Legislative Documents

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Soft, Elastic Macroporous Monolith by Templating High Internal Phase Emulsions with Aminoclay: Preparation, Pore Structure and Use for Enzyme Immobilization

We describe the preparation of macroporous monolithic structures by templating high internal phase emulsions with platelike aminoclay nanoparticles. We demonstrate that choice of surfactant affords control over pore structure within the monolith. Scanning electron microscopy shows that using anionic surfactant (sodium dodecyl sulfate) leads to the formation of closed pores that template oil droplets in the emulsion, whereas cationic surfactant (cetyltrimethylammonium bromide) results in the formation of a network-like structure that does not directly replicate the oil droplets. Of particular interest are monoliths prepared using nonionic surfactant (Pluronic F127); this results in the formation of an interconnected open pore monolith, which is soft, and exhibits remarkable elasticity: they can recover from compressive strains as large as 80%. As a consequence of this, these monoliths are robust and do not crack on air drying at room temperature despite experiencing large (≈ 45%) volume shrinkage. We intercalate glucose oxidase enzyme in the aminoclay and use these constructs to prepare monoliths with an interconnected porous structure. We demonstrate monolith porosity can be tuned by increasing the oil volume fraction. Increasing the oil fraction in the emulsion from 74 to 82.6% increased the monolith porosity from 72.5 to 84.4%, resulting in an increase in enzyme activity. Enzymes encapsulated in the monoliths are stable against chaotropic solvents and changes in pH

Fire-Retardant, Self-Extinguishing Inorganic/Polymer Composite Memory Foams

Polymeric foams used in furniture and automotive and aircraft seating applications rely on the incorporation of environmentally hazardous fire-retardant additives to meet fire safety norms. This has occasioned significant interest in novel approaches to the elimination of fire-retardant additives. Foams based on polymer nanocomposites or based on fire-retardant coatings show compromised mechanical performance and require additional processing steps. Here, we demonstrate a one-step preparation of a fire-retardant ice-templated inorganic/polymer hybrid that does not incorporate fire-retardant additives. The hybrid foams exhibit excellent mechanical properties. They are elastic to large compressional strain, despite the high inorganic content. They also exhibit tunable mechanical recovery, including viscoelastic “memory”. These hybrid foams are prepared using ice-templating that relies on a green solvent, water, as a porogen. Because these foams are predominantly comprised of inorganic components, they exhibit exceptional fire retardance in torch burn tests and are self-extinguishing. After being subjected to a flame, the foam retains its porous structure and does not drip or collapse. In micro-combustion calorimetry, the hybrid foams show a peak heat release rate that is only 25% that of a commercial fire-retardant polyurethanes. Finally, we demonstrate that we can use ice-templating to prepare hybrid foams with different inorganic colloids, including cheap commercial materials. We also demonstrate that ice-templating is amenable to scale up, without loss of mechanical performance or fire-retardant properties

Fire-Retardant, Self-Extinguishing Inorganic/Polymer Composite Memory Foams

Polymeric foams used in furniture and automotive and aircraft seating applications rely on the incorporation of environmentally hazardous fire-retardant additives to meet fire safety norms. This has occasioned significant interest in novel approaches to the elimination of fire-retardant additives. Foams based on polymer nanocomposites or based on fire-retardant coatings show compromised mechanical performance and require additional processing steps. Here, we demonstrate a one-step preparation of a fire-retardant ice-templated inorganic/polymer hybrid that does not incorporate fire-retardant additives. The hybrid foams exhibit excellent mechanical properties. They are elastic to large compressional strain, despite the high inorganic content. They also exhibit tunable mechanical recovery, including viscoelastic “memory”. These hybrid foams are prepared using ice-templating that relies on a green solvent, water, as a porogen. Because these foams are predominantly comprised of inorganic components, they exhibit exceptional fire retardance in torch burn tests and are self-extinguishing. After being subjected to a flame, the foam retains its porous structure and does not drip or collapse. In micro-combustion calorimetry, the hybrid foams show a peak heat release rate that is only 25% that of a commercial fire-retardant polyurethanes. Finally, we demonstrate that we can use ice-templating to prepare hybrid foams with different inorganic colloids, including cheap commercial materials. We also demonstrate that ice-templating is amenable to scale up, without loss of mechanical performance or fire-retardant properties

Omniphilic Polymeric Sponges by Ice Templating

Sponges that absorb a large quantity of solvent relative to their weight, independent of the solvent polarity, represent useful universal absorbents for laboratory and industrial spills. We report the preparation of macroporous polymer sponges by ice templating of polyethylenimine aqueous solutions and their cross-linking in the frozen state. The as-prepared monolith is hydrophilic and absorbs over 30-fold its weight in water. Modification of this sponge using valeroyl chloride renders it omniphilic; viz., a modified sponge absorbs over 10-fold its dry weight of either water or hexane. Modification using palmitoyl chloride that has a longer chain length results in the preparation of a hydrophobic sponge with a water contact angle around 130°, which retains its oleophilicity underwater. The solvent absorbed in these sponges can be simply squeezed out, and the sponges are stable to several hundred cycles of compression. The large pore sizes of these sponges allow rapid absorption of even high viscosity solvents such as pump oil. Finally, we demonstrate that these sponges are also able to separate apolar oils that are emulsified in water using surfactants. These high porosity sponges with controllable solvophilicity represent inexpensive, high performance universal absorbents for general solvent spills

Nanoparticle Size Controls Aggregation in Lamellar Nonionic Surfactant Mesophase

We show that the size of silica nanoparticles influences the nature of their aggregation in an aqueous solution of a relatively hydrophobic nonionic surfactant, C₁₂E₄. We present results for dispersions of silica nanoparticles with sizes varying from 8 to 26 nm, in a 75: 25 C₁₂E₄/water system, that forms a lamellar phase, L_α, at room temperature. Addition of silica particles does not affect the formation of the L_α phase. Nanoparticles smaller than about 11 nm aggregate irreversibly in the C₁₂E₄/water system. However, nanoparticles larger than about 15 nm aggregate in the L_α phase, but are dispersed at temperatures above the L_α order–disorder temperature. Thus, in contrast to the smaller particles, aggregation of silica nanoparticles larger than about 15 nm is reversible with temperature. We use small-angle neutron scattering (SANS) to demonstrate that these results can be explained by the size-dependent wrapping of nanoparticles by surfactant bilayers. Larger particles, above 15 nm in size, are sterically stabilized by the formation of an adsorbed surfactant bilayer. The cost of bilayer bending inhibits adsorption onto the highly curved surfaces of smaller particles, and these “bare” particles aggregate irreversibly

Elastic Compressible Energy Storage Devices from Ice Templated Polymer Gels treated with Polyphenols

Design and fabrication of rechargeable energy storage devices that are robust to mechanical deformation is essential for wearable electronics. We report the preparation of compressible supercapacitors that retain their specific capacitance after large compression and that recover elastically after at least a hundred compression–expansion cycles. Compressible supercapacitors are prepared using a facile, scalable method that readily yields centimeter-scale macroporous objects. We ice template a solution of polyethylenimine in green tea extract to prepare a macroporous cross-linked polymer gel (PG) whose walls are impregnated with green tea derived polyphenols. As the PG is insulating, we impart conductivity by deposition of gold on it. Gold deposition is done in two steps: first, silver nanoparticles are formed on the PG walls by in situ reduction by polyphenols and then gold films are deposited on these walls. Gold coated PGs (GPGs) were used as electrodes to deposit poly­(3,4-ethylenedioxythiophene) as a pseudocapacitive material. The specific capacitance of PEDOT coated GPGs (PGPG) was found to be 253 F/g at 1 A/g. PGPG could be compressed and expanded over a hundred cycles without any suffering mechanical failure or loss of capacitative performance. The capacitance was found to be 243 F/g upon compressing the device to 25% of its original size (viz. compressive strain = 75%). Thus, even large compression does not affect the device performance. This device shows power and energy densities of 2715 W/kg and 22 Wh/kg, respectively, in the uncompressed state. The macroporous nature of PGPG makes it possible to fill the PGPG pores with gel electrolyte. We report that the gel electrolyte filled supercapacitor exhibited a specific capacitance of 200 F/g, which increased by 4% upon 75% compression

Large Centimeter-Sized Macroporous Ferritin Gels as Versatile Nanoreactors

Organized assemblies of bionanoparticles such as ferritin provides templates that can be exploited for nanotechnological applications. Organization of ferritin into well-defined three-dimensional assemblies is challenging and has attracted considerable attention recently. We have synthesized, for the first time, large (centimeter-sized) self-standing macroporous scaffold monoliths from ferritin bionanoparticles, using dynamic templating of surfactant H₁ domains. These scaffolds comprise three-dimensionally connected strands of ferritin, organized as a porous gel with porosity ∼55 μm. The iron oxide inside the ferritin scaffold can be easily replaced with catalytically active monodisperse zerovalent transition metal nanoparticles using a very simple protocol. Since the ferritin is cross-linked in the scaffold, it is significantly robust with enhanced thermal stability and better tolerance toward several organic solvents in comparison to the native ferritin bionanoparticle. In addition, the scaffold macropores facilitate substrate and reagent transport and hence the monoliths containing active Pd or iron oxide nanoparticles inside apo-ferritin bionanoparticles were used as a recyclable heterogeneous catalyst for the oxidation of 2,3,6-trimethyl phenol to 2,3,6-trimethyl-1,4-benzoquinone (precursor for Vitamin E synthesis) and for Suzuki–Miyaura cross-coupling reaction in both aqueous and organic solvents. The protein shell around the nanoparticles protects them from agglomeration, a phenomenon that otherwise plagues nanoparticles-based catalysis. The presence of macropores allow the ferritin scaffold to act as catalytic monolith for continuous flow reactions having rapid reaction rates, while offering a low pressure drop. Finally, the Pd@apo-ferritin scaffold was immobilized inside a steel cartridge and used for the continuous flow hydrogenation of alkenes to their corresponding alkanes for 15 cycles without any loss of activity

Large PAMAM Dendron Induces Formation of Unusual <i>P</i>4₃32 Mesophase in Monoolein/Water Systems

Compact macromolecular dendrons have previously been shown to induce the formation of discontinuous inverse micellar assemblies with <i>Fd</i>3<i>m</i> symmetry in monoolein/water systems. Here, we demonstrate that a large PAMAM dendron (G5: fifth generation) induces the formation of a very unusual mesophase with <i>P</i>4₃32 symmetry. This mesophase had previously been observed in monoolein/water systems only on addition of cytochrome <i>c</i>. The <i>P</i>4₃32 mesophase can be considered an intermediate phase between the bicontinuous <i>Ia</i>3<i>d</i> and discontinuous micellar mesophases. We present a detailed investigation of the phase behavior of monoolein/water as a function of G5 concentration and temperature. Addition of 1% G5 in 85/15 monoolein/water system induces a transition from the L_α to <i>Ia</i>3<i>d</i> phase. Further increase in G5 concentration to above 2% induces the formation of the <i>P</i>4₃32 phase. In contrast to this, incorporation of lower generation PAMAM dendrons (G2–G4) in monoolein/water yields a qualitatively different phase diagram with the formation of the reverse micellar <i>Fd</i>3<i>m</i> phase. PAMAM dendrons of all generations, G2–G5, bear terminal amine groups that interact with the monoolein headgroup. The compact molecular architecture of the dendrons and these attractive interactions induce bending of the monoolein bilayer structure. For smaller dendrons, G2–G4, this results in the formation of the <i>Fd</i>3<i>m</i> phase. However, the large size of the G5 dendron precludes this and a rare intermediate phase between the <i>Ia</i>3<i>d</i> and discontinuous micellar phase, and the <i>P</i>4₃32 mesophase forms instead

Ultrathin Sheets of Metal or Metal Sulfide from Molecularly Thin Sheets of Metal Thiolates in Solution

Materials that exist as single molecule thick two-dimensional sheets are in great demand because they hold promise as precursors for synthesis of layered functional materials. We demonstrate that metal thiolates, that exist as lamellar assemblies in the neat state, can be disassembled into individual molecular sheets simply by dilution in apolar organic solvents and that these can form ultrathin metallic layers on substrates upon heat treatment. We establish the pathway to the disassembly of metal thiolates in solution using a combination of techniques, including X-ray diffraction, light scattering, FTIR, and TEM. Our results indicate that the lamellar structure of Pd-thiolates is preserved in toluene up to a concentration of 300% w/v and the average intersheet distance is unchanged. Interestingly, the dynamics of the Pd-thiolate sheets remain correlated even on diluting them up to 30% w/v, though the disorder within the lamellar stacks increases with a decrease in their coherence length. Finally, at dilutions less than about 5% w/v, individual sheets of these structures can be accessed that are isolated and directly observed using TEM. Heat treatment of the ultrathin films of metal thiolates deposited on appropriate substrates resulted in the formation of metal or metal sulfides with retention of sheetlike morphologies