Tailoring mechanical properties of highly porous polymer foams: Silica particle reinforced polymer foams via emulsion templating

The aim of this work was to synthesise highly open porous low-density polymer foams with superior mechanical properties by the polymerisation of the organic phase of concentrated emulsions. The continuous organic phase of the concentrated emulsion template occupying up to 40 vol% was polymerised leading to polymer foams with much improved mechanical properties. The Young's modulus as well as the crush strength of the foams was further increased dramatically by reinforcing the polymer phase with nanosized silica particles. To ensure that the silica particles were covalently incorporated into the polymer network, methacryloxypropyltrimethoxysilane (MPS) was added to the formulation, which reacts with the silica via hydrolysis reactions. The Young's modulus of silica reinforced foams increased by 280% and the crush strength by 218% in comparison to foams without reinforcement.     

Ceramic foams and micro-beads from emulsions of a preceramic polymer

A commercially available solid silicone resin was dissolved in a solvent and emulsified via stirring in the presence of water and surfactant to form three different types of emulsions, namely water-in-oil (w/o), water-in-oil-in-water (w/o/w) and oil-in-water (o/w), by following different preparation procedures. After curing, thermosets possessing different morphologies, ranging from highly porous (monolithic) foams to porous micro-beads and solid micro-beads, formed. The samples kept their shape upon pyrolysis, and resulted in ceramic foams (via w/o) and porous micron sized (∼200 μm) spherical particles (via w/o/w) having more than 80 vol% of total porosity, while with o/w emulsification solid SiOC ceramic particles with an average diameter of ∼100 μm formed. Both surfactant and water altered the IR spectra for emulsion-derived thermoset samples, in comparison to the pure cured resin, but upon pyrolysis similar amorphous ceramics were obtained from all samples.     

Emulsion-templated porous polymers: A retrospective perspective

PolyHIPEs are porous emulsion-templated polymers synthesized within high internal phase emulsions (HIPEs). HIPEs are highly viscous, paste-like emulsions in which the major, “internal” phase, usually defined as constituting more than 74% of the volume, is dispersed as discrete droplets within the continuous, minor, “external” phase. The surge in polyHIPE research and development parallels that of porous polymers in general and reflects the increasing number of potential applications (reaction supports, separation membranes, tissue engineering scaffolds, controlled release matrices, responsive and smart materials, and templates for porous ceramics and porous carbons). This review focuses upon the research and development in polyHIPEs through the prism of the work in our laboratory. The review includes an overview of the developments in polymerization chemistry, in the types of monomers, in the types of stabilization, in the generation of more complex polyHIPE-based systems (e.g. interpenetrating polymer networks, hybrids, bicontinuous polymers), and in unusual materials systems such as water-retaining polyHIPEs and shape-memory polyHIPEs.     

碳泡沫的乳液法制备条件研究

采用轧液聚合的方法,以间苯二酚、甲醛的水溶液为水相,以液体石蜡为油相,经搅拌、固化、碳化等过程后得到破泡沫样品.其密度为(0.25～0.4)g/cm2,比表面积为(500～700)m2/g,该方法制备的碳泡沫,具有开孔结构,孔径分布比较均匀,且孔径大小可调节,制备条件对乳液体系的稳定性以及所得的碳泡沫样品结构形耽有较大的影响.     

Preparation of flexible polyhedral particles via concentrated emulsion templating polymerization

This paper presents recent efforts on the preparation of flexible polyhedral particles via concentrated emulsion templating polymerization in which the hydrophilic monomer (acrylamide) and hydrophobic monomer (butyl acrylate) are polymerized simultaneously in the continuous and dispersed phase, respectively. Such templating polymerization has been enhanced in our systems owing to the introduction of acrylamide monomer and their higher polymerization rate in continuous phase as compared with butyl acrylate in dispersed phase. Diffusion between the different phases was also inhibited. Furthermore, the stability of the concentrated emulsion and the molecular weight of the produced poly(butyl acrylate) were found to be significantly affected by the amount of redox initiator. The morphology of the particles could be controlled by varying the volume fraction of the dispersed phase and the polyhedral particles were achieved at higher volume fraction. Copyright © 2005 Society of Chemical Industry     

Controlled preparation of porous polysulfone monolith via concentrated emulsion templating using an aminated polysulfone as surfactant

A methodology for preparing porous polysulfone (PSF) monolith via concentrated emulsion templating was proposed. A regular emulsion was first prepared using a solution of PSF in chloroform as the continuous phase and deionized water as the dispersed one. After the emulsion was formed, the liquid species in the emulsion was allowed to be evaporated. The solvent chloroform was first removed and the emulsion was transformed to a concentrated emulsion. Further removing the aqueous species, a porous PSF monolith was obtained. To keep the system stable throughout the process, an aminated polysulfone rather than conventional surfactants was employed. The effects of chloroform and water fractions, the nature and loading of the macromolecular surfactant, the evaporating temperature on the pore structure were investigated. Controlled porous structure with different pore size and porosity could be obtained through the method. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.     

Preparation of highly open porous styrene/acrylonitrile and styrene/acrylonitrile/organoclay polymerized high internal phase emulsion (PolyHIPE) foams via emulsion templating

Highly open porous crosslinked styrene/ acrylonitrile (SAN) polymerized high internal phase emulsion (PolyHIPE) foams containing various amounts of acrylonitrile (AN) were prepared by the polymerization of the continuous organic phase of high internal phase emulsions with an 85 vol % aqueous internal phase. The mean diameter of voids varied in the range 12.4–19.8 μm. The void diameter increased up to 10% AN, but beyond this limit, the diameter decreased. To improve the mechanical properties of the copolymer foams, the organic phase of the emulsion containing 20% AN was reinforced with organomontmorillonites with different surface modifiers. The effects of the organoclay on the equilibrium torque value of the emulsifying systems, as an approximate characteristic of the emulsion viscosity, and on the morphology and mechanical properties of the resulting foam were investigated. Scanning electron micrographs exhibited an open‐cell polyHIPE structure for all of the SAN/organoclay polyHIPE foams. The incorporation of organoclays within the emulsion copolymer foam significantly decreased the mean size of voids and intercellular pores compared with those of the copolymer foam without reinforcement. In fact, the presence of organoclay may have acted as a cosurfactant to improve the performance of the nonionic surfactant in the concentrated emulsions. The X‐ray diffraction patterns and transmission electron micrographs showed an intercalated nanocomposite structure for the organoclay‐reinforced copolymer foams. On the other hand, the addition of a more hydrophilic organoclay, that is, 3 wt % Cloisite30B, to the concentrated emulsion decreased the Young's modulus and significantly improved the crush strength of the emulsion copolymer foam. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Semiinterpenetrating polymer network latexes via concentrated emulsion polymerization

Latexes of semiinterpenetrating polymer networks (SIPN) of polyurethane (PU) and poly(methyl methacrylate) (PMMA) were prepared via the concentrated emulsion polymerization. In this procedure, a partially cross-linked PU was first prepared in a low polarity solvent from the appropriate precursors. Subsequently, MMA and an initiator were introduced into the solution, and the solution was used as the dispersed phase of a concentrated emulsion in water. Finally, SIPN latexes were obtained via the polymerization of the concentrated emulsion. For comparison purposes, SIPN materials have been also prepared via bulk polymerization. The studies with differential scanning calorimetry and transmission electronic microscopy showed that partial interpenetration was achieved in the SIPN latexes. The tensile behavior and particle morphology of the SIPN materials were investigated by changing the proportion of PU, the molar ratio of NCO/OH, the theoretical cross-link density, and the concentration of the initiator. The SIPN latexes prepared possess a high toughness. © 1995 John Wiley & Sons, Inc.     

The potential of Kraft black liquor to produce bio-based emulsion-templated porous materials

Emulsion-templated porous monoliths based on castor oil-in-black liquor and on 1,2-dichloroethane-in-black liquor medium internal phase emulsions have been prepared in order to evaluate a possible valorisation of that undervalued by-product of the paper mill Kraft process. The cross-linking behaviour of the different polymers originally contained in the black liquor was investigated. It appears that both lignin and hemicellulose fragments are involved. Characterisation of the monoliths by scanning electronic microscopy and mercury intrusion porosimetry showed that using either castor oil or 1,2-dichloroethane allowed to obtain macrocellular morphology along with a high porosity. However, higher concentration of the internal phase is possible in emulsions prepared with 1,2-dichloroethane than with castor oil, leading to more attractive materials from both chemical and environmental aspects.     

One-step process to create porous structures in cross-linked polymer films via breath-figure formations during in situ cross-linking reactions

This work demonstrates a new strategy of producing honeycomb-like porous structures in cross-linked polymer films via a simple one-step synthesis/fabrication process. This is based on the “breath figure” formation during the in situ cross-linking of reactive monomer solutions. A chloroform solution, containing tert-butyl acrylate monomer and tetraethylene glycol dimethacrylate cross-linker, was cross-linked upon UV radiation under a moist and nitrogen saturated chamber. Micron-sized pores with reasonable uniformity were obtained in the cross-linked polymer films. The size, shape, uniformity and ordering of the pores show significant dependences on the processing conditions. Using this method, porous structures were also achieved in a commercially available photo-active resin, NOA 65, illustrating the generality of this approach.     

Formation of porous natural-synthetic polymer composites using emulsion templating and supercritical fluid assisted impregnation

Summary Porous natural-synthetic polymer composites were prepared using an alginate emulsion templating step followed by supercritical carbon dioxide (sc-CO₂) assisted impregnation (and subsequent polymerisation) of synthetic monomer mixtures. In the impregnation step, an initiator and either 2-hydroxyethylmethacrylate (HEMA), butylmethacrylate (BMA), ethyleneglycoldimethacrylate (EGDMA) or trimethylolpropanetrimethacrylate (TRIM) monomers, respectively, were used. After impregnation into the porous alginate foam, the synthetic monomer(s) were polymerised in situ, forming porous composites with increased stiffness. A number of methods were used to assess the effects of the impregnation/polymerisation process including uniaxial compression testing, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), helium pycnometry and Fourier transform infra-red (FTIR) spectroscopy. Our results suggest that alginate foams impregnated with HEMA show higher weight gains and are stiffer than those impregnated with BMA. Such stiffer porous composites are potentially better suited than the unmodified materials in applications such as tissue engineering (cell-seeded) scaffolds, where mechanical conditioning is desired to stimulate cells for development of neo tissue growth.     

Geopolymer assembly by emulsion templating: Emulsion stability and hardening mechanisms

This work investigates emulsion templating to synthesize hexadecane oil/geopolymer composites. In a system with hexadecane as the internal (dispersed) phase and an alkali activated continuous phase without added surfactant, adding aluminosilicate clay particles does not increase resistance against creaming or coalescence, while adding a surfactant (L35 or CTAB) stabilizes the solid-liquid interface. Infrared studies and rheological studies of the associated geopolymerization determined that the presence of the organic phase or surfactant has no significant effect on the geopolymerization kinetics, as determined by the change in time of the Si-O-T IR stretching frequency and the rheological moduli involved during the process. The stabilization of the organic template is reminiscent of Pickering emulsion even though we employ a much greater amount of inorganic material for geopolymer formation. Although the addition of surfactant has a significant effect on the behavior of the paste, the percolation of the network remains unmodified, highlighting the fact that the phenomenon is not dependent on viscosity. Finally, rheological measurements were used to obtain the mass fractal dimension of the as-made gel network, which is able to differentiate the interfacial effect between surfactant molecules with a slightly denser interphase when a cationic surfactant is used.     

Novel micro-spherical Si3N4 nanowire sponges from carbon-doped silica sol foams via reverse templating method

A novel kind of nanowire sponges, namely Si₃N₄ nanowire-weaving microspheres, synthesized from a simple, convenient, high-efficient approach are proposed here. As the reverse template, three-dimensional foam skeleton structure with uniform pores and ultrathin pore walls is constructed via the effective particle-stabilized foam method, where the silica sol and carbon black are chosen as the raw materials, providing the sufficient space for the growth of nanowires during the carbothermal reduction reaction process. The formation mechanism of this novel sponge is studied via multiple characterization methods. Si₃N₄ nanowires formed microspheres possess uniform and curving morphology due to the stable environment for growing via vapor–solid mechanism, leading to the relatively high specific surface area of 86.77 m²/g. Owing to in-situ oxidation process, micro-spherical SiO₂ nanowire sponges with similar morphology are synthesized, which present diameter in range of 20-40 nm and specific surface area of 50.47 m²/g. This work provides insights for the design of high-performance nanowire sponges with promising applications in the filtration, thermal insulators, and catalyst supports fields.     

Preparation of silica nanospheres and porous polymer membranes with controlled morphologies via nanophase separation

ABSTRACT: We successfully synthesized two different structures, silica nanospheres and porous polymer membranes, via nanophase separation between silica sol and polymer. Silica sol, which was in-situ polymerized from tetraorthosilicate, was used as a precursor. Subsequently, it was mixed with a polymer that was used as a matrix component. It was observed that nanophase separation occurred after the mixing of polymer with silica sol and subsequent evaporation of solvents, resulting in organizing various structures, from random network silica structures to silica spheres. In particular, silica nanospheres were produced by manipulating the mixing ratio of polymer to silica sol. The size of silica beads was gradually changed from micro- to nanoscale, depending on the polymer content. At the same time, porous polymer membranes were generated by removing the silica component with hydrofluoric acid. Furthermore, porous carbon membranes were produced by using carbon source polymer through the carbonization process.     

Ceramic microspheres with controlled porosity by emulsion-ice templating

Silicon Carbide porous microspheres were fabricated using a preceramic polymer by emulsion-ice templating. An oil-in-water macroemulsion was prepared by adding an organic solution, comprising polycarbosilane and cyclohexane, to the aqueous phase containing a nonionic surfactant. Upon directional freezing and freeze drying, microspheres with aligned pores were obtained. The influence of processing parameters was assessed. In particular, the solidification temperature affected size and morphology of the macroporosity. Our strategy enables an independent control of macro and nanoporosity. Indeed, the thermal treatment can be optimized to tune the micro-porosity at the nanoscale as well as the specific surface area of the samples.The emulsion-ice templating technique was optimized to produce microspheres with multimodal macroporosity up to 90 vol.% in the range 1–30 μm, with micro- and meso-pores with diameter up to 6 nm, and specific surface area as high as 117 m² g⁻¹.     

反相浓乳液方法制备多孔聚丙烯酸丁酯弹性体材料

以丙烯酸丁酯为单体,二乙烯基苯为交联剂,偶氮二异丁腈为引发剂,山梨糖醇酐单油酸酯为乳化剂,水为分散相,用反相浓乳液法制备了泡孔型结构的聚丙烯酸丁酯(PBA)弹性体材料,考察了聚合反应温度、乳化剂用量、分散相体积分数对PBA弹性体材料泡孔结构的影响,并通过扫描电镜对泡孔结构进行了表征。结果表明,聚合反应温度宜控制为50~60℃;随着乳化剂质量分数从10%增加到30%,PBA弹性体的孔径逐渐减小,并且泡孔间的通道数量增多;随着分散相体积分数的增加,PBA弹性体材料的泡孔直径和通道直径逐渐增大,孔隙率增加,密度降低。     

Fabrication and stability of porous poly(allylamine) hydrochloride (PAH)/poly(acrylic acid) (PAA) multilayered films via a cleavable-polycation template

Porous films were fabricated from nonporous layer-by-layer multilayers composed of a blend of positively charged disulfide-containing polyamidoamine and poly(allylamine hydrochoride), and negatively charged poly(acrylic acid), followed by removal of cleavable disulfide-containing polycation after incubation in 1 mM DTT solution. The thickness of original multilayered films decreased with the increase of incubation time in DTT solution. Atomic force microscopy (AFM) measurements and electrochemical analysis demonstrated the formation of nanopores with sizes ranging from 50 to 120 nm. The formed porous films were stable in buffer solution at pHs ranging from 7.4 to 1.6, whereas they showed slight changes in pore number and pore size when incubated in PBS buffer at a pH of 10.0. This research might provide a universal method for the fabrication of noncrosslinked porous multilayered films.     

Aging of reticulated Si-SiC foams in porous burners

Abstract

Abstract

Si-SiC open cell foams with porosity >87% and high pore sizes (4-7?mm) are commonly employed as active zone in porous burners for heat radiation applications. In a porous burner, the solid porous body let the heat recirculate from the hot combustion products to the incoming reactants. The result is that the flame is confined within the foam, meaning high thermomechanical loadings on its constituent material. A set of commercial Si-SiC foams from the same production batch was aged with flat porous burners. Thermal cycles ramp-up, dwell and cooling, as well as burner set-up (power: 15?kW, fuel/air ratio: 1·5), were chosen based on previous experience. Before aging, each foam was first cut in bars ready for bending tests, reassembled into the burner foam configuration and operated. As produced and aged samples were physically, mechanically and chemically analysed and results compared.     

Effect of raw materials on the pore morphologies of carbon foams prepared through templating method

The present paper reports about the effects of raw materials, processed through templating method, on the pore microstructures and pore size distribution of carbon foams (CFs). Biomaterials along with polyurethane and phenolic resin were employed to prepare CFs. To further investigate the adjustability of the pore microstructures and pore size distribution, several kinds of chemical additives/fillers, including activated charcoal, NaCl, and silicon, were used. Surface morphological studies were carried out using scanning electron microscope (SEM), and pore size distribution was analysed by high-pressure Hg porosimetry. The results showed that the structures of the precursor played a dominant role in determining the final pore microstructures. Chemical additives/fillers affect the average pore sizes, pore size distributions, and the pore walls. High amount of macropores are found in all the samples with the radius ranging from 2 to 4?μm. It is practical to adjust the pores using different raw materials and chemical additives/fillers.     

A new ambient temperature crosslinking system for emulsion polymers

A new system is proposed for the crosslinking of urea-groups dispersions with dialdehydes at ambient temperature. Film properties are comparable with those achieved by the best standard crosslinking reactions.