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- Perspectives on the electrically induced properties of electrospun cellulose/liquid crystal devicesPublication . Rosu, C.; MANAILA MAXIMEAN, DOINA; Kundu, S.; Almeida, Pedro L.; Danila, O.A mat of electrospun cellulose fibers are deposed on transparent conductive oxide covered glass, and two such plates enclose a nematic liquid crystal. Thus two new types of Cellulose based Polymer Dispersed Liquid Crystal devices, based on hydroxypropylcellulose and Cellulose Acetate and the nematic liquid crystal E7 have been obtained. The current-voltage characteristics indicates ionic type conduction. Heating-cooling cycles have been applied on the samples and the activation energies have been determined. Simultaneously with the thermo-stimulated currents, the optical transmission dependence on the d.c. electric field and temperature was registered. ON-OFF switching times have been determined for different control voltages. (C) 2011 Elsevier B.V. All rights reserved.
- Impedance spectroscopy and electro-optic switching times of a liquid crystal-hydroxypropylcellulose network compositePublication . MANAILA MAXIMEAN, DOINA; Barar, A.; Ganea, C. P.; Almeida, Pedro L.; Danila, OctavianThis paper presents electric and electro-optic studies conducted on a new composite, namely hydroxypropylcellulose network with liquid crystal fillings. The composite was manufactured using the electrospinning method, and deposited on indium tin oxide glass. In terms of electric characterization, the samples were subjected to impedance spectroscopy, their equivalent circuit model was deduced, and the corresponding electric parameters were computed based on the Cole-Cole diagrams and frequency plots of the two impedance components. In terms of electro-optic studies, the optical transmission of the sample under a varying steady-state alternative regime voltage was recorded, and the saturation threshold field was determined. Also, the switching times of the sample with respect to a step signal were determined.
- Filling in the voids of electrospun hydroxypropyl celulose network: dielectric investigationsPublication . MANAILA MAXIMEAN, DOINA; Danila, Octavian; Ganea, Constantin Paul; Almeida, Pedro L.Here we describe an organic electro-optic device, obtained using electrospun hydroxypropyl cellulose (HPC) polymer fibres and nematic liquid crystals (LC). Its working mechanism is similar to that of a classic polymer-dispersed liquid crystal (PDLC) device. The scanning electron microscopy of the HPC deposited fibres shows a mat of fibres with diameters in the nano and micron size range. Dielectric spectroscopy measurements allow the determination of the dependence of the dielectric constant and electric energy loss on frequency and temperature as well as the determination of the activation energy. The electro-optic study shows a very good optical transmission curve, with an “on”-“off” switching voltage of less than 1V/μ m.
- Electrical properties of a liquid crystal dispersed in an electrospun cellulose acetate networkPublication . MANAILA MAXIMEAN, DOINA; Danila, Octavian; Almeida, Pedro L.; Ganea, Constantin PaulElectro-optical devices that work in a similar fashion as PDLCs (polymer-dispersed liquid crystals), produced from celulose acetate (CA) electrospun fibers deposited onto indium tin oxide coated glass and a nematic liquid crystal (E7), were studied. CA and the CA/liquid crystal composite were characterized by multiple investigation techniques, such as polarized optical microscopy, dielectric spectroscopy and impedance measurements. Dielectric constant and electric energy loss were studied as a function of frequency and temperature. The activation energy was evaluated and the relaxation time was obtained by fitting the spectra of the dielectric loss with the Havriliak–Negami functions. To determine the electrical characteristics of the studied samples, impedance measurements results were treated using the Cole–Cole diagram and the three-element equivalent model.