Polymerization-induced Phase Separation Research Articles

Macroporous-Enabled Highly Deformable Layered Hydrogels with Designed pH Response.

Environment-responsive hydrogel structures are of great interest in materials research and have a wide range of applications. By using a flow lithography technique, we report a one-step and high-throughput fabrication method for the synthesis of highly pH-responsive hydrogels with designed shape transformations. In this method, heterogeneous hydrogels with porous and nonporous layers are synthesized using a single UV exposure in a microfluidic channel. During the UV polymerization, the porous layers, which are formed by using polymerization-induced phase separation (PIPS), significantly increase the swelling capability and enhance the swelling rate of the hydrogels. Because the flow-lithography approach allows various patterns of porous/nonporous layers with great control and enables the simple integration of PIPS, resultant layered hydrogels show extraordinary deformations with desired pH response. More importantly, our fabrication approach can not only make 2D deformation of hydrogel structures such as bending but also can achieve 3D structural deformation such as helical and buckling structures, enabled by nonuniform UV polymerization we developed.

Flexible, ferroelectric nanoparticle doped polymer dispersed liquid crystal devices for lower switching voltage and nanoenergy generation

Flexible polymer dispersed liquid crystal (F-PDLC) devices were fabricated using transparent conducting ITO/PET film. Polymerization induced phase separation (PIPS) method was used for pure and ferroelectric BaTiO3 (BTO) and ZnO doped PDLC devices. The distribution of nanoparticles in the PDLC and the formation of micro cavities were studied using field emission scanning electron microscopy (FESEM). It was observed that the addition of ferroelectric BTO nanoparticles has reduced the threshold voltage (Vth) and saturation voltage (Vsat) of FNP-PDLC by 85% and 41% respectively due to the spontaneous polarization of ferroelectric nanoparticles. The ferroelectric properties of BTO and ZnO in the fabricated devices were investigated using dynamic contact electrostatic force microscopy (DC EFM). Flexing the device can generate a potential due to the piezo-tribo electric effect of the ferroelectric nanomaterial doped in the PDLC matrix, which could be utilized as an energy generating system. The switching voltage after multiple flexing was also studied and found to be in par with non-flexing situations.

Gas permeation properties of a metallic ion-cross-linked PIM-1 thin-film composite membrane supported on a UV-cross-linked porous substrate

Abstract Metallic ion-cross-linked polymer of intrinsic microporosity (PIM-1) thin-film composite (TFC) membranes supported on an ultraviolet (UV)-cross-linked porous substrate were fabricated. The UV-cross-linked porous substrate was prepared via polymerization-induced phase separation. The PIM-1 TFC membranes were fabricated via a dip-coating procedure. Metallic ion-cross-linked PIM-1 TFC membranes were fabricated by hydrolyzing the PIM-1 TFC membrane in an alkali solution and then cross-linking it in a multivalent metallic ion solution. The pore size and porous structures were evaluated by low-temperature N2 adsorption–desorption analysis. The membrane structure was investigated by field-emission scanning electron microscopy. The effects of heat treatment and pore-forming additives on the gas permeance of the UV-cross-linked porous substrate are reported. The effects of different pre-coating treatments on the gas permeance of the metallic ion-cross-linked PIM-1 TFC membrane are also discussed. The metallic ion-cross-linked PIM-1 TFC membrane displayed high CO2/N2 selectivity (23) and good CO2 permeance (1058 GPU).

Fracture behavior characterization of arcan polycaprolactone based polymer composites prepared by polymerization induced phases separation

Polycaprolactone (PCL) based polymer composites have several potential engineering applications. This study investigated the fracture toughness of polycaprolactone based polymer composites under mode I, mode II, and mixed mode I&II, according to the use of Arcan composite specimens. The specimen was prepared through a polymerization‐induced phase separation (PIPS) process by diffusing polycaprolactone within an epoxy matrix. The thermal properties and morphology of the specimen fracture surfaces were characterized firstly. After that shape memory performance of the prepared specimen was preliminarily studied by measuring the recovered strain and stress. Specimens were tested under compression according to ASTM D6641. Arcan specimens used in this study for studying the fracture behavior under different fracture modes were prepared using a Waterject. The effect of loading angles on the fracture behavior was investigated as well. The results show that Arcan specimen has advantages on studying the fracture behavior of polycaprolactone based polymer composite under different fracture modes. It found that the average size decreases as the amount of PCL increasing. The globules are uniformly distributed across the fracture surfaces. The shape memory test shows that the larger programmed strain the larger recovered stress. In addition, the increase of PCL amount leads to the decrease of composite KIC but the increase of KIIC (i.e., improved shear resistance). We envision application of the developed Arcan test fixture as a testing device to exam the crack healing efficiency under different fracture modes. POLYM. COMPOS., 40:1198–1208, 2019. © 2018 Society of Plastics Engineers

Polymerization-Induced Phase Separation Formation of Structured Hydrogel Particles via Microfluidics for Scar Therapeutics

Excessive scar formation can form disabling contractures that result in a debilitating psychological outcome. Sustainable hydrophobic corticosteroid release in vivo is essential to regulate the wound healing process. Functional hydrogel particles are widely applied for sustainable release. However, due to the limited aqueous solubility of hydrophobic compounds, most of the corticosteroid is released from the hydrogels within seconds, causing undesirable scar formation and recurrence. In this study, a novel polymerization-induced phase separation is investigated to form well-defined polyethylene glycol diacrylate (PEGDA) core/alginate shell structured hydrogel particles using microfluidics without toxic organic solvents. Based on their wettability preference, hydrophobic corticosteroid-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles are compartmentalized in the PEGDA core during polymerization to control the corticosteroid release. The distribution of the PLGA nanoparticles is precisely regulated by the phase separation boundary and characterized using a fluorescent dye. The thickness of the shell and partition coefficients are determined using the UV intensity and irradiation period. Upon encapsulation of the PLGA nanoparticles within the poly(PEGDA) core, a long-term corticosteroid treatment is developed and effective scar therapeutic outcomes are evaluated using both in vitro and in vivo models.

Hierarchically Structured Porous Spinels via an Epoxide-Mediated Sol-Gel Process Accompanied by Polymerization-Induced Phase Separation.

Enhancing the activity and stability of catalysts is a major challenge in scientific research nowadays. Previous studies showed that the generation of an additional pore system can influence the catalytic performance of porous catalysts regarding activity, selectivity, and stability. This study focuses on the epoxide-mediated sol–gel synthesis of mixed metal oxides, NiAl2O4 and CoAl2O4, with a spinel phase structure, a hierarchical pore structure, and Ni and Co contents of 3 to 33 mol % with respect to the total metal content. The sol–gel process is accompanied by a polymerization-induced phase separation to introduce an additional pore system. The obtained mixed metal oxides were characterized with regard to pore morphology, surface area, and formation of the spinel phase. The Brunauer–Emmett–Teller surface area ranges from 74 to 138 m2·g–1 and 25 to 94 m2·g–1 for Ni and Co, respectively. Diameters of the phase separation-based macropores were between 500 and 2000 nm, and the mesopore diameters were 10 nm for the Ni-based system and between 20 and 25 nm for the cobalt spinels. Furthermore, Ni–Al spinels with 4, 5, and 6 mol % Ni were investigated in the dry reforming of CH4 (DRM) with CO2 to produce H2 and CO. CH4 conversions near the thermodynamic equilibrium were observed depending on the Ni content and reaction temperature. The Ni catalysts were further compared to a noble metal-containing catalyst based on a spinel system showing comparable CH4 conversion and carbon selectivity in the DRM.

Versatile preparation of surface-skinless particles of epoxy resin-based monoliths using a well-defined diblock copolymer surfactant

This is the first report on a versatile and facile preparation method for well-defined and surface-skinless epoxy resin-based monolithic particles by polymerization-induced phase separation in an oil-in-oil emulsion system in the presence of a designed block copolymer.

Effect of FeCl2 on the pore structure of porous carbon obtained from phenol formaldehyde resin and ethylene glycol

Homogeneous porous carbons were obtained from phenolic resin/ethylene glycol resin mixtures based on polymerization-induced phase separation and template method. The effect of FeCl2 content (ωFe) on the pore structure of the porous carbons was systematically investigated. The addition of iron favors the formation of porous pores with large pore size, fine carbon skeleton and uniformly distributed pore structure. With ωFe increasing from 0% to 1%, the average pore size and apparent porosity of the porous carbons increase from 14 to 190 nm and from 25.6% to 63.3%, respectively. Iron ions can be used as a template and catalyst to change the pore structure of porous carbons.

Effects of a chemically modified multiwall carbon nanotubes on electro-optical properties of PDLC films

ABSTRACTPolymer dispersed liquid crystal (PDLC) films are fabricated by well-known polymerization-induced phase separation method. In this paper, the dispersion of multi-walled carbon nanotubes (MWCNT) in liquid crystals has been enhanced by chemical modification and we have investigated their effects on the morphology, electro-optical properties and conductivity of the PDLC films. Results indicated that the threshold voltage and the saturation voltage of PDLC films decreased with the increase of the doping concentration of MWCNT or chemically modified MWCNT, because carbon nanotubes can enhance the electric field by reducing the resistivity of the medium and increasing the capacitance of the cells. It can be viewed obviously that the contrast ratio of the PDLC films doped with the chemically modified MWCNT is higher than that of the MWCNT.

20 renewable biowastes derived carbon materials as green counter electrodes for dye-sensitized solar cells

Twenty types of biowastes derived carbon materials (BCM) synthesized by a facile one-step pyrolysis were developed as counter electrodes for the configuration of dye-sensitized solar cells (DSSCs). The biowastes selected for the BCM preparation were divided into three groups: (i) eleven woods, including weeping willow, phoenix, camphor, Chinese fir, maple, peach, poplar, cypress, tea-oil camellia, orange, and chinaberry; (ii) seven leaves, including pine needles, camphor, palm, maple, poplar, Chinese fir, and red after-wood; and (iii) two papers, namely filter paper and facial tissue. Each of the BCM based DSSCs shows a higher efficiency than the graphite based counterparts. The efficiencies of the DSSCs employing the BCM prepared from woods and leaves vary in a range 1.23% -1.91% and 1.07%-1.85%, respectively, while that of the devices using the graphite is 0.77%. The peak efficiency in both groups of the wood and leaf based cells is achieved by employing the phoenix wood and the palm leaf as the raw materials, respectively. Compared with the porous BCM obtained from the woods and leaves, the fibrous BCM fabricated from the papers show better efficiencies of around 4.70% for use in the DSSCs. The high efficiency is mainly attributed to the superior catalytic activity and faster electron transportation for tri-iodide (I3−) reduction induced by the unique morphological and structural characteristics of the paper derived BCM, such as hierarchical fibrous carbon skeletons at nanometer and micron scales, abundant exposed microcrystal edges and defects, rough surface at nanoscale with rich burrs and convex microstructures, and oxygen-containing surface functional groups. Furthermore, the efficiency of the DSSCs employing the paper derived BCM is equal to about 88% of that of the devices using the mesoporous carbon synthesized from the phenolic resin mixtures based on polymerization-induced phase separation.

Effect of monomer concentration and functionality on electro-optical properties of polymer-stabilised optically isotropic liquid crystals

ABSTRACTOptically isotropic nature can open a new type of high-performance liquid crystal (LC) displays. The main features emerge from the interaction between LC and polymer network at the interface. At this point, we investigated the influence of cross-linking monomer concentration and functionality on electro-optic properties of optically isotropic liquid crystal (OILC) obtained by polymerisation-induced phase separation method. Interestingly, we obtained a pore-like network structure constructed by highly interlinked polymer beads in acrylate monomers and achieved fast decay response time (0.6 ms). We found that the voltage-dependent hysteresis was mostly eliminated (~0.25%), and the contrast ratio was enhanced (1:1550) for high functional monomers. The result inspires a simple way to optimise the materials to fabricate a high-performance OILC device and it shows high-transparency, low-driving voltage, hysteresis-free and sub-millisecond response time.

Polymerization induced shaping of Pickering emulsion droplets: From simple hollow microspheres to molecularly imprinted multicore microrattles

The design and fabrication of polymer microspheres with structural complexity in Pickering emulsion systems is a pioneering topic in recent years. Herein we report a synthesis of structured and molecularly imprinted multicore rattle-type microspheres through a facile method based on the Pickering emulsion polymerization using silica nanoparticles as the only stabilizer. The void inside the sphere was induced by the polymerization-driven phase separation approach tailoring by the interface interaction. However, the imprinting template of bisphenol A (BPA) is found to serve also as the heterogeneous nuclei, whose superimposition on the polymerization induced phase separation creates the opportunities for the formation of the multicores encapsulated in the shell. A simple adjustment on the composition of the oil phase enabled the evolution of sphere internal structures from single void to multicores. Specifically, the reversibly incorporated BPA on the polymer spheres can be removed by extraction with the molecular information left and immobilized by crosslinking as the imprinted sites. The imprinted spheres can be used to selectively rebind BPA, which was comprehensively evaluated by a batch of rebinding experiments. The rattle-like microspheres recognized BPA molecules from their analogues and effectively removed them from the matrix with accelerated adsorption kinetics, which shows potential applications in the environmental or analytic fields where the removal or separation of BPA as an endocrine-disrupting chemical is in high demand.

Porous carbon monoliths with pore sizes adjustable between 10 nm and 2 μm prepared by phase separation – New insights in the relation between synthesis composition and resulting structure

Porous carbon monoliths with tunable porosity are promising materials for a variety of applications like energy storage and adsorption. But the synthesis of carbons with monolithic shape and controlled porosity is often time-consuming and expensive. Here, micro-/macroporous and micro-/mesoporous carbon monoliths were synthesized via a simple process of polymerization induced phase separation of resorcinol and formaldehyde followed by drying at ambient pressure and carbonization. The carbon monoliths are mechanically stable and exhibit specific surface areas between 390 and 1100 m2·g−1. The size of the macro- and mesopores can be tailored over a wide range from approximately 10 nm to 2 μm by simply altering the solvent composition during the synthesis of the organic monoliths. The influence of solvent composition and resorcinol concentration on the pore size in the carbon monoliths was investigated with a focus on the smaller pore sizes and an exponential relation was observed. Finally, selected monoliths were activated in a stream of CO2 to produce hierarchically porous monoliths with specific surface areas between 1000 and 2400 m2·g−1. The activated monoliths were characterized in terms of their CO2 adsorption and showed adsorption capacities of up to 3.10 mmol·g−1 at 298 K.

Polymerization-induced phase separation for the fabrication of magnetic sponges for oil spill reclamation

Magnetic sponges were fabricated from polymerization-induced phase separation, and their properties for oil spill reclamation were investigated. Magnetic sponges exhibit high selectivity from oil to water because of their high hydrophobicity (with water contact angles of approximately 140°). The interconnected macroporous structures enable equilibrium absorption in a few minutes and provide high absorption capacities, from 9.9 to 20.3gg−1. The presence of magnetic nanoparticles helps collect sponges with the use of an external magnetic field when the sponges break into small pieces. Their facile preparation and excellent performance make these magnetic sponges excellent candidates for oil spill reclamation.

A Facile All-Solution-Processed Surface with High Water Contact Angle and High Water Adhesive Force.

A series of sticky superhydrophobicity surfaces with high water contact angle and high water adhesive force is facilely prepared via an all-solution-processed method based on polymerization-induced phase separation between liquid crystals (LCs) and epoxy resin, which produces layers of epoxy microspheres (EMSs) with nanofolds on the surface of a substrate. The morphologies and size distributions of EMSs are confirmed by scanning electron microscopy. Results reveal that the obtained EMS coated-surface exhibits high apparent contact angle of 152.0° and high water adhesive force up to 117.6 μN. By varying the composition of the sample or preparing conditions, the sizes of the produced EMSs can be artificially regulated and, thus, control the wetting properties and water adhesive behaviors. Also, the sticky superhydrophobic surface exhibits excellent chemical stability, as well as long-term durability. Water droplet transportation experiments further prove that the as-made surface can be effectively used as a mechanical hand for water transportation applications. Based on this, it is believed that the simple method proposed in this paper will pave a new way for producing a sticky superhydrophobic surface and obtain a wide range of use.

Anisotropy Enhanced Phase Separation in Polymer Dispersed Liquid Crystals

Phase separated blends of polymers and low molecular weight liquid crystals, commonly known as polymer dispersed liquid crystals in short PDLCs, are investigated. These materials offer a realm of applications in modern technologies, including sensors, commutable windows, display devices and telecommunication systems. A particular attention is given to the effects of anisotropy of the liquid crystal on the phase behavior under equilibrium and non equilibrium conditions. The theoretical formalism used is based on the lattice model of isotropic mixing, combined with standards theories of nematic and smectic-A orders. Considering the equilibrium phase behavior, we find that the nematic order enhances the polymer / solvent phase separation, and that the osmotic pressure shows substantial changes for relatively small polymer volume fractions. We find that the anisotropy enhanced phase separation is more pronounced for a smectic-A liquid crystal, and the miscibility gap is widened. The kinetics of swelling by nematic LCs is examined using a linear solvent diffusion process, with a rate of swelling directly related to the derivative of the osmotic pressure. An abrupt swelling / de-swelling transition is found, due to overwhelming effects of the anisotropic interaction beyond the threshold LC concentration. Anisotropy enhanced phase separation is also investigated in the method of synthesis based on the polymerization induced phase separation mechanism. We find that the kinetics of separation during early stages of polymerization is faster, due to the anisotropic interaction of the low molecular weight solvent. The kinetics speed up is favored by the long range viscous flow effects due to hydrodynamic interactions. A limited selection of experimental data in the literature is chosen to validate some theoretical predictions obtained from the present formalisms.

Recovering Rare Earth Elements from Aqueous Solution with Porous Amine-Epoxy Networks.

Recovering aqueous rare earth elements (REEs) from domestic water sources is one key strategy to diminish the U.S.'s foreign reliance of these precious commodities. Herein, we synthesized an array of porous, amine-epoxy monolith and particle REE recovery sorbents from different polyamine, namely tetraethylenepentamine, and diepoxide (E2), triepoxide (E3), and tetra-epoxide (E4) monomer combinations via a polymer-induced phase separation (PIPS) method. The polyamines provided -NH2 (primary amine) plus -NH (secondary amine) REE adsorption sites, which were partially reacted with C-O-C (epoxide) groups at different amine/epoxide ratios to precipitate porous materials that exhibited a wide range of apparent porosities and REE recoveries/affinities. Specifically, polymer particles (ground monoliths) were tested for their recovery of La3+, Nd3+, Eu3+, Dy3+, and Yb3+ (Ln3+) species from ppm-level, model REE solutions (pH ≈ 2.4, 5.5, and 6.4) and a ppb-level, simulated acid mine drainage (AMD) solution (pH ≈ 2.6). Screening the sorbents revealed that E3/TEPA-88 (88% theoretical reaction of -NH2 plus -NH) recovered, overall, the highest percentage of Ln3+ species of all particles from model 100 ppm- and 500 ppm-concentrated REE solutions. Water swelling (monoliths) and ex situ, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) (ground monoliths/particles) data revealed the high REE uptake by the optimized particles was facilitated by effective distribution of amine and hydroxyl groups within a porous, phase-separated polymer network. In situ DRIFTS results clarified that phase separation, in part, resulted from polymerization of the TEPA-E3 (N-N-diglycidyl-4-glycidyloxyaniline) species in the porogen via C-N bond formation, especially at higher temperatures. Most importantly, the E3/TEPA-88 material cyclically recovered >93% of ppb-level Ln3+ species from AMD solution in a recovery-strip-recovery scheme, highlighting the efficacy of these materials for practical applications.

Thermal mending in E-glass reinforced poly(ε-caprolactone)/epoxy blends

Blends of difunctional epoxy monomer with a 4,4′-diaminodiphenylsulfone hardener and poly(ε-caprolactone) (PCL) were used as a self-healing matrix in woven glass fibre-reinforced polymer composites (FRPs). FRPs with these blends (containing 0, 25 and 37vol% of PCL in the blend) were manufactured through Vacuum Assisted Resin Infusion Moulding at high temperature and the matrix, resulting from polymerization induced phase separation, consisted of interconnected epoxy particles embedded in PCL. With 25vol% PCL in the matrix, similar storage modulus and interfacial shear strength as compared to unmodified systems have been observed, however toughness was decreased by 40%. Up to 45% toughness recovery and over 100% stiffness recovery were observed over several cycles when the blend matrix composite samples were re-tested after a thermal cycle at 150°C for 30 min. These composites can thus provide efficient crack healing, but remain more sensitive to initial crack propagation due to confinement of the thermoplastic phase.

Effect of homopolymer in polymerization-induced microphase separation process

We report on the phase separation behaviors of polymerization mixtures containing a polylactide macro-chain transfer agent (PLA-CTA), styrene, divinylbenzene, hydroxyl-terminated PLA (PLA-OH), and a molecular chain transfer agent which enable the ability to tune the pore size of a cross-linked polymer monolith in a facile manner. Cross-linked monoliths were produced from the mixtures via reversible addition-fragmentation chain transfer (RAFT) polymerization and converted into cross-linked porous polymers by selective removal of PLA while retaining the parent morphology. We demonstrate that pore sizes are tunable over a wide range of length scales from the meso- to macroporous regimes by adjusting the ratio of PLA-CTA to PLA-OH in the reaction mixture which causes the phase separation mechanism to change from polymerization-induced microphase separation to polymerization-induced phase separation. The possibility of increasing porosity and inducing simultaneous micro- and macrophase separation was also realized by adjustments in the molar mass of PLA which enabled the synthesis of hierarchically meso- and macroporous polymers.

Impact of dye on the switching responses of polymer dispersed ferroelectric liquid crystal

ABSTRACTPolymer dispersed ferroelectric liquid crystals (PDFLCs) have disclosed an enormous approach for use in electro-optic and display technology since ferroelectric liquid crystals (FLCs) have inherently fast switching speeds. In this work, we equipped dichroic PDFLC using dye-doped chiral SmC* liquid crystal (LC) and ultra-violet (UV) curable polymer by polymerization induced phase separation (PIPS) method. All fundamental material aspects like optical transmissions, spontaneous polarization, threshold voltage, contrast ratio and response time as a function of applied voltage, temperature, and dye concentration were examined. In the electro-optic study, 82% transmission with a threshold field value ∼0.6 V/μm was observed for PDFLC, however, 90% transmission was achieved with a threshold field ∼0.3 V/μm at the dye concentration of 0.125% (wt./wt.). As a result, present dichroic PDFLC device shows microseconds switching response, higher polarization value and superior contrast, at low dye concentration.