Polymerization-induced Phase Separation Method Research Articles

Preparation and Characterization of Bilayer Polymer-Dispersed Liquid Crystals Doped with Gd2O3 Nanoparticles and Rhodamine B Base Fluorescent Dye.

Using the polymerization-induced phase separation (PIPS) method, bilayer polymer-dispersed liquid crystal (PDLC) films with a PDLC-PVA-PDLC structure were prepared in this work. It was found that all PDLC performance indexes were affected by polymer mesh size after comparing the microscopic morphology and electro-optical properties of samples with different monomer ratios. Gd2O3 nanoparticles and rhodamine B base fluorescent dyes introduced into the bilayer PDLC optimized the samples' electro-optical properties and developed new functionalities. In addition, the bilayer PDLC doped with Gd2O3 and rhodamine B base held excellent progressive driving functions as well as stable durability properties. Samples doped with Gd2O3 nanoparticles and rhodamine B base also produced excellent anti-counterfeiting effects under UV irradiation at different angles, further exploiting the application potential of PDLC.

A novel low-voltage fast-response electrically controlled dimming film based on fluorinated PDLC for smart window applications

A fluorinated polymer dispersed liquid crystal (PDLC) film with low operating voltage and high contrast ratio was successfully fabricated via the ultraviolet-initiated polymerization induced phase separation method. Effects of chemical structure and weight ratio of fluorinated monomers on the properties of PDLC films were systematically investigated through characterization of electro-optical response, micro morphology, optical spectrum and thermal analysis. Compared with the primitive sample, the addition of fluorinated monomers effectively improves the electro-optical properties of the film. The threshold voltage (Vth) is decreased by 39.7 % from 6.3 V to 3.8 V and the saturation voltage is reduced by 30 % from 15.8 V to 11.8 V for a 20 μm-thick film. Besides, the contrast ratio is improved to 110. Meanwhile, its thermal stability and hydrophobic property are also improved. Additionally, due to the abundance of C-O and C-F bonds in these compounds and the porous structure, the prepared film allows for transmittance modulation of sunlight. This research is anticipated to provide an innovative approach to optimize the performance of PDLC films for practical applications.

Energy saving phase change energy storage thermochromic liquid crystal display

Phase change energy storage microcapsules (PCESM) improve energy utilization by controlling the temperature of the surrounding environment of the phase change material to store and release heat. In this paper, a phase change energy storage thermochromic liquid crystal display (PCES-TC-LCD) is designed and prepared for the first time. The as-prepared PCES-TC-LCD has a stable bilayer structure, where the lower layer is a thermochromic LC layer produced by centrifugal spin coating and high temperature curing, and the upper layer is a polymer-stabilized liquid crystal (PSLC) film with phase change energy storage properties obtained by polymerization-induced phase separation method. The prepared PCES-TC-LCD can realize the functions of triple-field driven and phase change energy storage, which has strong research value. In the performance experiments, the electro-optical properties of PCES-TC-LCD were analyzed and optimized by three sets of experiments on liquid crystal content, polymerization time, and PCESM content. In the film formation study, PCES-TC-LCD based on rigid/flexible substrates were prepared, respectively. The phase change energy storage function of PCES-TC-LCD was performed by differential scanning calorimetry (DSC) and infrared thermography. The devices formed on rigid or flexible substrates with stable phase change energy storage performance, which has great application value by reducing the external energy input, prolonging the thermochromic time and achieving energy saving effects.

Fluorescent Dye-Doped Brightening Polymer-Stabilized Bistable Cholesteric Liquid Crystal Films.

Brightening polymer-stabilized bistable cholesteric liquid crystal (PSBCLC) films with doped fluorescent dyes were prepared using the polymerization-induced phase separation (PIPS) method. The transmittance performance behavior of these films in both states (focal conic and planar) and absorbance change in multiple dye concentrations were studied using a UV/VIS/NIR spectrophotometer. The change occurring in dye dispersion morphology with different concentrations was obtained by means of the polarizing optical microscope. The maximum fluorescence intensity of different dye-doped PSBCLC films was measured using a fluorescence spectrophotometer. Moreover, the contrast ratios and driving voltages of these films were calculated and recorded to demonstrate film performance. Finally, the optimal concentration of dye-doped PSBCLC films with a high contrast ratio and a relatively low drive voltage was found. This is expected to have great potential applications in cholesteric liquid crystal reflective displays.

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.

Dye-Sensitized Solar Cell Based on TiO2 Anode Thin Film with Three-Dimensional Web-like Structure.

TiO2 films with a three-dimensional web-like porous structure were prepared using the photo polymerization-induced phase separation method integrated with the pulling coating process. By adjusting the ratio of the substance in the precursor sol and the coating times, the relationships between the sol ratio, the coating times, the film structure, and the performance of the DSC were studied. The optimal film structure was found and a detailed description is given. The performance of the DSC was further improved by introducing the barrier layer and the surface-modified layer of the TiO2 coating. This promoted the short-circuit current density and the photoelectric conversion efficiency of the DSC, the mechanism of which was also investigated. Ultimately, the photoelectric conversion efficiency of the DSC based on the TiO2 anode films with a three-dimensional web-like structure was stabilized at a higher level as a result of the structural improvement.

Optically isotropic nano-size encapsulation of nematic liquid crystals with a high-filling factor

• Oil-in-water encapsulation gives nanosize drops that can be coated on substrates. • Optically isotropic film can switch to an anisotropic state by voltage application. • Highly improved electro-optical performances are in a good agreement with extended Kerr effect. The filling factor of LCs in the LC-polymer composite system is a crucial factor for the electro-optic performance of optically isotropic liquid crystal (OILC) devices. The polymerization-induced phase separation method is well-known method to fabricate the OILCs; however, this method spontaneously limits the filling factor by ∼ 40%, which is inadequately low, owing to low-LC concentration in the mixtures. To overcome such intrinsic problem, we propose an encapsulated LC which is fabricated by means of oil-in-water encapsulation. Through this approach, the filling factor of LCs is effectively increased up to 67.8% because the capsules are closely packed. Consequently, we achieve a thin-composite film of nano-size LC encapsulation whose isotropic state is reliably switched to anisotropic state in response to an external electric field with low-operation voltage ( E th = 1.4 V/μm and E op = 4.6 V/μm), fast-response time ( τ on = 0.5 ms, τ off = 2.2 ms), and hysteresis-free electro-optic behavior. The highly improved electro-optic performances of the proposed encapsulated LC device would give versatile applications in blooming free-form flexible displays and various tunable photonic systems.

Electro-optical characteristics of polymer-dispersed liquid crystal containing copper (II) phthalocyanine as a function of UV irradiation time

We describe a method of dispersing copper (II) phthalocyanine that can expand the application range of polymer-dispersed liquid crystals (PDLCs) among smart-window technologies. Property changes were monitored during the polymerization-induced phase separation method as the ultraviolet (UV) irradiation time was increased from 70 to 175 s. With increasing UV irradiation time, the number of droplets in the polymer matrix within the PDLC increased, while the droplet size decreased, as observed by polarized optical and low vacuum-scanning electron microscopies. Voltage–transmittance and response time were measured to observe the effects on electro-optical properties; the threshold and saturation voltages increased with increasing UV-irradiation time. The falling time of the response decreased with increasing irradiation time; a fast switching time of < 20 ms was observed in all cases. This study provides the performance of the produced PDLC varies according to the UV irradiation time, and conditions and processes necessary for producing blue PDLC are presented.

Faster switching polymer dispersed liquid crystal devices incorporated with functionalized SWCNTs

Polymer dispersed liquid crystals (PDLCs) were fabricated using acrylate-based UV curable monomer and a low birefringent nematic liquid crystal, 5PCH, by polymerization induced phase separation method. The effect of ODA-SWCNT dispersion on electro-optical properties of PDLC was investigated and compared with the undoped PDLC. The total response time reduces by 70%, and threshold voltage decreases by 42% in PDLC prepared with 0.015 wt% ODA-SWCNT nanocomposites of 5PCH, compared to the PDLC prepared with pure 5PCH. The optical transparency and sharpness of the image in ON-state was found to be remarkably better in the ODA-SWCNT incorporated PDLC as compared to the PDLC prepared with pure 5PCH.

Evaluation of mechanical properties of porous carbon material whose structure is formed by the polymerization-induced phase separation method

It is well known that the mechanical behavior of porous materials strongly depends on porosity and pore morphology. On the other hand, their complex shape and structure make the reproduction of deformation and failure by simulation difficult. In such a case, analyses using model reflecting the complex structure of porous material (image based modeling) are quite effective. Although model of porous carbon obtained by using FIB-SEM and X-ray CT have been conducted and material properties have been evaluated,(1) the relationship between geometric structure and mechanical properties has not yet been generalized. Therefore, the objective of this study is to evaluate the relationship between geometry and mechanical properties of carbon monolith, which is a porous material with controllable geometric factors and mechanical properties. Strut length, thickness and the joint diameter of struts are selected as geometric factors and image based modeling is conducted for reconstruction model obtained by X-ray CT. Design guidelines for mechanical properties of porous materials will be discussed in the presentation.

Biomimetic Porous Fluoropolymer Films with Brilliant Whiteness by Using Polymerization‐Induced Phase Separation (Adv. Mater. Interfaces 1/2022)

Biomimetic Porous Fluoropolymer Films In article number 2101485, Binhai Yu, Shudong Yu, and co-workers prepare biomimetic porous fluoropolymer films with brilliant whiteness by using polymerization-induced phase separation method. With a well-tailored pore morphology, the as-prepared porous fluoropolymer films feature a comparable scattering ability to the benchmark Cyphochilus scale. With such remarkable scattering performance, the porous fluoropolymer films can find many applications, such as optoelectronic devices and daytime passive radiative cooling.

Biomimetic Porous Fluoropolymer Films with Brilliant Whiteness by Using Polymerization‐Induced Phase Separation

AbstractInspired by the Cyphochilus scale with extreme whiteness, fluoropolymer is used as the matrix to prepare highly scattering porous polymer films through polymerization‐induced phase separation (PIPS) method. The mixture used for the PIPS technique contains a fluoride monomer, a UV photoinitiator, and porogens (cyclohexanol and perfluorooctanol). By carefully tuning the mixture parameters (cyclohexanol–perfluorooctanol and monomer–porogen weight ratios), the porous morphology can be well tailored, which induces different scattering performances. With an optimized formulation (50 wt% monomer, 25 wt% cyclohexanol, and 25 wt% perfluorooctanol), the porous film with a thickness of 55 µm can achieve an average total reflectance of ≈90%, featuring a measured transport mean free path of 1.3–1.7 µm (comparable to the 1.5 µm of the benchmark Cyphochilus scale). Further, the porous films are applied to the light‐emitting diode (LED) device and it is demonstrated that they can effectively improve the light extraction efficiency of the LED and thus enhance the luminous performance. Due to the simplicity, cost‐effectiveness, and scalability of the PIPS method, the as‐developed porous fluoropolymer films with such excellent scattering ability can find many potential applications not only in the field of optoelectronics, but also in various complex scenarios, such as daytime passive radiative cooling.

Electro-optically oriented Kerr and orientational phase study of normal mode polymer dispersed liquid crystals – Effect of dispersion of nanoparticles

The electro-optically oriented polymer dispersed liquid crystals (PDLCs) have importance for their optical transmission, scattering and optical phase modulation characteristics. In the reported work, pristine and nanoparticles (NPs) dispersed normal mode PDLCs were prepared using polymerization induced phase separation method by taking mixture of liquid crystals (LCs), polymeric material and minute concentration of NPs. Experimentally, temperature dependent polarized optical microscopic textural behavior of NPs dispersed PDLC showed the reduction in the phase transition temperature from nematic to isotropic compared to normal mode pristine PDLC sample. The morphological results also show that droplet size is bigger in NPs dispersed PDLCs than pristine. The much lower voltage (approximately half to the pristine PDLC) is required to reorient the LCs inside the NPs dispersed PDLC containing bigger sizes’ droplets. Here, two step electro-optical curves are obtained in both type of PDLCs. Correspondingly, optical phase shifts in PDLCs are measured theoretically and increase in the Kerr phase is found with dispersion of NPs, however Kerr phase is lesser than orientational phases in both normal mode pristine and NPs dispersed PDLCs. Moreover, the induced birefringence is found increased proportionally to the square of the applied electric field and Kerr constant value is one order of magnitude higher for NPs dispersed PDLC than pristine.

The influence of polymer on optical and thermal properties of nematic liquid crystals

Polymer is substance which consists of large number of molecules and plays a very important in our everyday life. In the present study the effect of different concentration of polymer Poly Methyl Methacrylate on the optical and thermal properties of nematic liquid crystal were investigated. The polymer was dispersed in the liquid crystal by polymerization induced phase separation method. The physical properties were investigated using differential scanning calorimetry and polarized optical microscopy. We found various textures according to the molecular order and orientation of the liquid crystal and polymer in constrained regions separated by phase boundaries. These composite materials can be used to enhance contrast ratio with more stability for display application and smart window.

Enhancement of electro-optical properties of polymer dispersed liquid crystals by doping with nano-sized electrospun fibers

In this paper, in the mixed system of five kinds of acrylate polymeric monomers, nematic liquid crystals and reticular nanofiber films, the polymer dispersed liquid crystal (PDLC) films were prepared by the polymerization-induced phase separation method, and their properties were analyzed by combining the electro-optical curves and microstructure. The experimental results have proved that the cavity size of the polymer network can be controlled by adjusting the ratio of photo-polymeric monomers and the content of liquid crystal, thus directly affecting the electro-optical properties of PDLC films. This research will improve the potential technical applications of PDLC devices inflexible displays.

Regeneration of β‐Cyclodextrin Based Membrane by Photodynamic Disulfide Exchange — Steroid Hormone Removal from Water

AbstractThe occurrence of steroid hormones in water and their serious impact on human and ecosystem demand high performance materials for efficient removal of such micropollutants. Here, an affinity membrane is developed for hormone removal with regenerable binding sites. By using photodynamic disulfides as a linker, UV induced detachment of β‐CD ligands from the membrane surface is demonstrated. The macroporous base membrane is first fabricated via a polymerization induced phase separation method using 2‐hydroxyethyl methacrylate (HEMA) and ethylene dimethylacrylate (EDMA) monomers. Then the affinity membranes are prepared by immobilizing β‐CD ligands to the poly(HEMA‐co‐EDMA) base membrane through the 2‐carboxyethyl disulfide linker. The β‐CD functionalized affinity membrane shows a 30% increase of E2 hormone uptake compared with the base membrane, attributed to the formation of CD‐hormone host–guest inclusion complexes. The photodynamic disulfide linkers enable UV‐induced detachment of blocked β‐CD ligands from and reattachment of fresh β‐CD ligands to the membrane surface after each adsorption cycle, thus conferring the affinity membrane with excellent regenerative properties. It is anticipated that the use of dynamic covalent bonds for binding ligands will be of interest for developing smart affinity membranes with regenerable and readjustable surface properties.

Bioinspired high-scattering polymer films fabricated by polymerization-induced phase separation.

Inspired by the porous scale of the bright white beetle Cyphochilus, a polymerization-induced phase separation method is proposed to fabricate bioinspired high-scattering polymer films with porous structures. With an optimized formulation, the porous films with a mean pore size of ∼200nm feature a broadband reflectance of ∼71% at a thickness of 16 µm and are measured to have a transport mean free path of ∼3µm. The porous films with high reflectivity enable the application on light-emitting diodes and have great potential in other similar optoelectronic fields.

Preparation and electrooptic study of reverse mode polymer dispersed liquid crystal: Performance augmentation with the doping of nanoparticles and dichroic dye

ABSTRACTReported herein, the preparation, morphological, and electrooptic (EO) characterization of reverse mode polymer dispersed liquid crystals (PDLCs) with nematic liquid crystal (LC) and UV curable polymer optical adhesive using polymerization induced phase separation method. The PDLCs are switchable between transparent and opaque states due to the homeotropic and planar alignment of LC in their OFF and ON states of applied voltage, respectively. Further, effect of doping of a fixed concentration of azo dye and silica nanoparticles (NPs) on morphological, EO and response characteristics of same PDLC sample was also analyzed. Experimental results showed that doped reverse mode PDLCs have the higher OFF state optical transmission and boost up in the scattering ON state compared with pristine reverse mode PDLC. The phenomenon is also supported by extinction coefficient and absorption study based on Beer's law. The threshold and operating voltages were found reduced ~1.56 and ~1.73 times for NPs and (NPs + dye) doped reverse mode PDLCs, respectively, along with better contrasts to the pristine reverse mode PDLC. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48745.

Toward high-rate supercapacitor: Preparation of hierarchical porous carbon binder-free electrode with controllable texture

Hierarchical porous carbon (HPC) as binder-free electrode attracts enormous attention due to its favorable structure, which is advantageous for the improvement of supercapacitor capacitance and rate capability. In this paper, texture controllable HPC binder-free electrode with high capacitive performance is successfully prepared by polymerization induced phase separation method. Solvents with various viscosities and hydroiodic acid with various amounts are used to regulate the texture. The desired hierarchical porous structure endows the carbon material with a high specific surface area and ideal transportation paths. The optimized HPC binder-free electrode reaches a high specific capacitance of 180.6 F g−1 at 0.2 A g−1 in a two-electrode configuration in 6 M KOH. Surprisingly, the capacitance of the electrode still remains 79.1% (142.9 F g−1) at 100 A g−1. Furthermore, energy density of the supercapacitor device ranges from 6.27 Wh kg−1 to 4.23 Wh kg−1 with the power density ranging from 100 W kg−1 to 46195 W kg−1.

A tunable magnetic axis microdevice using polymer-dispersed liquid crystal doped with magnetic nanoparticles

This work proposes a magnetic microdevice with a tunable magnetic axis. The proposed device was realized by patterning a polymer-dispersed liquid crystal (PDLC) material doped with magnetic nanoparticles. An in situ technique of re-polarizing the magnetic axis of the device using small magnetic fields was also presented. The PDLC-based microdevice was fabricated using the standard polymerization-induced phase separation method and a simple lithography process. The re-polarization was achieved by applying a moderate magnetic field of less than 30 mT. The locomotion of the device, including translational motion, rotational motion, and magnetic re-polarization, was demonstrated in a polydimethylsiloxane microfluidic channel by using two pairs of Helmholtz coils. The measured results also showed that the time required for magnetic re-polarization decreases with the intensity of the magnetic field applied. The velocities of the devices driven in the microfluidic channel with different magnetic field gradients were also measured.