Internal Phase Emulsion Templating Research Articles

An approach for the scalable production of macroporous polymer beads

A tubular co-flow reactor to produce macroporous polymer beads by polymerization of medium and high internal phase emulsion (M/HIPE) templates was developed. This reactor allows for improved production rates compared to tubing based microfluidic devices. Water-in-oil (W/O) M/HIPEs, containing methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) monomers in the continuous phase, were injected into a re-circulating carrier phase. The continuous phase of the emulsion droplets was UV polymerized in situ, resulting in polyM/HIPE beads. The emulsion composition was adjusted to produce poly(MMA-co-EGDMA) porous polymer beads with a protective crust and an interconnected internal pore structure. HCl loaded beads were produced by adding the active ingredient into the dispersed emulsion phase, leading to HCl encapsulation in the porous structure of the beads after polymerization. Even after exposure to ambient conditions for 24 h, 60% of the HCl remained in the beads, indicating good encapsulation efficiencies. Thus, it is possible to use such macroporous beads as delivery vehicles.

Preparation of hierarchically porous carbons with enhanced porosity and energy storage capacity through an internal phase-external phase coefficient HIPE templating

High internal phase emulsion (HIPE) templating is a versatile strategy to prepare porous polymers and carbons. However, the prepared porous carbon materials usually show low specific surface area (SSA) due to the feature of macropores, which hampered their wider applications. This work developed a novel strategy, namely internal phase-external phase coefficient HIPE (IP-EP coHIPE) templating, to prepare polymer-derived hierarchically porous carbons (HPCs) with high SSA. In the strategy, sodium alginate (SA) aqueous solution was selected as the internal phase and emulsified in external oil phase containing divinylbenzene (DVB). HPCs were obtained by sequentially polymerizing the external phase, crosslinking the internal phase and carbonization. The testing results indicated that this strategy provided HPCs with notably enhanced porosity and increased SSA when compared with conventional HIPE method via the further utilization of the void space of polyHIPE-based HPCs via a facile way. The porous architectures of HPCs can be adjusted by changing the volume fraction and/or the concentration of the internal phase, respectively. The potential applications of the obtained HPCs were evaluated as the electrode material of supercapacitor. The specific capacitance of optimized HPC-based supercapacitor is 306 F/g, much higher than that based on general polyHIPE-derived HPC (145 F/g) at 1 A/g, which can be attributed to its enhanced porosity, hierarchically porous architecture and high SSA (2289 m 2 /g). • Hierarchically porous carbons (HPCs) were prepared through an internal phase-external phase coefficient HIPE templating. • This strategy provided HPCs with notably enhanced porosity and increased specific surface area. • The HPC-based supercapacitors present satisfied energy storage performance and excellent application prospects.

Permeable emulsion-templated porous polyepoxides

Porous polyepoxides are attractive materials for a range of applications. Liquid foam precursors can be net-shaped by moulding. We report preparation of permeable polyepoxide, Araldite®2020, foams with porosities in the range of 45–60% from surfactant-stabilised W/O medium internal phase emulsion templates. Alteration of internal phase volume ratio and surfactant concentration were used to tailor the properties of the resulting polyMIPEs. These polyepoxide foams had elastic moduli in the range of 60–200 MPa and compression strengths between 2 and 6.5 MPa with permeabilities up to 200 mD. The theoretical average molecular weight between crosslinks was 534 g mol−1, while the foams had 500 ± 50 g mol−1. Swelling tests confirmed the excellent chemical stability of the porous epoxy. However, the swelling ratio depended on the polarity of the solvents used. It decreased with decreasing solvent polarity.

Janus Nanoshards Prepared Based on High Internal Phase Emulsion Templates for Compatibilizing Immiscible Polymer Blends

Janus Nanoshards Prepared Based on High Internal Phase Emulsion Templates for Compatibilizing Immiscible Polymer Blends

3D Printable and Sub‐Micrometer Porous Polymeric Monoliths with Shape Reconfiguration Ability by Miniemulsion Templating

AbstractPorous monoliths prepared by high internal phase emulsion (HIPE) templating have received various attentions in the fields of catalysis, separation, and tissue engineering. However, the application of the monoliths from HIPE is limited by their poor mechanical performance and the difficulty of fabricating hierarchically porous structures. Additive manufacturing is an emerging technique that achieves high design freedom by depositing materials layer‐by‐layer. This work designs medium internal phase emulsion (MIPE) ink with the concept of miniemulsion to prepare 3D printable porous polymeric monoliths with sub‐micrometer pores. High shear energy is used to reduce the droplet size of the internal phase and jam the emulsion ink. The jammed MIPE ink shows prominent shear‐thinning behavior and appropriate elastic modulus for direct ink writing (DIW). After printing, the external phase composed of stearyl acrylate and hexanediol diacrylate can be cured by photopolymerization to produce poly(MIPE) with interconnected pores in the size of several hundred nanometers. The printed poly(MIPE) demonstrates high mechanical strength and can be reprogrammed into complex geometries difficult for the common DIW processes. The proposed technique provides a new route to fabricate hierarchically porous monoliths with a drastic change of pore dimension, high mechanical strength, and tunable shape reconfiguration.

Emulsion templated polymer monoliths containing cellulose nanocrystals: Synthesis and adsorption properties

AbstractCellulose nanocrystals (CNCs) loaded hierarchical macroporous polymer monoliths were synthesized through high internal phase emulsion (HIPE) templating. For this purpose, unmodified CNCs were used as nanofiller in various amounts during HIPE preparation. The effect of CNCs loading on the hierarchical pore structure and mechanical properties was investigated. It was demonstrated that mechanical strength was significantly improved by CNCs loading. In order to reveal an application field, adsorptive property of resulting monoliths was investigated against Nile blue dye. The results showed that the maximum adsorption capacity of cationic Nile blue was 54% for the neat monolith, while it was 70% for the monolith prepared by 9 wt% CNCs loading. Meanwhile, the kinetic evaluation of the experimental adsorption data revealed that the adsorption follows pseudo‐second‐order kinetic model and it is consistent with Freundlich isotherm.

Cellulose nanocrystals supported—PolyHIPE foams for low‐temperature latent heat storage applications

AbstractParaffin‐based shape‐stabilized composite phase change materials (PCM) containing surface modified cellulose nanocrystals (CNCs) for thermal energy storage applications were prepared. In this respect, a three‐step experimental procedure consisting nanoparticle modification, macroporous foam synthesis, and composite PCM preparation was implemented. While CNCs were modified via freeze‐templating, high internal phase emulsion (HIPE) templating was used for the synthesis of polymeric foams ‐ known as polyHIPEs. Meanwhile a simple method was applied to impregnate n‐hexadecane (HD), which is a paraffin‐based PCM within the polyHIPE foam matrix. It was demonstrated that surface modified CNCs can be efficiently used to prepare polyHIPE foams with improved properties. It was also shown that the impregnation of HD into the ‐polyHIPE foam matrix supported by CTAB‐CNCs can be achieved with an incorporation rate of up to 55.7%. Moreover, the phase transition temperature and thermal energy storage capacity of the obtained composite PCM was determined as 22.7°C and 117 J/g, respectively.

Hierarchically Porous Monolith with High MOF Accessibility and Strengthened Mechanical Properties using Water‐in‐Oil High Internal Phase Emulsion Template

AbstractHigh internal phase emulsion (HIPE) is a promising template for the construction of metal‐organic framework (MOF)‐based hierarchically porous monoliths. However, the current approaches still suffer from many issues, such as MOF embedment in polymer matrix and poor mechanical performance. In this work, a co‐stabilization strategy is employed to prepare water‐in‐oil HIPEs and the corresponding MOF‐based poly‐HIPEs. The effects of emulsifier concentration, type and volume of continuous oil phase, and type of initiator are thoroughly investigated. ZIF‐8 particles with size comparable to the thickness of the cellular wall are adopted to avoid the problem of MOF embedment. As a result, the obtained monolith shows enhanced mechanical properties and a hierarchically porous structure with ≈80% of ZIF‐8 accessible. Due to these unique features, the ZIF‐8‐based hierarchically porous monoliths exhibit greatly accelerated adsorption kinetics in iodine removal, showing great promise for future industrial applications.

Layer-by-Layer (LbL) Surface Augmented Modification of Poly(Styrene/Divinylbenzene)High Internal Phase Emulsion for Carbon Dioxide Capture.

In this study, we used amines electrolyte solution with layer-by-layer (LbL) technique to modify and increase the CO2 adsorption capacity of highly porous polymer from high internal phase emulsion template polymer. This perspective presents the extraordinary versatility of emulsion templating polymerization, which has emerged with the growing numbers of HIPE systems and modification. In this study, we used polyHIPE prepared from styrene (S) and divinylbenzene (DVB) with varying ratios; 80:20, 20:80, and 0:100 to improve the surface area, thermal properties, and mechanical properties of the materials. Furthermore, the surface of the polyHIPE was modified by LbL technique to increase the adsorption efficiency. This technique consisted of two main layers, the primary layer of poly(diallyldimethylammonium chloride) (PDADMAC) and polystyrene sulfonate (PSS) and the secondary layer, which was the CO2 adsorbing layer, of polyethylene imine (PEI) or tetraethylene pentamine (TEPA). Poly(S/DVB)HIPE modified by PEI terminated as the secondary coating showed the highest CO2 adsorption capacity, with up to 42% (from 0.71 to 1.01 mmol/g). The amine-multilayered modified material still possessed an open cell structure, since the solution did not block the pore structure of the poly(S/DVB)HIPE and was suitable for being used as an adsorbent in adsorption technology.

One-Pot Fabrication of Hierarchically Bicontinuous Polystyrene Monoliths with Homogeneous Skeletons and Glycopolymer Surfaces.

The hierarchically bicontinuous polystyrene monoliths (HBPMs) with homogeneous skeletons and glycopolymer surfaces are fabricated for the first time based on the medium internal phase emulsion (MIPE) templating method via activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP). The synergistic self-assembly of amphiphilic diblock glycopolymer (ADG) and Pluronic F127 (PF127) at the oil/water interface via hydrogen bonding interaction contributes to the formation of bicontinuous MIPE with deformed neighboring water droplets, resulting in the highly interconnected HBPM after polymerization. There is a bimodal pore size distribution in the HBPM, that is, through pores (150-5000nm) and mesopores (10-150nm). The HBPMs as prepared show excellent biocompatibility, homogeneous skeletons, strong mechanical strength, and high bed permeability, overcoming the practical limitations of the second generation of polystyrene (PS) monoliths. Glycoprotein concanavalin A (Con A) can be easily and quickly separated by the HBPM in hydrophilic interaction chromatography (HILIC) mode. These results suggest the HBPMs have great potentials in catalysis, separations, and biomedical applications.

A Natural Rubber Waste Derived Surfactant for High Internal Phase Emulsion Templating of Poly(Dicyclopentadiene)

AbstractThe use of a surfactant derived from the degradation of natural rubber gloves via cross‐metathesis with methyl acrylate and subsequent saponification of the ester group for the stabilization of water in dicyclopentadiene high internal phase emulsions is described. The versatility of the resulting high internal phase emulsion is demonstrated by polymerizing the continuous dicyclopentadiene phase via ring‐opening metathesis polymerization yielding macroporous poly(dicyclopentadiene) foams with a porosity of 82%. The use of the ionic surfactant allows for the preparation of foams, which are resistant to absorb water. This property is hitherto not accessible with protocols involving the use of nonionic surfactants commonly employed in emulsion templating of polymers.

Development of terpene based sorbents via emulsion templating: Synthesis and swelling behavior

Polymeric sorbent materials exhibiting excellent swelling capacity were developed using high internal phase emulsion (HIPE) templating approach. Precursor HIPEs were prepared by using continuous phases that composed of mixtures of β-myrcene (monomer) and 1,3-butanediol dimethacrylate (crosslinker). The influence of β-myrcene concentration on the emulsion stability and crosslinking was investigated. Swelling behaviors of resulting polyHIPEs in different solvents were studied. It was found that the maximum swelling capacities were reached 713%, 667% and 310% in benzene, toluene and hexane, respectively.

Preparation of N-doped porous carbons via high internal phase emulsion template

Heteroatom doped porous carbon materials have great application prospects in supercapacitors. In the present study, an approach of preparing N-doped porous carbon (NPC) was proposed from porous poly(resorcinol-formaldehyde-melamine) monoliths which were prepared by high internal phase emulsion (HIPE) template. Melamine was dissolved in the external phase and copolymerized, acting as the N source and porous structure regulator to provide micropore-dominant NPCs. The structure, morphology, specific surface area (SSA), and chemical composition of the samples were systematically studied. With melamine content increasing, N-doping content in NPC increased while the SSA of NPC increased at first and then decreased. When the content of N is 8.42 ​wt%, the obtained NPC showed the highest SSA of about 1670 ​m2 ​g−1. Furthermore, high N doping content could improve the electronic conductivity and provide additional pseudocapacitance of NPC. Under the combined influences of proper N content and high porosity, the prepared NPC electrodes revealed excellent specific capacitance (228.0 ​F ​g−1 at 1.0 ​A ​g−1), favorable circling stability, and prominent rate capability in a three-electrode system with 6 ​M KOH solution as the electrolyte.

Surface-initiated ARGET ATRP of poly(glycidyl methacrylate) from macroporous hydrogels via oil-in-water high internal phase emulsion templates for specific capture of Enterovirus 71

Surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) was applied to graft poly(glycidyl methacrylate) (PGMA) brushes from macroporous hydrogel templating from oil-in-water high internal phase emulsion (O/W HIPE), and the grafted hydrogel was further heparinized as stationary phase of affinity chromatography for Enterovirus 71 (EV71) purification. Acrylate functional monomer containing isobutyl bromide (HEMA-BiBB) was synthesized and introduced into oil phase for macroporous hydrogel with ATRP initiator-anchored surface. With the increase of HEMA-BIBB dosage, the average pore size of hydrogel increased and the specific surface area decreased. Bromine atomic percent of hydrogel reached the maximum of 1.56 % when the HEMA-BiBB dosage was 1.0 g. The corresponding heparinized hydrogel possessed the highest amount of carboxyl group (56.8 μmol per column). Interconnected macropore (1.71 μm) and high porosity (84.2 %) of heparinized hydrogel ensured an excellent permeability (2.1 × 10−13 m2). Meanwhile, grafted PGMA brushes afforded abundant epoxy groups for immobilizing high density of heparin, which endowed hydrogel with outstanding adsorption capability for EV71. Immobilized heparin ligands were competent in specific capture of EV71 by receptor-ligand interaction. Besides, enhanced hydrophilicity of heparinized hydrogel avoided the irreversible and nonspecific adsorption of proteins. As a result, heparinized hydrogel demonstrated superior adsorption selectivity and capability for EV71 (dynamic adsorption capacity: 1275 ng per column, recovery: 86.2 %). The developed heparinized PGMA-grafted macroporous hydrogel was promising to be applied in the large-scale production of EV71 for vaccine industry.

Biomass‐Derived Acetylenic Polymer Monoliths Prepared by High Internal Phase Emulsion Template Method and Used for Adsorbing Cationic Pollutants

AbstractA new type of biobased porous polymer monolith is prepared starting from biomass, ferulic acid (FA), via high internal phase emulsion (HIPE) template polymerization method. FA is transferred into an acetylenic monomer, which undergoes catalytic HIPE polymerization, eventually forming a porous monolith named as PolyHIPE. The phenolic hydroxyl groups in the monolith are functionalized with sodium hydroxide, forming PolyHIPE‐Na+ and meanwhile transforming the initial hydrophobic monolith into a hydrophilic one. The formation and structure of the monoliths are characterized with Fourier transform infrared (FT‐IR), NMR, and scanning electron microscope (SEM) techniques. The adsorption capacity of the monoliths is further investigated. PolyHIPE‐Na+ exhibits high adsorption capacity toward methylene blue (MB) and cetyltrimethylammonium bromide (CTAB) from simulated wastewater. The adsorption behavior of PolyHIPE‐Na+ is found to fit the pseudo second order kinetic model better. The adsorption isotherm can be well described by the Langmuir isotherm model. The maximum adsorption capacity for MB and CTAB are 1016 and 1390 mg g−1, respectively. The biobased FA derived monolithic adsorbent also shows desirable recycling usability and stability in adsorption−desorption cycles.

Polydimethylsiloxane nanocomposite macroporous films prepared via Pickering high internal phase emulsions as effective dielectrics for enhancing the performance of triboelectric nanogenerators.

Polydimethylsiloxane (PDMS) nanocomposite (NC) macroporous films were prepared by a Pickering high internal phase emulsion (HIPE) templating technique and used as effective dielectrics for enhancing the performance of triboelectric-nanogenerators (TENGs). HIPEs were formulated using commercial PDMS and water as the continuous and dispersed phase, respectively. The formation and solidification of PDMS-based HIPEs were possible through stabilization with silver-nanoparticles (Ag-Nps) and surfactant (Span 20) mixtures. The resulting PDMS-NC-polyHIPE films presented an interconnected 3D macroporous structure with Ag-Nps on their porous surface. The addition of different amounts of Ag-Nps (0, 4, 20, 28, 36 wt%) in HIPE formulations allowed modification of the pore size, total pore volume and dielectric properties of the tribo-materials. Results revealed that both the porosity and dielectric properties of these materials play an important role in enhancing the output performance of TENGs. Thus, the best TENG based on the PDMS-NC-polyHIPE film was achieved with 20 wt% of Ag-Nps, with voltage, current and power values of 4.88 V, 0.433 μA and 2.1 μW, respectively, which gives over 3.28-fold power enhancement compared with the reference TENG (based on a PDMS film without porosity or Ag-Nps). Therefore, the preparation of tribo-materials through a Pickering HIPE templating technique provides a novel, effective and easy way for the improvement of the TENG's performance.

Porous scaffolds with the structure of an interpenetrating polymer network made by gelatin methacrylated nanoparticle-stabilized high internal phase emulsion polymerization targeted for tissue engineering.

The interlacing of biopolymers and synthetic polymers is a promising strategy to fabricate hydrogel-based tissue scaffolds to biomimic a natural extracellular matrix for cell growth. Herein, open-cellular macroporous 3D scaffolds with a semi-interpenetrating network were fabricated through high internal phase emulsion templating. The scaffolds are prepared by (I) the curing of PEG diacrylate (PEGDAC) and gelatin methacrylate (GelMA) in the continuous aquatic phase of a coconut oil-in-water emulsion stabilized by GelMA nanoparticles, and (II) the removal of the internal phase. The effect of the main contributing parameters such as pH, GelMA content, and GelMA/PEGDAC weight ratio on the emulsion features was investigated systematically. Due to the isoelectric point of GelMA at around pH 6, the GelMA particle (aggregation) size decreased at both sides of pH from 1000 to 100–140 nm because of the increased number of positive and negative charges on GelMA. These GelMA nanoparticles were able to produce stable emulsions with narrowly distributed small emulsion droplets. Moreover, the stability and emulsion droplet size were enhanced and increased, respectively, with GelMA content increasing and GelMA/PEGDAC weight ratio decreasing. These trends lie in the prevented coalescence phenomenon caused by the improved viscosity and likely partially formed network by GelMA chains in the continuous phase. Hence, the following formulation was selected for scaffold preparation: φoil = 74%, pH = 12, GeMA = 4 wt%, and GelMA/PEGDAC = 10/8. Then, PCL in different contents was infiltrated into the scaffold to balance hydrophilicity and hydrophobicity. The cell culture assay proved that the scaffold with a pore size of 60–180 μm and containing 51.2 wt% GelMA, 10.3 wt% PEG, and PCL 27.2 wt% provided a suitable microenvironment for mouse fibroblast cell (L929) adhesion, growth, and spreading. These results show that this strategy suggests promising culture for tissue engineering applications.

Porous PS- and PMMA-based polymeric monoliths prepared by PEO-PS block copolymers stabilized High internal phase emulsion templates

In this contribution, two well-defined amphiphilic block copolymers, i.e., polystyrene-b-poly(ethylene oxide)-b-polystyrene (PS-b-PEO-b-PS) and poly(ethylene oxide)-b-polystyrene (PEO-b-PS) were synthesized through activators regenerated by electron transfer atom transfer radical polymerization. The as-prepared block copolymers with similar molar mass successfully served as stabilizer for preparing both styrene (St) and methyl methacrylate (MMA) containing HIPEs. The properties of HIPE and the effects of processing conditions (e.g., type and concentration of stabilizer, shearing rate, and aqueous phase volume) on the morphology of the resulting polyHIPEs were investigated by the rheology and scanning electron microscopy analysis. The results show that the block copolymer stabilized HIPEs and the corresponding polyHIPEs possess higher strength compared with the samples stabilized by span80. In addition, PS-based polyHIPEs from the block copolymer stabilized emulsion have an almost closed-cell structure, while PMMA-based polyHIPEs have an open-cell structure. Moreover, it is proven that the concentration of stabilizer plays a critical role in preparing PMMA-based polyHIPEs with high-porosity. It is believed that other functional polymeric porous monoliths can be readily prepared through HIPE templating by using the commonly known PEO-PS block copolymers without the sophisticated surfactant design.

Hierarchically porous poly(glycidyl methacrylate) through hard sphere and high internal phase emulsion templating

A combination of high internal phase emulsion and hard sphere templating approach was applied to prepare poly (glycidyl methacrylate-co-ethylene glycol dimethacrylate) with connected porous morphology on multiple levels. Hierarchical porous structure is evident with hard template derived pores with average diameters approx. 85 μm, skeletal emulsion templated pores with average diameter approx. 3 μm and with a third level of interconnecting pores. Monoliths of polymer with hierarchical porous structure were reacted with tris(2-aminoethyl)amine to yield amino derivatives with high loadings of amino groups (8.2 mmol of amino groups per gram). Despite mild reaction conditions efficient functionalization was achieved suggesting interconnected porous structure facilitated mass transfer to and from the interior of the monoliths.

Hydrolytic Degradation of Porous Crosslinked Poly(ε-Caprolactone) Synthesized by High Internal Phase Emulsion Templating.

Porous poly(ε-caprolactone) (PCL) scaffolds were fabricated using the high internal polymerization emulsion (HIPE) technique. Bis(ε-caprolactone-4-yl) (BCY) was utilized as crosslinker. The crosslinking density and the volume fraction of the dispersed phase were varied in order to study the potential effect of these parameters on the hydrolytic degradation at 37 °C and 60 °C. After different hydrolysis times the remaining solid samples were analyzed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), while the degradation products in the aqueous aging solutions were analyzed by laser desorption ionization-mass spectrometry (LDI-MS). The effect of temperature on the degradation process and release of degradation products was, as expected, significant. The temperature effect was also shown by FTIR analysis that displayed a pronounced increase in the intensity of the hydroxyl-group absorption band after 70 days of hydrolysis at 60 °C indicating significant cleavage of the polymer chains. LDI-MS analysis proved the release of oligomers ranging from dimers to hexamers. The product patterns were similar, but the relative m/z signal intensities increased with increasing time, temperature and crosslinking density, indicating larger amounts of released products. The latter is probably due to the decreasing degree of crystallinity as a function of amount of crosslinker. The porous structure and morphology of the scaffolds were lost during the aging. The higher the crosslinking density, the longer the scaffolds retained their original porous structure and morphology.