Polymerization Induced Phase Separation Process Research Articles

Robust Photocatalytic MICROSCAFS® with Interconnected Macropores for Sustainable Solar-Driven Water Purification.

Advanced oxidation processes, including photocatalysis, have been proven effective at organic dye degradation. Tailored porous materials with regulated pore size, shape, and morphology offer a sustainable solution to the water pollution problem by acting as support materials to grafted photocatalytic nanoparticles (NPs). This research investigated the influence of pore and particle sizes of photocatalytic MICROSCAFS® on the degradation of methyl orange (MO) in aqueous solution (10 mg/L). Photocatalytic MICROSCAFS® are made of binder-less supported P25 TiO2 NPs within MICROSCAFS®, which are silica-titania microspheres with a controlled size and interconnected macroporosity, synthesized by an adapted sol-gel method that involves a polymerization-induced phase separation process. Photocatalytic experiments were performed both in batch and flow reactors, with this latter one targeting a proof of concept for continuous transformation processes and real-life conditions. Photocatalytic degradation of 87% in 2 h (batch) was achieved, using a calibrated solar light simulator (1 sun) and a photocatalyst/pollutant mass ratio of 23. This study introduces a novel flow kinetic model which provides the modeling and simulation of the photocatalytic MICROSCAFS® performance. A scavenger study was performed, enabling an in-depth mechanistic understanding. Finally, the transformation products resulting from the MO photocatalytic degradation were elucidated by high-resolution mass spectrometry experiments and subjected to an in silico toxicity assessment.

Micron-Sized Thiol-Functional Polysilsesquioxane Microspheres with Open and Interconnected Macropores: Preparation, Characterization and Formation Mechanism.

Polysilsesquioxane (PSQ) microspheres have shown promise in many fields, but previous studies about porous PSQ microspheres are scarce. Herein, we fabricated novel micron-sized thiol-functional polysilsesquioxane (TMPSQ) microspheres with open and interconnected macropores by combining inverse suspension polymerization with two-step sol-gel and polymerization-induced phase separation processes, without using phase-separation-promoting additives or sacrificial templates. The chemical composition of the TMPSQ microspheres was confirmed using FTIR and Raman spectroscopy. The morphology of the TMPSQ microspheres was characterized using SEM and TEM. TGA was employed to test the thermal stability of the TMPSQ microspheres. Mercury intrusion porosimetry and nitrogen adsorption-desorption tests were performed to investigate the pore structure of the TMPSQ microspheres. The results showed that the TMPSQ microspheres had open and interconnected macropores with a pore size of 839 nm, and the total porosity and intraparticle porosity reached 70.54% and 43.21%, respectively. The mechanism of porous generation was proposed based on the morphological evolution observed using optical microscopy. The macropores were formed through the following four steps: phase separation (spinodal decomposition), coarsening, gelation, and evaporation of the solvent. The macropores can facilitate the rapid mass transfer between the outer and inner spaces of the TMPSQ microspheres. The TMPSQ microspheres are promising in various fields, such as catalyst supports and adsorbents.

Design Rationale for CO2 Separation Membranes with Micropatterned Surface Structures.

Here, we report the design rationale of CO2 separation membranes with micropatterned surface structures. Thin film composite (TFC) membranes with micropatterned surface structures were fabricated by spray coating amine-containing hydrogel particles on the top of micropatterned porous support membranes, which were synthesized by a polymerization-induced phase separation process in a micromold (PIPsμM). The pore size of the support membranes was optimized by tuning the proportion of good and poor solvents for the polymerization process so that the microgels would be assembled as a defect-free separation layer. The relationship between the size of the micropatterned structures on the surface of the support membrane and the thickness of the separation layer was optimized to maximize the surface area of the separation layer. The rationally designed micropatterned TFC membrane showed a CO2 permeability (835.8 GPU) proportional to the increase in surface area relative to the flat membrane with a high CO2/N2 selectivity of 58.7. The rational design for micropatterned TFC membranes will enable the development of inexpensive and high-performance functional membranes not only for CO2 separation but also for other applications such as water treatment and membrane reactors.

Multifunctional Separator for Li-Ion Batteries Enabling Acid Scavenging and Long Cyclability

The membrane separator is indispensable in lithium-ion batteries (LIBs), electrically isolating the electrodes while hosting liquid electrolyte for facile ion transport. Microporous polyolefin materials, consisting of polyethylene (PE) and/or polypropylene (PP), represent the state-of-the art in separator technology. They offer sufficient mechanical properties, chemical inertness, effective pore sizes <100 nm, porosity ranging from 30-78%, and relatively low costs. However, safety issues associated with thermal shrinkage above 70℃ and poor electrolyte wettability are significant limitations. Replacing these conventional polyolefin separators with multifunctional microporous membranes provides opportunities to address these limitations and other challenges in lithium ion batteries. LiMn2O4 cathodes, for example, attract widespread interest due to the abundance and low cost of Mn, especially in comparison to Co, and reasonable energy densities. However, these cathodes do not provide the calendar and cycle life of the layered oxide cathodes, especially at elevated temperatures (>50°C), due to dissolution of Mn and structural instabilities.1 One of the underlying reasons is the presence of HF in commercial LiPF6-carbonate electrolytes; HF will attack and dissolve the Mn, leading to severe capacity decay, as shown in Figure 1.2 Chemically active multifunctional separator can scavenge HF from the electrolyte, improving the stability of LiMn2O4, but they must be fabricated by low cost, scalable processes without compromising other separator properties.Herein, a multifunctional separator will be described, wherein poly(4-vinylpyridine) (P4VP) is incorporated into separators prepared by polymerization induced phase separation (PIPS). In PIPS, a homogenous solution of difunctional monomers and porogen is polymerized; the difunctional monomers polymerize and crosslink while the porogen phase separates into nanoscale domains. Our previous study employed PIPS to prepare highly porous and thermally stable separators, exhibiting comparable ion transport to conventional Celgard 2500 Polypropylene (PP) separators and negligible thermal shrinkage at 150 °C (digital images in Figure 1).3 Moreover, when incorporated into LIB half cells, these separators enable better electrochemical performance than Celgard 2500 separators due to their reduced thicknesses and superior electrolyte uptake. In the study, P4VP is integrated with the PIPS process to scavenge both HF and PF5 (precursor to HF) through acid-base interactions. A thin layer of P4VP coating was fabricated via initiated chemical vapor deposition (iCVD) process and makes full use of high porosity of separators due to the conformal nature of the coating, increasing the surface area to scavenge the acids. The P4VP-coated PIPS separator enables better capacity retention in Mn-based cathode materials, relative to cells using inert polyolefin separators. The scavenged concentration of HF and transition metal will be compared to validate the HF scavenging property. Post-mortem analysis of the Li anode also confirms the suppression of Mn dissolution and deposition on the anode at elevated temperatures (50°C).

Exploring the use of oligomeric carbonates as porogens and ion-conductors in phase-separated structural electrolytes for Lithium-ion batteries

Phase-separated structural battery electrolytes (SBEs) have the potential to enhance the mechanical stability of the electrolyte while maintaining a high ion conduction. This can be achieved via polymerization-induced phase separation (PIPS), which creates a two-phase system with a liquid electrolyte percolating a mesoporous thermoset. While previous studies have used commercially available liquid electrolytes, this study investigates the use of novel oligomeric carbonates to enhanced the safety of the SBEs. Increasing the carbonate chain length significantly enhances the thermal stability of the SBEs. Tuning the molecular structure of the liquid electrolyte has a significant effect on the PIPS process and SBE morphology. Using a combination of analyses on a series of wet and dried SBEs, the complex interplay between the phases is interpreted. When an increased pore size is achieved, it leads to a lower MacMullin number (NM). A conductivity of 2 × 10−5 S/cm with a NM=13 could be achieved, while maintaining a thermal stability up to 150 °C. The present study demonstrates a versatile approach to tailor this type of electrolyte.

Cell structures, phase morphologies and impact toughness of phenolphthalein poly(ether ether ketone)/epoxy composite foams

AbstractThermoplastic phenolphthalein poly(ether ether ketone) (PEK‐C) /epoxy composite foams were prepared by free foaming process (Fre‐foams) and limited foaming process (Lim‐foams), respectively, and the effects of PEK‐C content and foaming methods on the cell structures, phase morphologies, and impact strength of epoxy foams were investigated. The results showed that the gas pressure in the bubbles promoted the resin curing process and polymerization‐induced phase separation process (PIPS) during the free foaming process, while the resin curing process and PIPS were highly constrained in Lim‐foams. The incorporation of PEK‐C in the Fre‐foams showed superior improvement in impact strength compared with the PEK‐C/epoxy Lim‐foams. By adding 12 wt% PEK‐C, the specific impact strength of Fre‐foams could be enhanced by 72%, and the improved specific impact strength was because the phase‐inverted structures could prevent crack initiation and propagation, and moreover the presence of PEK‐C led to significantly refine cell structure and reduce foam density. Interestingly, the impact strength of Lim‐foams was nearly independent on the PEK‐C content, it was attributed to the obviously increased cell size with increasing PEK‐C content, and also that the phase separation process was not carried out.

Polymerization Induced Phase Separation in Composite Latex Particles during Seeded Emulsion Polymerization

Multiphase structured latex particles have been studied and produced for decades; however, the mechanism governing the polymerization induced phase separation process in such particles remains incomplete. These particles are typically produced by starting with a first, single phase polymer particle dispersion, and then a second polymer, nearly always thermodynamically phase incompatible with the first, is polymerized within those seed particles. The Gibbs free energy change upon demixing is the driving force inducing polymer–polymer phase separation during polymerization (PIPS). However, the ultimate extent of phase separation is dictated by resistances to mutual polymer chain diffusion within the latex particles. Here, we have elucidated and quantified the contributions of thermodynamic driving force and kinetic diffusive limitations to polymer–polymer phase separation within composite nanoparticles. We present a means to evaluate both the influence of chemistry and process conditions on a master plot pr...

Characterisation of polymerisation-induced phase separation process in polymer-dispersed liquid crystals based on hydroxyalkyl-methacrylate matrices

ABSTRACTHydroxyalkyl-methacrylates are very well-known hydrogel-forming biocompatible polymers. In this work, polymer-dispersed liquid crystals (LCs) based on hydroxyethyl- and hydroxypropyl-methacrylate (HEMA and HPMA) matrices are synthesised and characterised. Two different LCs from the cyano-biphenyl family (4ʹ-pentyl-4-cyanobiphenyl [5CB] and 4ʹ-octyl-4-cyanobiphenyl [8CB]) are used. Polymerisation kinetics, phase transitions, and morphologies generated during the polymerisation-induced phase separation process are analysed. Phase separation is observed at very low conversions, where a polymer-rich phase is initially segregated and this produces an increase in the low-conversion polymerisation rate (ascribed to the auto-acceleration effect of free-radical polymerisations in the polymer-rich phase). The liquid crystalline transition temperature decreases as the concentration of LC decreases, indicating that this phase is impurified. The liquid crystal 8CB is found to be less miscible than 5CB with the polymer matrices, so the LC-rich phase for 5CB is more impurified and its total volume in the material is smaller.

Effect of alignment layer on polymer-dispersed liquid crystal random laser

The surface orienting effect of rubbed polyimide alignment layer on the random lasing (RL) properties of dye-doped polymer-dispersed liquid crystal (DDPDLC) was studied experimentally. Two groups of experiment were done and nematic liquid crystal E7 was used. In the first group, the samples were 25 μm non-oriented DDPDLC sample (N-DDPDLC) and 25 μm one-side oriented DDPDLC sample (P-DDPDLC). In the second, the samples were 10 μm N-DDPDLC and 10 μm P-DDPDLC sample. The results showed that compared to the N-DDPDLC, P-DDPDLC has a lower threshold, and the 10 μm P-DDPDLC has a lower threshold compared to the 25 μm P-DDPDLC. Apparently, the P-DDPDLC cell has stronger RL spike. The oriented layer changed the phase separation structure of DDPDLC which formed hierarchical structure so as to enhance the scattering intensity of system. It is a good way to reach high efficient random laser emission by tailoring the size and morphology of PDLC through surface orientation and Polymerization-induced phase separation process.

Metal-resin bonding mediated by epoxy monolith layer

An epoxy monolith layer with porous structure is fabricated on the surface of a stainless steel (SUS) plate by polymerization induced phase separation process as the mediator for the bonding of SUS and various thermoplastic resin plates. Bonding strength is evaluated in the presence and absence of the epoxy monolith layer by a tensile lap shear test. The morphology of fracture surfaces is observed by scanning electron microscopy (SEM) in order to clarify the anchor effect of molten resins into the pores of the epoxy monoliths. The bonding strength values are calculated to be 1.2‒2.7 MPa based on an apparent adhesion area for the bonding of SUS with polyethylene, polypropylene, polyoxymethylene and acrylonitrile–butadiene–styrene copolymer in the presence of the epoxy monolith mediator. These values are 2‒30 times higher than those for direct metal-resin bonding. By the SEM observation, stretched needle-like structures were detected on the both fracture surfaces of the resins and the epoxy monoliths. The direct observation of the stretched debris out of the holes located at the monolith surfaces indicates the significant anchor effect for the present metal-resin bonding system. The bonding system mediated by the epoxy monolith layer is conveniently used for the bonding of dissimilar materials such as metals and resins without any special process and apparatus.

Morphological control and switchable photoluminescence responses of silica nanoparticles-modified polymer-dispersed liquid crystal composite films

An electro-optic tunable device is fabricated by the incorporation of silica nanoparticles as a dopant into polymer-dispersed liquid crystal composite film followed by UV curing through polymerisation-induced phase separation process. These silica-modified fibrous aggregates of polydimethylsiloxane provide stability to the nematic liquid crystal molecules. The interaction between dispersed silica nanoparticles and modified polymer network improves the polymer/liquid crystal interface, which was successfully analysed through scanning electron microscopy. It also controlled the birefringence in nematic liquid crystal droplets and provided optical stability to the off-state (opaque) scattering of an electro-optic device. The electrical tuning of photoluminescence intensity during the stage triggering from ‘Switch OFF state’ to ‘Switch ON state’ shows dependence on the morphology of composite films. It can find out potential applications in electrically switchable shutters in display market.

Hierarchically organized silica monoliths: influence of different acids on macro- and mesoporous formation

The influence of different acids, such as hydrochloric acid, sulfuric acid, nitric acid, hydrobromic acid and acetic acid on the polymerization-induced phase separation process in the formation of hierarchically organized silica monoliths was investigated in detail. Special emphasis is given to systems synthesized from tetrakis(2-hydroxyethoxy)silane (EGMS) or tetramethoxysilane (TMOS) as the silica source in the presence of Pluronic® P123 serving as structure-directing agent. The obtained silica monoliths exhibited a co-continuous and cellular macroporous structure comprising 2D hexagonally arranged mesopores with high specific surface areas ranging from 320–787 m2 g−1 independent of the applied silane precursor and regardless whether hydrochloric acid or sulfuric acid was used. A drastic change in macropore morphology to closed pores or particulate structures was observed for nitric, bromic as well as acetic acid. For sulfuric and nitric acid, the influence on the mesostructure was not as pronounced and 2D hexagonally arranged mesopores were obtained. With bromic and acetic acid a loss in mesopore ordering has been observed. Best developed hierarchically organized networks with respect to a co-continuous, cellular macroporous network, specific surface area and 2D hexagonally arranged mesopores were obtained for EGMS as well as for TMOS with P123 in sulfuric acid.

Effect of liquid crystal concentration on electro-optical properties of polymer dispersed liquid crystal lens for smart electronic glasses with auto-shading and auto-focusing function

Polymer dispersed liquid crystal lenses were prepared from a mixture of prepolymer (NOA 65) and E7 liquid crystal. The mixture of polymer dispersed liquid crystal was polymerized by ultraviolet (UV) curing in the polymerization induced phase separation process. With liquid crystal concentration, electro-optical properties of polymer dispersed liquid crystal lens devices including transmittance, driving voltage, response times, contrast ratio and slope of the linear region of the transmittance-voltage were measured and optimized for smart electronic glasses. The optimum concentration for polymer dispersed liquid crystal lens was NOA 65 of 40% and E7 liquid crystal concentration of 60%. This is the first report of the use of the polymer dispersed liquid crystal lens for smart electronic glasses with auto-shading and/or auto-focusing functions.

Effect of UV intensity on the electro-optical properties of polymer dispersed liquid crystal lens for smart electronic glasses

Polymer dispersed liquid crystal (PDLC) lenses were made from a mixture of prepolymer (NOA 65) and E7 liquid crystal (LC). The mixture of polymer dispersed in LC was polymerized by ultraviolet (UV) irradiation in the polymerization induced phase separation process. With varying UV curing intensity in this process, the electrooptical properties of PDLC lens device such as transmittance, driving voltage, response times, contrast ratio (C/R) and slope of the linear region of the transmittance-voltage were measured and optimized for application to smart electronic glasses with auto-shading and auto-focusing functions. The optimum UV intensity for the PDLC lenses was more than 580 µW/cm2. These results were improved compared to our previously reported data[1] for the application of these PDLC lenses to smart electronic glasses with auto-shading and/or auto-focusing functions.

Enhanced ordering in polymer stabilised ferroelectric liquid crystal guest–host composites: evidence by polarised fluorescence spectroscopy

Guest–host polymer stabilised ferroelectric liquid crystal (PSFLC) composite films have been prepared by polymerisation-induced phase separation process. A small quantity (0.1, 0.25 and 0.5 wt %) of anthraquinone dye in PSFLC host matrix was homogeneously dispersed to create molecular ordering in fibrils network of guest–host composite film. Ordered twisted fibril morphology was clearly observed through optical polarising microscope and thus we determined the order parameter from the dichroism measurements with the help of polarised fluorescence spectroscopy, which impacts the significant contribution of dye molecules into the smectic layers of the host polymer stabilised ferroelectric matrix.

Biologically induced transition of bio-silica sol to mesoscopic gelatinous flocs: a biomimetic approach to a controlled fabrication of bio-silica structures

Siliceous sponges form their skeletal elements, the spicules, enzymatically via the sponge-specific enzyme silicatein. The enzymatic product of silicatein in vitro is a bio-silica polymer that is not processed/hardened by phase separation. In the present study we applied a two-phase system to investigate the transition of bio-silica, formed by silicatein, from the lucid state to the opaque/turbid state. We report for the first time that the polyether polyethylene glycol [PEG] causes a rapid transition of the lucid bio-silica to the opaque/turbid state. For the experiments the recombinant silicatein from the demosponge Suberites domuncula had been used. This process is rapid (1 h) and proceeds at ambient temperatures and low (<1 mM) ortho-silicate concentrations. The condensed material can be easily eye-inspected; it has been characterized by microscopy as a smooth and solid gel. The presence of PEG displays an accelerating effect on the enzymatic polycondensation reaction. In a second part of this study a natural, sponge protein has been isolated. The 22–24 kDa protein, termed the spicule-binding protein, causes a likewise increased sol–gel transition of bio-silica. The gene corresponding to this protein was identified in S. domuncula and found to encode for a protein containing the nidogen domain. The recombinant protein, the nidogen-related protein, was prepared and likewise found to induce gelation of bio-silica due to phase separation. It is proposed that the PEG-induced phase separation process follows a mechanism during which PEG together with silicatein neutralizes the negative surface charges of the formed bio-silica nanoparticles. Further on it is adopted that the phase separation process, caused by the nidogen-like protein (spicule-binding protein), can be ascribed best to a polymerization-induced phase separation process. It is concluded that the induction of the gelation process of bio-silica described here can be used during biomimetic fabrication of new bio-silica structures.

Polymerization-induced Phase Separation: Phase Behavior Developments and Hydrodynamic Interaction

The process of polymer synthesis based on polymerization-induced phase separation (PIPS) is revisited from the theoretical point of view. Cahn–Hilliard–Cook theories for spinodal decomposition are adapted to describe the kinetics of phase separation and deduce the time-resolved scattering function, while the double reaction model is used to describe the kinetics of polymerization. Coupling of these two kinetics is provided by the Carother's equation relating the fraction of reacted monomers to the degree of polymerization at time t, denoted N(t). It is argued that the approach to criticality is governed by a critical parameter, χc, that is different from the usual parameter for spinodal decomposition, χs, deduced from the second derivative of the free energy. While the latter parameter depends on the reciprocal degree of polymerization N−1(t), the former one depends on its time integral. This leads to significant consequences on the phase behavior developments during the PIPS process. Hydrodynamic interactions are found to speed up the emergence of instability modes. Although the qualitative trends remain similar to those of the Rouse dynamics, important quantitative changes are found due to the long-range viscous flow effects.

Analysis of effects of oxidized multiwalled carbon nanotubes on electro-optic polymer/liquid crystal thin film gratings

This work focuses on experimentally demonstrating the modification in diffusion kinetics, formation of holographic polymer dispersed liquid crystal gratings and an improvement in its electro optic response by doping them with multi-walled carbon nanotubes. Results indicate a faster rise and fall times which is attributed to the reduction in size of the liquid crystal droplets formed and a reduction in switching voltage due to change in dielectric properties of the medium as manifested by a rise in capacitance. Real time diffraction efficiency measurements reveal a time delay in the appearance of the diffracted order due to non-participation of the nanotube in the polymerization induced phase separation process. An analysis of this effect is presented based on the Stoke-Einstein's diffusion equation incorporating shape anisotropy of the nanotubes.

Investigation of the photopolymerization-induced phase separation process in polymer dispersed liquid crystal

A novel experimental method involving simultaneous resistivity and transmittance measurements was used to examine the polymerization-induced phase separation process. Measuring the resistivity and transmittance of a polymer dispersed liquid crystal (PDLC) cell allows the polymerization and phase separation to be monitored during the PDLC formation process. To verify the utility of this method, resistivity data were compared with conversion data obtained by photo differential scanning calorimetry (DSC) and FTIR analysis using NOA65 and an NOA65-E7 mixture. The resistivity data of NOA65 (a neat prepolymer without liquid crystals) were identical to the conversion data obtained by photo-DSC and FTIR analysis. However, the resistivity data of the NOA65-E7 mixture (a prepolymer with liquid crystals) differed from the conversion data because the resistivity of the NOA65-E7 mixture was affected by the degree of liquid crystal phase separation and monomer conversion. The photopolymerization was slower and the degree of conversion was higher for the NOA65-E7 mixture than for the neat prepolymer due to dilution and plasticization effects, respectively.

Sol−Gel Processing of a Glycolated Cyclic Organosilane and Its Pyrolysis to Silicon Oxycarbide Monoliths with Multiscale Porosity and Large Surface Areas

This study is related to the preparation of silicon oxycarbide monoliths comprising a hierarchical network build-up from the pyrolysis of monolithic organosilica gels. A novel glycol-modified 1,3,5-trisilacyclohexane-carbosilane “[Si(OCH2CH2OH)2CH2]3” was processed via a polymerization-induced phase separation process in hydrochloric acid solution containing the Pluronic P123 block copolymer and potassium chloride. Highly porous organosilica monoliths with interconnected macropores and a large amount of uniformly sized polymer-templated mesopores within the macroscopic framework domains were obtained after supercritical fluid extraction. The monoliths were pyrolyzed in argon atmosphere at 1000 °C to yield silicon oxycarbide monoliths by maintaining the hierarchical porosity of the organosilica gel. Both the organosilica gels and the silicon oxycarbide monoliths were thoroughly investigated with standard characterization techniques. If no salt was used for the preparation of organosilica gels, no distinct ...