Photopolymerization-induced Phase-separation Method Research Articles

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.

Controllable fabrication and characterization of porous C/TiO2 nanocomposite films as solar selective absorber

Abstract Porous C-TiO 2 nanocomposite films prepared by photopolymerization-induced phase-separation method (PIPS) exhibited three dimensional interconnected pores structure. Scanning electron microscopy (SEM), atomic force microscope (AFM), thermo-gravimetric and differential thermal analysis (TG-DTA), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, UV–Vis-NIR spectrophotometer are employed to characterize the structure and optical properties. The results illustrated that the photomonomer pentaerythritol triarylate (PETA) directly affects the relative molecular weight of polymer formed by photopolymerization to regulate the morphology and residual carbon of C-TiO 2 nanocomposite films, and ultimately affects the solar selective absorption properties. The single layer of as-prepared porous C-TiO 2 nanocomposite films exhibits high solar absorptance (α = 0.766–0.863) with low thermal emittance (e = 0.06–0.12), yielding an optimized photothermal conversion efficiency η = α-e of (0.706–0.762) corresponding to a wide redundancy PETA concentration 0.3–0.9 (molar ratio to Ti precursor). The proportion of residual carbon contributed by PVP, PETA and poly-PETA, and other substances of the sol is 40.2%, 56.2% and 3.6%, respectively, which might be regulated by a suitable annealing process. Based on these results, porous C-TiO 2 nanocomposite films are proved to be a novel candidate material for mid-temperature solar selective absorber coatings.

Preparation and characterization of porous carbon–titania nanocomposite films as solar selective absorbers

Newly proposed selective solar absorbers of porous carbon–titania nanocomposite films with a well-defined interconnected macropores structure were prepared via a polymer-assisted photopolymerization-induced phase-separation method. The microstructure and optical properties of as-deposited nanocomposite films were characterized and discussed in detail. The results show that non-ionic water-soluble polymer polyvinylpyrrolidone works as a sol modifier advantaging the mean size of the interconnected macropores, residual carbon content, and films thickness, but suppresses the order degree of the carbon remained in the films. The high-resolution transmission electron microscopy demonstrated that a small amount of graphite particles with size of around 1.1nm embedded in the cavity of the porous while the wall of the porous consists of amorphous carbon and titania composites. The single layer of as-prepared porous C/TiO2 nanocomposite films exhibits high solar absorptance (α=0.928–0.959) with low thermal emittance (ε=0.074–0.105), yielding an optimized photothermal conversion efficiency η=α−ε of 0.864 corresponding to a film thickness of around 338nm, indication of such film is fair enough to serve as an excellent solar absorber.

Porous carbon–titania nanocomposite films for spectrally solar selective absorbers

Selective solar absorbers based on composition of porous titania and carbon with a well-defined interconnected macropores structure have been fabricated by a photopolymerization-induced phase-separation method in the framework of a sol–gel technique. Scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, thermogravimetric and differential thermal analysis, Fourier transform infrared spectroscopy, and spectroscopic ellipsometry were used to characterize the C–TiO2 films. The results showed that the macroporous structures of the films could be tuned by changing the reaction parameters. The reduction of the HNO3 concentration in the solution effectively decreases the mean size of pores, carbon content, and the thickness of the nanocomposite films, leading to an optimization of the spectral selective absorption performance. The solar absorptance (α) and thermal emittance (ε) of the optimized single layer film with a thickness of about 300nm were about 0.95 and 0.12, respectively. The films also show good stability under the high temperature (~500°C). Based on these results, porous carbon–titania composite films proved to be a good candidate as solar selective absorbers.

A liquid crystal polymer based single layer chemo-responsive actuator

A single layer, mono-component, fast, stable, and controllable curling motion actuator is prepared from a mixture of di-acrylate mesogenic monomer and 5CB using a photo-polymerization induced phase separation method. This actuator is capable of sensing water in acetone.

Preparation and characterization of TiO2 anode film with hierarchical structure by photo-induced polymerization method

The TiO2 photoanode film with hierarchical structure which consists of porous structure and spinodal phase separation structure with macroporous continuous skeleton was fabricated by photopolymerization induced phase separation method. The influence of the different photomonomers, different coating layers and different heat treatment temperatures on the structure and photoelectric property of TiO2 film has been investigated and the possible mechanism was proposed. The performances of the TiO2 anode film were characterized by scanning electron microscopy, X-ray diffraction and I–V test. The results indicated that, in contrast with the TiO2 anode film with single structure, the as-prepared TiO2 anode film with hierarchical structure showed higher photoelectric conversion efficiency which is 0.272 %. Even though the photoelectric conversion efficiency is not very high, the strategy presented in the paper should be valuable and it still provides the ideas for the new structure and new preparation method on photoanode film of dye-sensitized solar cells, meanwhile, it lays the foundation for designing the solar cells with high photoelectric conversion efficiency.

Polymer network microstructures and electro-optical properties of a pressure-sensitive cholesteric liquid crystal device

We present a pressure-sensitive polymer dispersed cholesteric liquid crystal (PDCLC) device, in which a cholesteric liquid crystal (ChLC) is encapsulated by a polymer network via an ultraviolet photopolymerization induced phase separation method. The effects of the acrylate monomer concentration and functionality on the network morphology, and the electro-optic behaviour of the PDCLC device were studied. The results demonstrated that the electro-optic properties, including reflectivity and the contrast ratio of the pressure-sensitive device, were improved as the ChLC droplet size increased. An appropriate network density in the system limited the flow of the ChLC and allowed high-resolution lines to be drawn on the device. Additionally, the critical pressure switching of the device from a focal conic state to a planar state was investigated. The device developed in this study has promising applications in many fields such as flexible display devices and optical sensors.

Dye-Sensitized Solar Cells Based on Three-Dimensional Web-Like Structure Anodes

TiO2 films with three-dimensional web-like structure have been prepared by the photo polymerization-induced phase separation method (PIPS). Scanning electron microscopy and X-ray diffraction were used to characterize the as-prepared TiO2 films. The results showed that the film texture could be tuned by changing the composition of the precursor solution. The TiO2 film with web-like structure exhibited high photocatalytic activity for the degradation of methylene blue (MB) dye. The as-prepared films were used as the photo-anodes in dye-sensitized solar cells (DSCs). The photoelectric conversion efficiency of the DSCs was significantly enhanced by changing the POGTA/TTB in the precursor solution. Because of the increased dye adsorption active sites and efficient electron transport in the TiO2 anode film, a photoelectric conversion efficiency of 3.015% was obtained.

Fabrication and characterization of macroporous TiO 2 films by photo polymerization-induced phase separation method

Macroporous TiO 2 films have been fabricated by a photo polymerization-induced phase separation method without any surfactant and colloidal templates. The gel TiO 2 films deposited from the precursor solution containing photo monomer dipentaerythritol pentaacrylate were irradiated by the ultraviolet light. After that, the films were heat-treated at 600 °C for 10 min. The scanning electron microscopy results showed that TiO 2 films with macroporous structures could be obtained. The macroporous structure could be controlled by changing the reaction parameters. The as-prepared TiO 2 films exhibited much higher photocatalytic activity for the decomposition of methylene blue dye than that of the dense TiO 2 film.

Surfactant-Free Synthesis of Macroporous TiO2 Films by a Photopolymerization-Induced Phase-Separation Method

TiO2 films with controlled macroporous structures have been prepared from the precursor solution containing photomonomer dipentaerythritol pentaacrylate by a photopolymerization-induced phase-separation method (PIPS) in the absence of any surfactant and colloidal templates. The gel TiO2 film deposited from the precursor solution by dip-coating was irradiated with the ultraviolet light for some time. During the irradiation process, the polymerization of the photomonomer was induced, which resulted in the phase-separation in the film system. At the end of the polymerization reaction, two phases existed in the film, one was the emerging polymer rich phase, and another was the residual monomer-TiO2 oligomer-rich phase. After heat-treatment at 600 °C, the entire polymer decomposed and a well-defined interconnected macroporous TiO2 films could be obtained. X-ray diffraction, scanning electron microscopy, atomic force microscopy, thermogravimetric, and differential thermal analysis were used to characterize the macroporous TiO2 films. The results showed that the macroporous texture could be tuned by changing the composition of the precursor solution and the type of the reactive monomer. Polyvinylpyrrolidone was introduced into the system to slow the solvent evaporation. Highly macroporous TiO2 films prepared by the PIPS method exhibited much higher photocatalytic activity for the decomposition of methylene blue dye than the dense TiO2 film.

Controlled preparation of macroporous TiO 2 films by photo polymerization-induced phase separation method and their photocatalytic performance

TiO 2 films with controlled macroporous structures have been prepared from the precursor solution containing photo monomer pentaerythritol tetraacrylate by a photo polymerization-induced phase separation method (PIPS) in the absence of any surfactant and colloidal templates. The gel TiO 2 film deposited from the precursor solution by dip-coating was irradiated with ultraviolet light for some time. During the irradiation process, the polymerization of the photo monomer was induced, which resulted in the phase separation in the film system. After the reaction, two phases existed in the film, one was the emerging polymer rich phase, another was the residual monomer–TiO 2 oligomer rich phase. After heat-treatment at 600 °C, the entire polymer decomposed and a well-defined interconnected macroporous TiO 2 films could be obtained. X-ray diffraction, scanning electron microscopy, atomic force microscopy, thermogravimetric and differential thermal analysis were used to characterize the macroporous TiO 2 films. The results showed that the macroporous texture could be tuned by changing the composition of the precursor solution. The solvent evaporation was controlled by the addition of polyvinylpyrrolidone. Highly macroporous TiO 2 films prepared by the PIPS method exhibited much higher photocatalytic activity for the decomposition of methylene blue dye than the dense TiO 2 film.

A4-sized flexible ferroelectric liquid-crystal displays with micro color filters

— We demonstrated an A4-paper-sized flexible ferroelectric liquid-crystal (FLC) color displays fabricated by using a new plastic-substrate-based process which was developed for large-sized devices. Finely patterned color filters and ITO electrodes were formed on a plastic substrate by a transfer method to avoid surface roughness and thermal distortion of the substrate, which induce disordering of the FLC molecular alignment. The thickness of an FLC/monomer solution sandwiched by two plastic-film substrates was well controlled over a large area by using flexographic printing and lamination techniques. Molecular-aligned polymer walls and fibers were formed in the FLC by a two-step photopolymerization-induced phase-separation method using UV-light irradiation. A fabricated A4-sized flexible-sheet display for color-segment driving was able to exhibit color images even when it was bent.

Polymer-Dispersed Cholesteric Liquid Crystals Reflecting In the Infrared Region

Polymer-Dispersed Cholesteric Liquid Crystals(PDCLC)have been obtained using different cholesteric liquid crystals mixtures by the Photopolymerization-Induced Phase Separation method. PDCLC samples of different thickness and different LC concentrations have been studied. The selective reflection spectra for different voltages have shown maximum reflectivity in the infrared region.

PDLC Systems in Elliptical Capillaries

Large liquid crystal droplets have been obtained in capillaries with elliptical cross-section by photopolymerization-induced phase separation method. The liquid crystal alignment inside droplets has been studied. The preliminary studies of electrically-tunable waveguide properties of such structure have been done.

PDLC Systems in Elliptical Capillaries

Large liquid crystal droplets have been obtained in capillaries with elliptical cross-section by photopolymerization-induced phase separation method. The liquid crystal alignment inside droplets has been studied. The preliminary studies of electrically-tunable waveguide properties of such structure have been done.

Thick polymer-stabilized liquid crystal films for microwave phase control

This article describes the use of thick polymer-stabilized liquid crystal films in a new design for microwave variable phase shifters. A fine μm-order sized polymer network was formed in a 100-μm-thick liquid crystal film, using a photopolymerization-induced phase-separation method to stabilize the molecular alignment of the liquid crystal. Measurement of the electro-optic properties of the liquid crystal film revealed that the relaxation response time of the liquid crystal alignment was drastically decreased by doping the polymer at a concentration of several wt %. A new variable phase shifter composed of a microstrip transmission line (length: 193 mm, width: 200 μm) was also fabricated by using the liquid crystal film as the dielectric material. This device exhibited a microwave phase shift of −80° at a frequency of 20 GHz, when a drive voltage of 70 Vrms was applied vertically to the liquid crystal film.

Relaxation time of polymer ball type PDLC films

Abstract “Polymer ball” polymer dispersed liquid crystal (PDLC) samples were fabricated by the photo-polymerization induced phase separation method and their relaxation behaviour was studied. It was found that upon removal of the applied electric field, the transmittance of the “polymer ball” PDLC sample decays exponentially from T on to T memo with a relaxation time constant in the order of msec. It was found that the measured relaxation time constant decreases as the curing time increases and the LC concentration increases.

Studies of polymer ball type polymer dispersed liquid crystal films

Abstract ‘Reverse’ or ‘polymer ball’ polymer dispersed liquid crystal (PDLC) samples were prepared by a photopolymerization induced phase separation method. A detailed study of the effects of the sample preparation parameters, such as curing time, curing intensity, and liquid crystal concentration are reported. It was found that by adjusting these parameters, we were able to change the morphology of these ‘polymer ball’ PDLC samples and thus change their optical characteristics. Incomplete polymerization of the PDLC samples results in a higher threshold voltage and a lower ON state transmission. When the amount of monomer is too low, the shape of the resulting polymer ball becomes irregular, and the sample has a larger threshold voltage and a larger saturation voltage.