Patent Application
20220298321
Aspects herein relate to three-dimensional porous polyurea networks, three-dimensional porous carbon networks, uses thereof, and methods of manufacture.
Three-dimensional porous architectures are a desirable form factor for many materials as they allow installation of new properties into a material not possessed by the non-porous form of a material. Porous architectures possessing nanostructured features, such as nanopores or nanoparticulate solid frameworks, are further desirable in many cases as they can possess new and/or more extreme properties than porous architectures without nanostructured features.
Aerogels are an example of a porous architecture possessing nanostructured features. Aerogels are materials comprised of three-dimensional assemblies of nanoparticles or nanostructures that exhibit high porosity materials and ultra-low densities Aerogel materials are typically produced by forming a gel that includes a porous solid component and a liquid component and then removing the liquid component by supercritically, subcritically, or freeze drying the wet gel to isolate the porous solid component. This porous solid component is an aerogel. Supercritical drying involves the liquid being transformed into a fluid above its critical point and removing the fluid while leaving the porous solid structure generally intact. Subcritical drying involves evaporation of the liquid below its critical point in a way that leaves the porous solid structure generally in tact. Freeze drying involves freezing of the liquid component and sublimation of the resulting solid in a way that leaves the porous solid structure generally in tact.
The large internal void space in aerogels and other nanostructured and non-nanostructured three-dimensional porous networks generally provides for a low dielectric constant, a low thermal conductivity, and a high acoustic impedance. These materials have been considered for a number of applications including thermal insulation, lightweight structures, and impact resistance.
Articles and methods for manufacturing three-dimensional porous polyurea networks and three-dimensional porous carbon networks are described.
Polyurea aerogels can be prepared by mixing an isocyanate with water and a trialkylamine in forming a sol-gel material and subsequently drying the sol-gel material to form the polyurea aerogel. The sol-gel material may be dried supercritically or subcritically. The density of polyurea aerogels can be tailored by controlling the concentration of isocyanate in the initial mixture. For example, increasing the amount of isocyanate in forming the sol-gel material may give rise to a polyurea aerogel having an increased density. Conversely, decreasing the amount of isocyanate in forming the sol-gel material may give rise to a polyurea aerogel having a lower density. The morphology of polyurea aerogels can also be tailored by controlling the amount of isocyanate in the composition during manufacture. Including a low amount of isocyanate in the initial mixture to form the sol-gel material may give rise to a polyurea aerogel having a fibrous morphology. Also, having an increased amount of isocyanate in the initial mixture to form the sol-gel material may give rise to a polyurea aerogel having a particulate morphology. In some cases, a polyurea aerogel may have a fibrous morphology which may or may not include features of a particulate morphology when the density of the aerogel is less than about 200 mg/cc. Further, polyurea aerogels may exhibit reduced flammability characteristics, for example, when having a density of greater than about 150 mg/cc.
Carbon aerogels may also be manufactured from polyurea aerogels through a conversion step. Once a polyurea aerogel is formed, the aerogel may be subject to a pyrolysis step, giving rise to a carbon skeleton in the aerogel, hence, forming the carbon aerogel. In some embodiments, a polyurea aerogel having a fibrous morphology that is subject to the pyrolysis step may give rise to a carbon aerogel also having a fibrous morphology. In some cases, carbon aerogels having a fibrous morphology may have a density of less than about 150 mg/cc.
In some cases, three-dimensional porous polyurea networks not considered aerogels may be produced. Likewise, three-dimensional porous carbon networks not considered aerogels may be derived from such three-dimensional polyurea networks.
Various embodiments of the present invention provide certain advantages. Not all embodiments of the invention share the same advantages and those that do may not share them under all circumstances.
Further features and advantages of the present invention, as well as the structure of various embodiments of the present invention are described in detail below with reference to the accompanying drawings.
The accompanying drawings are not intended to be drawn to scale. For purposes of clarity, not every component may be labeled in every drawing. Various embodiments of the invention are described, by way of example, in the accompanying drawings. In the drawings:
Aspects described relate to three-dimensional polyurea networks including polyurea aerogels and methods of manufacturing three-dimensional porous polyurea networks.
A polyurea aerogel may be prepared by mixing an isocyanate reactant, such as diisocyanate or triisocyanate, with water and a trialkylamine (e.g., trimethylamine, triethylamine, tributylamine) in a solvent (e.g., acetone, DMSO) to form a sol-gel material including polyurea. The sol-gel material may subsequently be dried supercritically, subcritically, or by freeze drying to form a polyurea aerogel. Mixture of a diisocyanate or triisocyanate reactant with water and a trialkylamine results in in-situ amine formation which reacts further with unreacted isocyanate to form polyurea. A number of characteristics, such as density, nanomorphology, porosity, pore size, surface area, flammability, and mechanical strength can be controlled by the chemical identity and concentration of the isocyanate.
Polyurea aerogels of the present invention may exhibit certain characteristics, for example, related to various degrees of density, morphology and flammability. In some embodiments, the density of the polyurea aerogel is controlled by varying amounts of di- or triisocyanate prepared in an initial manufacturing step. The morphology of the polyurea aerogel may also be controlled. In some embodiments, for example, a polyurea aerogel exhibits a fibrous morphology. In other embodiments, a polyurea aerogel has a particulate ball-like morphology. In some cases, the morphology of a polyurea aerogel relates to the density of the polyurea aerogel. Morphologies of a polyurea aerogel can be tailored according to usage of varying amounts of di- or triisocyanate during manufacture of the polyurea aerogel. In some embodiments, polyurea aerogels manufactured exhibit high mechanical strength properties and are generally not flammable or exhibit low flammability.
Porous polyisocyanate-based organic networks can be prepared by mixing an organic polyisocyanate and an isocyanate trimerization catatlyst, 1,4-diazobicyclo[2.2.2] octane (DABCO), to form a polymeric gel and supercritically drying the gel to produce a polyisocyanate-based aerogel. Such aerogels and their methods of manufacture are described in U.S. Pat. No. 5,484,818 entitled “Organic aerogels,” and is incorporated herein by reference in its entirety. Polyurea aerogels described herein are prepared via in situ formation of amines by reaction of isocyanates with water where the density, nanomorphology, porosity, pore size, surface area, flammability, and mechanical strength can be suitably tuned.
Aspects described herein may also relate to three-dimensional porous carbon networks including aerogels and methods of manufacturing three-dimensional porous carbon networks. In manufacturing a three-dimensional porous carbon network, a three-dimensional porous polyurea network may be prepared as a precursor to the three-dimensional porous carbon network. For example, in manufacturing a carbon aerogel, a polyurea aerogel may be prepared as a precursor to the carbon aerogel. As discussed, in some embodiments, the polyurea aerogel may be prepared by mixing a diisocyanate or a triisocyanate reactant with water and a trialkylamine and subjecting the mixture to agitation to form a sol-gel material. Then, the sol-gel material is supercritically, subcritically, or freeze dried, resulting in the polyurea aerogel. Once formed, the polyurea aerogel is then pyrolyzed to form a carbon aerogel. In some embodiments, carbon aerogels may have electrically conductive properties.
Once pyrolyzed, three-dimensional porous carbon networks may retain the same or similar morphology as the polyurea precursor. Accordingly, in some embodiments, carbon aerogels produced from polyurea aerogels having a fibrous morphology by methods described herein may also exhibit a fibrous morphology. In other embodiments, carbon aerogels prepared from pyrolysis of polyurea aerogels having a particulate morphology may also have a particulate morphology.
In some embodiments, polyurea or carbon aerogels of different densities may be prepared by varying the concentration of triisocyanate (e.g., Desmodur N3300A), or diisocyanate, in the sol-gel material. In some embodiments, the density of polyurea aerogels or carbon aerogels prepared from pyrolysis of polyurea aerogels may be between, for example, about 1 mg/cc and about 550 mg/cc, or between about 15 mg/cc and about 500 mg/cc. In some embodiments, the density of polyurea aerogels or carbon aerogels prepared from pyrolysis of polyurea aerogels may be less than about 900 mg/cc, less than about 500 mg/cc, less than about 150 mg/cc, less than about 90 mg/cc, less than about 10 mg/cc, or less than about 1 mg/cc. Previously, it had been challenging to produce open-pore mesoporous materials at a low density that are durable and made from inexpensive chemicals and recyclable solvents. Aerogels presented herein include an open-cell mesoporous foam that is not fragile and remains durable at densities as low as 0.04 g/cc. By comparison, silica aerogels at such low density may exhibit extremely fragile mechanical properties.
The density of polyurea or carbon aerogels prepared in accordance with methods described may be appropriately tailored based on the concentration of isocyanate material included in the initial mixture. For example, when preparing a polyurea or carbon aerogel, including more isocyanate material in the initial mixture may give rise to a polyurea or carbon aerogel having a greater density. Similarly, including less isocyanate material in the initial mixture during preparation of a polyurea or carbon aerogel may result in a polyurea or carbon aerogel having less density.
The morphology of aerogels described herein may be appropriately controlled. In some embodiments, the morphology of a polyurea or carbon aerogel may be controlled based on the amount of isocyanate incorporated into the initial mixture of isocyanate, water and trialkylamine. In some cases, for example, a suitable mixture having a smaller amount of isocyanate in forming a sol-gel material, upon drying of the sol-gel material, may give rise to a polyurea aerogel or carbon aerogel (after pyrolysis) having a more fibrous morphology as compared to an aerogel having been prepared from a similar mixture yet having a larger amount of isocyanate. On the other hand, a suitable mixture having a larger amount of isocyanate, when the sol-gel material is appropriately formed and dried, may result in a more particulate-type morphology as compared to an aerogel prepared from a similar mixture that includes a larger amount of isocyanate. Low-density polyurea and carbon aerogels may exhibit fibrous morphology, whereas high-density polyurea and carbon aerogels may show a particulate morphology.
Aerogels discussed herein may have fibrous morphologies where the aerogels may include nanofibers having various diameters and lengths. In some embodiments, fibrous morphologies of aerogels include fibers having an average diameter ranging between about 1 nm and about 500 nm (e.g., between about 10 nm and about 400 nm, between about 100 nm and about 300 nm) or less than 500 nm (e.g., less than 400 nm, less than 300 nm, less than 200 nm). In some embodiments, fibrous morphologies of aerogels include fibers having an average length of at least 50 nm and may extend into the micron length scale.
Polyurea aerogels discussed herein may have advantageous mechanical strength properties. In some embodiments, the compressive strength of polyurea aerogels may be between about 200 MPa and about 1 GPa, between about 400 MPa and about 800 MPa, or between about 600 MPa and about 700 MPa (e.g., at least 640 MPa). The specific energy, as calculated by the area under a compressive stress-strain curve, can be between about 10 J/g and about 200 J/g, between about 50 J/g and about 150 J/g, or between about 80 J/g and about 120 J/g (e.g., at least 105 J/g).
Three-dimensional porous polyurea networks having a certain density level may exhibit flame retardancy properties. In some embodiments, by a flame test, low-density polyurea aerogels were found to burn completely, but high-density polyurea aerogels did not sustain a flame. In some cases, low density polyurea aerogels burn completely but high density polyurea aerogels do not sustain a flame. For example, as shown in
Isocyanate (N═C═O) is a reactive functional group and may undergo reaction with a number of nucleophiles.
Any appropriate diisocyanate, triisocyanate, or any other isocyanate, may be used as a monomer in forming a three-dimensional porous polyurea network such as a polyurea aerogel. Examples of suitable, yet not limiting, diisocyanate monomers include Desmodur N3200 diisocyanate, toluene diisocyanate (Mondur TDS), and MDI (Mondur CD). Examples of suitable, yet not limiting, triisocyanate monomers include Desmodur N3300A triisocyanate and Desmodur RE triisocyanate.
In some embodiments, polyurea aerogels are obtained upon base-catalyzed crosslinking of resorcinol-formaldehyde (RF) wet gels with triisocyanates. The outer surface layer of the porous solid component of the gel may include polyurea formed via an Et3N-catalyzed reaction of triisocyanate with residual water in an acetone or acetonitrile crosslinking bath.
In some embodiments, aerogels are made by reaction of a triisocyanate such as Desmodur N3300A with water in the presence of a catalyst, such as triethylamine in an acetone or acetonitrile solvent. The density and microscopic morphology exhibited by the resulting aerogel may be correlated to the amount of triisocyanate, water, and catalyst utilized in the manufacturing process. In some cases, triisocyanate may be useful as monomers to produce lower density aerogels exhibiting fibrous morphology. Such a result may be due to early phase separation due to low solubility of the three-dimensional polymer arising from the triisocyanate.
In various embodiments, the concentration of catalyst (e.g., Et3N), the concentration of monomer and the concentration of water may be varied to affect different characteristics of polyurea aerogels. For example, to be discussed further below, including an increasing amount of monomer (e.g., isocyanate) will result in a polyurea aerogel having a generally increased bulk density and a decreased percent porosity. Further, in some cases, increasing the amount of catalyst (e.g., Et3N) and water may decrease the overall gelation time of the aerogel. In some cases, varying the concentration of water and trialkylamine added in preparing polyurea aerogels may have an effect on the gelation time, yet no effect on the nanomorphology of the resulting aerogels. However, in some embodiments, varying the concentration of monomer (di- or triisocyanate) may have a direct effect on both the gelation time and the nanomorphology of polyurea aerogels.
Polyureas may result from the reaction of isocyanates with multifunctional nucleophiles such as polyamines. In a similar vein, polyurethanes may result from the reaction of isocyanates with multifunctional nucleophiles such as polyols. High-surface-area polyurethanes as the stationary phase for chromatographic separations may be formed via reaction in CH2Cl2 of polymeric methylene diphenyl diisocyanate (MDI, e.g., Mondur MR) and a pentafunctional oligomer based on oxypropylation of diethylenetriamine. Such materials are obtained as precipitates rather than gels, however, use of sugar derivatives as polyols and more polar solvents for the reaction medium may yield gels and eventually aerogels. For example, toluene diisocyanate may be used to crosslink and induce pyridine-catalyzed gelation of cellulose acetate and cellulose acetate butyrate acetone solutions. Wet gels may be dried to aerogels with SCF CO2.
In forming gels used in thermal superinsulation applications, a DABCO-catalyzed reaction in DMSO/ethyl acetate mixtures of an MDI derivative (e.g., Lupranat M205, a BASF product similar to Suprasec DNR by ICI) with saccharose and pentaerythritol may give rise to nanoparticulate polyurethane aerogels where the macro- vs. the mesoporosity are controlled by adjusting the Hildebrand solubility parameter via the DMSO/ethylacetate ratio. Aerogels having lower thermal conductivities than standard polyurethane foams may be formed (0.022 vs. 0.030 W m−1 K−1, respectively, at room temperature and atmospheric pressure and comparable bulk densities of ˜0.2 g cm−3). Further, crosslinking of cellulose acetate in acetone with Lupranat M205 isocyanate and dibutyltin laurate as a catalyst results in aerogels that include a natural cellulose product, demonstrating high elastic moduli (in the 200-300 MPa range at bulk densities ρb in the range 0.75-0.85 g cm−3) and low thermal conductivities ranging from 0.029 W m−1 K−1 (at atmospheric pressure) to 0.006 W m−1 K−1 (at 2×10−5 mbar) for samples with ρb of 0.25 g cm−3.
In some embodiments, polyurea aerogels may be synthesized in acetone via Et3N-catalyzed reaction of MDI or polymeric MDI type of isocyanates and triamines. Polyurethane aerogels may be made from similar or the same isocyanates and an ethylene oxide modified polyether polyol (e.g., Multranol 9185). Polyurea aerogels may be nanoparticulate like silica and polyurethane aerogels may be nanofibrous. For various densities (e.g., 0.12-0.13 g cm −3), polyurea aerogels may demonstrate lower thermal conductivities than polyurethane aerogels (0.018-0.019 W m−1 K−1, vs. 0.02+7 W m−1 K−1, respectively). Both polyurea and polyurethane aerogels, however, may exhibit higher thermal conductivity and density values than that of silica aerogels (0.012 W m−1 K−1) at 0.09 g cm−3.
Polyureas may also be obtained indirectly from isocyanates and water via a reaction sequence that initially yields an amine via an unstable carbamic acid, shown in Reaction (1).
Subsequently, the amine reacts with yet-unreacted isocyanate yielding urea (eq 2).
In some instances, Reaction (2) takes place much faster than Reaction (1), because amines are stronger nucleophiles than water. The seq/uence of Reactions (1) and (2) may be used for the environmental curing of films containing unreacted isocyanate groups, while, owing to the CO2 side product generated by the reaction, such reactions may also be involved in the formation of polyurethane foams w/here a small amount of water added in the reaction mixture acts as a foaming agent.
Synthesis of mechanically strong polyurea aerogels via reaction of isocyanates with water, which had not previously been reported before, may be advantageous in that it bypasses the use of expensive amines. In some embodiments, the gelation process may be employed with triisocyanates such as Desmodur N3300A or Desmodur RE yielding polyurea monoliths over a wide density range (e.g., 0.016-0.55 g cm−3). Diisocyanates such as Desmodur N3200, toluene diisocyanate (TDI), or monomeric MDI may also gel at higher concentrations. In some instances, however, polyurea aerogels produced from triisocyanates may exhibit more robust characteristics than polyurea aerogels prepared from diisocyanates.
Aerogels derived from triisocyanates such as Desmodur N3300A may not only exhibit variable nanomorphologies that are tunable as a function of density, but such aerogels may also exhibit exceptional mechanical properties which are comparable to those of x-aerogels. X-aerogels, methods of manufacture, and their use are described in U.S. Pat. No. 7,771,609 entitled “Methods and Compositions for Preparing Silica Aerogels” and is incorporated herein by reference by its entirety.
Aerogels derived from triisocyanates such as Desmodur RE may provide for a high-yield conversion to carbon aerogels. Carbon aerogels derived from diisocyanates such as Desmodur N3200 may also be produced.
As discussed further below, such materials may exhibit a significant degree of versatility and multifunctionality. For example, aerogels having density-gradient monoliths may include a high-density nanoparticulate end that combines high mechanical strength with flame retardancy.
After allowed to age, gels are removed from their molds and subject to a process of solvent exchange. In some embodiments, solvent exchange involves contacting or immersing the gel in an aprotic solvent, such as for example, acetone, pentane, or acetonitrile. Such solvents may enable the formation of CO2-containing voids in the overall composition. However, it can be appreciated that any suitable solvent may be utilized. Solvent exchange may be performed a number of times prior to drying of the sol-gel, for example, with supercritical CO2 to form an aerogel. In some cases, the gel may be dried at an elevated temperature (e.g., 40° C.) under ambient pressure. In some embodiments, supercritical drying is conducted in an autoclave where the temperature of the autoclave is raised above the critical point of CO2 and the pressure is released isothermally (e.g., at 40° C.). In other embodiments, subcritical drying is used to dry the sol-gel material, forming the aerogel. In some embodiments, and as shown in
Further, and as discussed, carbon aerogels may be produced by subjecting polyurea aerogels described herein to an additional step of pyrolysis. In some embodiments, a polyurea aerogel is placed in an inert atmosphere (e.g., Ar) at a high temperature (e.g., 800° C.), yielding an aerogel having a carbon skeleton. In some embodiments, the skeleton of the carbon aerogel is made of purely carbon material. In some embodiments, carbon aerogels formed by methods discussed may exhibit a fibrous morphology. For example, pyrolyzing a polyurea aerogel having a fibrous morphology (e.g., low-density) may result in a carbon aerogel also having a fibrous morphology. Depending on various parameters, carbon aerogels may exhibit a particulate morphology. For example, pyrolyzing a polyurea aerogel having a particulate morphology (e.g., high-density) may give rise to a carbon aerogel that has a similar particulate morphology. Carbon aerogels may also contain electrically conductive characteristics.
Three-dimensional porous polyurea and carbon networks (e.g., aerogels) discussed may be suitable for use in a number of applications. Aerogels may generally be used for applications including thermal insulation (e.g., architectural, automotive industrial applications, aircraft, spacecraft, clothing), acoustic insulation (e.g., buildings, automobiles, aircrafts), dielectrics (e.g., for fast electronics), supports for catalysts, and as hosts of functional guests for chemical, electronic and optical applications. In some cases, three-dimensional porous polyurea networks including polyurea aerogels may be useful for applications that involve, for example, manufacture of super insulating materials, lightweight structures, impact dampeners and nonflammable materials. Three-dimensional porous polyurea networks including polyurea aerogels may be useful in applications that involve, for example, absorption of oil or other hydrophobic materials. In some instances, such materials may be capable of absorbing 5, 15, 20, 25, or more times their weight in oil or other hydrophobic material, as illustratively shown in
Some embodiments comprise a method of manufacturing a polyurea aerogel, the method comprising: mixing an isocyanate and water and a trialkylamine in a solvent to form a sol-gel material; and drying the sol-gel material to form the polyurea aerogel. In some embodiments, the isocyanate is a triisocyanate. In some embodiments, the isocyanate is a diisocyanate. In some embodiments, the trialkylamine is a triethylamine. Certain embodiments further comprise agitating a mixture of the isocyanate, water and trialkylamine to form the sol-gel material. In some embodiments, manufacturing the polyurea aerogel comprises manufacturing a variable density polyurea aerogel. In some embodiments, drying the sol-gel material comprises supercritically drying the sol-gel material. In some embodiments, drying the sol-gel material comprises subcritically drying the sol-gel material. In some embodiments, the solvent comprises acetone. In some embodiments, the solvent comprises DMSO.
Certain embodiments relate to a method of manufacturing a three-dimensional nanostructured network of polyurea, the method comprising: mixing an isocyanate and water and a trialkylamine in a solvent to form a sol-gel material; and drying the sol-gel material to form the three-dimensional nanostructured network of polyurea.
Some embodiments relate to a method of controlling density in a polyurea aerogel, the method comprising: mixing an isocyanate and water and a trialkylamine to form a sol-gel material; and supercritically drying the sol-gel material to form the polyurea aerogel, wherein mixing an increasing amount of the isocyanate to form the sol-gel material gives rise to an increasing density in the polyurea aerogel. In some embodiments, mixing a decreasing amount of the isocyanate to form the sol-gel material gives rise to a decreasing density in the polyurea aerogel.
Some embodiments relate to a method of controlling morphology in a polyurea aerogel, the method comprising: mixing an isocyanate and water and a trialkylamine to form a sol-gel material; and supercritically drying the sol-gel material to form the polyurea aerogel, wherein mixing a decreasing amount of the isocyanate to form the sol-gel material gives rise to an increasingly fibrous morphology in the polyurea aerogel. In some embodiments, mixing an increasing amount of the isocyanate to form the sol-gel material gives rise to an increasingly particulate morphology in the polyurea aerogel.
Certain embodiments relate to a fibrous aerogel comprising: a three dimensional network of nanoparticles including polyurea, the three dimensional network having fibrous morphology and a density of less than about 900 mg/cc. Some embodiments relate to an insulator, a lightweight structural material, an impact dampening material comprising the fibrous aerogel.
Some embodiments relate to a fibrous aerogel comprising: a three dimensional network of nanoparticles including polyurea, the three dimensional network having fibrous morphology and a density of less than about 150 mg/cc. In some embodiments, the three dimensional network of nanoparticles has a density of less than about 150 mg/cc.
Certain embodiments relate to a non-flammable aerogel comprising: a three dimensional network of nanoparticles including polyurea, the three dimensional network having a density of greater than about 150 mg/cc and exhibiting a reduced flammability. In some embodiments, the three dimensional network has a particulate morphology.
Some embodiments relate to a method of manufacturing a carbon aerogel, the method comprising: mixing an isocyanate and water and a trialkylamine to form a sol-gel material; supercritically drying the sol-gel material to form a polyurea aerogel; and pyrolyzing the polyurea aerogel to form the carbon aerogel. In some embodiments, the isocyanate is a triisocyanate. In some embodiments, the isocyanate is a diisocyanate. In some embodiments, the trialkylamine is a triethylamine. Some embodiments further comprise agitating a mixture of the isocyanate, water and trialkylamine to form the sol-gel material.
Certain embodiments relate to a fibrous aerogel comprising: a three dimensional network of nanoparticles including a purely carbon skeleton, the three dimensional network having fibrous morphology and a density of less than about 900 mg/cc. Some embodiments relate to an electrode, a battery, a super capacitor device, an insulator, a ballistic material, an ablative material, an armor comprising the fibrous aerogel.
Some embodiments relate to a fibrous aerogel comprising: a three dimensional network of nanoparticles including a purely carbon skeleton, the three dimensional network having fibrous morphology and a density of less than about 150 mg/cc. In some embodiments, the three dimensional network of nanoparticles has a density of less than about 90 mg/cc.
Certain embodiments relate to a hierarchically porous polyurea foam exhibiting nanometer-scale pores, micron-scale pores, and macroscopic voids.
Some embodiments relate to a method of manufacturing hierachially porous polyurea foams, the method comprising: mixing an isocyanate and water and a trialkylamine in a solvent to form a sol-gel material; and drying the sol-gel material to form the polyurea aerogel. In some embodiments, the solvent comprises a solvent which enables formation of CO2-containing voids. In some embodiments, the solvent comprises
DMSO. In some embodiments, the solvent comprises acetone. In some embodiments, drying the sol-gel material comprises supercritically drying the sol-gel material. In some embodiments, drying the sol-gel material comprises subcritically drying the sol-gel material.
Certain embodiments relate to a method of manufacturing hierachially porous carbon foams, the method comprising: mixing an isocyanate and water and a trialkylamine in a solvent to form a sol-gel material; drying the sol-gel material to form the polyurea aerogel; and pyrolyzing the polyurea aerogel to form the carbon aerogel. In some embodiments, the solvent comprises a solvent which enables formation of CO2-containing voids. In some embodiments, the solvent comprises DMSO. In some embodiments, the carbon foam is etched to introduce micropores. In some embodiments, CO2 is used to etch the carbon foam. In some embodiments, the carbon foam exhibits nanometer-scale pores, micron-scale pores, and macroscopic voids. In some embodiments, drying the sol-gel material comprises supercritically drying the sol-gel material. In some embodiments, drying the sol-gel material comprises subcritically drying the sol-gel material. In some embodiments, the solvent comprises acetone.
Certain embodiments relate to a method of absorbing a liquid-phase material comprising contacting the liquid-phase material with a three-dimensional porous polyurea network. In some embodiments, the liquid-phase material is oil. In some embodiments, the three-dimensional porous polyurea network is an aerogel.
Polyurea aerogels were prepared from monomers of Desmodur N3300A triisocyanate, Desmodur RE triisocyanate, Desmodur N3200 diisocyanate, toluene diisocyanate (Mondur TDS) and MDI (Mondur CD), obtained from Bayer Corporation. Desmodur RE was supplied as a solution in ethyl acetate, which was removed with a rotary evaporator before use. Anhydrous acetone was produced from lower grade solvent by distilling over P2O5. Triethylamine (99% pure) was purchased from ACROS and was distilled before use.
Polyurea aerogels of different densities were prepared by varying the concentration of the monomer by dissolving samples of Desmodur N3300A in amounts of 1.375 g, 2.75 g, 5.5 g, 11.0 g, 16.5 g and 33 gin constant volume (94 mL) of dry acetone. Subsequently, for each monomer concentration, separate amounts of water at 1.5, 3.0, and 4.5 mol equivalents was added, and sols were obtained by adding triethylamine at 0.3%, 0.6% and 0.9% w/w relative to the total weight of the isocyanate monomer plus solvent. The final N3300A monomer concentrations were approximately 0.029 M, 0.056 M, 0.11 M, 0.21 M, 0.30 M, and 0.52 M. Thus, in one example, 1.375 g (0.0028 mol) of N3300A was dissolved in 94 mL of dry acetone, 1.5 mol equivalents of water (0.073 mL, 0.0042 mol) was added on top and finally the sol was obtained by adding 0.26 mL of triethylamine (0.3% w/w as defined above). The sol was shaken vigorously and was then poured into polypropylene syringes used as molds (AirTite Norm-Ject syringes without needles purchased from Fisher, Part No. 14-817-31, 1.40 mm I.D.). The top part of the syringes were cut off with a razor blade and, after the syringes were filled with the sol, they were covered with multiple layers of Parafilm and solutions were left to gel for approximately 24 h.
For comparison, gels with other isocyanates (Desmodur RE, Desmodur N3200 and Mondur TDS) were made by varying the amount of the monomer in such a way that the final molar concentrations of the monomers in the sols would be equal to those used for N3300A. For Desmodur RE triisocyanate, it was possible to obtain gels over the entire concentration range used with Desmodur N3300A. Gels from Desmodur N3200 and Mondur TDS were obtained for monomer concentrations above ˜0.20 M. Formulations and gelation times are summarized in Tables 4-11. Gels were aged for a day. Subsequently, gels were removed from their molds and were placed individually into fresh acetone ˜4× the volume of each gel. The solvent was exchanged two more times, every 24 h. Finally, wet gels were dried into polyurea aerogels with CO2 extracted supercritically. Alternatively, xerogels are obtained by ambient drying of acetone-filled wet gels, while aerogel-like materials are obtained from the two highest density samples (those made with [N3300A] at 0.3 or 0.5 M) by exchanging acetone with pentane (4 washes), followed by drying at 40° C. under ambient pressure.
Variable density polyurea aerogels were synthesized using a system similar to that shown in
Drying with SCF CO2 was conducted in an autoclave (SPI-DRY Jumbo Critical Point Dryer, SPI Supplies, Inc., West Chester, Pa.). Samples submerged in the last wash solvent were loaded in the autoclave and were extracted at 14° C. with liquid CO2 until no more solvent (acetone) came out. Then the temperature of the autoclave was raised above the critical point of CO2 (31.1° C., 73.8 bar), and the pressure was released isothermally at 40° C. All dry gels were in cylindrical form so that bulk (envelope) densities (ρb) were determined from their mass and volume, which in turn was determined from the geometric dimensions of each sample.
Skeletal densities (ρs) were determined using helium pycnometry with a Micromeritics AcuuPyc II 1340 instrument. Porosities, H, were determined from the ρb and ps values according to: P=100×[(1/ρb)−(1/ρs)]/(1/ρb). Surface areas (σ) were measured by nitrogen sorption porosimetry using a Micromeritics ASAP 2020 Surface Area and Pore Distribution Analyzer. Samples for surface area and skeletal density determinations were outgassed for 24 h at 80° C. under vacuum before analysis. Polyurea aerogels were characterized chemically by infrared spectroscopy (IR) in KBr compressed pellets using a Nicolet-FTIR Model 750 Spectrometer, and by solids13C NMR spectroscopy with samples ground in fine powders on a Bruker Avance 300 Spectrometer with 75.475 MHz carbon frequency using magic angle spinning (at 7 kHz), 7 mm rotors, broad band proton suppression, and the CPMAS TOSS pulse sequence for spin sideband suppression. The operating frequency for 13C was 75.483 MHz. 13C NMR spectra were externally referenced to the carbonyl of glycine (176.03 ppm relative to tetramethylsilane). SEM was conducted with samples coated with Au—Pd using a Hitachi S-4700 field emission microscope. The crystallinity of the polyurea samples was determined by x-ray diffraction (XRD) using a Scintag 2000 diffractometer with Cu Kα radiation and a proportional counter detector equipped with a flat graphite monochromator. The identity of the fundamental building blocks of the two materials was probed with small angle neutron scattering (SANS) using ˜2 mm thick discs cut with a diamond saw from cylinders, on a time of flight, low-Q diffractometer, LQD, at the Manuel Lujan Jr. Scattering Center of the Los Alamos National Laboratory. The scattering data were reported in the absolute units of differential cross section per unit volume (cm−1) as a function of Q, the momentum transferred during a scattering event. Thermogravimetric analysis TGA was conducted under N2, with a TA Instruments Model 2920 apparatus at a heating rate of 10° C./min. Quasistatic mechanical characterization (compression testing) was conducted according to the ASTM D695-02a standard on cylindrical specimens, using a MTS machine (Model 810) equipped with a 55000 lb load cell, as described previously. According to that ASTM standard, the height-to-diameter ratio of the specimen should be 2:1; typical samples were ˜1.3 cm in diameter, ˜2.6 cm long.
A number of SEM images will now be described. The SEM image of
The behavior under compression of high density PUA aerogels was assessed, with results shown in
In the example illustrated in
The synthesis of homogeneous samples and density gradient samples of polyurea aerogels, their materials characterization, and certain application specific properties are described.
Synthesis of uniform-density polyurea (PUA) aerogels and a photograph or representative samples made of Desmodur N3300A (densities reported below for each sample are in mg cm−3) is shown in
Wet gels were aged to ensure complete reaction of the monomer, solvent-exchanged (washed) with pure acetone and dried in an autoclave with liquid CO2 taken out at the end as a SCF. Washes were collected and no residual (unreacted) isocyanate was detected. Acetone wet gels are left to dry under ambient conditions and undergo extensive shrinkage and yield xerogel-like materials. Alternatively, by applying a method developed with polyurea-crosslinked silica aerogels, wet gels made with the two highest isocyanate concentrations (˜0.3 and 0.5 M) and solvent-exchanged with a low vapor pressure/surface tension solvent like pentane can be dried under ambient pressure at slightly elevated temperature (e.g., 40° C.), yielding materials similar in appearance and properties to those obtained by the SCF CO2 route. Ambient pressure drying was used for making larger monolithic aerogel pieces for evaluation in certain aeronautical and anti-ballistic applications.
Density-gradient polyurea aerogel samples were prepared using two pumps, one to transfer high concentration sol into a mold, while a second pump transfers and constantly dilutes the high concentration sol with a low concentration one the low concentration sol could be replaced with solvent. To minimize convective mixing of the two solutions in the mold, a rubber O-ring was fit inside the upper lip of the cylindrical mold, connected to a vertical wire. The sol slides down the wire, is spread around by the ring and slides down again along the inside walls of the mold. Appearance-wise, density-gradient aerogels were monolithic and indistinguishable from the uniform-density samples.
Formulations and Gelation Times of Samples Using Desmodur N3300A, Desmodur N3200, Desmodur RE and Mondur TDS
a Acetone-soaked wet-gels dried under ambient temperature and pressure.
b Single sample.
c Average of 5 samples dried with SCF CO2.
d Pentane-soaked wet-gels dried under ambient pressure at 40° C.
e Shrinkage = 100 × (sample diameter − mold diameter)/(mold diameter). Mold diameter: 1.40 cm.
f Single sample, average of 50 measurements.
a Average of 5 samples. (Mold diameter: 1.40 cm.)
b Shrinkage = 100 × (sample diameter − mold diameter)/(mold diameter).
c Single sample, average of 50 measurements.
d By the 4 × VTotal/σmethod. For the first number, VTotal was calculated by the single-point adsorption method; for the number in brackets VTotal was calculated via VTotal = (1/ρb) − (1/ρs).
e Calculated via r = 3/ρsσ.
a Average of 5 samples. (Mold diameter: 1.40 cm.)
b Shrinkage = 100 × (sample diameter − mold diameter)/(mold diameter).
c Single sample, average of 50 measurements.
d By the 4 × VTotal/σmethod. For the first number, VTotal was calculated by the single-point adsorption method; for the number in brackets VTotal was calculated via VTotal = (1/ρb) − (1/ρs).
e Calculated via r = 3/ρsσ.
a Average of 5 samples. (Mold diameter: 1.40 cm.)
b Shrinkage = 100 × (sample diameter − mold diameter)/(mold diameter).
c Single sample, average of 50 measurements.
d By the 4 × VTotal/σmethod. For the first number, VTotal was calculated by the single-point adsorption method; for the number in brackets VTotal was calculated via VTotal = (1/ρb) − (1/ρs).
e Calculated via r = 3/ρsσ.
a Average of 5 samples. (Mold diameter: 1.40 cm.)
b Shrinkage = 100 × (sample diameter − mold diameter)/(mold diameter).
c Single sample, average of 50 measurements.
d By the 4 × VTotal/σmethod. For the first number, VTotal was calculated by the single-point adsorption method; for the number in brackets VTotal was calculated via VTotal = (1/ρb) − (1/ρs).
e Calculated via r = 3/ρsσ.
a Average of 5 samples. (Mold diameter: 1.40 cm.)
b Shrinkage = 100 × (sample diameter − mold diameter)/(mold diameter).
c Single sample, average of 50 measurements.
d By the 4 × VTotal/σmethod. For the first number, VTotal was calculated by the single-point adsorption method; for the number in brackets VTotal was calculated via VTotal = (1/ρb) − (1/ρs).
e Calculated via r = 3/ρsσ.
25 ± 1.35
a Average of 5 samples. (Mold diameter: 1.40 cm.)
b Shrinkage = 100 × (sample diameter − mold diameter)/(mold diameter).
c Single sample, average of 50 measurements.
d By the 4 × VTotal/σmethod. For the first number, VTotal was calculated by the single-point adsorption method; for the number in brackets VTotal was calculated via VTotal = (1/ρb) − (1/ρs).
e Calculated via r = 3/ρsσ.
a Average of 5 samples. (Mold diameter: 1.40 cm.)
b Shrinkage = 100 × (sample diameter − mold diameter)/(mold diameter).
c Single sample, average of 50 measurements.
d By the 4 × VTotal/σmethod. For the first number, VTotal was calculated by the single-point adsorption method; for the number in brackets VTotal was calculated via VTotal = (1/ρb) − (1/ρs).
e Calculated via r = 3/ρsσ.
a Average of 5 samples. (Mold diameter: 1.40 cm.)
b Shrinkage = 100 × (sample diameter − mold diameter)/(mold diameter).
c Single sample, average of 50 measurements.
d By the BJH-desorption method; in brackets: width at half maximum.
e Calculated via r = 3/ρsσ.
Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modification, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.
This application is a continuation of U.S. patent application Ser. No. 16/374,958, filed Apr. 4, 2019, which is a continuation of U.S. patent application Ser. No. 13/214,061, filed Aug. 19, 2011, which claims the benefit of U.S. Provisional Application No. 61/375,757, filed Aug. 20, 2010, each of which is incorporated herein by reference in its entirety for all purposes.
This invention was made with government support under Grant Numbers CHE-0809562 and CMMI-0653919 awarded by the National Science Foundation. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61375757 | Aug 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16374958 | Apr 2019 | US |
| Child | 17515983 | US | |
| Parent | 13214061 | Aug 2011 | US |
| Child | 16374958 | US |
