Search

Abstract: This article illustrates the application of using polymer stabilization in creating a new nanocomposite material with clay soil. Various tests with different polymer contents were performed to study the effect of using polypropylene as a stabilizing agent on both microstructure and geotechnical clay properties. These experiments showed that the resulting nanocomposites acted as nanofiller materials which decreased the plasticity and compressibility parameters of the treated clay. The initial structural analysis helped in a better understanding of the modified microstructure and the measured size of induced nanocomposites. The constructed inclusions filled the inter-assembling pores thus notably producing a higher vertical effective yield stress which again reduced the volumetric shrinkage and created isotropic and compressible materials with a lesser extent of desiccation cracks. It also increased the tensile and the shear strength of the stabilized clay with an increase in the nanocomposites size. This technique can be effectively used for road embankments and slope stabilization. [Copyright &y& Elsevier]

• The toron polymorphism in chiral nematics with smectic-A phase beneath is observed. • The polymerization preserves toron structure with fast switching property. • Numerical simulations reveal the effect of anchoring strength and nematic elasticity on toron polymorphism. Toron is one of the fundamental chiral topological textures appearing in many spintronic and soft matter systems. Here we report on the observation of torons in cholesteric liquid crystals with positive dielectric anisotropy (Δ ε > 0). In addition, the materials show smectic-A phase beneath the cholesteric phase, enabling us to see the pretransitional effect on the formation of the torons. In detail, we investigated the relation of toron formability and the external stimuli in terms of temperature and electric field. Importantly, the divergence of the elastic constants (K 22 and K 33) in the vicinity of the nematic-smectic-A phase transition causes the transition from the toron to the homeotropic alignment. The results reveal that both the homeotropic anchoring strength and the frustrated confinement of the cholesteric helix are important to determine whether the toron texture is selected among other textures like fingers. The confinement ratio, i.e. the ratio of cell thickness to cholesteric pitch, for the incidence of torons was found to be in a wide range of about 0.82 ∼ 1.5. We also show that the torons can be polymer-stabilized so that they retain over a wide temperature window. Even more importantly, the orientational state of the polymer-stabilized toron can be changed by an electric field, realizing fast switching between the dark and bright states. The system may find applications in electric-driven diffraction gratings or privacy protection films with a sub-millisecond response time. [ABSTRACT FROM AUTHOR]

The behavior of two newly formulated bi-component orthoconic antiferroelectric liquid crystalline (OAFLC) systems, i.e., the Compound A + Compound B mixture system and Compound C + Compound B mixture system has been discussed in light of temperature and concentration dependencies of helical pitch length, spontaneous polarization, relaxation time, bulk viscosity, and the anchoring energy strength coefficient, together with static dielectric permittivity (ε) and dielectric anisotropy. Compound A + Compound B mixtures possess spontaneous polarization between 190–340 nC.cm−2 and fast relaxation times between 190–320 µs in the smectic antiferroelectric SmCA* phase at room temperature. Compound C + Compound B mixtures also have a spontaneous polarization in the range of 190–280 nC.cm−2 and relaxation times in the range of 190–230 µs at room temperature. Most of the mixtures have a helical pitch below one micrometer in the SmCA* phase. These advanced mixtures show a broad temperature range of the antiferroelectric SmCA* phase, fast switching of molecules under an applied electric field, negative dielectric anisotropy and a short helical pitch, confirming the advantage of designing new polymer-stabilized OAFLC that is targeted for novel application in sensing devices, utilizing the fast responsive electro-optical modulation elements. [ABSTRACT FROM AUTHOR]

Blue phase liquid crystals (BPLCs) composed of double-twisted cholesteric helices are promising materials for use in next-generation displays, optical components, and photonics applications. However, BPLCs are only observed in a narrow temperature range of 0.5–3 °C and must be stabilized with a polymer network. Here, we report on controlling the phase behavior of BPLCs by varying the concentration of an amorphous crosslinker (pentaerythritol triacrylate (PETA)). LC mixtures without amorphous crosslinker display narrow phase transition temperatures from isotropic to the blue phase-II (BP-II), blue phase-I (BP-I), and cholesteric phases, but the addition of PETA stabilizes the BP-I phase. A PETA content above 3 wt% prevents the formation of the simple cubic BP-II phase and induces a direct transition from the isotropic to the BP-I phase. PETA widens the temperature window of BP-I from ~6.8 °C for BPLC without PETA to ~15 °C for BPLC with 4 wt% PETA. The BPLCs with 3 and 4 wt% PETA are stabilized using polymer networks via in situ photopolymerization. Polymer-stabilized BPLC with 3 wt% PETA showed switching between reflective to transparent states with response times of 400–500 μs when an AC field was applied, whereas the application of a DC field induced a large color change from green to red. [ABSTRACT FROM AUTHOR]

We used a polymer network to improve the response time of a vertical aligned (VA) mode liquid crystal display (LCD). The polymer network was anisotropic and was oriented in the same direction as the liquid crystal in the dark state. We studied the effect of pretilt angle and polymer concentration and measured the transmittance as well as scattering. With the polymer network, the turn-off time of VA-LCD significantly improved while the contrast ratio remained high. [ABSTRACT FROM PUBLISHER]

Polymer-stabilized ferroelectric liquid crystals may show monostable and V-shaped electrooptical characteristics. We have investigated the dependence of their characteristics on the photocuring condition, especially ultraviolet light intensity. Furthermore, we offer a new scheme of the photocure being done under an electroclinic effect. The bistability of ferroelectric liquid crystals remains partially in the case of a weak ultraviolet light intensity and the saturation voltage increases as the ultraviolet light intensity increases. The tilt angle decreases as the ultraviolet light intensity increases. The decrease of tilt angle cannot be suppressed even in polymer-stabilized ferroelectric liquid crystals fabricated using the electroclinic effect. [ABSTRACT FROM AUTHOR]

We have studied the optically compensated splay (OCS) mode applied to polymer stabilization technique using polymerization of reactive mesogen (RM) to reduce or eliminate critical voltage, setting voltage, and phase transition time from bend to splay state. The pretilt angle of almost vertically aligned liquid crystal directors could be lowered through the polymerization of UV-curable RM and applied voltage, at surfaces of vertical alignment layers. To confirm initial stable splay state, we investigated electro-optic characteristics according to concentration of RM in this paper. [ABSTRACT FROM AUTHOR]

The article focuses on the issue of polymer-stabilized pretilt angle on the surface of nanoparticle-induced vertical alignment surface. It mentions that the vertical-alignment surface is for multi-domain vertical-alignment liquid-crystal display. It notes that multi-domain vertical-alignment liquid-crystal display was demonstrated through introduction of polyhedral oligomeric silsesquioxane (POSS) nanoparticles.

Abstract: In this study, the influence of cyclic wetting and drying on swelling behavior of polymer-stabilized expansive clays has been investigated. Such a study is required to assess the long-term behavior of these soils in geotechnical applications. Three expansive soils with different plasticity indexes were obtained from a region around Tehran (capital of Iran). These soils were stabilized by different amounts of two polymers, Urea Formaldehyde and Melamine Formaldehyde. The swelling tests have shown that these polymers decreased the swelling potential of the expansive soils. Cyclic swelling and shrinkage potential and cyclic swelling pressure tests were performed on both treated and un-treated expansive clays. In addition, to simulate partial shrinkage, specimens were dried to their initial water contents in each cycle. Variations in grain size distributions and Atterberg limits of both treated and un-treated expansive soils due to cycles of wetting and drying were assessed. The microfabric changes were also studied by scanning electron microscopy (SEM). The results showed that the suppression of swelling in polymer-stabilized specimens was not lost after the first cycle and the swelling potential and pressure of treated specimens were less than those of un-treated specimens during the cyclic wetting and drying; nevertheless, in cyclic swelling and shrinkage, the swelling potential and pressure of all specimens started decreasing after the first cycle. All of the specimens reached equilibrium after the fourth cycle. [ABSTRACT FROM AUTHOR]

We have analyzed the effect of polymer stabilization on the helical structure of FLCs, such as polymer stabilization strength and molecular-alignment-structural deformation, by the conoscopic figures of polymer-stabilized ferroelectric liquid crystals (PSFLCs) observed from computer simulation and experiment. In this study, we research the conoscopic figures and the polymer stabilization strength of PSFLCs fabricated using a new FLC material and several types of monomer. In the case using a photocurable monoacrylate LC-1, the elastic constant of PSFLC is as large as that of pure FLC. On the other hand, in the case of diacrylate 2A363, the elastic constant is one hundred times larger. Therefore, the polymer stabilization strength and the characteristics of PSFLC may be widely controlled by mixing several types of monomer. [ABSTRACT FROM AUTHOR]

Liquid crystal displays (LCDs) are widely used for mobile devices. They are usually edgelit that a LED light source is installed at the edge of the displays and the produced light is spread out through a light waveguide plate to illuminate the display. We developed a polarizing light waveguide plate from polymer stabilized nematic liquid crystal. It can convert unpolarized light from the edgelight into linearly polarized light by selective scattering. It can greatly increase the light efficiency of edgelit LCDs. [ABSTRACT FROM AUTHOR]

Polymer-stabilized ferroelectric liquid crystals (PSFLCs), in which a photocurable mesogenic monomer is doped into a ferroelectric liquid crystal and a UV photocure is carried out in the SmA or the SmC* phase under the application of a bipolar AC electric field, show the monostable and V-shaped electrooptical characteristics, and thus are expected to be a newly developed materials for LC devices. In this study, in order to increase the thermal reliability of PSFLCs, we fabricate a new PSFLC photocured at the nematic (N) phase, and then investigate its characteristics in terms of the electrooptical effect and the X-ray diffraction. Results show that the PSFLC photocured at the N phase does not become monostable because the chevron angle does not coincide with the tilt angle. [ABSTRACT FROM AUTHOR]

Polymer stabilization is a technique for stabilizing a liquid crystal molecular orientation. The effect of polymer stabilization on the helical structure of FLCs can be analyzed by the observation of the conoscopic figures of polymer-stabilized ferroelectric liquid crystals (PSFLCs) obtained from the computer simulation and the experiment. In this study, we investigate the conoscopic figures of PSFLCs fabricated using a new acrylate polymer having an alkyl spacer part between main- and mesogenic side-chain. The strength of polymer stabilization originated in the side-chain becomes lower due to the alkyl spacer. Although the polymer stabilization usually increases the threshold electric field, the increase may be controlled by utilizing a suitable spacer. [ABSTRACT FROM AUTHOR]

A polymer-stabilized ferroelectric liquid crystals (PSFLCs), in which photocurable mesogenic monomers are doped into an FLC and then a UV photocure is carried out in the SmC* phase under the application of a bipolar AC electric field, can exhibits monostable and V-shaped electrooptical characteristics. In this research, the time-resolved ellipsometry is applied to the PSFLCs, and we investigate the dependence of the molecular reorientational motion of the PSFLC on the photocuring condition such as the tilt angle which FLC molecules take in the photocure stage. The measurement results show that the dynamic behavior of PSFLC-molecular reorientation strongly depends on the photocuring condition of the tilt angle in addition to the concentration of polymer. Furthermore, the molecular reorientation of the PSFLC is 2-steps motion originated in the difference of the threshold voltage between near and far from polymer. [ABSTRACT FROM AUTHOR]

The effect of rubbing treatment on the molecular orientation is investigated for the vertically aligned ferroelectric LC (VA-FLC) cell having an inter-digit electrode to apply an in-plane electric field. The FLC material with large cone angle (CS-2005 (Chisso Co. Ltd.)) was used since a sufficient high contrast ratio is obtained due to the large effective optical retardation even if the cell thickness is thin. The E-O characteristic was measured for not only normal VA-FLC cells but also polymer-stabilized VA-FLC cells. In the polymer stabilized VA-FLC, the FLC material doped with small amount of photo-curable mesogenic monomers was used. For the VA-FLC cell, it is effective to carry out the rubbing treatment on one side substrate or both side substrates which are assembled with the anti-parallel cell configuration. A half-V shaped T-V characteristics were obtained by implementing the polymer-stabilization technology. [ABSTRACT FROM AUTHOR]

The photorefractive effect of photoconductive-polymer-stabilized ferroelectric liquid crystals (FLCs) was investigated. A photoconductive acrylate monomer and an electron acceptor compound were mixed with an FLC, and the mixtures were photopolymerized in the ferroelectric phase. A photoconductive polymer network was formed in the FLC medium, and a polymer-stabilized FLC was obtained. The photorefractive effect was evaluated by a two-beam coupling experiment. A large gain coefficient was obtained in the polymer-stabilized FLCs. [ABSTRACT FROM AUTHOR]

We examine the differences in electro-optical behavior of weakly polymer stabilized cholesteric liquid crystals (PSCLC) when formed using either a flood lit UV lamp, a flood lit UV laser, or a holographically patterned UV laser. Both samples formed with the UV laser exhibit symmetry in their dynamic electro-optical properties relative to the front and rear surface of the polymerized cell. These cells exhibit a reversible ∼100 nm blue shift tuning of the notch upon application of a field when the reflectivity is measured from either side. The UV lamp sample exhibits large differences in behavior when examined from the front or back relative to the direction of the polymerizing source. The front surface exhibits tuning of the notch while measurements from the back surface yield only the typical binary switching behavior of a CLC. The overall switching fields in flood lit UV laser and UV laser holographically patterned samples are also considerably lower. These differences are explained due to the presence of a strong polymer gradient across the cell gap in the UV lamp flood lit samples which is not present for the UV laser stabilized samples. We also present novel electro-optical results when these laser cured cells are examined in transmittance mode. Strong anchoring at the two surfaces causes a strong anisotropic local LC structure across the cell gap when a field is applied. The two local environments next to each surface act to strongly pin the CLC structure whereas within the bulk, ample reorientation of the LC molecules occurs. When probed in transmission, unusual fringe patterns which change with the strength of the applied field are observed. [ABSTRACT FROM AUTHOR]

Stabilized reverse twisted nematic liquid crystal devices (RTN-LCDs) were fabricated using formation of a polymer matrix under UV irradiation with an applied voltage (sustain voltage) in the vicinity of the alignment layers. In the absence of an applied voltage, the non-stabilized RTN structure gradually returns to a splay twist structure. The sustain voltage was decreased with an increase in temperature. A stabilized long-pitch supertwisted nematic (LPSTN) structure could also be formed during the RTN structure stabilization process with a much lower sustain voltage at a temperature near the clearing point. The chiral pitch for the LPSTN structure is longer than that for a typical STN structure. LPSTN-LCDs similar to RTN-LCDs show a large reduction in both the threshold and saturation voltage compared with those for TN-LCDs consisted of the same LC materials. Furthermore, a notable feature of LPSTN-LCDs is a change to a TN structure when a high voltage is applied. A black state can be realized due to the change from the LPSTN structure to the RTN structure unlike the typical STN mode under the crossed nicols condition. In contrast STN-LCDs retain their color due to the retardation because the RTN and LPSTN states are considered topologically equivalent. [ABSTRACT FROM AUTHOR]

Vertically aligned liquid crystal (LC) surrounded by polymer wall, which is also known as locked-super homeotropic (LSH) mode has several advantages such as rubbing- and spacer-free, wide-viewing angle and stable LC dynamics against external pressure. However, the LSH mode shows slow response time due to the instantaneous collision between the LC molecules when a vertical electric field is applied, because the reorientation of chiral doped vertically aligned LC is only determined by the polymer wall. We found that the slow response time can be improved by surface polymer-stabilized technique where surface pretilt angle is defined on alignment layers. This technology can be used in any shape of polymer wall. (PACS 42.79.Kr, 85.60.-q). [ABSTRACT FROM AUTHOR]

Abstract: The research was focused on synthesis of proton conductive, easily degradable polymer membranes, which can be used as a model system to verify the efficiency of transition metal ions (TMI) in prevention of polymer degradation. Two polymers composed of 2-hydroxyethyl methacrylate (HEMA), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), and styrenesulfonic acid (SS) were synthesized. The copolymers were characterized by gel permeation chromatography (GPC), elementary analysis, and FTIR and fluorescence spectroscopies. The results allowed determination of weight-average molecular weight and the copolymer composition. The protons of sulfonic groups were substituted by paramagnetic transition metal ions of various spin states (Cr3+, S =3/2 and Mn2+, S =5/2) with the loading varying from 0.5 up to 10mol%. The effectiveness of spin catalysis was checked by EPR. The results obtained indicate enhancement of polymer stability in the presence of Mn2+. [Copyright &y& Elsevier]

Polymer-stabilized ferroelectric liquid crystals (PSFLCs), in which a photocurable mesogenic monomer is doped into a ferroelectric liquid crystal and a UV photocure is carried out in the SmC* phase under the application of a bipolar AC electric field, show the monostable V-shaped electrooptical characteristics. In this research, we investigate the dependence of the molecular reorientational motion on the photocuring condition such as the tilt angle which FLC molecules take in the photocure stage and the frequency of the bipolar AC electric field, in terms of the response time measured from the electrooptical characteristics. [ABSTRACT FROM AUTHOR]

The use of automatically operating shutters for welding is since long a recognized application of liquid crystals with an important market. With the advent and success of the new pulsed welding technique the conventional welding helmets based on nematic liquid crystals are facing difficulties because the nematics are not responding fast enough to stroboscopically follow the changing intensity of the arc during pulsed welding. Ferroelectric liquid crystals (FLCs) here offer new possibilities. Our new FLC-based visor, with a switching time of about 200 microseconds, blocks the high light intensity during the sparks and opens the visor between pulse sparks. This new type of FLC visor thus significantly increases the visibility of the object under work compared to traditional nematic liquid crystal helmet visors, where the relaxation (several milliseconds) is too slow to open the visor between pulses. [ABSTRACT FROM AUTHOR]

By doping photo-curable monomers showing properties of a low driving voltage into FLC media and performing an appropriate photo-curing, we succeeded in fabricating novel Polymer-stabilized FLCDs exhibiting V shaped switching (PSV-FLCDs) with τ = 100 μs to 200 μs and with a free from the temperature dependence of operating voltage within 3 mV/°C in the range from -5°C to 50°C. We also demonstrate a field sequential full color LCD with 4 inch diagonal and 254 ppi that is capable of displaying moving images without blurring and break. [ABSTRACT FROM AUTHOR]

The effect of polymer stabilization on the helical structure of ferroelectric liquid crystal (FLC) and the deformation of the helical structure under the application of an electric field has not been cleared. In this study, conoscope observations for polymer-stabilized (PS) FLCs were performed, and we try to examine the polymer anchoring strength from the comparison between the experimental and the computer simulation results. It is found that the helical structure can be stabilized by introducing polymer networks, and the elastic constant of PSFLC may increase in different classes even in a few polymer concentration. Furthermore, it is found that the polymer stabilization can suppress the temperature variation of the elastic constant. [ABSTRACT FROM AUTHOR]

Director profiles and electrooptical properties in polymer-stabilized π cells used in optically compensated bend (OCB) liquid crystal displays (LCDs) are theoretically investigated by introducing an additional term which expresses the effect of polymer stabilization on the free energy density. The conditions required to stabilize the bend alignment definitively have been theoretically clarified and experimentally confirmed. As a result, the bend alignment is successfully stabilized even if the twist state is more stable than the bend state before the application of polymer-stabilization treatment. [ABSTRACT FROM AUTHOR]

Horizontally surface-stabilized orthoconic antiferroelectric liquid crystals (OAFLCs) provide excellent contrast electrooptic switching. However, in very thin cells the bulk relaxation to the anticlinic state tends to be slow because the synclinic state is upheld by the surfaces. In cells thin enough to accomplish a surface-stabilized state of today's short-pitch OAFLC mixtures, the field-induced synclinic (ferroelectric) states often become metastable making the corresponding bright electrooptic state prevail for long times after the electric field is switched off. Fast relaxation is then achieved by specially designed waveforms.By introducing a polymer network formed by in-situ photopolymerization of a small concentration of a commercial reactive monomer dissolved in the OAFLC, we have succeded to drastically reduce the time for relaxation from the synclinic to the anticlinic state after switching off the field down to about 3 milliseconds at room temperature, without the use of any tailored electronic waveforms. The relaxation time of the polymer stabilized OAFLCs (PS-OAFLCs) is thus shorter than in todays nematic liquid crystal displays, which make PS-OAFLCs attractive for use in future high-contrast, blur-free displays. [ABSTRACT FROM AUTHOR]

We used optical Bragg reflections to study the effects of photo-polymer networks on the phase transitions of four heterocyclic esters that exhibit various frustrated chiral smectic phases. When polymerization is carried out in the SmC* phase, this phase is stabilized at the expense of the intermediate phases. However, in non-radiated samples, which contained traces of the polymer, the intermediate phases are stabilized at the expense of the SmC* phase. The wavelengths selectively reflected by the SmC* A phase are longer than those reflected by the SmC* phase and the stability of the SmC* A is unaffected by polymerization. [ABSTRACT FROM AUTHOR]

We studied the effect of polymer networks on the temperature dependence of the optical Bragg reflections of an antiferroelectric liquid crystal which forms the chiral ferroelectric (SmC*), intermediate and antiferroelectric (SmC A *) phases. When polymerization is carried out in the SmC* phase, this phase is stabilized at the expense of the intermediate phases and the corresponding Bragg wavelengths follow a non-Landau description. When polymerization is in the SmA phase, the Bragg wavelengths of the SmC* and SmC A * phases are largely temperature independent. The intermediate phases are stabilized at the expense of the SmC* phase in non-radiated samples, which contain traces of the photo-polymer. The range over which the SmC A * is stable is unaffected by polymerization. [ABSTRACT FROM AUTHOR]

The transition between stable colloidal dispersions and coagulated or flocculated systems is a decisive process in practical applications of million of tons of bentonites (containing the clay mineral montmorillonite). Dispersion into the colloidal state requires the transformation of the original bentonite into the sodium form, for instance by soda activation. Therefore, we review here the coagulation of sodium montmorillonite dispersions by inorganic and organic cations and the influence of compounds of practical interest such as phosphates, cationic and anionic surfactants, alcohols, betaine-like molecules and polymers like polyphosphates, tannates, polyethylene oxides with cationic and anionic end groups, and carboxy methylcellulose. Typical properties of the sodium montmorillonite dispersions are the very low critical coagulation concentrations, the specific adsorption of counterions on the clay mineral surface, and the dependence of the cK values on the montmorillonite content in the dispersion. In most cases coagulation occurs between the negative edges and the negative face. The phosphates Na2HPO4, NaH2PO4 and Na4P2O7 increase the edge charge density and change the type of coagulation from edge (−)/face (−) to face (−)/face (−) with distinctly higher cK values. Polyanions like polyphosphate and tannate stabilize in the same way. Carboxy methylcellulose causes steric stabilization. Montmorillonite particles with adsorbed betaine-like molecules provide an example of lyosphere stabilization. [Copyright &y& Elsevier]

In this paper, we report that the electrooptic (EO) performance of a polymer stabilized ferroelectric liquid crystal display (PS-FLCD) exhibiting half-V-shaped switching using an FLC material which has no SmA phase-R2301 (Clariant Japan) depends on the surface alignment conditions such as photoalignment and rubbing. It is shown that an FLCD cell fabricated using the photoalignment technique, which produces weak azimuthal anchoring, results in a superior EO performance at a low saturation operation voltage and for a wide cone (deflection) angle compared to those fabricated under a weak-rubbing condition. [ABSTRACT FROM AUTHOR]

A procedure for predicting thermodynamic, dynamic, and rheological properties of polymerically stabilized colloidal dispersions in good solvents by mapping onto an effective hard sphere dispersion is investigated and evaluated for its range of applicability. Configurational pressures and energies, calculted by Monte Carlo simulations, are used to assess the model's accuracy for predicting thermodynamic data. Similarly, long-time self-diffusivities, calculated by equilibrium Brownian Dynamic simulations, are used to assess the model's feasibility for predicting dynamic properties. Finally, zero shear viscosities are calculated by the method of hydrodynamic preaveraging and compared to rheological measurements. The various testing methods demonstrate the effectiveness of the procedure and suggest the model's range of applicability. [ABSTRACT FROM AUTHOR]

We propose a fabrication method for a zero-pretilt nematic liquid crystal cell using UV-curable polymer. The zero pretilt angle can be obtained by UV curing of reactive mesogen monomers mixed with planar alignment material while a vertical electric field is applied to a liquid crystal cell assembled after the rubbing process. We demonstrate that the pretilt angle of a nematic liquid crystal cell can be decreased to 0.082° by employing the proposed method. [ABSTRACT FROM AUTHOR]

Blue phase liquid crystals (BPLCs) composed of double-twisted cholesteric helices are promising materials for use in next-generation displays, optical components, and photonics applications. However, BPLCs are only observed in a narrow temperature range of 0.5-3 °C and must be stabilized with a polymer network. Here, we report on controlling the phase behavior of BPLCs by varying the concentration of an amorphous crosslinker (pentaerythritol triacrylate (PETA)). LC mixtures without amorphous crosslinker display narrow phase transition temperatures from isotropic to the blue phase-II (BP-II), blue phase-I (BP-I), and cholesteric phases, but the addition of PETA stabilizes the BP-I phase. A PETA content above 3 wt% prevents the formation of the simple cubic BP-II phase and induces a direct transition from the isotropic to the BP-I phase. PETA widens the temperature window of BP-I from ~6.8 °C for BPLC without PETA to ~15 °C for BPLC with 4 wt% PETA. The BPLCs with 3 and 4 wt% PETA are stabilized using polymer networks via in situ photopolymerization. Polymer-stabilized BPLC with 3 wt% PETA showed switching between reflective to transparent states with response times of 400-500 μs when an AC field was applied, whereas the application of a DC field induced a large color change from green to red.

Hindered amine light stabilizers are used to protect polymers from heat- and light-induced degradation. In this study the oligomeric stabilizer Tinuvin 622 was analysed in-depth employing high performance liquid chromatography/time of flight mass spectrometry (HPLC/TOF-MS) to differentiate products of different manufacturers in respect of their terminating groups and oligomer length. Additionally, the behaviour of the stabilizer in uncured and cured polyester powder coatings was investigated regarding its interaction with the other coating components and chemical changes during the crosslinking process. The extraction efficiency was determined as a function of oligomer length and coating colour. • Novel analytical methods for characterization of the oligomeric hindered amine light stabilizer Tinuvin 622. • Differentiation of batches from different sources according to terminating groups and oligomer length. • Elucidation of the fate of Tinuvin 622 in cured and uncured polyester powder coatings. • Investigations of possible reactions of the stabilizer with crosslinker present in the investigated coatings. [ABSTRACT FROM AUTHOR]

Liquid Crystal Chambers: A Single-Step Dual Stabilization of Smart Window by the Formation of Liquid Crystal Physical Gels and the Construction of Liquid Crystal Chambers (Adv. Funct. Keywords: liquid crystal physical gel; photoisomerization; photopolymerization; polymer stabilization; smart window Liquid crystal physical gel, photoisomerization, photopolymerization, polymer stabilization, smart window. [Extracted from the article]

Smart windows are very attractive because they not only provide comfortable indoor conditions for cars and buildings, but also protect privacy. However, current smart windows have problems such as high energy consumption, slow response time, and poor stability. To solve these problems, a single‐step dual stabilization (SSDS) is newly proposed for the fabrication of robust liquid crystal (LC) smart windows switching fast at low voltage. Upon irradiating ultraviolet light on the selected area of the nematic (N) LC optical cell with photoisomerizable macrogelators (B3AZ) and photopolymerizable monomers, NLC physical gels (LCPGs) and partition walls are simultaneously constructed. LCPGs play a role of light shutter under a low electric field (9.6 Vpp) which is ten times lower than that of the conventional polymer‐stabilized LC‐based smart windows. Partition walls constructed by the selected area photopolymerization significantly enhance the mechanical stabilities. Based on the experimental results, it is realized that the NLC layer generated near the partition walls makes the LCPGs respond to a low voltage. Robust SSDS smart windows could open new doors for the development of high‐performance smart windows. [ABSTRACT FROM AUTHOR]

It has previously been shown that for polymer-stabilized cholesteric liquid crystals (PSCLCs) with negative dielectric anisotropy, the position and bandwidth of the selective reflection notch can be controlled by a direct-current (DC) electric field. The field-induced deformation of the polymer network that stabilizes the devices is mediated by ionic charges trapped in or near the polymer. A unique and reversible electro-optic response is reported here for relatively thin films (≤5 μm). Increasing the DC field strength redshifts the reflection notch to longer wavelength until the reflection disappears at high DC fields. The extent of the tuning range is dependent on the cell thickness. The transition from the reflective to the clear state is due to the electrically controlled, chirped pitch across the small cell gap and not to the field-induced reorientation of the liquid crystal molecules themselves. The transition is reversible. By adjusting the DC field strength, various reflection wavelengths can be addressed from either a different reflective (colored) state at 0 V or a transparent state at a high DC field. Relatively fast responses (~50 ms rise times and ~200 ms fall times) are observed for these thin PSCLCs.

The cholesteric liquid crystal phase at or near normal incidence selectively reflects circularly polarized light matching the handedness of the helicoidal superstructure. At large angles of incidence, both senses of circularly polarized light are reflected over a certain wavelength range. Stabilizing the cholesteric liquid crystal phase with low concentrations of polymer network that maintains structural chirality allows the pitch (and accordingly, the selective reflection) to be adjusted with an electric field. Here, the behavior of these polymer stabilized cholesteric liquid crystals is investigated at large angles of incidence, to determine how the total reflection evolves when the polymer network is deformed by an external DC field. Strong, unpolarized reflection is observed in polymer stabilized cholesteric liquid crystals at oblique angles over a wide range of field values. As the application of a DC electric field can adjust the position or bandwidth of the total reflection in polymer stabilized cholesteric liquid crystals, these reconfigurable devices could find potential end use in optical applications where polarization independent properties are needed, such as spectroscopy and polarimetry. The total reflection of polymer‐stabilized cholesteric liquid crystals at oblique angles is adjusted with an applied electric field. The control of the unpolarized and highly attenuating response is potentially useful in spectroscopy or polarimetry. [ABSTRACT FROM AUTHOR]

High-quality alignment control of liquid crystals (LCs) for ultrahigh-definition large-sized display is a challenging task. A conventional rubbing method has obvious limitations for fabricating large-sized displays with a small pixel size and an uneven inner surface. To comply with the current trend, we propose a simple and reliable polyimide-less in situ photoalignment. It was achieved using a visible-light-sensitive azo-dye and a mesogenic acrylate, both doped to host LCs. Without using a pretreated alignment layer, mono- and multidomain uniaxial alignments of LC molecules were induced by linearly polarized visible light (LPVL) and subsequently stabilized by unpolarized UV-light irradiation. The stepwise process was monitored by adopting a fluorescent indicator. By loading the mixture into a confined cell, azo-dyes were spontaneously adsorbed at inner surfaces of the cell, whereas reactive mesogens (RMs) were homogeneously dissolved in an LC host. The molecular orientational anisotropy of dyes at the surface, induced by LPVL, aligned the LC director perpendicular to the polarization direction. Upon the second step, UV-irradiation, the RMs in an LC host were photopolymerized into thin interfacial layers, stabilizing the aligned LC director. The overlaid cross-linked RM layers secured a thermal and a radiative stability of LC alignment. The RM layers completely screened the effect of azo-dyes, which can be easily randomized by heat and irradiation. The interfacial RM layer functioned as a permanently stable alignment layer. It provided sufficient azimuthal anchoring strength together with heat and light stabilities, which are essential for practical applications. Such sequential interfacial modifications through dual-wavelength processes can completely avoid interference between forming alignment and stabilization layers, inevitable if the same wavelength light is used. The proposed method provides a simple fabrication process and reliable alignment characteristics by employing effective in situ photoalignment and without using a traditional alignment layer. Therefore, it meets a current trend in the display market toward ultrahigh-resolution and large-area displays.