Wet-spun porous fibers from high internal phase emulsions: Continuous preparation and high stretchability

Although high internal phase emulsion (HIPE)-templating is promising to prepare macroporous materials (polyHIPEs) with controllable shapes and tuneable property, fibrous polyHIPEs with stretchability and their continuous preparation are still challenging. Here, we report the fabrication of polyHIPE fibers in a continuous manner through wet spinning of HIPEs. The successful fabrication of polyHIPE fibers depends on HIPE dispersed phase fractions, ammonia-catalyzed interfacial reaction and wet spinning. Dry polyHIPE fibers exhibit tunable diameters, hierarchically porous structures, high stability to temperature and to various solutions, and high stretchability (with a high tensile strain of 155%), which is hard to achieve for polyHIPEs. The polyHIPE fibers show enhanced uptakes to both water (14.4 ml g⁻¹) and organic solvents (up to 26.3 ml g⁻¹), and the amphiphilic swelling is rare for polyHIPEs. Moreover, the dry polyHIPE fibers show good thermal insulation, similar to that of cotton. Simple wet spinning, combining with HIPEs with tuneable composition, is promising for preparing various polyHIPE fibers for various potential applications.     

Carbon nanotubes in emulsion‐templated porous polymers: Polymer nanoparticles,sulfonation, and conductivity

Sulfonated polymers are of interest for ion exchange resins, reaction supports, and membranes for separation, filtration, fuel cells, and electrochemical devices. Sulfonic groups have been introduced into polystyrene (PS) through exposure to sulfuric acid, and carbon nanotubes (CNTs) have been added to polymers to enhance proton conductivity without creating an electronic percolation pathway. PolyHIPEs, emulsion‐templated porous polymers with highly interconnected hierarchical open‐cell porous structures, are synthesized through polymerization in the external phases of high internal phase emulsions (HIPEs). In this article, the synthesis of PS‐based CNT‐filled polyHIPEs, their structure, sulfonation, and conductivity are described. Adding CNT dispersions to the HIPEs produced polymer nanoparticle–covered polyHIPEs from polymerization within the water‐soluble surfactant micelles in the internal aqueous phase droplets. The CNTs migrated from the HIPE's aqueous phase droplets into the HIPE's organic phase and formed interconnected bundles within the polyHIPE walls, reflecting a reduction in the surfactant's ability to disperse the CNTs. The water adsorption in the hygroscopic sulfonated polyHIPEs increased the conductivity by several orders of magnitude. The conductivity of the sulfonated polyHIPE containing CNTs was more than an order of magnitude greater than that of the sulfonated polyHIPEs with no CNTs. The CNTs act as “bridges,” enhancing the connection between existing conductive pathways. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4369–4377     

Tough interconnected polymerized medium and high internal phase emulsions reinforced by silica particles

Emulsion templating using high internal phase emulsions is an effective route to prepare low density and high porosity macroporous polymers known as polymerized high internal phase emulsions (polyHIPEs). Conventional polyHIPEs, synthesized from surfactant stabilized w/o emulsions have low permeabilities and poor mechanical properties. We present interconnected open macroporous low density nanocomposites produced by polymerizing the continuous phase of emulsion templates, which contained styrene, polyethyleneglycoldimethacrylate, and silylated silica particles. Polyethyleneglycoldimethacrylate and the silylated silica particles acted as crosslinker. The functionalized silica particles were incorporated into the polymer, which resulted in a significant improvement of the mechanical properties of the polyHIPEs without affecting the interconnected and permeable pore structures. The polyHIPEs contained up to 60 wt % silylated silica particles. Young's modulus of the reinforced macroporous polymers increased up to 600% compared with nonreinforced macroporous polymers. The mechanical performance was further increased by increasing the foam density of the macroporous nanocomposites from around 200 to 370 g/cm³ by raising the organic phase volume of the emulsion templates from 20 to 40 vol %. The macroporous polymers synthesized from less concentrated emulsions also possessed interconnected open porous although less permeable structures. The polyHIPE nanocomposites have a permeability of about 200 mD, whereas the polyMIPE nanocomposites still have permeabilities of around 50 mD. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1979–1989, 2010     

Thermoresponsive Macroporous Scaffolds Prepared by Emulsion Templating

A versatile method to prepare non‐covalently crosslinked polyHIPEs hydrogels from oil‐in‐water high internal phase emulsions (HIPEs) whose aqueous phase contained thermo‐responsive linear polymers is described. The interconnected pore structure of the polyHIPEs is maintained by reversible physical aggregation of thermo‐responsive polymer chains in an aqueous environment. This method to prepare interconnected porous hydrogels using a thermal trigger in the guise of thermo‐responsive polymers by emulsion templating requires no chemical reaction during solidification of the template. This particular feature could provide a safer route to injectable scaffolds as issues of polymerisation/crosslinking chemistry and residual initiator fragments or monomers do not arise     

Preparation of emulsion‐templated fluorinated polymers and their application in oil/water separation

A series of emulsion‐templated fluorinated polymers (polyHIPEs) were first synthesized with introducing 2‐(perfluorohexyl)ethyl methacrylate (PEM) to the external phase of water‐in‐styrene high internal phase emulsion (HIPE) templates. The morphology (i.e., void size and its distribution) of these porous materials could be tuned simply by changing PEM and/or surfactant amount. The synergistic effect between the surface chemistry and surface architecture allowed the polyHIPEs to possess hydrophobicity with a water contact angle of 151°. The superhydrophobicity and oleophilicity of the polyHIPEs, together with their highly open porous structure, make the material a very competitive candidate as a filtration material for oil/water separation in practice with the efficiency of separating dichloromethane from the oil/water mixture of 95%. Such oil/water separating capacity was maintained after 10 cycles of filtration of oil/water, indicating the cyclic usage of the polyHIPE is feasible. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1508–1515     

The synthesis of chloropropyl-functionalized silica hybrid monolithic column with modification of N,N-dimethyl-N-dodecylamine for capillary electrochromatography separation

A chloropropyl-functionalized silica (CP-silica) hybrid monolithic column was synthesized within the confines of a capillary via the sol–gel process using tetramethoxysilane (TMOS) and (3-chloropropyl)-trimethoxysilane (CPTMS) as the precursors. The resulting CP-silica hybrid monolith inside the capillary showed homogeneous macroporous morphology and was well attached to the inner wall of the capillary. The obtained CP-silica hybrid monolithic capillary column demonstrated the inherent hydrophobic property and could be applied as a reversed-phase stationary phase in CEC directly. Due to the great chemical reactivity of the incorporated chloro groups on the hybrid silica monolithic matrix, the chloropropyl moieties on the surface of the hybrid silica monolith matrix could be conveniently further modified by a tertiary amine of N,N-dimethyl-N-dodecylamine (DMDA) via the nucleophilic substitution reaction at 70 °C to introduce a dodecyl groups (C12) onto the CP-silica hybrid monolithic matrix. The resulting C12-silica hybrid monolithic column not only demonstrated the significantly enhanced hydrophobic property in the separation of alkylbenzenes in reversed-phase capillary electrochromatography (RP-CEC), but also the strong electroosmotic flow (EOF) in a wide pH range. Five alkylbenzenes could be baseline separated in 3 min with column efficiency ranging from 189 700 to 221 000 N/m with a 70% ACN running buffer in CEC.     

Enantioseparation on cellulose dimethylphenylcarbamate-modified zirconia monolithic columns by reversed-phase capillary electrochromatography

This work reports the preparation of monolithic zirconia chiral columns for separation of enantiomeric compounds by capillary electrochromatography (CEC). Using sol–gel technology, a porous monolith having interconnected globular-like structure with through-pores is synthesized in the capillary column as a first step in the synthesis of monolithic zirconia chiral capillary columns. In the second step, the surface of the monolith is modified by coating with cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) as the chiral stationary phase to obtain a chiral column (CDMPCZM). The process of the preparation of the zirconia monolithic capillary column was investigated by varying the concentrations of the components of the sol solution including polyethylene glycol, water and acetic acid. CDMPCZM is mechanically stable and no bubble formation was detected with the applied current of up to 30 μA. The enantioseparation behavior of the CDMPCZM columns was investigated by separating a set of 10 representative chiral compounds by varying the applied voltage and pH and organic composition of the aqueous organic mobile phases.     

Preparation of polyHIPE via CuAAC “click” chemistry and its application as a highly efficient adsorbent of Cu(II) ions

A hydrophilic emulsion‐templated porous polymer (polyHIPE) is synthesized by CuAAC “click” chemistry. Herein, a 4,4′‐diazidostilbene‐2,2′‐disulfonic acid disodium salt‐4H₂O (DAS) and tripropargylamine in the mixture of water and N,N‐dimethylformamide solution is used as external phase of the high internal phase emulsion template, and paraffin liquid is involved as the internal phase. The resulting polyHIPE has a well‐defined interconnected pore structure, which could be tailored by changing preparation parameters, such as reagent content, internal phase volume fraction, and surfactant concentration. Thermal analysis shows that the polyHIPE is stable under 180 °C. Owing to the presence of a large number of sodium sulfonate groups from the reagent DAS and the triazoles groups produced in the reaction, the polyHIPE is proved to be a highly efficient adsorbent of heavy metal ion (i.e., up to 52 mg/g for Cu(II) ions) in water. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2129–2135     

Polymerized pickering HIPEs: Effects of synthesis parameters on porous structure

A polyHIPE is a highly porous polymer synthesized from monomers within the external phase of a high internal phase emulsion (HIPE). The large amount of difficult to remove surfactant needed for HIPE stabilization can affect the properties of the resulting polymer. A Pickering emulsion is a surfactant‐free emulsion stabilized by solid particles that preferentially migrate to the interface. In this article, the synthesis of crosslinked polyacrylate polyHIPEs based on Pickering HIPEs stabilized using silane‐modified silica nanoparticles is described and the effects of the synthesis parameters on the porous structure are discussed. The silane chemistry, silane content, and nanoparticle content had significant effects on the size of the polyhedral, relatively closed‐cell polyHIPE voids that resulted from aqueous‐phase initiation. Increasing the mixing intensity reduced the wall thickness and produced a more open‐cell structure. The locus of initiation had a significant effect on polyHIPE morphology. Organic‐phase initiation yielded larger, more spherical voids from the more extensive coalescence before the structure could be “locked‐in” at the gel point. Most significantly, the nanoparticles were located within the polymer walls rather than at the interface, as might be expected. The void walls were shown to be an assembly of nanoparticle agglomerate shells that become embedded within the polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1516–1525, 2010     

使用含离子涂层柱的毛细管电泳和毛细管电色谱的研究进展

 毛细管电色谱是近年发展起来的高效、高选择性的微分离技术。与一般的毛细管电泳和使用ODS反相填料的毛细管电色谱相比 ,含离子涂层柱的毛细管电泳和毛细管电色谱能提供较大且可控的电渗流 ,便于拓宽分离对象 ,优化分离条件。对使用含离子涂层柱的毛细管电泳和电色谱的特点、发展和应用状况进行了综述。     

Properties and Applications of Mixed Packing Capillary Electrochromatography

Mixed packing capillary electrochromatography (MP CEC) with the stationary phase comprising a physical mixture of strong cation exchange (SCX) phase and octadecysilyl (ODS) phase was developed. With the existence of a sulfonic acid group on the surface of SCX, not only could the electroosmotic flow (EOF) remain high at low pH, but also the hydrophilicity of the stationary phase was increased greatly, leading to broad adaptable ranges of both pH and organic modifier concentration in the mobile phase. At the same time, with the coexistence of C₁₈ on the surface of ODS, both the retention and the resolution of samples were improved. Accordingly, MP CEC combined the advantages of both SCX and ODS columns. Effects of operation parameters on EOF and the capacity factors of solutes as well as the retention mechanism of such a column were studied systematically. In addition, MP CEC columns were used in the analysis of strong polar solutes as well as for the high speed separation of acidic, basic, and neutral compounds in a single run.     

Synthesis and characterisation of low density porous polymers by reversible addition-fragmentation chain transfer (RAFT)

PolyHIPE foams with densities of 0.05–0.1 g cm^?3 have been prepared by the polymerisation of the continuous phase of high internal phase emulsions (HIPEs). The internal aqueous phase in HIPE occupies more than 74 % of the total volume, which leads to highly porous and open-cell morphologies. In this paper a method of preparing polyHIPE foams by using reversible addition-fragmentation chain transfer (RAFT) polymerisation has been investigated. Polystyrene-co-polymethyl methacrylate (PS-co-PMMA) has been studied and by using a variety of characterisation methods, it was possible to compare the polyHIPEs prepared by the conventional free radical polymerisation (FRP) to those by RAFT polymerisation. Scanning electron microscopy images have confirmed the presence of a cellular polyHIPE structure. PS-co-PMMA polyHIPEs made by RAFT have significantly narrower molecular weight distribution with values for the polydispersity index (PDI) for PS-co-PMMA between 1.46 and 2.08 compared to 4.68 observed by FRP. The effects of different concentrations of the RAFT agent on structure, glass transition temperature (T _g) and PDI of PS-co-PMMA polyHIPE foams are presented.     

Capillary electrochromatography on silica columns: factors influencing performance

Much capillary electrochromatography (CEC) work is carried out on bonded silica packings which offer many advantages: the number of such packings which are available; the fact that the chemistry of bonding and the separation process are fairly well understood; and the possibility of the transfer to CEC of existing HPLC methods. Packing methods for the preparation of CEC columns have been investigated. The problems inherent in the use of burned-in frits remains an obstacle, but can be at least partially overcome by minimising the length and by silanisation. The influence of a variety of mobile phase variables on aspects of CEC is in agreement with theory for: ionic strength, organic content (including isoeluotropy), and pH. Temperature can be used as a variable to change column selectivity in CEC. The influence of pH on electroosmotic flow (EOF) by changing the degree of ionisation of residual silanol groups is similar for a wide range of neutral bonded groups, but is much less marked for bonded sulphonic acid groups. The EOF may be reversed for bonded groups containing nitrogen.     

Influence of emulsification process on structure–properties relationship of highly concentrated reverse emulsion-derived materials

Water-in-Oil high internal phase emulsions (HIPEs) whose continuous phase is polymerizable gave access to highly porous polymeric materials (polyHIPEs). These emulsions were prepared with a laboratory-made homogenizer whose shear frequency and time could be varied to study the influence of the emulsification conditions on the polyHIPEs morphology. Intensive and/or long shear induced a reduction of the cell and connection diameters without any modification of the material global porosity. The mechanical properties were evaluated by estimating the Young’s modulus from compression tests. The mechanical behavior was analogous for all materials possessing a characteristic polyHIPE structure, even if cell sizes were different between samples.     

Silica-based monolithic capillary columns—Effect of preparation temperature on separation efficiency

The temperature effects during the sol–gel process and ageing of the silica-based monolith on the structure and separation efficiency of the capillary columns (100 μm i.d., 150 mm) for HPLC separations were studied. The tested columns were synthesized from a mixture of tetramethoxysilane, polyethylene glycol and urea under the acidic conditions. The temperature was varied from 40 °C to 44 °C and formation of bypass channels between the silica mold and the capillary wall was examined. The temperature of 43 °C was estimated as optimal for preparation of efficient silica capillary columns which were subsequently modified by octadecyldimethyl-N,N-diethylaminosilane or covered by poly(octadecyl methacrylate) and tested using standard mixture of alkylbenzenes under the isocratic conditions.     

Acrylic Acid “Reversed” PolyHIPEs

Summary: An oil‐in‐water high internal phase emulsion consisting of acrylic acid, water, and a crosslinker (N,N′‐methylene bisacrylamide) as the water phase, and toluene as the oil phase was successfully stabilised to sustain thermal initiation of radical polymerisation resulting in porous open‐cellular monolithic material. The type of initiator used influenced the average pore size ranging from approx. 708 nm to approx. 1 087 nm, as determined by mercury porosimetry.

Schematic of the preparation of an oil‐in‐water‐type polyHIPE (high internal phase emulsion).     

Affinity monolithic capillary columns for glycomics/proteomics: 1. Polymethacrylate monoliths with immobilized lectins for glycoprotein separation by affinity capillary electrochromatography and affinity nano-liquid chromatography in either a single column or columns coupled in series

In this report, microcolumn separation schemes involving monolithic capillary columns with immobilized lectins, and relevant to nanoglycomics/nanoproteomics were introduced. Positive and neutral monoliths based on poly(glycidyl methacrylate-co-ethylene dimethacrylate) were designed for achieving lectin affinity chromatography (LAC) by nano-LC and CEC. The positive monoliths (i.e., monoliths with cationic sites) afforded relatively high permeability in nano-LC but lack predictable EOF magnitude and direction, while neutral monoliths provided a good compromise between reasonable permeability in nano-LC and predictable EOF in CEC. Lectin affinity nano-LC permitted the enrichment of classes of different glycoproteins having similar N-glycans recognized by the immobilized lectin, whereas lectin affinity CEC provided the simultaneous capturing and separation of different glycoproteins due to differences in charge-to-mass ratio. Also, this investigation demonstrated for the first time the coupling of lectin capillary columns in series (i.e., tandem columns) for enhanced separation of glycoproteins by LAC using the CEC modality. Furthermore, in the coupled columns format, glycoforms of a given glycoprotein were readily separated.     

Capillary electrochromatography of 1-phenyl-3-methyl-5-pyrazolone derivatives of some mono-and disaccharides

Summary A packing procedure was adopted for capillary electrochromatography (CEC) that produces capillary columns with high separation efficiencies. The columns were fully packed, 50 cm long, with UV detection being performed through the packed section 30 cm from the inlet end. The CEC experiments were run at ambient pressure, with no additional pressure applied to the ends of the column. The stationary phase (octadecyl silica (ODS), 5 μm) promoted a high velocity electroosmotic flow (EOF), enabling rapid and efficient separation of a hydrocarbon test mixture. Some 1-phenyl-3-methyl-5-pyrazolone (PMP) derivatives of mono- and disaccharides were baseline separated, using a 5 mM NaH₂PO₄ in 80% acetonitrile and 20% water (v/v) buffer solution. CEC shows promise for future applications in carbohydrate analysis. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Performance of metal complex substituted polysiloxanes in capillary electrophoresis and capillary electrochromatography

Two novel polysiloxanes containing the metal complex, Co(TACN)(3+)2 (TACN= 1,4,7-triazacyclononane) were used as coatings for capillary electrophoresis (CE) and capillary electrochromatography (CEC). Through crosslinking and covalent bonding, the positively charged polymers were bonded to silica supports. In both CE and CEC, these coatings exhibited strong, pH-independent, and anodic electroosmotic flow (EOF), and had excellent long-term stability. Successful separations of aromatic acids were achieved in CE. In CEC, separation of alkylbenzenes (7 min) and basic compounds (20 min) was achieved with higher resolving power than conventional octadecyl silica packings. These polymers represent a new class of coatings for CE and CEC that generate pH-independent EOF.     

Capillary columns with in situ formed porous monolithic packing for micro high-performance liquid chromatography and capillary electrochromatography.

Capillary columns with monolithic stationary phase were prepared from silanized fused-silica capillaries of 75 microns I.D. by in situ copolymerization of divinylbenzene either with styrene or vinylbenzyl chloride in the presence of a suitable porogen. The porous monolithic support in this study was used either directly or upon functionalization of the surface to obtain a stationary phase that was appropriate for the separation of peptides by capillary electrochromatography (CEC). The main advantages of monolithic columns are as follows. They do not need retaining frits, they do not have charged particles that can get dislodged in high electric field, and they have relatively high permeability and stability. Whereas such columns are designed especially for CEC, they find application in micro high-performance liquid chromatography (mu-HPLC) as well. Five different porogens were employed to prepare the monolithic columns that were examined for permeability and porosity. The flexibility of fused-silica capillaries was not adversely affected by the monolithic packing and the longevity of the columns was satisfactory. This may also be due to the polymerization technique, which resulted in a fluid-impervious outer layer of the monolith that precluded contact between the fused-silica surface and the liquid mobile phase. For the most promising columns, the conductivity ratios and the parameters of the simplified van Deemter equation, both in mu-HPLC and CEC, were evaluated. It was found that the efficiency of the monolithic columns in CEC was significantly higher than in mu-HPLC in the same way as observed with capillary columns having conventional particulate packing. This is attributed to the relaxation of band-broadening with electroosmotic flow (EOF) with respect to that with viscous flow. It follows then that the requirement of high packing uniformity to obtain high efficiency may also be relaxed in CEC. Angiotensin-type peptides were separated by CEC with columns packed with a monolithic stationary phase having fixed n-octyl chains and quaternary ammonium groups at the surface. Plate heights of about 8 microns were routinely obtained. The mechanism of the separation is based on the interplay between EOF, chromatographic retention and electrophoretic migration of the positively charged peptides. The results of the complex migration process, with highly nonlinear dependence of the migration times on the organic modifier and the salt concentration, cannot be interpreted within the framework of classical chromatography or electrophoresis.