene- or octafluoro­biphenylene-based bis-hydroxy­benzaldehydes with hexamethylene­diamine. The polymers feature the simultaneous combination of azo and azomethine groups inside one conjugated block. The synthesized polymers can be solution cast into flexible solid films with tensile strength of about 24 MPa. We found that the obtained Azo-Pam polymers have an amorphous structure (T g ∼ 134 °C) and high thermal stability (up to 300 °C). Their optical spectra depend on the solvent type and its pH which influence the dynamical equilibrium between the tautomeric forms. It also determines the balance between the main (azo form) and the ionized form in the solvent and allows to purposefully regulate the absorption maxima. We demonstrate the ability to record optical information using Azo-Pam films in the form of polarization gratings (holograms) with a regulated diffraction efficiency. A uniform orientation of liquid crystal is achieved by a polarized UV irradiation of glass substrates covered with the polymer Azo-Pam-II. The obtained data show that the synthesis strategy of the Azo-Pam polymers is an effective instrument for designing a wide range of stimuli-responsive and optical active materials.

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Under pulsed or a.c. electric fields, colloidal suspensions of nanorods can show strong electro-optic effects, such as the Kerr effect, with fast response times (a few ms), which makes them good candidates for some commercial applications. For this purpose, suspensions of Pigment red 176 nanorods in dodecane were recently developed and their physical properties have been studied. We report here on the investigation of the orientational order induced by electric fields in isotropic suspensions of pigment nanorods by three different techniques: transient electric birefringence, transient electric dichroism, and in-situ small-angle X-ray scattering under electric field ("Electro-SAXS"). We show that, in spite of the apolar character of the solvent, the Maxwell-Wagner-O'Konski mechanism (i.e. the polarization of the counter-ion cloud around each particle) is responsible for the field-induced alignment of the nanorods. Although the particles are only weakly charged and the dielectric constant of dodecane is low, the pigment nanorods effectively behave as metallic particles in an insulating matrix and reach strong values (S~0.5) of the induced nematic order parameter at moderate field amplitudes (~1 V/µm). This study confirms the feasibility of using suspensions of Pigment red 176 nanorods in dodecane for electro-optic applications.

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