Polymerization-induced Phase Separation Research Articles

Mechanically and thermally robust microporous copolymer separators for lithium ion batteries

Next generation, multifunctional separators can enhance energy storage, power, and safety performance of lithium ion batteries but must be simple to fabricate and incorporate with existing roll-to-roll manufacturing. This study presents a strategy to facilely prepare these separators using UV-initiated polymerization-induced phase separation (PIPS), wherein microporous polymer separators are fabricated directly from constituent monomers and ethylene carbonate (EC) porogen. This enables a wide compositional design space as co-monomers with specific chemical functionality can be readily incorporated into the PIPS precursor mixture. Herein, 1,4-butanediol diacrylate (BDDA) was copolymerized with poly(ethylene glycol) diacrylate (PEGDA) to increase the acrylate conversion in the photopolymerization and improve mechanical properties. By tuning the ratio of PEGDA and EC, separators with high porosity (41.3%) and effective ionic conductivity (2.09 mS cm−1) were prepared. Inclusion of PEGDA was essential to increasing the elastic modulus to > 345 MPa, which is required for cell assembly by roll-to-roll manufacturing. All separators prepared were shown to enable reversible cycling of lithium metal/LiNi0.5Mn0.3Co0.2O2 half-cells for 100 cycles. Unlike conventional polyolefin separators, which were shown to melt at 160 °C and shrink by up to 29.8% at elevated temperatures, the PIPS separators possess exceptional, safety-enhancing thermomechanical properties, undergoing no phase transitions or thermal shrinkage.

Improving PDLC electro-optical performance using a photomask multi-step polymerisation method

ABSTRACT Polymer-dispersed liquid crystals (PDLCs) have been intensively studied for their light scattering properties and are of great use in electro-optical display devices. In this paper, high performance PDLCs were prepared by a multi-step polymerisation method using a photomask through a polymerisation-induced phase separation (PIPS) process. The effect of the photomask on the polymerisation of polymerisable monomers was investigated and it was confirmed that the photomask could effectively polymerise the polymerisable monomers in the light-transmitting fraction preferentially to form polymer-dominated spacer columns. In the subsequent complementary polymerisation process, the liquid crystal content of the previously unpolymerised fraction increases, which leads to a decrease in threshold and drive voltage and an increase in contrast of the PDLC film. Compared to conventional polymerisation methods, the multi-step polymerisation method can reduce the threshold voltage to 38.5 V, the drive voltage to 55.8 V and the contrast to 42, which greatly improves the overall electro-optical properties of PDLC, and the formation of spacer columns improves the bonding of the film, offering new possibilities for achieving energy efficient PDLC films and flexible films.

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.

Hard block length distribution of thermoplastic polyurethane determined by polymerization-induced phase separation

Three thermoplastic polyurethanes (TPUs) based on the same monomers and composition were produced in bulk by hand and machine casting methods. The soft segment was PTHF® 1000 and the hard segment was made of 1,4-butanediol and 4,4′-methylene diphenyl diisocyanate (MDI). The hard segment content amounted to 30%. The hand cast TPUs were prepared at 80 and 125 °C. The temperature conditions for the machine prepared sample were comparable to that of the hand casting process at 125 °C. The samples prepared at high temperature were transparent, whereas the sample produced at low temperature was translucent. The latter showed some crystallinity and in crystallization studies it crystallized more readily than the transparent samples. The distinctions in transparency and crystallization behavior were ascribed to differences in the hard block length distribution. Using thermal fractionation – a series of successive self-nucleation and annealing steps – the minor differences in hard block length distribution could be shown and quantified. The TPU synthesized at low temperatures possessed the longer hard blocks. These facilitated crystallization by enhancing nucleation and crystal growth. Superstructures, induced by the longer hard blocks, scattered visible light and reduced the transparency.

The role of nanomesh fibres loaded with BaTiO3 nanoparticles on the electro-optical performance of PDLC devices

In this paper, polymer-dispersed liquid crystal (PDLC) films were prepared from a blend of prepolymer, liquid crystal and BaTiO3 (BTO) nanoparticle-laden nanofibres films by a polymerisation-induced phase separation (PIPS) method. By contrasting the microstructure and electro-optical curves of various proportions of monomer types, it was demonstrated that the hole size of the polymer network had a significant influence on the electro-optical nature of the PDLC films. nanofibres films loaded with different BTO nanoparticle contents were introduced into the liquid crystal mixture specimens, and the alterations in the polymer network, electro-optical nature of these specimens were analysed using SEM images, EDS and electro-optical curves. The electro-optical nature of the nanofibres films doped with PDLCs were found to be improved and the ageing resistance was greatly enhanced. Therefore, the development of PDLC films with faster response times and better electro-optical nature of reticular nanofibres films doped with PDLCs will significantly improve the promising technological applications of PDLC-based equipment for optical windows, displays, energy storage and flexible devices.

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.

Role of semiconductor nanoparticles on electro-optical performance of PDLC devices

ABSTRACT The performance of polymer dispersed liquid crystal (PDLC) can be adjusted according to the needs of the application by controlling its composition ratio and microstructure. The clatter-based PDLC film with polymerisation-induced phase separation was prepared by ultraviolet curing method, and semiconductor nanoparticles were doped in it. The effects of semiconductor nanoparticles doping on the morphology, electrical and optical properties of PDLC films were investigated. Research showed that the addition of semiconductor nanoparticles reduced the rise time, threshold voltage, saturation voltage, and enhances contrast. The development of PDLC doped with semiconductor nanoparticles’ film which has faster rise time, lower threshold voltage, lower saturation voltage and better contrast will significantly increase the potential of PDLC-based devices in smart windows, sensors and flexible equipment application. At the same time, semiconductor nanoparticles had the characteristics of high fluorescence efficiency, wide absorption, narrow emission and bright colours. When PDLC doped with semiconductor nanoparticles is used as smart glass, the optical properties of semiconductor nanoparticles can be used to absorb light in part of the wavelength band and convert it into light in another wavelength band. In addition, it can have variable colours to make the appearance more beautiful while expanding the scope of its use.

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.

The role of nanomesh fibres loaded with fluorescent materials on the electro-optical performance of PDLC devices

ABSTRACT In this paper, polymer-dispersed liquid crystal (PDLC) films were prepared from a mixture of prepolymer, liquid crystal and phosphor-loaded reticular nanofibres films by a polymerisation-induced phase separation (PIPS) process. By comparing the microstructure and electro-optical curves of samples with different ratios of monomer types and liquid crystal contents, it was demonstrated that the cavity size of the polymer network had a significant effect on the electro-optical properties of the PDLC films. Reticular nanofibres films loaded with different phosphor contents were introduced into the liquid crystal mixture samples and the changes in the polymer network, electro-optical and fluorescence properties of these samples were analysed using SEM images, electro-optical curves and fluorescence curves. The electro-optical and fluorescence properties as well as the fluorescence properties of reticulated nanofibres films doped with PDLCs loaded with fluorescent materials were found to be improved and the anti-ageing properties are also greatly increased. Therefore, the development of meshed nanofiber membrane-doped PDLC films with faster response time, better optoelectronic properties, and better fluorescence properties will greatly improve the applications of PDLC-based devices in smart windows, sensors, energy efficiency and Potential technical applications in flexible devices.

Facile Fabrication of Hierarchically Porous Boronic Acid Group-Functionalized Monoliths With Optical Activity for Recognizing Glucose With Different Conformation.

At present, various materials based on helical polymers are nanoparticle or microsphere, which is not ease of use in practical application. Accordingly, facile preparation hierarchically porous monolith based on helical polymer needs to be developed. Herein, hierarchically porous boronic acid group-functionalized monoliths that exhibited optical activity were fabricated with a facile method based on crosslinking and polymerization-induced phase separation (CPIPS). Chiral substituted acetylene and achiral substituted acetylene with a boronic acid group were used as monomers. By regulating the composition of the pre-polymerization solution, the permeability and macropore size of the porous structure could be controlled. The hierarchically porous structure and large surface area were confirmed by scanning electron microscopy and nitrogen gas adsorption/desorption isotherms. In particular, the boronic acid functional group that can interact with a cis-diol group was successfully introduced on the skeleton surface of the monoliths. Further, the main chain of the copolymer that constituted the monoliths exhibited a high cis content and tacticity, and the monoliths showed good optical activity. Thus, the present study established a facile method to synthesize hierarchically porous boronic acid group-functionalized monoliths with optical activity via CPIPS, and the monoliths showed potential in recognition, separation, and adsorption of compound with chirality and cis-diol groups.

Effects of formulation composition and CeO2 nanoparticles doping on the morphologies of polymer spacer columns and electro-optical properties of PDLC

Polymer dispersed liquid crystal (PDLC) with polymer spacer columns were prepared by ultraviolet (UV) stepwise polymerization induced phase separation (PIPS) process. The influences of the formulation composition, such as the internal proportion of monomers and the liquid crystal (LC) content, on the morphologies of polymer spacer columns and electro-optical properties of PDLC films, were researched. Due to the difference in cross-linking density and polymerization rate, PDLC films exhibit different morphologies of polymer spacer columns and electro-optic properties. Based on the above, the CeO2 nanoparticles were doped into PDLC films. The influences of the doping content of CeO2 nanoparticles on the polymer network and electro-optical properties of PDLC were studied, and the EDS spectra were used to characterize the extent of dispersion of CeO2 nanoparticles in the polymer matrix. The results of the study showed that the contrast ratio (CR) of PDLC film increases from 10.9 to 27.3 at 0.8% CeO2 nanoparticles doping, while the saturation voltage (Vsat) decreases from 71.3 V to 47.9 V. Therefore, the work offers a new approach to the preparation of PDLC films with excellent comprehensive performance.

Multi-field driven thermochromic films and preparation of multi-color patterns

ABSTRACT In this paper, multi-field driven thermochromic films (TCF) were successfully prepared firstly. The upper layer is polymer-dispersed liquid crystal (PDLC) film prepared by polymerisation-induced phase separation (PIPS), and the lower layer is thermochromic liquid crystal microcapsule film prepared by centrifugal spin-coating method. The effects of diluent content, liquid crystal content and spin coating speed on the electro-optical properties and morphology of the thermochromic films were investigated by three sets of experiments secondly. Finally, multi-field driven multi-colour patterns were successfully prepared by film formation on conductive glass and flexible conductive films. Thermal ageing tests proved that the thermochromic films possess better service life, which provides a possibility for the wide application of liquid crystal films.

Ring-Opening Polymerization of Triaziridine Compounds in Water: An Extremely Facile Method to Synthesize a Porous Polymer through Polymerization-Induced Phase Separation.

Dissolution of trifunctional aziridine compounds, 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate] (3AZ) and tetramethylolmethane-tri-β-aziridinylpropionate (3AZOH), in water initiates a ring-opening polymerization and successful yields the corresponding network polymers via cationic polymerization. The polymerization of 3AZ induced phase separation and produced porous polymers under a wide range of monomer concentrations and polymerization temperatures. The phase separation rate in the 3AZ/water system was estimated by quantifying the turbidity by means of light transmission where transmittance decreased with an increase in the content of phase-separated materials. The rate increased with an increase in reaction temperature. The 3AZ porous polymers showed characteristic surface morphologies, which were formed by connected particles with diameters of about 4-5 μm. The porous polymers were not breakable by the compression test under 50 N. The Young's modulus of the 3AZ porous polymers increased with an increase in polymerization temperature, which may be accounted for by cross-linking through the formation of quaternary ammonium salt formed by a termination reaction. The 3AZ porous polymer absorbed various solvents.

Carbon ablators with porosity tailored for aerospace thermal protection during atmospheric re-entry

Porous carbon ablators offer cost-effective thermal protection for aerospace vehicles during re-entry into planetary atmospheres. However, the exploration of more distant planets requires the development of ablators that are able to withstand stronger thermal radiation conditions. Here, we report the development of bio-inspired porous carbon insulators with pore sizes that are deliberately tuned to enhance heat-shielding performance by increasing scattering of high-temperature thermal radiation. Pore size intervals that promote scattering are first estimated using an established model for the radiative contribution to the thermal conductivity of porous insulators. On the basis of this theoretical analysis, we identify a polymer additive that enables the formation of pores in the desired size range through the polymerization-induced phase separation of a mixture of phenolic resin and ethylene glycol. Optical and electron microscopy, porosimetry and mechanical tests are used to characterize the structure and properties of porous insulators prepared with different resin formulations. Insulators with pore sizes in the optimal scattering range reduce laser-induced damage of the porous structures by up to 42%, thus offering a promising and simple route for the fabrication of carbon ablators for enhanced thermal protection at high temperatures.

Nano-doped PDLC combined with photochromic material for bifunctional optical control films

ABSTRACT Controlling light intensity and colour are the two main functions required to realise smart windows. In this paper, the bifunctional optical control films were prepared by combining a nano-doped polymer-dispersed liquid crystal (PDLC) with the photochromic material. The nano-doped PDLC was prepared by mixing the nematic liquid crystals, UV-curable liquid mixture, and ZrO2 nanoparticles through a polymerization-induced phase separation (PIPS) process. The electro-optical properties of the PDLCs were significantly improved compared to the initial hybrid system; furthermore, the driving voltage reached a minimum of 20.7 V with 0.8 wt% of ZrO2 doping. Spin-coated photochromic powder enabled PDLC films to switch between coloured and colourless under UV or solar irradiation. The bifunctional PDLC films with lower threshold voltage, lower saturation voltage, and better contrast, have shown significant application in areas of smart windows.

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.

Novel “Rubber” electrolyte will be applied to long-lasting, safer future EV batteries

Solid-state lithium metal batteries (LMBs) have become a potential component, as they provide a considerable safety upgrade by eliminating flammable organic solvents. Solid polymer electrolytes (SPEs) are also a promising candidate, owing to their non-toxicity, low-manufacturing cost, and comparatively soft nature that allows the development of a seamless interface with the electrodes. Polymerization-induced phase separation (PIPS) controls the connectivity of phase-separated structures and domain size, enabling the co-continuous nanostructures’ formation. Researchers of a study published in Nature envisioned that outstanding mechanical and ionic properties could be realized, provided ionic conducting materials form a 3D interconnected phase inside a mechanically strong elastomer matrix via PIPS.

Cationic Curing of Epoxy–Aromatic Matrices for Advanced Composites: The Assets of Radiation Processing

Cross-linking polymerization of multifunctional aromatic monomers initiated by exposure to high energy radiation continues to be explored as a promising alternative to thermal curing for the production of high-performance composite materials. High-energy radiation processing offers several advantages over thermosetting technology by allowing for fast and out-of-autoclave curing operations and for its adaptability in the manufacturing of large and complex structures at reduced energy costs. The present article covers the basic aspects of radiation curing by cationic polymerization of epoxy resins, providing a status report on recent investigations conducted in our group to improve the properties of epoxy matrices and gain better control over the process for producing composites. A selection of results based on blends prepared with different composition of epoxy aromatics, transfer agents, thermoplastic toughening agents and onium salt initiators exemplifies the importance of the composition on polymerization kinetics and on the properties of resulting materials. The superiority of radiation-triggered polymerization-induced phase separation of thermoplastic additives is emphasized by the obtained morphology of toughened materials. The low initial temperature and fast curing of the reactive blends limits the expansion of phase-separated thermoplastic domains, resulting in an enhancement of the toughness.

Highly flexible and electrically controlled grating enabled by polymer dispersed liquid crystal

Liquid crystal (LC) materials have dielectric and optical anisotropy and are candidates for the preparation of electrically controlled tunable diffraction gratings. Flexible LC gratings have the advantages of high flexibility, light weight, small size, and attachability. At present, the electronically controllable flexible LC grating needs to be further studied. In this paper, polymer-dispersed liquid crystal (PDLC) is poured into the flexible cell made of ITO-PET, and 1D and 2D flexible PDLC gratings are prepared by the method of polymer-induced phase separation. It can realize the modulation of the grating diffraction order through an external electric field under different curvature radii, and it also has the characteristics of the low driving voltage, low saturation voltage, and fast response. The driving voltage and saturation voltage of the 1D flexible PDLC grating are 0.8 V and 12 V, the cell thickness is 5.2 μm, and the rise and decay times are 3.225 ms and 98.29 ms, respectively, the first-order diffraction efficiency at the center is 9.1%. For the 2D flexible PDLC grating, the driving voltage and saturation voltage are 2.5 V and 16.5 V, the cell thickness is 5.2 μm, the rise and decay times are 3.362 ms and 75.46 ms, respectively, the first-order diffraction efficiency at the center is 7.58%.

Interfacial AIE for Orthogonal Integration of Holographic and Fluorescent Dual-Thermosensitive Images.

Orthogonal integration of thermosensitive images is of vital significance for advanced anticounterfeiting, which however remains formidably challenging due to the trade‐off that facile thermoresponse needs easy molecular motion while robust imaging requires molecular restriction. Herein, a viable approach is demonstrated to tackle the challenge by in situ fixing a predesigned aggregation induced emission luminogen (AIEgen) at the polymer/liquid crystal (LC) interface via precisely controlled interfacial engineering, in which the AIEgen is enriched in LC phases during polymerization induced phase separation and subsequently driven to the interface by the interfacial thiol‐ene click reaction. Crosstalk‐free integration of holographic and fluorescent dual‐thermosensitive images with high sensitivity, high contrast ratio, and robust performance is successfully realized in a single unit, attributed to the simultaneously LC‐facilitated AIEgen molecular motion and polymer‐restricted AIEgen diffusion at the interface. The exciting characteristics of these orthogonally integrated dual images will enable them to prevent illegal replication and thus are expected to be promising for high‐security‐level anticounterfeiting applications.