Multiscale Porosity from Thermoreversible Poly(vinylidene fluoride) Gels in Diethyl Azelate

Poly(vinylidene fluoride) (PVF₂) produces thermoreversible gels in a series of diesters. The polymer-solvent complexation occurred for intermittent number of carbon atoms n ⩾ 2 and the enthalpy of complexation increased with increasing n. The gels were dried by replacing the diesters with low boiling solvent like cyclohexane (bp. 80 °C) and methylcyclohexane (bp. 99 °C). The porosity of the dried gels was measured using Poremaster-60. For PVF₂-DEAZ gel meso and macro porosity have been observed. The former pore dimensions have been attributed for polymer-solvent complexation while the macroporosity has been attributed for caging of solvent between the PVF₂ fibrils The porosity measured from nitrogen adsorption isotherms using BJH method indicate presence of minimum pore diameter of 3.8 nm for the 10% dried gel of PVF₂.     

Polymeric Multiporous Materials from Fibrillar Networks

Summary: Poly(vinylidene fluoride) (PVF₂) forms thermoreversible gels with liquid alkyl diesters as well as with camphor which is solid at room temperature. The diesters are replaced by another low boiling solvent cyclohexane by solvent exchange technique while camphor is dried just by exposing the material in vacuum to yield highly porous materials. Nano pores are generated as a result of solvent removal from polymer-solvent intercalates whereas macropores are contributed by percolation of polymer fibrils. The porosity thus created covers a wide range from 3 nm to 400 µm producing multiporous materials. Pores greater than 6 nm are measured by mercury intrusion porosimetry (MIP) and pores of diameter less than 6 nm is observed by N₂ adsorption porosimetry. The dried samples show two melting regions, low temperature hump for porous portion and high temperature peak for bulk portion. The porous materials have the ability to absorb water-soluble herbicides from around 10-ppm aqueous solution as indicated in UV spectrophotometric experiment.     

Thermoreversible Gelation of Poly(vinylidene fluoride) – Camphor System

Poly (vinylidene fluoride) (PVF₂) produces thermoreversible gel in camphor when quenched to 25°C from the melt under sealed condition. The SEM micrograph of dried PVF₂/camphor gel (Wequation/tex2gif-inf-3.gif= 0.25) indicates presence of fibrillar network structure and the gels at different composition shows reversible first order phase transition. The phase diagram of the gel suggest the formation of a polymer- solvent complex. The melting enthalpy gives a stoichiometric composition of the complex at Wequation/tex2gif-inf-5.gif= 0.25. This corresponds to a molar ratio of PVF₂ monomer/camphor ≈ 4/5. Temperature-dependent synchroton experiments further support the conclusions derived from the phase diagram.     

利用呼吸图案法制备聚(苯乙烯-b-丙烯腈)有序多孔薄膜

以自制的聚(苯乙烯-b-丙烯腈)(PS-b-PAN)嵌段共聚物为成膜材料, 采用呼吸图案法制备了有序多孔薄膜, 采用扫描电子显微镜(SEM)对薄膜形貌进行了分析, 研究了聚合物浓度、溶剂种类及共聚物结构对薄膜结构的影响. 结果表明, 薄膜表层为多孔结构, 且孔为圆形、以六方阵列形式排列; 薄膜表层下面是蜂窝状结构.以三氯甲烷(CHCl₃)为溶剂时, 在较高浓度下制备的薄膜表层孔间距较大, 蜂窝结构尺寸较小, 且形成了多层结构. 与CHCl₃为溶剂时相比, 挥发速度较快的二硫化碳(CS₂)作溶剂时制备的多孔薄膜有序性较好, 薄膜表层孔径和孔间距均较大, 蜂窝结构尺寸较小. 以没有PAN链段的聚苯乙烯大分子引发剂(PS-Cl)为成膜材料时, 制备的薄膜表层没有形成多孔结构, 而是形成了窝状结构. 同时, 通过对薄膜表层晕的研究证明了多孔薄膜表层缺陷是由水滴处于液膜下较深的位置造成的.     

Comparison of deconvoluted plasma DSC curves on patients with solid tumors

Melting of crystalline compounds inside the nanopores of open-morphology porous systems was studied on a model system, consisted of 1-octadecene and silica gels with different pore sizes, by means of thermogravimetry, differential scanning calorimetry and powder X-ray diffraction. The parameters of silica gels porous structure (surface area, pore size and volume) were calculated using N₂ adsorption data. To describe the experimental results, a new thermodynamic model of crystallites melting inside the nanopores of irregular shape was established. This model allows an analytical prediction for the shift of phase transition temperature and melting enthalpy (latent heat of melting) due to the surface tension effects. To a first approximation, both parameters must linearly depend on the specific ratio of the total surface of pores to their total volume, and experimental studies have mostly confirmed this result for the melting of 1-octadecene confined inside the pores of a wide range of various silicas (with the pores of different sizes and geometry).

     

On the nanostructure of micrometer-sized cellulose beads

The analysis of the porosity of materials is an important and challenging field in analytical chemistry. The gas adsorption and mercury intrusion methods are the most established techniques for quantification of specific surface areas, but unfortunately, dry materials are mandatory for their applicability. All porous materials that contain water and other solvents in their functional state must be dried before analysis. In this process, care has to be taken since the removal of solvent bears the risk of an incalculable alteration of the pore structure, especially for soft materials. In the present paper, we report on the use of small-angle X-ray scattering (SAXS) as an alternative analysis method for the investigation of the micro and mesopores within cellulose beads in their native, i.e., water-swollen state; in this context, they represent a typical soft material. We show that even gentle removal of the bound water reduces the specific surface area dramatically from 161 to 109 m² g⁻¹ in cellulose bead sample type MT50 and from 417 to 220 m² g⁻¹ in MT100. Simulation of the SAXS curves with a bimodal pore size distribution model reveals that the smallest pores with radii up to 10 nm are greatly affected by drying, whereas pores with sizes in the range of 10 to 70 nm are barely affected. The SAXS results were compared with Brunauer–Emmett–Teller results from nitrogen sorption measurements and with mercury intrusion experiments.     

Stress During Drying of Two Stone Consolidants Applied in Monumental Conservation

The object of this paper is to evaluate behaviour during drying of two stone consolidants: Wacker OH and Tegovakon V, containing tetraethoxysilane. During drying, the gel network contracts due to capillary pressure generated by solvent evaporation. When the consolidant dries inside the stone porous structure, the shrinkage is constrained in all three dimensions. In these conditions, the dried gel suffers a high stress that could cause it to crack. When there is a free surface, as for a consolidant layer on the surface of a pore, the stress can relax in the direction normal to the surface. In this case, the stress is controlled by network rigidity.The rigidity of the gel network has been evaluated by mercury porosimetry, while pore size, which controls capillary pressure, has been determined by nitrogen adsorption. The shrinkage of gels under mercury pressure is characterised by high moduli. This fact suggests a high rigidity of the networks. The small pore radii found in the network (<3 nm) indicate that high capillary pressures are generated within the gel network.     

Bioactive sol–gel scaffolds with dual porosity for tissue engineering

Scaffolds containing dual porosity at the nano and macroscale appear to exhibit improved performance in terms of crystallization of hydroxycarbonate apatite plus cell adhesion and proliferation, as well as vascularization. The aim of the present work is to develop a novel, simple sol–gel process for the preparation of silica-based bioactive porous bone tissue scaffold, with a pore structure consisting of interconnected pores of both 100’s of micrometers and 10’s of nanometers in size, optimized for enhanced bone regeneration performance. SiO₂–CaO and SiO₂–CaO–P₂O₅ porous glass monoliths have been prepared with a dual pore structure including pores of both ~50–200 micrometers and a few to 10’s of nanometers in size, based on polymerization-induced phase separation together with the sol-gel transition, by adding a water soluble polymer to the precursor sol. The nanopore (~5–40 nm) structure of such macroporous gel skeletons was tailored by solvent exchange, followed by heat treatment at 600–700 °C. The overall pore structure has been studied by Scanning Electron Microscopy (SEM), N₂-adsorption (BET), Mercury intrusion porosimetry and Infrared spectroscopy. The scaffold bioactivity, tested in simulated body fluid, has been demonstrated by means of DRIFTS, SEM and X-ray diffraction measurements.     

Preparation and Characterization of Porous Titania by Modified Sol-Gel Method

Mesoporous titania, especially anatase, is attractive due to its potential applications. A novel method to control pore structure of titania, surfactant- or polymer modification, is proposed. The wet gels and gel films, prepared from Ti(O-nC₄H₉)₄ were dried at 90°C and annealed at 500°C after immersion in surfactant or polymer solutions, and mesoporous anatase was obtained. The pore size, pore volume and specific surface area of the surfactant-modified bulk gels, estimated from N₂ absorption-desorption curves, are more than twice larger than those of the gels without modification. The pore size of the surfactant-modified gel films, observed by SEM, are similar to that of the bulk gels. The pore size obviously depended on the size of micelles. The pore size of the gels modified with hydrophilic polymers hardly increased, but the pore volume and the specific surface area increased.     

Poly(amide-imide)-Silica Gel Hybrids: Synthesis and Characterization

Several poly(amide-imide)-silica gel hybrids containing metal salts were prepared by the sol-gel reaction. Poly(amide-imide)s were prepared by low temperature polycondensation reaction of trimellitic anhydride (TMA) and diisocyanates [isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), and 4,4′-methylenebis(phenyl isocyanate) (MDI). The inherent viscosities of the poly(amide-imide)s obtained ranged from 0.39–0.69 dL/g in DMAc. The hydrolysis and condensation reaction of tetramethoxysilane (TMOS) to form a silica gel network was affected in DMAc containing 5% LiCl, CaCl₂ or ZnCl₂ during the formation of poly(amide-imide)s. Films could be cast from DMAc solution and gradual evaporation of the solvent afforded pale yellow to amber colored hybrids in which the salts were dispersed at the molecular level. About 30–60% polymer was incorporated in the hybrids. Pyrolysis of the polymer silica gel hybrid samples at 600°C resulted in the formation of porous silica. Pore size and surface area studies on representative porous silica gels, SiG–4, SiG–5, and SiG–8, obtained upon the pyrolysis of the corresponding hybrids HPAI-4, HPAI-5 and HPAI-8, indicated that the silica gels were mesoporous in nature and had narrow pore size distribution (pore radius = 1.8 nm) with a surface area of 371 m²/g, 335 m²/g and 300 m²/g, respectively. The bottle shaped pores exhibited a pore volume of 0.227 cm³/g, 0.314 cm³/g and 0.280 cm³/g, respectively. Computer simulation modeling studies indicated that the poly(amide-imide) chains were not coiled and there was no agglomeration of the chains.     

Characterization of Hydrophobic SiO2 Powders Prepared by Surface Modification on Wet Gel

Hydrophobic porous silica has been prepared by surface modification of TEOS (tetraethylorthosilicate) wet gel with 6 and 12 vol.% of TMCS (trimethylchlorosilane). We characterized the products by using FT-IR, TGA, DTA, N₂ adsorption/desorption, contact angle and SEM. Surface silanol groups of the gel were widely replaced by–Si(CH₃)₃ to result in a hydrophobic SiO₂ powder as confirmed by contact angle measurements with H₂O, 1-butanol and ethanol. The modified dried gels had a surface area of 950–1000 m²/g (average pore size 120 Å), compared to the non-modified surface which had a surface area of 690 m²/g (average pore size 36 Å). The adsorption/desorption isotherm curves indicated they had similar pore characteristics as aerogels prepared by the supercritical drying process.     

Polymer-solvent interactions in thermoreversible gels of isotactic poly(methyl methacrylate) as studied by measurement of 1h NMR relaxation of the solvent

Dynamic structure and polymer-solvent interactions in solutions and gels of isotactic (i) poly(methyl methacrylate) (PMMA) in butyl acetate (BAC) were characterized by measurements of nonselective and selective ¹H NMR spin-lattice relaxation times of the solvent. In thermoreversible gels, the existence of i-PMMA-BAC complex, where the life-time of the bound solvent is − 100 ms or shorter, was confirmed. Although the correlation time of the solvent bound in i-PMMA-BAC complex is 5-10 times longer than for the free solvent, there is still a relative motional freedom for complexed solvent molecules. The same behaviour observed recently for thermoreversible gels of syndiotactic PMMA indicates the same character of polymer-solvent complexes in gels of both stereoregular forms of PMMA.     

Nanostructured carbon—Ni(OH)2 composites

Deposition of Ni(OH)₂ from an aqueous solution of Ni(N₃)₂ onto highly porous carbon matrices of two types with different porous structure afforded high-purity nanostructured hydroxide—carbon composites with a regular spatial morphology, which are filled with Ni(OH)₂ nanocrystallites (up to 30.9 wt.%) and have high values of specific suface area (up to 1875 m² g^–1) and porosity (up to 2.65 cm³ g^–1). Largeand small-angle X-ray diffraction and low-temperature nitrogen absorption on composites showed that nanocrystallites with a brucite-type layered structure form as plates with a thickness of 2—4 nm and a size along the developed face (001) of 25—30 nm in mesopores and on the outer surface of matrices. The degree of mesopore filling with crystallites depends on the mesopore size and the composition of composites; the micropores remain mainly unfilled. The increase in the hydroxide content results in pore size redistribution: in general, the distribution curves shift in favor of smaller mesopore sizes; the portion of pores with sizes comparable with the thickness of filler nanoplates (3—6 nm), as well as the portion of mid-sized pores (20—30 nm) decrease significantly in favor of smaller pores (8—12 nm). Partial blocking (clogging) of pores with filler nanocrystallites was also observed.     

Mucoadhesive vaginal film of fluconazole using cross-linked chitosan and pectin

A series of silica gels (Si-40, Si-60, Si-100) and related carbon–silica gels, prepared by carbonization of CH₂Cl₂ at a surface of silica gels at 550 °C, characterized using FTIR/PAS, SEM/EDX, and nitrogen adsorption, was investigated upon interactions with polar (water, dimethylsulfoxide), weakly polar (chloroform), and nonpolar (n-hexane, n-decane, benzene, toluene) adsorbates using adsorption and differential scanning calorimetry methods. Features of confined space effects, such as freezing/melting point depression and melting delay, depend strongly on pore sizes, pore wall structure, type and amount of adsorbates, and the degree of pore filling. Melting curves of both polar and nonpolar adsorbates bound in broad pores (Si-60 and Si-100 based materials) can include two–three peaks around melting point, but for Si-40-based materials, a number of similar peaks is smaller. This occurs due to step-by-step melting of frozen structures located in broader pores and the absence of similar effects in narrower pores. The present study shows that complex carbon–silica gel adsorbents can be more effective adsorbents than simple silica gels due to the presence of a number of surface sites of various polarity and structure.

     

Design of hierarchical porous aluminas by using one-pot synthesis and different calcination temperatures

Hierarchical aluminas with pore sizes ranging from a few nanometers to micrometers were obtained using an one-pot sol?Cgel synthesis. The aluminas were synthesized under acid conditions from aluminum isopropoxide in presence of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer template and decahydronaphthalene as emulsifier agent. High-resolution transmission electron microscopy, small-angle X-ray scattering, nitrogen physisorption isotherms and mercury intrusion porosimetry provided evidences of porous structure at different hierarchical levels. The produced aluminas possess hierarchical structure composed of different family of pores that coexist in form of cylinders, pyramids and stacking of platelets. The morphology observed by electron microscopy suggests that the cylindrical pores result from the stacking platelets and that the cylinders and pyramidal pores form the walls of macropores of circular section. These aluminas with hierarchical porous architecture present large surface areas (ca. 435?m² g^?1) and pore volumes (ca. 2.1?cm³ g^?1), tunable pore-size distributions and good thermal stability.     

TOF-GISANS investigation of polymer infiltration in mesoporous TiO2 films for photovoltaic applications

The structure of porous TiO₂ films and TiO₂:poly(N-vinylcarbazole) (PVK) composite films is investigated with time-of-flight grazing incidence small-angle neutron scattering (TOF-GISANS). The TiO₂ films have been prepared by application of a sol–gel process with a diblock copolymer as structure directing agent, and the conductive polymer PVK is infiltrated in the porous network by spin coating and solution casting. The films show a hierarchical pore structure with mesopores 52 nm in size and additional large macropores with a diameter of about 180 nm. By matching the scattering contrast of the TiO₂ with the polymer information about the penetration of the polymer in the pores is determined. Whereas in the PVK film prepared by solution casting the pores are filled to a high degree; in the spin coated film, PVK wets only the TiO₂ pore walls and forms a solid overlying layer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1628–1635, 2010     

Photoreduction of 9,10-Phenanthrenequinone in the Presence of Dimethacrylate Oligomers and Their Polymers

The effective rate constants for the photoreduction (k_H) of 9,10-phenanthrenequinone (PQ) in the presence of dimethacrylate monomers (ethylene glycol dimethacrylate (DMEG), triethylene glycol dimethacrylate (TGM-3), and oligocarbonate dimethacrylate (OKM-2)) and porous polymers based on them have been spectrophotometrically determined. The values of k_H in the presence of DMEG and TGM-3 in benzene solutions and in the monomer media are two times greater than in the presence of OKM-2. The values of k_H for PQ in pores of polyDMEG, polyTGM-3, and polyOKM-2 are approximately identical and do not depend on the pore size (up to hundreds of nanometers) and the specific surface area.     

Monodisperse porous polymer particles: Formation of the porous structure

Monodisperse porous styrene-divinylbenzene copolymer particles were prepared via seeded emulsion polymerization using a mixture of linear polymer (polystyrene seed) and non-solvent as inert diluent. Experimental evidence was presented to describe the mechanism of formation of porous polymer particles during the copolymerization and solvent extraction stages, in which porosity was a consequence of phase separation in the presence of diluents. Pore structure formation was investigated by changes in copolymerization kinetics, gel content, crosslinking density, particle morphology, surface area, pore volume, and pore size distribution. The process of copolymerization was presented, based on the concepts of production, agglomeration, and fixation of the interior gel microspheres of polymer particles. A portion of linear polymer used as diluent was found to participate in the network structure while the porous matrix was built-up. The influence of the removal of the linear polymer from the matrix pores during the solvent extraction process on the porous structure was also discussed.     

Preparation of porous CaCO3/PAM composites by CO2 in water emulsion templating method

Emulsion templating is an effective method to prepare well-defined porous polymeric materials. In this paper, porous CaCO₃/polyacrylamide (PAM) composites were prepared by emulsion templating polymerization in supercritical CO₂(scCO₂) by using a commercial grade surfactant (FC4430), therefore, the amount of the fillers and the pore size distribution of the composites can be modulated based on the demands of those potential applications as biomaterials. Calcium carbonate crystals can be in situ synthesized in the porous PAM matrix, and the morphology of CaCO₃ varied with the conditions of the reaction, the results indicated that three kinds of crystals were observed in the porous matrix. The results of scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) showed that the macropores in PAM were interconnected and with narrow pore size distributions.