Internal Phase Emulsion Templating Research Articles

Combined Porogen Leaching and Emulsion Templating to produce Bone Tissue Engineering Scaffolds.

Bone has a hierarchy of porosity that is often overlooked when creating tissue engineering scaffolds where pore sizes are typically confined to a single order of magnitude. High internal phase emulsion (HIPE) templating produces polymerized HIPEs (polyHIPEs): highly interconnected porous polymers which have two length scales of porosity covering the 1–100 μm range. However, additional larger scales of porosity cannot be introduced in the standard emulsion formulation. Researchers have previously overcome this by additively manufacturing emulsions; fabricating highly microporous struts into complex macroporous geometries. This is time consuming and expensive; therefore, here we assessed the feasibility of combining porogen leaching with emulsion templating to introduce additional macroporosity. Alginate beads between 275 and 780 μm were incorporated into the emulsion at 0, 50, and 100 wt%. Once polymerized, alginate was dissolved leaving highly porous polyHIPE scaffolds with added macroporosity. The compressive modulus of the scaffolds decreased as alginate porogen content increased. Cellular performance was assessed using MLO-A5 post-osteoblasts. Seeding efficiency was significantly higher and mineralized matrix deposition was more uniformly deposited throughout porogen leached scaffolds compared to plain polyHIPEs. Deep cell infiltration only occurred in porogen leached scaffolds as detected by histology and lightsheet microscopy. This study reveals a quick, low cost and simple method of producing multiscale porosity scaffolds for tissue engineering.

One-pot synthesis of polymer-reinforced silica aerogels from high internal phase emulsion templates

HypothesisConventional strategies for strengthening silica aerogels through polymer modification always lead to a significant density increase and an obvious sacrifice of thermal insulation performance. In this work, we propose a facile one-pot method for the preparation of polymer-reinforced silica aerogels via polymerization of water-in-oil high internal phase emulsion (HIPE) templates. ExperimentsHyperbranched vinyl-modified polyethoxysiloxane (VPEOS) is used as both emulsion stabilizer and silica source. FT-IR spectra of VPEOS are recorded to confirm the successful incorporation of vinyl groups. The pore structure of polymer-functionalized silica aerogels is characterized by a scanning electron microscope (SEM), nitrogen adsorption–desorption and mercury intrusion porosimetry. FindingsThe Young’s modulus is increased from 0.69 to 19.28 MPa, nearly 28 times that of unmodified silica aerogels. Moreover, the silica aerogels present a superhydrophobicity with a water contact angle of 152.4° and good thermal insulation. The superior performance properties of the polymer-reinforced silica aerogels over pure silica aerogels may guarantee their wide applications in energy and aerospace fields.

C/W emulsion‐templated macroporous anionic monolith: Application for dye removal

AbstractA clean, sulfonated, highly adsorptive macroporous monolith was constructed using a carbon dioxide‐in‐water (C/W) high internal phase emulsion template. The random copolymerization of N‐hydroxyethyl acrylamide and sodium styrene sulfonate in the water phase was initiated with persulfate. The chemical composition of the novel sulfonated monolith was confirmed by Fourier transform infrared spectroscopy and energy‐dispersive X‐ray spectroscopy, and the interconnected pore structure was confirmed by scanning electron microscopy (SEM). Results showed that the void sizes were 47–92 μm and that the interconnected pore throats were approximately 10–30 μm. Such a hydrophilic, anionic macroporous material exhibited excellent adsorption properties for cationic dyes. The maximum adsorption capacity of the monolith for methylene blue (MB) and malachite green (MG) reached 1,316 and 2,624 mg/g, respectively, in 500–800 mg/L dye solution at 25°C. Furthermore, the kinetics and thermodynamic parameters of the adsorption process were examined. Experimental data exhibited that adsorption kinetically followed the pseudo‐second‐order model. The removal rates of MG and MB both exceeded 90% after six regenerations. The adsorption mechanism of the adsorbent was demonstrated preliminarily. The dynamic adsorption operation of MB was conducted in a fixed column, and the breakthrough curve data were fitted using the Thomas and bed depth service time models. All these findings indicated the potential industrial applications of adsorptive sulfonated macroporous monolith.

A Convenient and Versatile Strategy for the Functionalization of Silica Foams Using High Internal Phase Emulsion Templates as Microreactors.

Functional porous materials show extensive applications in the environment, biology, aerospace, and so on. In this work, the generation of silica foams and functionalization of pore surface were simultaneously realized through an interfacial sol-gel reaction within high internal phase emulsion (HIPE) microreactors, where a hyperbranched polyethoxysiloxane (PEOS) was used as the sole stabilizer for the HIPEs. With various functional substances containing amino, epoxy, and carboxyl groups initially dissolved in the aqueous phase of HIPEs, these functional groups could be grafted onto the pore surface in the process of forming silica foams. Amino-functionalized silica foam showed fast adsorption of sunset yellow, and the adsorption capacity could reach as high as 1213.13 mg/g. Sodium polyacrylate-modified silica foam exhibited good adsorption capacity of cationic dyes and metal ions, e.g., 280.11 mg/g to methylene and 226.24 mg/g to Cu(II). Epoxy-functionalized silica foam particles were confirmed with a pronounced activity at the oil/water interface due to their Janus-like surface, which could be used as Pickering stabilizer. This HIPE-based synthesis strategy for silica foams shows promising future in adsorption, emulsion stabilization, and compatibilization.

Tuning the pore architectures of hierarchically porous carbons from high internal phase emulsion template by polyaniline-coated CNTs

The work reported the preparation of hierarchically porous carbons (HPCs) with adjustable pore architectures using high internal phase emulsion (HIPE) template with the presence of polyaniline-coated carbon nanotubes (PANI-CNTs). PANI-CNTs were obtained via in situ polymerization of aniline in CNT suspension as confirmed by scanning electron microscope (SEM) and thermogravimetric analysis (TGA). Porous polydivinylbenzene (PDVB) monoliths were prepared by polymerizing the continuous phase of HIPE with PANI-CNTs dispersed in the internal phase. After carbonization and activation, HPCs with variable pore architectures were obtained. As observed by SEM, the PANI-CNTs showed notable influence on the pore architectures of PDVBs and HPCs. The void size of PDVB precursor reduced with the increase of the mass ratio of PANI to CNT, as well as the content of PANI-CNTs. Nitrogen adsorption/desorption measurements indicated the coexistence of mesopores and micropores, namely, hierarchical pores. The specific surface area (SSA) of HPC increased along with the content of PANI-CNTs from 1893 to 2392 m2/g. The capability of HPCs as the electrode material of supercapacitor was evaluated via electrochemical tests. The results indicated that the HPC with optimized pore architecture showed a higher specific capacitance (168.6 F/g) than the contrast sample (130.9 F/g) at 1 A/g. The better capacitance performance of HPC obtained with the presence of PANI-CNTs could be attributed to the reasonable hierarchical pores, higher SSA, and higher graphitization degree.

Engineering bicontinuous polymeric monoliths through high internal phase emulsion templating

Preparation of two-component materials having morphologies with bicontinuous minor and major components is challenging. An innovative method has been developed to synthesize bicontinuous polymeric monoliths based on high internal phase emulsion (HIPE) templating. This work demonstrated a protocol of dual-hydrophobic bicontinuous material of glassy polystyrene (PS) and elastic poly(butyl acrylate) (PBA). The PS scaffold was prepared through polymerizing styrene (St) as the external phase of HIPE with an aqueous free radical initiator, in the presence of divinylbenzene (DVB) as a crosslinker. The resulting PS scaffolds were then employed as templates to absorb butyl acrylate (BA) mixed with ethylene glycol dimethylacrylate (EGDMA). Results suggested that the polymeric monoliths possessed a bicontinuous structure and good compatibility in the bulk state. This work provides a new approach for the synthesis of bicontinuous two-component materials.

One-pot synthesis of bimodal (macro-meso, micro-mesoporous) silica by polyHIPE: parameter studies

Porous silica with hierarchical organization of pore structure is desired for a variety of applications such as, chromatography, sensing, control release, scaffold for biomedical applications and catalysis. Highly porous polymers obtained from high internal phase emulsion (HIPE) templating route have attracted increasing attention of researchers due to their hierarchical porous and interconnected structure with high porosity and low density. The novel method adopted in our approach combines redox initiated polymerization using HIPE polymerization and an in-situ sol–gel processing technique followed by calcination to obtain highly porous materials. The obtained materials have reminiscent of polyHIPE morphology containing pores and interconnected pore throats in micrometer size range with mesopores on the wall of macropores. The effect of concentration of TEOS, volume of dispersed phase, crosslinker concentration, shear rate and surfactant concentration as well as variation in calcination temperatures on the properties of silica materials were examined.

Polylactide-Based Chiral Porous Monolithic Materials Prepared Using the High Internal Phase Emulsion Template Method for Enantioselective Release.

Polylactide [PLA, two enantiomers: poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA)] has been widely applied as biomaterials because of its biocompatibility, biodegradability, and good mechanical capacity. However, the chirality of PLA materials has not been intensively explored yet. In the present study, chiral porous poly(high internal-phase emulsion)s (polyHIPEs) derived from enantiopure PLAs were successfully prepared via a HIPE template method. The resulting polyHIPEs show optical activity. More interestingly, the polyHIPEs demonstrate enantioselective release capacity, using cinchona alkaloid and naproxen as the model chiral drugs. Notably, PLLA-based polyHIPE shows enantioselectivity in both the drug-loading step and drug-releasing step, while PDLA-based polyHIPE fails. The interesting finding is essentially different from other chiral polymer materials reported earlier. The cytotoxicity test demonstrates that all the three types of polyHIPEs, PLLA-, PDLA-, and PDLLA-based polyHIPE show biocompatibility; however, their different chirality exerts varying effects on cell growth. Accordingly, special attention should be devoted to the chirality of PLA when used as biomaterials.

Efficient preparation of macroporous poly(methyl methacrylate) materials from high internal phase emulsion templates

Thermo- and photo-initiated polymerization of emulsion templates for making macroporous poly(methyl methacrylate) materials both suffer from low energy efficiency and require tedious sample preparation (removal of inhibitors, inert atmosphere) or specialized equipment to be used. Here, an easy and efficient method for the preparation of such open pore materials with up to 93% porosity is demonstrated by using redox-initiated polymerization in the oil phase of high internal phase emulsion templates. The method eliminates the need of heating/irradiation and monomer purification, thus reducing the preparation costs without sacrificing the mechanical properties of the porous materials. It also allows of two component HIPE curing systems to be made, stored and used in the field for a rapid preparation of open pore monoliths in spaces with complex geometry. This is demonstrated by the in situ preparation of a filter and a static mixer for foam generation. The proposed method has a considerable potential for further practical exploitation in filtration, separation, microfluidics, chromatography and other fields where porous materials are used.

PDMS-Infused Poly(High Internal Phase Emulsion) Templates for the Construction of Slippery Liquid-Infused Porous Surfaces with Self-cleaning and Self-repairing Properties.

Advanced liquid-repelling materials that resist both water-based and oil-based contaminants have significant applications in many fields. Herein, a novel protocol for the fabrication of a robust poly(high internal phase emulsion) (polyHIPE)-based slippery liquid-infused porous surface (SLIPS) system with combined self-repairing and self-cleaning properties is developed. Specifically, polystyrene-based polyHIPE (PS-HIPE) membranes with an interconnected porous structure were prepared from polymerization of the continuous oil phase in the water-in-oil HIPE templates. These polyHIPE membranes were used, for the first time, as porous substrates for loading low surface tension silicone oils as lubricating liquids for the fabrication of polyHIPE-based SLIPS membranes. These polyHIPE-based SLIPS membranes could easily repel both water- and oil-based contaminants (e.g., ink, milk, and coffee) with very low sliding angles (3.0 ? 1.3?) and could even repel solid contaminants (e.g., dust) upon washing with water. Meanwhile, such membranes exhibit excellent self-repairing properties so that physical scratching damage, such as cutting a trench, does not affect the liquid-repelling performance. The liquid-repelling ability could be recovered completely within 10 s. More significantly, such a SLIPS membrane shows excellent durability so that the water sliding angle of the SLIPS could be maintained at less than 5.0? for about 80 cycles owing to the regenerated poly(dimethylsiloxane) layer on the surface. This work represents a robust methodology to enrich the development of hydrophobic and oleophobic slippery surfaces, which is promising for many areas, such as biomedical, self-cleaning, antifouling, and self-repairing materials.

Macroporous scaffolds of cross-linked Poly(ɛ-caprolactone) via high internal phase emulsion templating

A high internal phase emulsion based ring-opening polymerization (HIPE-ROP) of ɛ-caprolactone (CL) was conducted to fabricate macroporous scaffold in a single-step. An oil-in-oil HIPE of CL was formed using high molecular weight olefin (C10-C16) dispersed in continuous medium comprised of CL, a bifunctional cross-linking monomer bis-ɛ-caprolactone-4-yl (BCY) and catalyst stannous octoate (Sn(Oct)2). The emulsion was stabilized using nonionic surfactant, pluronic F127 and polymerization was conducted at 120 °C without any inert atmosphere for a period of 8 h. Complete monomer conversion and cross-linking was achieved and am acroporous scaffold of desired shape was obtained, having in-situ generated porosity and interconnected pores. All chemicals were purposely used without any purification and the high temperature process prevented deactivation of catalyst. The HIPE-ROP developed in this way was found to be highly feasible for conducting otherwise moisture sensitive organo-metallic catalyst based ROP. The morphology of HIPE was directly transferred to macroporous structure of the scaffold in this process where pore size was reproducibly controlled by variation in volume fraction of dispersed phase and cross-link density. The resultant macroporous scaffold showed superior compressive loading and swelling capacity. The porous scaffolds also exhibited excellent osteoblast (MG63) attachment and proliferation. HIPE-ROP based macroporous scaffold of cross-linked PCL thus developed paved a new route to create porous scaffolds of aliphatic polyesters in a single step. The method also reflected high commercial viability by potential conversion into a continuous process.

Synthesis and in situ functionalization of microfiltration membranes via high internal phase emulsion templating

AbstractThe continuous phase of high internal phase emulsions (HIPEs) can be polymerized to produce highly porous materials, known as polyHIPEs. The aim of this work was to synthesize polyHIPE microfiltration membranes having a hydrophobic bulk and a hydrophilic surface to enhance their performance. Therefore, in situ functionalization was performed through interfacial copolymerization of a hydrophobic monomer (butyl acrylate) in the continuous phase with a hydrophilic monomer (sodium acrylate) in the disperse phase. The functionalization of polyHIPEs was studied by using conductometric titration and Fourier transform IR spectroscopy. We show that the surface charge density of poly(butyl acrylate)‐based polyHIPEs can be controlled by varying the concentration of sodium acrylate in the disperse phase. PolyHIPE microfiltration membranes have higher intrinsic permeability (around 1.31 × 10−8 m2) in comparison to conventional microfiltration membranes. The interfacial copolymerization of sodium acrylate increases the permeability of microfiltration membranes. In addition, the rejection of polyHIPE microfiltration membranes was studied for the separation of microalgae. © 2019 Society of Chemical Industry

Macroporous titania monoliths from emulsion templated composites

High internal phase emulsion (HIPE) templating approach, well known for the preparation of macroporous polymeric monoliths (polyHIPEs), was utilized for the synthesis of macroporous cellular interconnected titania ceramic monoliths. In order to derive the ceramic monolithic material from the precursor polymer, titania particles were introduced into the monomer containing emulsion phase. The morphology of the final ceramic monolith closely resembled the precursor polymer composite, featuring a 3D interconnected cellular structure with the first level of pores with an average diameter of 70–100 μm and channels connecting the first level of pores. Multifunctional acrylate monomer was used in a combination with photopolymerization for the preparation of composite polyacrylate/titania monolith. The ratio of particles to monomer and the temperature profile of sintering were the most important factors affecting the morphology of the final material. A significant increase in the modulus of the sintered material compared to the porous composite precursors was found.

Facile preparation of bioactive nanoparticle/poly(ε-caprolactone) hierarchical porous scaffolds via 3D printing of high internal phase Pickering emulsions

Bioactive and biocompatible scaffolds possessing hierarchical porous structures and tunable multi-functional performance have attracted increasing interest in the biomedical field, especially in bone tissue engineering. In this work, we report a convenient and effective approach to construct bioactive nanoparticle/poly(ε-caprolactone) (BNPCL) scaffolds with hierarchical porous structures based on solvent evaporation of 3D printed water-in-oil high internal phase emulsion (HIPE) templates, containing hydrophobically modified hydroxyapatite and silica nanoparticles in the oil phase. The hierarchical porous structures consist of mm-scale macropores formed by 3D printing and μm-scale micropores from HIPE templates. The micropore structures and mechanical properties of BNPCL scaffolds are easily tailored by varying the preparation conditions of the HIPE templates. An in vitro biomineralization study shows that BNPCL scaffolds possess excellent bioactivity because of effective formation of apatite particles on them. Moreover, the in vitro drug release studies using ibuprofen display the potential of BNPCL scaffolds as drug carriers. Furthermore, cell culture assays prove that BNPCL scaffolds have good cytocompatibility to effectively support cell adhesion, growth and proliferation. All the results imply that combining solvent evaporation with 3D printing of HIPE templates is a promising alternative approach to fabricate hierarchical porous scaffolds for bone tissue engineering applications.

Macrocellular Titanosilicate Monoliths as Highly Efficient Structured Olefin Epoxidation Catalysts

AbstractSelf‐standing macrocellular titanosilicate monolith foams are obtained using a one‐pot sol‐gel route and show excellent performance in the epoxidation of cyclohexene. Thanks to the High Internal Phase Emulsion (HIPE) templating method, the materials feature a high void fraction, a hierarchically porous texture and good mechanical strength. Highly dispersed Ti species can be incorporated in tetrahedral coordination in the silica matrix. These characteristics allow the obtained ‘SiTi(HIPE)’ materials to reach high catalytic turnover in the epoxidation of cyclohexene. The monoliths can advantageously be used to run the reaction in continuous flow mode.

Polyethylenimine-Grafted HKUST-Type MOF/PolyHIPE Porous Composites (PEI@PGD-H) as Highly Efficient CO2 Adsorbents

Searching for highly efficient and robust CO2 adsorbents is very important for CO2 capture, utilization, and storage. In this study, new polyethylenimine-grafted metal–organic framework (MOF)–polymer composites, abbreviated as PEI@PGD-H, were synthesized via high internal phase emulsion (HIPE) template polymerization of divinylbenzene and glycidyl methacrylate, followed by in situ generation of HKUST-type MOF in the presence of hydrophobic-modified CuO nanoparticles via the reaction of CuO with 1,3,5-benzenetricarboxylic acid and then polyethylenimine (PEI) functionalization via epoxy–amine reaction and amine–metal sites interaction. The coexistence of the hierarchical interconnected porous skeleton of poly(glycidyl methacrylate–divinylbenzene) (PGD), high specific surface area of MOF, and chemical CO2 adsorption of PEI endows PEI@PGD-H with high CO2 adsorption capacity, rate, and selectivity. PEI70@PGD-H shows a CO2/N2 separation factor as high as 76 and CO2 adsorption capacities of 4.3, 3.0, and 1.8 mmo...

Characterization of Orange Oil Powders and Oleogels Fabricated from Emulsion Templates Stabilized Solely by a Natural Triterpene Saponin.

A new facile route was reported to use the natural triterpene Quillaja saponin (QS)-stabilized orange emulsions as a template for the development of flavor oil powders and oleogels achieved by the tunable oil fraction and drying mode. A fibrosis network interfacial film from self-assembly of QS at the oil-water interface possibility contributed to the fabrication of stable emulsion precursors and subsequent oil powder and oleogels by packing oil droplets in the network structure. An oil powder containing as high as 93 wt % orange oil was obtained by spray drying, showing excellent stability, flowability, and reconstitution ability. Upon the medium water removal rate of freeze drying, porous structured solid products followed by oleogels by a simple shearing can be formed. Upon oven drying, a translucent oleogel with high oil loading of 98.2 wt % was obtained from the high internal phase emulsion template. The resulting oleogels showed tunable rheological and texture properties, thixotropic recovery by modulating the oil fraction and water evaporation rate, and reversibility to reconstituted emulsions. Structuring liquid oil into solid materials by simply drying the continuous water from solely QS-based emulsions is very encouraging and provides new insights into various functional applications in the fields of foods, pharmaceuticals, cosmetics, and agriculture.

Fabrication of micro-mesopores in macroporous poly (formaldehyde-melamine) monoliths via reaction-induced phase separation in high internal phase emulsion template

A one-step strategy of preparing hierarchical porous poly (formaldehyde-melamine) monoliths (PFM) with high specific surface area was proposed. Based on the high internal phase emulsion (HIPE) template, the removal of dispersed phase (liquid paraffins) and the reaction-induced phase separation in continuous phase (the solution of parafomaldehyde and melamine) could generate the macropores, mesopores and micropores in PFM simultaneously. As a result, the highest specific surface areas of the prepared PFM could reach 210 m2/g, which was obviously higher than that of traditional polyHIPE. The effect of the constitution of the continuous phase of HIPE on the macroporous morphologies, specific surface areas, and micropore volume of PFM were investigated in detail. Moreover, the formation mechanism of micropores and mesopores by reaction-induced phase separation was proposed. Finally, the obtained PFM was applied as CO2 absorbent and the adsorption properties were studied.

Superhydrophobic foam prepared from high internal phase emulsion templates stabilised by oyster shell powder for oil-water separation.

In this paper, poly(styrene-divinylbenzene) foams were synthesized using a high internal phase emulsion (HIPE) technique with Span 80 and with 900 °C calcined oyster shell powder as a co-emulsifier, 2,2′-azobisisobutyronitrile (AIBN) as an initiator and deionized water as the dispersing phase. SEM images revealed that the materials possess a hierarchical porous structure of nano/micro size, which resulted in saturated oil adsorption in only half a minute. The dispersing phase amount was investigated for its effect on adsorption. The optimized foams have 24.8–58.3 g g−1 adsorbencies for several organic solvents, and they demonstrated superhydrophobicity and excellent oleophilicity with the water contact angle (WCA) even close to 149° and oil contact angle approaching 0°. Moreover, the foams displayed high oil retention under pressure. The adsorption–centrifugation cycling results indicated high repeatability of the recovered foams. All of these features predicted the potential applications of superhydrophobic foams in oil–water separation.

A facile fabrication of porous fluoro-polymer with excellent mechanical properties based on high internal phase emulsion templating using PLA as co-stabilizer.

The stability of fluoro-high internal phase emulsion (fluoro-HIPE) systems and fluoro-polyHIPEs’ mechanical strength require further improvement to meet the requirements of future applications. In this study, we used polylactic acid (PLA) as a co-stabilizer to improve the stability of the fluoro-polyHIPE. The effects of concentration and molecular weight of PLA on the pores of the fluoro-polyHIPEs were investigated. The addition of PLA produced a porous material with narrower void size distributions, higher specific surface areas and enhanced mechanical properties compared to the fluoro-polyHIPE material without the additive. The resulting fluoro-polyHIPE showed smaller pore sizes (void diameters ranged from 1–3 μm) and an improved hydrophobic nature (contact angle can reach to 148.6°). The crush strength and Young's modulus values can reach 4.42 and 74.07 MPa, respectively, at a PLA addition of 25 wt% (oil phase composition), representing increases of 246% and 650% over fluoro-polyHIPE without PLA addition. The fluoro-poly-HIPE demonstrated excellent mechanical properties compared to many engineering foams, such as melamine, polystyrene, and even graphite foams. Improvements in the performance of porous fluoropolymer materials will be beneficial for many applications, such as chemical adsorption and separation, etc.