Polymer-dispersed Liquid Crystal Cell Research Articles

New graphene oxide doped polymer dispersed liquid crystal nanocomposites targeted to eco-friendly and energy-efficient smart windows

Graphene oxide-polymer dispersed liquid crystal (GO-PDLC) composites are proposed as a solution for energy-efficient switchable windows. These composites were prepared by incorporating varying concentrations of graphene oxide (GO) into a mixture of nematic liquid crystal (E7) and a UV–Vis curable resin using the polymerization-induced phase separation technique. The results indicate that the dispersion of GO at an optimum concentration of 0.005 wt% significantly affects the morphology, phase transition temperatures, and electro-optic properties of polymer dispersed liquid crystal (PDLC). In particular, the GO-PDLC composites exhibit a transition from an opaque to a transparent state at a remarkably low voltage (∼11.5 V) compared to pure PDLC cell. Dielectric analysis reveals that adding GO increases the permittivity, conductivity, and dielectric strength of PDLC composites. Moreover, the Cole-Cole plot indicates a non-Debye type relaxation in a higher frequency region. Furthermore, a blue shift in emission wavelength and enhanced photoluminescence intensity suggest alterations in electronic transitions within the composites. This comprehensive study provides valuable insights into optimizing the properties of PDLCs through the dispersion of GO, thereby offering promising prospects for their utilization in various optoelectronic applications.

Superior electro-optical switching properties in polymer dispersed liquid crystals prepared with functionalized carbon nanotube nanocomposites of LC for switchable window applications

In this work, we are reporting the results on electro-optical switching properties of polymer dispersed liquid crystal (PDLC) devices for switchable window related applications. The PDLC cells are prepared by mixing octadecylamine functionalized single-walled carbon nanotubes (ODA-SWCNT) nanocomposites of liquid crystals (LC) and acrylate-based monomer by polymerization induced phase separation method. The important switchable device parameters such as threshold voltage, switching voltage, response time, contrast ratio and effective refractive index are investigated. The PDLC cells prepared with 0.05 wt% ODA-SWCNT nanocomposites of the LC, 7CB show almost zero threshold field and 36% less driving field compared to PDLC prepared with pure 7CB. A distinct optical response (frequency doubling) phenomenon is observed for PDLC prepared with 0.03 and 0.05 wt% ODA-SWCNT nanocomposites of 7CB compared to PDLC cells prepared with pure 7CB and lower concentrations (<0.03 wt%) of ODA-SWCNT. The relaxation of optical transmittance is observed at low frequency even when the applied electric field (Eapp) is ON which is due to the strong induced internal electric field (due to free ions) which nullifies the Eapp. The physical mechanism of this unique optical behavior is discussed in detail. The PDLC prepared with 0.01 wt% ODA-SWCNT show 84% faster response time compared to PDLC prepared with pure 7CB. The working of prototype PDLC devices for use in switchable window related applications is reported. The results indicate that, the PDLC prepared with 0.05 wt% ODA-SWCNT nanocomposites of 7CB show high ON state clarity and high OFF state opacity compared to PDLC prepared with pure LC and lower concentrations of ODA-SWCNT.

Polarization-Dependent Gratings Based on Polymer-Dispersed Liquid Crystal Cells with In-Plane Switching Electrodes.

A diffraction grating of polymer-dispersed liquid crystal (PDLC) with polarization-selective characteristics is investigated. Electrically controllable gratings are produced using In-Plane Switching (IPS) electrodes. Indium tin oxide (ITO) electrodes with a stripe pattern are used to generate a horizontal electric field parallel to the substrate on a single glass substrate. It is known from the experimental results that the number of diffraction orders can be controlled by applied voltage. Except for the zeroth order, the consistently highest intensity can be obtained for every other order of diffraction, and the polarization direction of the diffraction is perpendicular to the direction of the electrode stripes. The polarization direction of the zeroth order diffraction is parallel to the direction of the electrode stripes. Therefore, it can be used as a filter for light polarization.

Electroactive despeckle diffuser using polymer dispersed liquid crystal in-plane switched by interdigitated electrodes

An electroactive despeckle diffuser (EADSD) is demonstrated using a polymer dispersed liquid crystal (PDLC) in-plane switched by two pairs of interdigitated electrodes whose directions are orthogonal. The mechanism underlying speckle suppression involves the time average of different speckle patterns during the exposure time of a detector, wherein the reorientation of LC molecules results in different speckle patterns. The introduction of interdigitated electrodes increases the diversity of the electric field in comparison with a conventional PDLC cell switched by a longitudinal electric field. Experimental results show that this device can reduce speckles more effectively owing to the more diverse electric field. The speckle reduction efficiency is approximately 55% when we drive the EADSD sample fabricated by 60 wt% E7: 40 wt% NOA65 under an exposure power of 6 mW/cm2 by bipolar triangle waveforms applied to the two pairs of interdigitated electrodes with frequencies of 20 Hz and peak voltage values of 150 V, and when the phase delay of the waveforms is 90° or 270°. The EADSD is static and does not require motors to achieve vibration, which make it a superior device for speckle reduction in laser displays.

Tunable terahertz phase shifter based on dielectric artificial birefringence grating filled with polymer dispersed liquid crystal

An active terahertz (THz) anisotropic manipulation is based on a structure combined polymer dispersed liquid crystal (PDLC) with sub-wavelength dielectric gradient grating. In this structure, the PDLC works as an adjustable anisotropic material due to the change of the optical axis direction induced by applying a biased electric field, while the dielectric grating serves as an artificial high birefringence material. By using an appropriate design, the THz birefringence of this structure can be enhanced or offset under different biased voltages, and the phase shift curve of this structure becomes flatter than that of the pure PDLC cell due to the dispersion manipulation of the grating. Moreover, the experimental results fit with the simulative designing, demonstrating that the phase shift of the structure can vary from π to 0 near 0.8 THz when the electric field increases from 0 to 80V, and this device realizes the function of polarization conversion as a tunable THz half-wave plate. This work exhibits potential applications in THz functional devices, such as actively controlled phase shifters and polarization convertors combined LC with artificial microstructure.

Tunable nonpolarizing guided-mode resonance filter incorporating electrically driving liquid crystal

A tunable nonpolarizing guided-mode resonance filter (GMRF) incorporating an electrically driving polymer-dispersed liquid crystal (PDLC) cell is designed, fabricated and demonstrated. By studying the dependence of the resonance wavelength on the grating period, the two-dimensional (2D) nonpolarizing GMRF is designed using different grating periods along the x and y axes at oblique incidence. The 2D electrically driving GMRF sample is fabricated through thin-film deposition, electron beam lithography and PDLC injection. Moreover, the resonance spectra of the fabricated sample are measured by a spectrometer and themeasuredresults areconsistentwiththetheory. Thus the nonpolarizing resonance spectra can be tuned by electrically driving the refractive index of PDLC cell inrealtime.

Highly conductive PEDOT:PSS film by doping p-toluenesulfonic acid and post-treatment with dimethyl sulfoxide for ITO-free polymer dispersed liquid crystal device

In this paper, the highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film realized by applying the doping technique and the post-treatment process is demonstrated. The conductivity of the spin coated PEDOT:PSS film enhanced greatly from 0.7 S/cm to 736 S/cm after 1.25% of p-toluenesulfonic acid solution (50 wt%) was doped into the PEDOT:PSS aqueous dispersion. The post-treatment using dimethyl sulfoxide further improved the conductivity to 1549 S/cm. The highly conductive PEDOT:PSS film was used as transparent electrode to fabricate ITO-free polymer dispersed liquid crystal (PDLC) cell. The experimental results showed that the electro-optical properties of the PDLC cell fabricated by the highly conductive PEDOT:PSS film were comparable to those of the PDLC cell constructed by ITO. This study reveals that the highly conductive PEDOT:PSS film is a prospective material for manufacturing ITO-free liquid crystal devices.

Electro-optical properties of normally transparent polymer dispersed liquid crystal cells with polymer wall and network structure

ABSTRACTNormally transparent-polymer dispersed liquid crystal (NT-PDLC) cells with polymer wall and network structure were developed using two kinds of UV curable monomers: one was bisphenol A dimethacrylate, used for polymer wall formation to secure mechanical stability, and the other was a reactive mesogen (RM) for the polymer network to yield high scattering of light. A two-step UV exposure method was applied for the structured NT-PDLC cells: the first UV exposure with a patterned mask for wall formation, and the second with no mask for the network. Parametric analysis of the E-O and mechanical properties of the NT-PDLC cells was carried out; monomer concentration, UV intensity, and time were selected as key parameters.

Enhancement of frequency modulation response time for polymer-dispersed liquid crystal

ABSTRACTThrough the ferroelectric nanoparticles of BaTiO3 (BTO) doping, the response time for the frequency modulation of the polymer-dispersed liquid crystal (PDLC) was improved. The BTO-doped PDLC cells were prepared by polymerisation induced phase separation (PIPS) process using UV light. The capacitance of the PDLC composites was measured with an impedance analyzer in the frequency range of 100 Hz–1 MHz at 1 V. The dynamic signal for the response time of the PDLC devices was monitored through a digital oscilloscope. The electro-optical properties of the PDLC were found to strongly depend on the doped BTO concentration. The BTO doping caused a large increase in the capacitance. The dielectric constants were drastically decreased in the samples with rather low BTO doping ratio at a high frequency. No outstanding difference in the rising time of the LC was observed in the BTO-doped PDLC device, but the falling time was significantly decreased from 0.334 to 0.094 s. The present results imply that the nanoparticle-doping technology could improve the electro-optical performance of the PDLC requiring fast response and frequency modulation, such as optical modulators and PDLC-hybrid electroluminescence device for flexible electronic devices.

Flexo-dielectro-optical spectroscopy of PDLC films modified by nano-rubbed PTFE layers

The electro-optical (EO) response of planar single layers of polymer-dispersed liquid crystal (PDLC) composites of relatively large nematic microdroplets modified by layers of teflon (PTFE), was studied. The PDLC films were prepared from liquid crystal E7 and photopolymer NOA-65 in cells assembled with parallel or orthogonal PTFE-covered glass plates. The influence of nanostructured PTFE polymer nanolayers on both the polarized and depolarized component of laser light transmitted through PDLC cells of both geometry of layer rubbing directions was determined. Flexo-dielectro-optical spectroscopy in the range of 10 Hz - 1 kHz was applied to examine the amplitude-frequency EO modulation by PTFE-modified PDLCs in dependence on the applied alternating-current electric field. Specific fall-downs in the frequency spectra of the first and second harmonic EO modulation by PTFE-modified PDLCs were observed, that could be tuned by the driving electric field.

フレキシブル部分駆動バックライトに適した柔軟なポリマー分散液晶セルの作製

フレキシブル部分駆動バックライトに適した柔軟なポリマー分散液晶セルの作製

Enhancement of Optical Transmittance of Polymer-Dispersed Liquid Crystal Cells

Enhancement of optical transmittance of polymer-dispersed liquid crystal (PDLC) cells was investigated by introducing a modification into the substrates. Surface treatment by rubbing was performed on both network-type and droplet-type PDLCs to investigate the effect on the optical transmittance of the cells. Differences in the transmittance of the PDLC in the polymer matrix were observed by introducing rubbing effect on network-type PDLC but not on droplet-type PDLC. These phenomena might be used to distinguish the application field of both types of PDLC cells by enhancing optical transmittance and scattering properties.

Polarization-independent distortion corrector fabricated using polymer-dispersed liquid crystals

We demonstrate a polarization-independent distortion corrector fabricated using a polymer-dispersed liquid crystal (PDLC) cell placed on the intermediate image plane of an optical system. At low voltage, a hazy PDLC cell scatters the incident rays and redirects the off-axis propagated chief ray. The chief ray approaches the principal point of the lens element, thereby decreasing image distortion. At high voltage, the PDLC cell becomes transparent, thereby restoring the image distortion. The PDLC-based distortion corrector is an easy-to-fabricate universal device that can be applied to various optical systems. With a large lens diameter, the distortion of a PDLC-corrected image is approximately 1/5 of that of an uncorrected image.

Effect of BaTiO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; Nanoparticle on Electro-Optical Properties of Polymer Dispersed Liquid Crystal Displays

Ferro nematic suspensions are the prominent materials to enhance the electro optical performance of liquid crystal displays. Electro optical properties of polymer dispersed liquid crystal (PDLC) display with the introduction of Barium Titanate nanoparticles have been investigated in this article and it is shown that there is a considerable enhancement in electro-optical response of the displays. The nanoparticles lower the switch-on electric field and thereby increase the optical transmission at certain voltages of the displays. The electro-optical characteristics of the PDLC cells were investigated with a He-Ne laser followed by MatLab calculations.

Enhanced contrast ratio and viewing angle of polymer-stabilized liquid crystal via refractive index matching between liquid crystal and polymer network

Long standing electro-optic problems of a polymer-dispersed liquid crystal (PDLC) such as low contrast ratio and transmittances decrease in oblique viewing angle have been challenged with a mixture of dual frequency liquid crystal (DFLC) and reactive mesogen (RM). The DFLC and RM molecules were vertically aligned and then photo-polymerized using a UV light. At scattering state under 50 kHz electric field, DFLC was switched to planar state, giving greater extraordinary refractive index than the normal PDLC cell. Consequently, the scattering intensity and the contrast ratio were increased compared to the conventional PDLC cell. At transparent state under 1 kHz electric field, the extraordinary refractive index of DFLC was simultaneously matched with the refractive index of vertically aligned RM so that the light scattering in oblique viewing angles was minimized, giving rise to high transmittance in all viewing angles.

Electrically Controlled Fast Response Cascading Tunable Polymer Dispersed Liquid Crystal Focusing Lenses

ABSTRACTWe experimentally demonstrated an electrically controlled variable focus optical system based on cascading polymer dispersed liquid crystal (PDLC) lens. Through adjusting external electric field applied on the hole‐type electrode of PDLC lens to change the spatial distribution of refractive index of PDLC, the plane PDLC cell can be functioned as a focusing lens with the variable focus length. In this article, we simulate the electromagnetic field distribution of the external electrical field, as well as analysis the corresponding principle and mathematic equation of its electrically controlled focusing length. The experimental results show that as external alternate current (AC) voltage is increased from 0 to 80 V, the focal length of single lens decreases from to 1.073 m, and that of the double lens from to 0.484 m. These experimental results are in good accordance with the simulation results. The experimental response time of PDLC tunable lens is less than 1 ms, which will bring benefits for the applications especially for the fast imaging system. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2830–2835, 2013

Electro-optical response of polymer-dispersed liquid crystal single layers of large nematic droplets oriented by rubbed teflon nanolayers

The surface orienting effect of rubbed teflon nanolayers on the morphology and electro-optical (EO) response of polymer-dispersed liquid crystal (PDLC) single layers of large nematic droplets was studied experimentally. In PDLC composites of the nematic liquid crystal (LC) E7 and NOA65 polymer, single droplets of LC with diameters as larger as 10 μm were confined in layers with a thickness of 10 μm, and the nematic director field was efficiently modified by nanostructuring teflon rubbing of the glass plates of the PDLC cell. For layered PDLCs arranged and oriented in this way, the modulated EO response by the dielectric oscillations of the nematic director exhibits a selective amplitude-frequency modulation controllable by both temperature and voltage applied, and is simply related to the LC droplet size. That may be of practical interest for PDLC-based modulators operating in the infrasound frequency range.

Selective Amplitude-frequency Electro-optical Modulation by Polymer-dispersed Liquid Crystal Films Aligned by Teflon Nanolayers

We report the amplitude-frequency electro-optical (EO) modulation by a specific type of polymer-dispersed liquid crystal (PDLC) composites – planar single layers of large nematic microdroplets aligned by teflon nanolayers. Such a surface modifying PDLC system exhibits a selective modulated 2nd harmonic EO response by the dielectric oscillations of the nematic director. The bandlike behavioural characteristic of the amplitude-frequency modulation of light, achieved by the single-layered PDLC films, can be tuned by AC voltage applied on the PDLC cell. This property can be applied to tunable EO modulators operating in the infrasound frequency range.

Single-layered PDLC films for electrically variable laser light reflection application

Electrically controllable two-beam reflection of coherent light double-passed through the microscale polymer-dispersed liquid crystal (PDLC) single layer is reported. By PDLC medium, the intensities of two reflected beams can be reciprocally changed by applying a suitable voltage in the range 0–100 V. The optical phase shift electrically induced for coherent light propagating in two passes through the single-layered PDLC film, as well as the additional phase shift externally introduced by the substrate of the PDLC cell, are responsible for the electrically controllable reflection in a pair of two beams with complementary voltage-dependent intensity behaviors.

PDLC-based VOA with a small polarization dependent loss

A polymer-dispersed liquid crystal (PDLC)-based variable optical attenuator (VOA) was demonstrated to exhibit a relatively small polarization dependent loss (PDL) in the optical communication C band. The influence of the PDLC characteristics, the temperature, as well as the wavelength of the laser irradiation, on the PDLC VOA performance was analyzed. The PDL, the insertion loss at saturated voltage, and the operating voltage of the PDLC-based VOA were reduced by optimizing the fabrication conditions and applying a bias voltage to the PDLC cells during polymerization-induced phase separation.