Microspheres containing polydisperse polymer nanospheres, and porous metal oxide microspheres

Abstract

Porous metal oxide microspheres are provided that exhibit high quality visible color in bulk. [Solution] Porous microspheres comprising a metal oxide having a continuous solid structure, each having two or more pore populations with different average pore sizes distributed throughout the volume of the porous microsphere. Preferably, the porous microspheres have an average diameter of 4.5 μm to 9.9 μm, an average porosity of 0.45 to 0.65, and an average pore size of 220 nm to 300 nm.

Description

Technical Field

[0001] Disclosed are porous metal oxide microspheres, a method for producing the same, and uses thereof. The microspheres are suitable for use, for example, as structural colorants.

[0002] Background of the Invention Conventional pigments and dyes rely on chemical structure and exhibit color by light absorption and reflection. Structural colorants rely on physical structure rather than chemical structure and exhibit color by light interference effects. Structural colorants are found in nature, for example, in bird feathers, butterfly wings, and certain gemstone roughs. A structural colorant is a substance containing a microscopic structural surface that is small enough to interfere with visible light to generate color. Such substances can be based on photonic materials such as, but not limited to, opal, inverse opal, photonic microsolids, photonic spheres, or composite photonic crystals. The term "photonic material" refers to a material having a certain degree of periodic change in its structure.

[0003] Structural colorants can exhibit high stability. Therefore, when present in bulk, structural colorants that exhibit different colors of visible light and are observable with the naked eye are desirable. Such structural colorants can be incorporated into consumer products in place of pigments or dyes that are less stable and / or less environmentally considerate.

[0004] It has been found that certain porous metal oxide microspheres exhibit high-quality colors in bulk. The microspheres provide visible colors in bulk.

[0005] Summary of the Invention Accordingly, a method for producing polymer microspheres containing polydisperse polymer nanospheres is disclosed, the method comprising producing a solution or dispersion of monodisperse polymer nanoparticles; producing a solution or dispersion of at least one additional monodisperse polymer nanoparticle; mixing each of the solutions or dispersions with one another; producing droplets of the mixture; and drying the droplets to obtain polymer microspheres containing polydisperse polymer nanospheres, wherein the average diameters of the monodisperse polymer nanoparticles in each of the solutions or dispersions are different.

[0006] Polymer microspheres containing two or more populations of monodisperse polymer nanospheres are also disclosed, wherein each population of monodisperse polymer nanospheres has a different average diameter. A bulk sample of the polymer microspheres can exhibit a color observable to the human eye.

[0007] A method for producing porous metal oxide microspheres is also disclosed, the method comprising producing a solution or dispersion of monodisperse polymer nanoparticles; producing a solution or dispersion of at least one additional monodisperse polymer nanoparticle; mixing each of the solutions or dispersions with one another, wherein a metal oxide is added to one or more of the solutions or suspensions and / or to the mixture to produce a dispersion of polymer nanoparticles and metal oxide; producing droplets of the dispersion; drying the droplets to obtain polymer template microspheres containing polydisperse polymer nanospheres and metal oxide; and removing the polymer nanospheres from the template microspheres to obtain porous metal oxide microspheres, wherein the average diameters of the monodisperse polymer nanoparticles in each of the solutions or dispersions are different.

[0008] Disclosed are also porous microspheres containing metal oxides, having an average diameter of about 0.5 μm to about 100 μm, and an average porosity of about 0.10 to about 0.90 or about 0.10 to about 0.80, wherein the porous microspheres have two or more pore populations, each population having an average pore diameter, and each population having a different average pore diameter; the average pore diameter is about 50 nm to about 999 nm; for example, the microspheres have a first pore population having an average pore diameter of about 50 nm to about 999 nm and a second pore population having an average pore diameter of about 50 nm to about 999 nm, and the first average pore diameter is different from the second average pore diameter.

[0009] Disclosed are also porous microspheres containing metal oxides, wherein the bulk sample of the porous microspheres exhibits a color observable to the human eye.

[0010] Also disclosed is a composition comprising a substrate and the present microspheres, for example, the composition is an aqueous formulation, an oil-based formulation, a coating formulation, an ink, a food, a plastic, a cosmetic formulation, or a material for medical or security applications.

[0011] The disclosure described herein is illustrated by way of example and not limitation in the accompanying drawings. For the sake of brevity and clarity of illustration, the features illustrated in the figures are not necessarily drawn to scale. For example, the dimensions of some features may be emphasized relative to other features for clarity. Further, reference numerals are repeated across the figures as appropriate to refer to corresponding or similar elements.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

[0013] Detailed Description of the Invention The present metal oxide microspheres, or photonic balls, can be manufactured using a polymeric sacrificial template. In one embodiment, an aqueous colloidal dispersion containing polymer nanoparticles and a metal oxide is produced, and the polymer particles are typically on the nanoscale. This aqueous colloidal dispersion is mixed with an oil continuous phase, for example, within a microfluidic device, to produce a water-in-oil emulsion. Emulsion water droplets are produced, collected, and dried to produce microspheres containing polymer nanoparticles and a metal oxide. The polymer nanoparticles (nanospheres) are then removed, for example, by calcination, to obtain micron-scale metal oxide particles (microspheres) of the spheres, which are highly porous and contain nanoscale pores. As a result of the polymer particles being polydisperse, the microspheres can contain different pore sizes.

[0014] FIG. 1 shows an overview of the production of the present porous microspheres. When the emulsion droplets containing polymer nanospheres and a metal oxide are dried to remove the solvent, an aggregate of microspheres containing polymer nanospheres is obtained, and the polymer nanospheres contain a metal oxide in the interstitial space therebetween (template microspheres or "direct structure"). The polymer nanospheres are polydisperse. The polymer nanospheres define the interstitial space. As a result of calcination, the polymer is removed, and the present metal oxide microspheres with a large porosity or void volume are obtained (inverse structure).

[0015] The porous metal oxide microspheres are preferably sintered, resulting in a thermally and mechanically stable continuous solid structure.

[0016] In some embodiments, the formation and collection of droplets occur within a microfluidic device. The microfluidic device is, for example, a narrow channel device connected to a collection reservoir that has a micron-scale droplet junction configured to produce droplets of uniform size. The microfluidic device houses a droplet junction having a channel width of, for example, from about 10 μm to about 100 μm. The device is made of, for example, polydimethylsiloxane (PDMS) and can be fabricated, for example, by soft lithography. When the aqueous dispersed phase and the oil continuous phase are fed into the device at specific rates, they are mixed within the device to produce an emulsion within the device, and emulsion droplets can be obtained. Alternatively, a water-in-oil emulsion may be used.

[0017] In some embodiments, the vibrating nozzle technique may be used. With these techniques, a dispersion is produced; droplets are formed; and the droplets are dropped into a bath of the continuous phase. The droplets are then dried and calcined. The vibrating nozzle apparatus is available from Buechi and includes, for example, a syringe pump and a pulsation unit. The vibrating nozzle apparatus may also include a pressure regulating valve.

[0018] The polymer nanoparticles have, for example, an average diameter of from about 50 nm to about 999 nm. The polymer nanospheres are polydisperse. In the present invention, a polydisperse sample of polymer nanospheres contains two or more monodisperse populations of polymer nanospheres, i.e., at least a first and a second monodisperse population of polymer nanospheres, and the first average particle size is different from the second average particle size.

[0019] Suitable template polymers include thermoplastic polymers. For example, the template polymer is selected from the group consisting of poly(meth)acrylic acid, poly(meth)acrylate, polystyrene, polyacrylamide, polyvinyl alcohol, polyvinyl acetate, polyester, polyurethane, polyethylene, polypropylene, polylactic acid, polyacrylonitrile, polyvinyl ether, its derivatives, its salts, its copolymers, and combinations thereof. For example, the polymer is polymethyl methacrylate, polyethyl methacrylate, poly(n-butyl methacrylate), polystyrene, poly(chlorostyrene), poly(alpha-methylstyrene), poly(N-methylolacrylamide), styrene / methyl methacrylate copolymer, polyalkylated acrylate, polyhydroxyl acrylate, polyamino acrylate, polycyano acrylate, polyfluorinated acrylate, poly(N-methylolacrylamide), polyacrylic acid, polymethacrylic acid, methyl methacrylate / ethyl acrylate / acrylic acid copolymer, styrene / methyl methacrylate / acrylic acid copolymer, polyvinyl acetate, polyvinyl pyrrolidone, polyvinyl caprolactone, polyvinyl caprolactam, its derivatives, its salts, and combinations thereof.

[0020] In certain embodiments, various polystyrenes such as polystyrene and polystyrene copolymers are included as the polymer template. Examples of polystyrene copolymers include copolymers with water-soluble monomers such as polystyrene / acrylic acid, polystyrene / poly(ethylene glycol) methacrylate, and polystyrene / styrene sulfonate.

[0021] Examples of the present metal oxides include oxides of transition metals, metalloids, and rare earths such as silica, titania, alumina, zirconia, ceria, iron oxide, zinc oxide, indium oxide, tin oxide, chromium oxide, mixed metal oxides, combinations thereof, and the like.

[0022] The wt / wt (weight / weight) ratio of the polymer nanoparticles to the metal oxide is, for example, from about 0.1 / 1 to about 10.0 / 1, or from about 0.5 / 1 to about 10.0 / 1.

[0023] The oil continuous phase contains, for example, an organic solvent, a silicone oil, or a fluorinated oil. In the present invention, "oil" means an organic phase immiscible with water. Examples of the organic solvent include hydrocarbons such as heptane, hexane, toluene, xylene, etc., and alkanols such as methanol, ethanol, propanol, and others.

[0024] The emulsion droplets are collected, dried, and the polymer is removed. Drying is carried out, for example, by microwave irradiation, in a thermal oven, under vacuum, in the presence of a desiccant, by spray drying techniques, or a combination thereof.

[0025] The polymer removal can be carried out, for example, by calcination, by pyrolysis, or using a solvent (solvent removal). Calcination is carried out, in some embodiments, at a temperature of at least about 200°C, at least about 500°C, at least about 1000°C, from about 200°C to about 1200°C, or from about 200°C to about 700°C. Calcination can be carried out for a suitable time, for example, from about 0.1 hour to about 12 hours, or from about 1 hour to about 8.0 hours. In other embodiments, calcination can be at least about 0.1 hour, at least about 1 hour, at least about 5 hours, or at least about 10 hours.

[0026] Alternatively, a dispersion containing polymer nanoparticles and a metal oxide is made using an oil dispersed phase and a water continuous phase so that a water-in-oil emulsion is formed. Similar to the case of water droplets, the oil droplets can be collected and dried.

[0027] Alternatively, a dispersion of polymer nanoparticles and metal oxide is produced and spray dried to produce polymer template microspheres without forming a liquid-in-liquid emulsion. In certain embodiments of the spray drying technique, a solution or dispersion is fed (e.g., supplied) to a spray nozzle connected to a compressed gas inlet. The feed is fed through the spray nozzle to form droplets. These droplets are surrounded by preheated gas in an evaporation chamber, such that the solvent evaporates to produce solid particles. The dried particles are carried through a cyclone by the drying gas and deposited in a collection chamber. Examples of the gas include nitrogen and / or air. In one embodiment of the present spray drying process, the liquid feed contains an aqueous or oil phase, polymer particles, and optionally a metal oxide. Polymer microspheres containing polymer nanospheres are obtained, and optionally a metal oxide is included in the interstitial space between the polymer nanospheres. The polymer nanospheres define the interstitial space. The spray drying method includes an inkjet spray drying method and apparatus.

[0028] In this spray drying technique, air can be regarded as the continuous phase with respect to the dispersed liquid phase (liquid-in-gas emulsion). In certain embodiments, the spray drying includes an inlet temperature from any of about 100 °C, about 105 °C, about 110 °C, about 115 °C, about 120 °C, about 130 °C, about 140 °C, about 150 °C, about 160 °C, or about 170 °C to any of about 180 °C, about 190 °C, about 200 °C, about 210 °C, about 215 °C, or about 220 °C. In some embodiments, a feed rate (feed flow rate) from any of about 1 mL / min, about 2 mL / min, about 5 mL / min, about 6 mL / min, about 8 mL / min, about 10 mL / min, about 12 mL / min, about 14 mL / min, or about 16 mL / min to any of about 18 mL / min, about 20 mL / min, about 22 mL / min, about 24 mL / min, about 26 mL / min, about 28 mL / min, or about 30 mL / min is used. The spray drying technique is disclosed, for example, in U.S. Patent Application Publication No. 2016 / 0170091.

[0029] Figure 4 is a representative diagram of the spray drying process of some embodiments of the present invention.

[0030] In certain embodiments of the spray drying technique, a feed solution or dispersion is supplied to a spray nozzle connected to a compressed gas inlet. The feed is fed through the spray nozzle to form droplets. These droplets are surrounded by a preheated gas in an evaporation chamber, and as a result, the solvent evaporates to produce solid particles. The dried particles are carried through a cyclone by a drying gas and deposited in a collection chamber. Examples of the gas include nitrogen and / or air. In this spray drying process, the liquid feed contains water, polymer nanoparticles, and metal oxides.

[0031] The microspheres are spherical or sphere-like and are on the micron scale, having an average diameter, for example, of about 0.5 micron (μm) to about 100 μm. The polymer nanoparticles used as a template are also spherical and are on the nanoscale, having an average diameter, for example, of about 50 nm to about 999 nm. The metal oxides used may also be in the form of particles, and the particles may be on the nanoscale.

[0032] The metal oxide of the dispersion may be prepared as a metal oxide or from a metal oxide precursor, for example, by a sol-gel technique.

[0033] When the polymer / metal oxide droplets are dried and the polymer is removed, microspheres having voids (pores) are obtained. Generally, in this process, each droplet gives one microsphere. The pore diameter depends on the size of the polymer particles. After the polymer is removed, some "shrinkage" or compression may occur, and the pore size becomes somewhat smaller than the original polymer particle size, for example, about 10% to about 40% smaller than the polymer particle size. The pore diameter varies (i.e., is polydisperse) as the size of the polymer particles varies.

[0034] In some embodiments, the pore diameter can range from about 50 nm to about 999 nm.

[0035] The average porosity of the present metal oxide microspheres can be relatively high, for example, about 0.10 or about 0.30 to about 0.80 or about 0.90. The average porosity of the microspheres means the total pore volume as a fraction of the total volume of the microspheres. The average porosity may also be referred to as "volume fraction".

[0036] In some embodiments, the porous microspheres may have a solid core (center), in which case they are generally porous towards the outer surface of the microspheres. In other embodiments, the porous microspheres may have a hollow core, in which case most of the porosity is directed towards the interior of the microspheres. In other embodiments, the porosity may be distributed throughout the volume of the microspheres. In other embodiments, the porosity may exist as a gradient, in which case the porosity is higher towards the outer surface of the microspheres and lower or zero towards the center (solid core); or the porosity is lower towards the outer surface and higher or completely porous towards the center (hollow).

[0037] Any of the porous microspheres has an average microsphere diameter that is larger than the average pore diameter. For example, the average microsphere diameter is at least about 25 times, at least about 30 times, at least about 35 times, or at least about 40 times larger than the average pore diameter.

[0038] In some embodiments, the ratio of the average microsphere diameter to the average pore diameter is, for example, from any of about 40 / 1, about 50 / 1, about 60 / 1, about 70 / 1, about 80 / 1, about 90 / 1, about 100 / 1, about 110 / 1, about 120 / 1, about 130 / 1, about 140 / 1, about 150 / 1, about 160 / 1, about 170 / 1, about 180 / 1, or about 190 / 1 to any of about 200 / 1, about 210 / 1, about 220 / 1, about 230 / 1, about 240 / 1, about 250 / 1, about 260 / 1, about 270 / 1, about 280 / 1, about 290 / 1, about 300 / 1, about 310 / 1, about 320 / 1, about 330 / 1, about 340 / 1, or about 350 / 1.

[0039] Polymer template microspheres containing polydisperse polymer nanospheres can generally provide metal oxide microspheres with pores having different pore sizes when the polymer is removed.

[0040] Without being bound by theory, it is believed that a bulk sample of the microspheres exhibits a saturated color with reduced undesirable light scattering when the porosity and / or the microsphere diameter and / or the pore size are within a specific range. Since colorants are used in bulk in, for example, paints, inks, coatings, cosmetics, or materials for medical or security applications, the color characteristics of the bulk sample are important. In some embodiments, white microspheres are desirable, for example, for use as a white colorant.

[0041] The porous microspheres mainly contain metal oxides, that is, they may consist essentially of metal oxides or consist of metal oxides. Advantageously, a bulk sample of the porous microspheres exhibits a color observable to the human eye. There may also be a light absorber in the microspheres, which can give a more saturated observable color. Examples of the absorber include inorganic pigments and organic pigments, such as broadband absorbers like carbon black. The absorber can be added, for example, by physically mixing the microspheres and the absorber, or by including the absorber in droplets that are then dried. In the case of carbon black, carbon black may be produced in situ from polymer decomposition using controlled calcination. These microspheres may not exhibit an observable color without the addition of a light absorber, but will exhibit an observable color if a light absorber is added.

[0042] The porous microspheres can be used as colorants for, for example, aqueous formulations, oily formulations, inks, coating formulations, foods, plastics, cosmetic formulations, or materials for medical or security applications. Examples of coating formulations include automotive coatings, architectural coatings, varnishes, and the like.

[0043] This porous metal oxide microsphere may exhibit angle-dependent color or angle-independent color. "Angle-dependent" color means that the observed color depends on the angle of incident light with respect to the sample or the angle between the observer and the sample. "Angle-independent" color means that the observed color does not substantially depend on either the angle of incident light with respect to the sample or the angle between the observer and the sample.

[0044] Angle-independent color can be achieved, for example, using polydisperse polymer nanospheres. Angle-independent color can also be achieved by promptly performing the step of drying the droplets to obtain polymer template microspheres without regularizing the polymer nanospheres. Angle-dependent color can be achieved by slowly performing the step of drying the droplets.

[0045] For example, the porous microsphere may contain about 60.0 wt% (weight percent) to about 99.9 wt% of metal oxide and about 0.1 wt% to about 40.0 wt% of one or more light absorbers with respect to the total weight of the microsphere.

[0046] Polymer microspheres containing polydisperse polymer nanospheres, methods for manufacturing them, and compositions containing them are also the subject of the present invention. The method includes manufacturing an aqueous dispersion of monodisperse polymer nanoparticles; manufacturing at least one further aqueous dispersion of monodisperse polymer nanoparticles; preparing an oil continuous phase; mixing the aqueous dispersion and the oil phase to produce a water-in-oil emulsion; producing emulsion droplets; and drying the emulsion droplets to obtain polymer microspheres containing polydisperse polymer nanospheres, where the average diameters of the monodisperse polymer nanoparticles in each dispersion are different.

[0047] Advantageously, the porous microsphere and the polymer microsphere can be monodisperse.

[0048] In the present invention, particle size is synonymous with diameter and is determined, for example, by a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The average particle size is synonymous with D50, which means that half of the population is above that point and half is below. The particle size refers to primary particles. The particle size can be measured by laser light scattering techniques using a dispersion or a dry powder.

[0049] Mercury porosimetry analysis was used to characterize the porosity of the microspheres. In mercury porosimetry, pressure is applied under control to a sample immersed in mercury. The mercury under external pressure penetrates into the voids / pores of the substance. The amount of pressure required for intrusion into the voids / pores is inversely proportional to the size of the voids / pores. The mercury porosimeter generates a volume and pore size distribution using the Washburn equation from the pressure versus intrusion data generated by the instrument. For example, a porous silica microsphere containing voids / pores with an average size of 165 nm has an average porosity of 0.8.

[0050] The term "bulk sample" means a population of microspheres. For example, a bulk sample of microspheres is simply a bulk population of microspheres of, for example, ≧0.5 mg, ≧0.7 mg, ≧1.0 mg, ≧2.5 mg, ≧5.0 mg, ≧10.0 mg, or ≧25.0 mg. A bulk sample of microspheres may substantially contain no other components. The term "porous microspheres" may mean a bulk sample.

[0051] The phrase "exhibiting a color observable to the human eye" means that the color is observed by an average person. This applies to any bulk sample distributed over any surface area, for example, from about 1 cm 2 to about 2 cm 2 to about 3 cm 2 to about 4 cm 2 to about 5 cm 2 or to about 6 cm 2 and from any of these to about 7 cm 2 to about 8 cm 2 to about 9 cm 2 to about 10 cm 2, about 11 cm 2 , about 12 cm 2 , about 13 cm 2 , about 14 cm 2 , or about 15 cm 2 Relates to a bulk sample distributed over a surface area up to any of the above. It may also mean observable by a CIE 1931 2° standard observer and / or a CIE 1964 10° standard observer. The background for color observation can be any background, for example, a white background, a black background, or a somewhat blackish background anywhere from white to black.

[0052] The term "~ of" may mean "including ~", for example, "dispersion of ~" may be interpreted as "dispersion including ~".

[0053] In this specification, terms such as "microsphere", "nanosphere", "droplet", etc. may mean, for example, their plural, their collection, their population, their sample, or their bulk sample.

[0054] The term "micro" or "microscale" means from about 0.5 μm to about 999 μm. The term "nano" or "nanoscale" means from about 1 nm to about 999 nm.

[0055] The terms "sphere" and "particle" may be interchangeable with each other.

[0056] The term "monodisperse" regarding a population of microspheres or nanospheres means that the particles have generally uniform shape and generally uniform diameter. This monodisperse population of microspheres or nanospheres may have, for example, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% of the number of particles having a diameter within ±7%, ±6%, ±5%, ±4%, ±3%, ±2%, or ±1% of the average diameter of the population. The term "monodisperse polymer nanoparticles" refers to a population of monodisperse polymer nanoparticles.

[0057] The term "polydisperse" with respect to nanospheres means that the sample contains a first monodisperse population having a first average diameter and at least a second monodisperse population having a second average diameter, and the first diameter is different from the second diameter. A microsphere polydisperse sample contains at least two monodisperse populations and may contain three, four, five, six, or other monodisperse populations each having a different average particle size. A polydisperse sample having only first and second monodisperse polymer nanospheres is a "two-mode" sample and has a two-mode particle size distribution.

[0058] The term "substantially free of other components" means containing other components at, for example, ≤5%, ≤4%, ≤3%, ≤2%, ≤1%, or ≤0.5% by weight. Similarly, the term "substantially absent" means almost or entirely absent.

[0059] "Matrix" may mean an aqueous or oily matrix or "medium", and the matrix can be a minor or major part of the final composition. Matrix may also mean solid, semi-solid, gel, liquid, paste, cream, etc.

[0060] Removing the polymer nanosphere monodisperse population gives a porous metal oxide microsphere having a corresponding pore population with an average pore diameter. Removing two or more polymer nanosphere monodisperse populations (polydisperse polymer nanospheres) gives a porous metal oxide microsphere having corresponding pore populations with different average pore diameters. That is, a porous metal oxide microsphere having two or more pore populations each having an average pore diameter, each population having a different average pore diameter, and these average pore diameters being from about 50 nm to about 999 nm.

[0061] The polymer nanosphere diameter of the polymer microsphere and the pore diameter of the porous microsphere can be, for example, two-mode, three-mode, four-mode, etc.

[0062] As used herein, the articles “a” and “an” refer to one or more than one (e.g., at least one) of the grammatical object. All ranges described herein include their endpoints. The term “about” as used throughout this specification is used to describe and account for small variations. For example, “about” can mean that a numerical value can vary by ±5%, ±4%, ±3%, ±2%, ±1%, ±0.5%, ±0.4%, ±0.3%, ±0.2%, ±0.1%, or ±0.05%. Whether or not explicitly stated, all numerical values are modified by the term “about”. Numerical values modified by the term “about” include the recited value. For example, “about 5.0” includes 5.0.

[0063] The U.S. patents, U.S. patent applications, and U.S. patent application publications described herein are hereby incorporated by reference.

[0064] Unless otherwise specified, all parts and percentages are by weight. Weight percentages (wt%) are based on the total composition excluding any volatiles, i.e., the dry solid components, unless otherwise specified.

[0065] A non-limiting first group of embodiments of the present disclosure relates to a method for producing polymer microspheres and includes the following.

[0066] In a first embodiment, a method for producing polymer microspheres comprising polydisperse polymer nanospheres is disclosed, the method comprising producing a solution or dispersion of monodisperse polymer nanoparticles; producing at least one additional solution or dispersion of monodisperse polymer nanoparticles; mixing each said solution or dispersion with one another; producing droplets of the mixture; and drying the droplets to obtain polymer microspheres comprising polydisperse polymer nanospheres, wherein the average diameter of the monodisperse polymer nanoparticles in each said solution or dispersion is different.

[0067] In some embodiments, drying the droplets can include microwave irradiation, oven drying, vacuum drying, drying in the presence of a desiccant, or a combination thereof.

[0068] In a second embodiment, the method of embodiment 1 includes mixing solutions or dispersions with each other and spray drying the mixture to obtain polymer microspheres. In a third embodiment, the method of embodiment 1 includes producing droplets using a vibrating nozzle. In a fourth embodiment, the method of embodiments 1 to 3, wherein the droplets are water droplets. In a fifth embodiment, the method of embodiments 1 to 3, wherein the droplets are oil droplets.

[0069] In a sixth embodiment, the method of embodiment 1 includes preparing a continuous phase and mixing a solution or dispersion with the continuous phase to produce an emulsion containing droplets of the dispersed solution or dispersion.

[0070] In a seventh embodiment, the method of embodiment 6 includes preparing an oil continuous phase and mixing an aqueous solution or dispersion with the oil continuous phase to produce a water-in-oil emulsion containing water droplets. In an eighth embodiment, the method of embodiment 6 includes preparing a water continuous phase and mixing an oily solution or dispersion with the continuous phase to produce an oil-in-water emulsion containing oil droplets. In a ninth embodiment, the method of embodiments 6 to 8 includes collecting the droplets.

[0071] In a tenth embodiment, the method of embodiment 9 includes drying the droplets to obtain polymer microspheres containing polydisperse polymer nanospheres. In an eleventh embodiment, the method of embodiments 6 to 10, wherein drying the droplets can include microwave irradiation, oven drying, vacuum drying, drying in the presence of a desiccant, or a combination thereof. In a twelfth embodiment, the method of embodiments 7 to 11, wherein the oil phase or solution or dispersion includes a hydrocarbon, a silicone oil, or a fluorinated oil. In a thirteenth embodiment, the method of embodiments 6 to 12, wherein the formation of the droplets is performed within a microfluidic device.

[0072] In the 14th embodiment, the method of embodiments 6 to 13, wherein the formation of the droplets is carried out in a microfluidic device accommodating a droplet junction having a channel width ranging from any one of about 10 μm, about 15 μm, about 20 μm, about 25 μm, about 30 μm, about 35 μm, about 40 μm, or about 45 μm to any one of about 50 μm, about 55 μm, about 60 μm, about 65 μm, about 70 μm, about 75 μm, about 80 μm, about 85 μm, about 90 μm, about 95 μm, or about 100 μm. In the 15th embodiment, the method of embodiment 13 or 14, including collecting emulsion droplets from the microfluidic device.

[0073] In the 16th embodiment, it includes producing a first solution or dispersion of first monodisperse polymer nanoparticles and producing a second solution or dispersion of second monodisperse polymer nanoparticles; for example, the wt / wt ratio of the first monodisperse polymer nanoparticles to the second monodisperse polymer nanoparticles ranges from any one of about 1 / 20, about 1 / 19, about 1 / 18, about 1 / 17, about 1 / 16, about 1 / 15, about 1 / 14, about 1 / 13, about 1 / 12, about 1 / 11, about 1 / 10, about 1 / 9, about 1 / 8, about 1 / 7, about 1 / 6, about 1 / 5, about 1 / 4, about 1 / 3, about 1 / 2, or about 1 / 1 to any one of about 2 / 1, about 3 / 1, about 4 / 1, about 5 / 1, about 6 / 1, about 7 / 1, about 8 / 1, about 9 / 1, about 10 / 1, about 11 / 1, about 12 / 1, about 13 / 1, about 14 / 1, about 15 / 1, about 16 / 1, about 17 / 1, about 18 / 1, about 19 / 1, or about 20 / 1, and is a method of any of the preceding embodiments.

[0074] In the 17th embodiment, the method of any of the preceding embodiments, wherein the polymer nanoparticles have an average diameter ranging from any one of about 50 nm, about 75 nm, about 100 nm, about 130 nm, about 160 nm, about 190 nm, about 210 nm, about 240 nm, about 270 nm, about 300 nm, about 330 nm, about 360 nm, about 390 nm, about 410 nm, about 440 nm, about 470 nm, about 500 nm, about 530 nm, about 560 nm, about 590 nm, or about 620 nm to any one of about 650 nm, about 680 nm, about 710 nm, about 740 nm, about 770 nm, about 800 nm, about 830 nm, about 860 nm, about 890 nm, about 910 nm, about 940 nm, about 970 nm, or about 990 nm.

[0075] In the 18th embodiment, the method of any of the preceding embodiments, wherein the polymer is selected from the group consisting of poly(meth)acrylic acid, poly(meth)acrylate, polystyrene, polyacrylamide, polyethylene, polypropylene, polylactic acid, polyacrylonitrile, derivatives thereof, salts thereof, copolymers thereof, and combinations thereof. In the 19th embodiment, the method of any of the preceding embodiments, wherein the polymer is selected from the group consisting of various polystyrenes, such as polystyrene copolymers such as polystyrene / acrylic acid, polystyrene / poly(ethylene glycol) methacrylate, or polystyrene / styrene sulfonate.

[0076] In the 20th embodiment, any method of the preceding embodiments, wherein the microspheres have an average diameter of from about 0.5 μm to about 100 μm. In the 21st embodiment, any method of the preceding embodiments, wherein the microspheres have an average diameter of from about 1 μm to about 75 μm, from about 2 μm to about 70 μm, from about 3 μm to about 65 μm, from about 4 μm to about 60 μm, from about 5 μm to about 55 μm, or from about 5 μm to about 50 μm; for example, any average diameter from any one of about 5 μm, about 6 μm, about 7 μm, about 8 μm, about 9 μm, about 10 μm, about 11 μm, about 12 μm, about 13 μm, about 14 μm, or about 15 μm to any one of about 16 μm, about 17 μm, about 18 μm, about 19 μm, about 20 μm, about 21 μm, about 22 μm, about 23 μm, about 24 μm, or about 25 μm. In the 22nd embodiment, any method of the preceding embodiments, wherein the microspheres have an average diameter from any one of about 4.5 μm, about 4.8 μm, about 5.1 μm, about 5.4 μm, about 5.7 μm, about 6.0 μm, about 6.3 μm, about 6.6 μm, about 6.9 μm, about 7.2 μm, or about 7.5 μm to any one of about 7.8 μm, about 8.1 μm, about 8.4 μm, about 8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μm, or about 9.9 μm.

[0077] In the 23rd embodiment, any method of the preceding embodiments, wherein the bulk sample of the polymer microspheres exhibits a color observable by the human eye. In the 24th embodiment, any method of the preceding embodiments, wherein the bulk sample of the polymer microspheres exhibits an angle-independent color observable by the human eye. In the 25th embodiment, any method of Embodiments 1 to 23, wherein the bulk sample of the polymer microspheres exhibits an angle-dependent color observable by the human eye.

[0078] In the 26th embodiment, any method of the preceding embodiments, wherein the microspheres are monodisperse. In the 27th embodiment, any method of the preceding embodiments, wherein the polymer microspheres are a bulk sample of the microspheres.

[0079] In the 28th embodiment, any method of the preceding embodiments, comprising adding a metal oxide to one or more of a solution or dispersion; or adding a metal oxide to a mixture.

[0080] In the 29th embodiment, polymer microspheres produced by any of the prior methods. In the 30th embodiment, a bulk sample of polymer microspheres produced by any of the prior methods.

[0081] A non-limiting second set of embodiments of the present invention relating to polymer microspheres includes the following.

[0082] Polymer microspheres comprising two or more populations of monodisperse polymer nanospheres, wherein each population of monodisperse polymer nanospheres has a different average diameter.

[0083] In the second embodiment, it includes a first population of monodisperse polymer nanoparticles and a second population of monodisperse polymer nanoparticles; for example, the wt / wt ratio of the first population of polymer nanospheres to the second population of polymer nanospheres is from any of about 1 / 20, about 1 / 19, about 1 / 18, about 1 / 17, about 1 / 16, about 1 / 15, about 1 / 14, about 1 / 13, about 1 / 12, about 1 / 11, about 1 / 10, about 1 / 9, about 1 / 8, about 1 / 7, about 1 / 6, about 1 / 5, about 1 / 4, about 1 / 3, about 1 / 2, or about 1 / 1 to any of about 2 / 1, about 3 / 1, about 4 / 1, about 5 / 1, about 6 / 1, about 7 / 1, about 8 / 1, about 9 / 1, about 10 / 1, about 11 / 1, about 12 / 1, about 13 / 1, about 14 / 1, about 15 / 1, about 16 / 1, about 17 / 1, about 18 / 1, about 19 / 1, or about 20 / 1. Polymer microspheres of Embodiment 1.

[0084] In the third embodiment, the polymer microspheres of Embodiment 1 or 2 having an average diameter from any one of about 100 nm, about 130 nm, about 160 nm, about 190 nm, about 210 nm, about 240 nm, about 270 nm, about 300 nm, about 330 nm, about 360 nm, about 390 nm, about 410 nm, about 440 nm, about 470 nm, about 500 nm, about 530 nm, about 560 nm, about 590 nm, or about 620 nm to any one of about 650 nm, about 680 nm, about 710 nm, about 740 nm, about 770 nm, about 800 nm, about 830 nm, about 860 nm, about 890 nm, about 910 nm, about 940 nm, or about 970 nm.

[0085] In the fourth embodiment, the polymer of the polymer microspheres of any of the preceding embodiments is selected from the group consisting of poly(meth)acrylic acid, poly(meth)acrylate, polystyrene, polyacrylamide, polyethylene, polypropylene, polylactic acid, polyacrylonitrile, its derivatives, its salts, its copolymers, and combinations thereof.

[0086] In the fifth embodiment, the polymer of the polymer microspheres of any of the preceding embodiments is selected from the group consisting of various polystyrenes, such as polystyrene copolymers such as polystyrene / acrylic acid, polystyrene / poly(ethylene glycol) methacrylate, or polystyrene / styrene sulfonate.

[0087] In the sixth embodiment, the polymers of each polymer nanosphere population are the same, and the polymer microspheres of any of the preceding embodiments. In the seventh embodiment, the polymers of each polymer nanosphere population are different, and the polymer microspheres of any of Embodiments 1 to 5.

[0088] In the eighth embodiment, a polymer microsphere of any of the previous embodiments having an average diameter of about 0.5 μm to about 100 μm. In the ninth embodiment, from about 1 μm to about 75 μm, about 2 μm to 70 μm, about 3 μm to about 65 μm, about 4 μm to about 60 μm, about 5 μm to about 55 μm, or about 5 μm to about 50 μm; for example, any of about 5 μm, about 6 μm, about 7 μm, about 8 μm, about 9 μm, about 10 μm, about 11 μm, about 12 μm, about 13 μm, about 14 μm, or about 15 μm to any of about 16 μm, about 17 μm, about 18 μm, about 19 μm, about 20 μm, about 21 μm, about 22 μm, about 23 μm, about 24 μm, or about 25 μm, a polymer microsphere of any of the previous embodiments having an average diameter. In the tenth embodiment, from any of about 4.5 μm, about 4.8 μm, about 5.1 μm, about 5.4 μm, about 5.7 μm, about 6.0 μm, about 6.3 μm, about 6.6 μm, about 6.9 μm, about 7.2 μm, or about 7.5 μm to any of about 7.8 μm, about 8.1 μm, about 8.4 μm, about 8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μm, or about 9.9 μm, a polymer microsphere of any of the previous embodiments having an average diameter.

[0089] In the twelfth embodiment, a polymer microsphere of any of the previous embodiments, wherein a bulk sample of the polymer microsphere exhibits a color observable by the human eye. In the thirteenth embodiment, a polymer microsphere of any of the previous embodiments, wherein a bulk sample of the polymer microsphere exhibits an angle-independent color observable by the human eye. In the fourteenth embodiment, a polymer microsphere of any of embodiments 1 to 12, wherein a bulk sample of the polymer microsphere exhibits an angle-dependent color observable by the human eye.

[0090] In the fifteenth embodiment, a polymer microsphere of any of the previous embodiments that is monodisperse.

[0091] In the sixteenth embodiment, a polymer microsphere of any of the previous embodiments further comprising a metal oxide.

[0092] A non-limiting third set of embodiments of the present invention related to a method for producing porous metal oxide microspheres includes the following.

[0093] In a first embodiment, a method for producing porous metal oxide microspheres is disclosed, the method comprising: producing a solution or dispersion of monodisperse polymer nanoparticles; producing at least one additional solution or dispersion of monodisperse polymer nanoparticles; mixing each of the solutions or dispersions with one another, wherein a metal oxide is added to one or more of the solutions or suspensions and / or a metal oxide is added to the mixture to produce a dispersion comprising polymer nanoparticles and a metal oxide; producing droplets of the dispersion; drying the droplets to obtain polymer template microspheres comprising polydisperse polymer nanospheres and a metal oxide; and removing the polymer nanospheres from the template microspheres to obtain porous metal oxide microspheres, wherein the average diameters of the monodisperse polymer nanoparticles in each of the solutions or dispersions are different.

[0094] In a second embodiment, the method of embodiment 1, comprising mixing solutions or dispersions with one another and spray-drying the mixture to obtain polymer template microspheres and removing the polymer nanospheres from the template microspheres.

[0095] In a third embodiment, the method of embodiment 1, comprising producing droplets using a vibrating nozzle. In a fourth embodiment, the method of embodiments 1 to 3, wherein the droplets are water droplets. In a fifth embodiment, the method of embodiments 1 to 3, wherein the droplets are oil droplets.

[0096] In a sixth embodiment, the method of embodiment 1, comprising preparing a continuous phase and mixing the dispersion with the continuous phase to produce an emulsion containing dispersed droplets of the dispersion. In a seventh embodiment, the method of embodiment 6, comprising preparing an oil continuous phase and mixing an aqueous dispersion with the oil continuous phase to produce a water-in-oil emulsion containing water droplets.

[0097] The method of Embodiment 6, including preparing a water continuous phase and mixing an oil dispersion and the continuous phase to produce an oil-in-water emulsion containing oil droplets. The method of Embodiment 9 includes collecting the droplets. The method of Embodiment 10 includes drying the droplets to obtain a polymer template microsphere containing polydisperse polymer nanospheres, which is the method of Embodiment 9.

[0098] The method of Embodiments 6 - 10, wherein drying the droplets includes microwave irradiation, oven drying, vacuum drying, drying in the presence of a desiccant, or a combination thereof.

[0099] The method of Embodiments 7 - 11, wherein the oil phase or solution or dispersion includes a hydrocarbon, a silicone oil, or a fluorinated oil.

[0100] The method of Embodiments 6 - 12, wherein the formation of the droplets is performed within a microfluidic device. The method of Embodiments 6 - 13, wherein the formation of the droplets is performed within a microfluidic device that houses a droplet junction having a channel width ranging from any one of about 10 μm, about 15 μm, about 20 μm, about 25 μm, about 30 μm, about 35 μm, about 40 μm, or about 45 μm to any one of about 50 μm, about 55 μm, about 60 μm, about 65 μm, about 70 μm, about 75 μm, about 80 μm, about 85 μm, about 90 μm, about 95 μm, or about 100 μm. The method of Embodiment 13 or 14 includes collecting emulsion droplets from the microfluidic device.

[0101] In the 16th embodiment, it includes manufacturing a first solution or dispersion of the first monodisperse polymer nanoparticles and manufacturing a second solution or dispersion of the second monodisperse polymer nanoparticles; for example, the wt / wt ratio of the first monodisperse polymer nanoparticles to the second monodisperse polymer nanoparticles is from any one of about 1 / 20, about 1 / 19, about 1 / 18, about 1 / 17, about 1 / 16, about 1 / 15, about 1 / 14, about 1 / 13, about 1 / 12, about 1 / 11, about 1 / 10, about 1 / 9, about 1 / 8, about 1 / 7, about 1 / 6, about 1 / 5, about 1 / 4, about 1 / 3, about 1 / 2, or about 1 / 1 to any one of about 2 / 1, about 3 / 1, about 4 / 1, about 5 / 1, about 6 / 1, about 7 / 1, about 8 / 1, about 9 / 1, about 10 / 1, about 11 / 1, about 12 / 1, about 13 / 1, about 14 / 1, about 15 / 1, about 16 / 1, about 17 / 1, about 18 / 1, about 19 / 1, or about 20 / 1, a method of any of the previous embodiments.

[0102] In the 17th embodiment, a method of any of the previous embodiments, wherein the polymer nanoparticles have an average diameter from any one of about 50 nm, about 75 nm, about 100 nm, about 130 nm, about 160 nm, about 190 nm, about 210 nm, about 240 nm, about 270 nm, about 300 nm, about 330 nm, about 360 nm, about 390 nm, about 410 nm, about 440 nm, about 470 nm, about 500 nm, about 530 nm, about 560 nm, about 590 nm, or about 620 nm to any one of about 650 nm, about 680 nm, about 710 nm, about 740 nm, about 770 nm, about 800 nm, about 830 nm, about 860 nm, about 890 nm, about 910 nm, about 940 nm, about 970 nm, or about 990 nm.

[0103] In the 18th embodiment, the polymer is selected from the group consisting of poly(meth)acrylic acid, poly(meth)acrylate, polystyrene, polyacrylamide, polyethylene, polypropylene, polylactic acid, polyacrylonitrile, derivatives thereof, salts thereof, copolymers thereof, and combinations thereof, according to any of the methods of the previous embodiments. In the 19th embodiment, the polymer is selected from the group consisting of various polystyrenes, such as polystyrene / acrylic acid, polystyrene / poly(ethylene glycol) methacrylate, or polystyrene / styrene sulfonate, according to any of the methods of the previous embodiments.

[0104] In the 20th embodiment, the metal oxide is one or more of silica, titania, alumina, zirconia, ceria, iron oxide, zinc oxide, indium oxide, tin oxide, or chromium oxide, according to any of the methods of the previous embodiments.

[0105] In the 21st embodiment, the wt / wt ratio of the total polymer nanoparticles to the metal oxide is from any of about 0.1 / 1, 0.5 / 1, about 1.0 / 1, about 1.5 / 1, about 2.0 / 1, about 2.5 / 1, or about 3.0 / 1 to any of about 3.5 / 1, about 4.0 / 1, about 5.0 / 1, about 5.5 / 1, about 6.0 / 1, about 6.5 / 1, about 7.0 / 1, about 8.0 / 1, about 9.0 / 1, or about 10.0 / 1, according to any of the methods of the previous embodiments.

[0106] In the 22nd embodiment, drying the droplets includes microwave irradiation, oven drying, vacuum drying, drying in the presence of a desiccant, or a combination thereof, according to any of the methods of the previous embodiments.

[0107] In the 23rd embodiment, removing the polymer nanospheres includes calcining the template microspheres at a temperature from any of about 200 °C, about 350 °C, about 400 °C, about 450 °C, about 500 °C, or about 550 °C to any of about 600 °C, about 650 °C, about 700 °C, or about 1200 °C for a time from any of about 0.1 hour, 1 hour, about 1.5 hours, about 2.0 hours, about 2.5 hours, about 3.0 hours, about 3.5 hours, or about 4.0 hours to any of about 4.5 hours, about 5.0 hours, about 5.5 hours, about 6.0 hours, about 6.5 hours, about 7.0 hours, about 7.5 hours, about 8.0 hours, or about 12 hours, according to any of the methods of the previous embodiments. Alternatively, the calcination can be carried out at a temperature of at least about 200 °C, at least about 500 °C, or at least about 1000 °C for a suitable time, such as at least about 0.1 hour, at least about 1 hour, at least about 5 hours, or at least about 10 hours.

[0108] In the 24th embodiment, the porous microspheres have an average diameter of about 0.5 μm to about 100 μm and an average porosity of about 0.10 to about 0.90 or about 0.10 to about 0.80; the porous microspheres each have two or more pore populations each having an average pore diameter, and each population has a different average pore diameter; the average pore diameter is about 50 nm to about 999 nm; for example, the porous microspheres have a first pore population having an average pore diameter of about 50 nm to about 999 nm and a second pore population having an average pore diameter of about 50 nm to about 999 nm, and the first average pore diameter and the second average pore diameter are different, according to any of the methods of the previous embodiments.

[0109] In the 25th embodiment, the porous microspheres have an average diameter of from about 1 μm to about 75 μm, from about 2 μm to about 70 μm, from about 3 μm to about 65 μm, from about 4 μm to about 60 μm, from about 5 μm to about 55 μm, or from about 5 μm to about 50 μm; for example, from any one of about 5 μm, about 6 μm, about 7 μm, about 8 μm, about 9 μm, about 10 μm, about 11 μm, about 12 μm, about 13 μm, about 14 μm, or about 15 μm to any one of about 16 μm, about 17 μm, about 18 μm, about 19 μm, about 20 μm, about 21 μm, about 22 μm, about 23 μm, about 24 μm, or about 25 μm, of the method of any of the preceding claims.

[0110] In the 26th embodiment, the porous microspheres have an average porosity of from any one of about 0.10, about 0.12, about 0.14, about 0.16, about 0.18, about 0.20, about 0.22, about 0.24, about 0.26, about 0.28, about 0.30, about 0.32, about 0.34, about 0.36, about 0.38, about 0.40, about 0.42, about 0.44, about 0.46, about 0.48, about 0.50, about 0.52, about 0.54, about 0.56, about 0.58, or about 0.60 to any one of about 0.62, about 0.64, about 0.66, about 0.68, about 0.70, about 0.72, about 0.74, about 0.76, about 0.78, about 0.80, or about 0.90, of the method of any of the preceding embodiments.

[0111] In the 27th embodiment, the porous microspheres have an average pore diameter of from any one of about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 100 nm, about 120 nm, about 140 nm, about 160 nm, about 180 nm, about 200 nm, about 220 nm, about 240 nm, about 260 nm, about 280 nm, about 300 nm, about 320 nm, about 340 nm, about 360 nm, about 380 nm, about 400 nm, about 420 nm, or about 440 nm to any one of about 460 nm, about 480 nm, about 500 nm, about 520 nm, about 540 nm, about 560 nm, about 580 nm, about 600 nm, about 620 nm, about 640 nm, about 660 nm, about 680 nm, about 700 nm, about 720 nm, about 740 nm, about 760 nm, about 780 nm, or about 800 nm, of the method of any of the preceding embodiments.

[0112] In the 28th embodiment, the porous microspheres have an average diameter ranging from any one of about 4.5 μm, about 4.8 μm, about 5.1 μm, about 5.4 μm, about 5.7 μm, about 6.0 μm, about 6.3 μm, about 6.6 μm, about 6.9 μm, about 7.2 μm, or about 7.5 μm to any one of about 7.8 μm, about 8.1 μm, about 8.4 μm, about 8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μm, or about 9.9 μm, and are made by any of the methods of the previous embodiments.

[0113] In the 29th embodiment, the porous microspheres have an average porosity ranging from any one of about 0.45, about 0.47, about 0.49, about 0.51, about 0.53, about 0.55, or about 0.57 to any one of about 0.59, about 0.61, about 0.63, or about 0.65, and are made by any of the methods of the previous embodiments.

[0114] In the 30th embodiment, the porous microspheres have an average pore diameter ranging from any one of about 220 nm, about 225 nm, about 230 nm, about 235 nm, about 240 nm, about 245 nm, or about 250 nm to any one of about 255 nm, about 260 nm, about 265 nm, about 270 nm, about 275 nm, about 280 nm, about 285 nm, about 290 nm, about 295 nm, or about 300 nm, and are made by any of the methods of the previous embodiments.

[0115] In the 31st embodiment, the porous microspheres have an average diameter ranging from any one of about 4.5 μm, about 4.8 μm, about 5.1 μm, about 5.4 μm, about 5.7 μm, about 6.0 μm, about 6.3 μm, about 6.6 μm, about 6.9 μm, about 7.2 μm, or about 7.5 μm to any one of about 7.8 μm, about 8.1 μm, about 8.4 μm, about 8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μm, or about 9.9 μm; an average porosity ranging from any one of about 0.45, about 0.47, about 0.49, about 0.51, about 0.53, about 0.55, or about 0.57 to any one of about 0.59, about 0.61, about 0.63, or about 0.65; and an average pore diameter ranging from any one of about 220 nm, about 225 nm, about 230 nm, about 235 nm, about 240 nm, about 245 nm, or about 250 nm to any one of about 255 nm, about 260 nm, about 265 nm, about 270 nm, about 275 nm, about 280 nm, about 285 nm, about 290 nm, about 295 nm, or about 300 nm, and are any of the methods of the previous embodiments.

[0116] In the 32nd embodiment, the porous microspheres contain from any one of about 60.0 wt% to about 99.9 wt% metal oxide, such as any one of about 60.0 wt%, about 64.0 wt%, about 67.0 wt%, about 70.0 wt%, about 73.0 wt%, about 76.0 wt%, about 79.0 wt%, about 82.0 wt%, or about 85.0 wt% to any one of about 88.0 wt%, about 91.0 wt%, about 94.0 wt%, about 97.0 wt%, about 98.0 wt%, about 99.0 wt%, or about 99.9 wt% metal oxide, based on the total weight of the microspheres, and are any of the methods of the previous embodiments.

[0117] In the 33rd embodiment, a method according to any of the preceding embodiments, wherein the porous microspheres contain one or more light absorbers in an amount of about 0.1 wt% to about 40.0 wt% based on the total weight of the microspheres, such as one or more light absorbers from any of about 0.1 wt%, about 0.3 wt%, about 0.5 wt%, about 0.7 wt%, about 0.9 wt%, about 1.0 wt%, about 1.5 wt%, about 2.0 wt%, about 2.5 wt%, about 5.0 wt%, about 7.5 wt%, about 10.0 wt%, about 13.0 wt%, about 17.0 wt%, about 20.0 wt%, or about 22.0 wt% to any of about 24.0 wt%, about 27.0 wt%, about 29.0 wt%, about 31.0 wt%, about 33.0 wt%, about 35.0 wt%, about 37.0 wt%, about 39.0 wt%, or about 40.0 wt%. In the 34th embodiment, a method according to any of the preceding embodiments, wherein the porous microspheres contain one or more light absorbers selected from the group consisting of inorganic pigments and organic pigments, such as carbon black.

[0118] In the 35th embodiment, a method according to any of the preceding embodiments, wherein a bulk sample of the porous microspheres exhibits a color observable by the human eye. In the 36th embodiment, a method according to any of the preceding embodiments, wherein a bulk sample of the porous microspheres exhibits an angle-independent color observable by the human eye. In the 37th embodiment, a method according to any of embodiments 1 to 35, wherein a bulk sample of the porous microspheres exhibits an angle-dependent color observable by the human eye.

[0119] In the 38th embodiment, a method according to any of the preceding embodiments, wherein the microspheres are monodisperse. In the 39th embodiment, a method according to any of the preceding embodiments, wherein the porous metal oxide microspheres are a bulk sample of the microspheres.

[0120] In the 40th embodiment, porous microspheres produced by any of the preceding methods. In the 41st embodiment, a bulk sample of microspheres produced by any of the preceding methods.

[0121] A non-limiting fourth set of embodiments of the present disclosure related to porous metal oxide microspheres includes the following.

[0122] In a first embodiment, there are provided porous microspheres comprising a metal oxide, having an average diameter of about 0.5 μm to about 100 μm and an average porosity of about 0.10 to about 0.80; having two or more pore populations, each having an average pore diameter, and each population having a different average pore diameter; the average pore diameter being about 50 nm to about 999 nm; for example, having a first pore population with an average pore diameter of about 50 nm to about 999 nm and a second pore population with an average pore diameter of about 50 nm to about 999 nm, and the first average pore diameter being different from the second average pore diameter.

[0123] In a second embodiment, the porous microspheres of embodiment 1 having an average diameter from about 1 μm to about 75 μm, from about 2 μm to about 70 μm, from about 3 μm to about 65 μm, from about 4 μm to about 60 μm, from about 5 μm to about 55 μm, or from about 5 μm to about 50 μm; for example, from any one of about 5 μm, about 6 μm, about 7 μm, about 8 μm, about 9 μm, about 10 μm, about 11 μm, about 12 μm, about 13 μm, about 14 μm, or about 15 μm to any one of about 16 μm, about 17 μm, about 18 μm, about 19 μm, about 20 μm, about 21 μm, about 22 μm, about 23 μm, about 24 μm, or about 25 μm.

[0124] In a third embodiment, the porous microspheres of embodiment 1 or 2 having an average porosity from any one of about 0.10, about 0.12, about 0.14, about 0.16, about 0.18, about 0.20, about 0.22, about 0.24, about 0.26, about 0.28, about 0.30, about 0.32, about 0.34, about 0.36, about 0.38, about 0.40, about 0.42, about 0.44, about 0.46, about 0.48, about 0.50, about 0.52, about 0.54, about 0.56, about 0.58, or about 0.60 to any one of about 0.62, about 0.64, about 0.66, about 0.68, about 0.70, about 0.72, about 0.74, about 0.76, about 0.78, about 0.80, or about 0.90.

[0125] In the fourth embodiment, a porous microsphere according to any of the previous embodiments, wherein the average pore diameter ranges from any one of about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 100 nm, about 120 nm, about 140 nm, about 160 nm, about 180 nm, about 200 nm, about 220 nm, about 240 nm, about 260 nm, about 280 nm, about 300 nm, about 320 nm, about 340 nm, about 360 nm, about 380 nm, about 400 nm, about 420 nm, or about 440 nm to any one of about 460 nm, about 480 nm, about 500 nm, about 520 nm, about 540 nm, about 560 nm, about 580 nm, about 600 nm, about 620 nm, about 640 nm, about 660 nm, about 680 nm, about 700 nm, about 720 nm, about 740 nm, about 760 nm, about 780 nm, or about 800 nm.

[0126] In the fifth embodiment, a porous microsphere according to any of the previous embodiments, having an average diameter ranging from any one of about 4.5 μm, about 4.8 μm, about 5.1 μm, about 5.4 μm, about 5.7 μm, about 6.0 μm, about 6.3 μm, about 6.6 μm, about 6.9 μm, about 7.2 μm, or about 7.5 μm to any one of about 7.8 μm, about 8.1 μm, about 8.4 μm, about 8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μm, or about 9.9 μm.

[0127] In the sixth embodiment, a porous microsphere according to any of the previous embodiments, having an average porosity ranging from any one of about 0.45, about 0.47, about 0.49, about 0.51, about 0.53, about 0.55, or about 0.57 to any one of about 0.59, about 0.61, about 0.63, or about 0.65.

[0128] In the seventh embodiment, a porous microsphere according to any of the previous embodiments, wherein the average pore diameter ranges from any one of about 220 nm, about 225 nm, about 230 nm, about 235 nm, about 240 nm, about 245 nm, or about 250 nm to any one of about 255 nm, about 260 nm, about 265 nm, about 270 nm, about 275 nm, about 280 nm, about 285 nm, about 290 nm, about 295 nm, or about 300 nm.

[0129] In the eighth embodiment, an average diameter ranging from any one of about 4.5 μm, about 4.8 μm, about 5.1 μm, about 5.4 μm, about 5.7 μm, about 6.0 μm, about 6.3 μm, about 6.6 μm, about 6.9 μm, about 7.2 μm, or about 7.5 μm to any one of about 7.8 μm, about 8.1 μm, about 8.4 μm, about 8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μm, or about 9.9 μm; an average porosity ranging from any one of about 0.45, about 0.47, about 0.49, about 0.51, about 0.53, about 0.55, or about 0.57 to any one of about 0.59, about 0.61, about 0.63, or about 0.65; and an average pore diameter ranging from any one of about 220 nm, about 225 nm, about 230 nm, about 235 nm, about 240 nm, about 245 nm, or about 250 nm to any one of about 255 nm, about 260 nm, about 265 nm, about 270 nm, about 275 nm, about 280 nm, about 285 nm, about 290 nm, about 295 nm, or about 300 nm. The porous microspheres of any of the preceding embodiments.

[0130] In the ninth embodiment, a metal oxide in an amount of about 60.0 wt% to about 99.9 wt% based on the total weight of the microspheres, for example, any one of about 60.0 wt%, about 64.0 wt%, about 67.0 wt%, about 70.0 wt%, about 73.0 wt%, about 76.0 wt%, about 79.0 wt%, about 82.0 wt%, or about 85.0 wt% to any one of about 88.0 wt%, about 91.0 wt%, about 94.0 wt%, about 97.0 wt%, about 98.0 wt%, about 99.0 wt%, or about 99.9 wt%. The porous microspheres of any of the preceding embodiments.

[0131] In the tenth embodiment, the metal oxide is selected from the group consisting of silica, titania, alumina, zirconia, ceria, iron oxide, zinc oxide, indium oxide, tin oxide, chromium oxide, and combinations thereof. The porous microspheres of any of the preceding embodiments. In the eleventh embodiment, the metal oxide is selected from the group consisting of silica, titania, alumina, and combinations thereof. The porous microspheres of any of the preceding embodiments.

[0132] In the 12th embodiment, one or more light absorbers in an amount of about 0.1 wt% to about 40.0 wt% based on the total weight of the microspheres, such as about 0.1 wt%, about 0.3 wt%, about 0.5 wt%, about 0.7 wt%, about 0.9 wt%, about 1.0 wt%, about 1.5 wt%, about 2.0 wt%, about 2.5 wt%, about 5.0 wt%, about 7.5 wt%, about 10.0 wt%, about 13.0 wt%, about 17.0 wt%, about 20.0 wt%, or about 22.0 wt%, and from any one of about 24.0 wt%, about 27.0 wt%, about 29.0 wt%, about 31.0 wt%, about 33.0 wt%, about 35.0 wt%, about 37.0 wt%, about 39.0 wt%, or about 40.0 wt%, of one or more light absorbers are included in the porous microspheres of any of the previous embodiments.

[0133] In the 13th embodiment, one or more light absorbers selected from the group consisting of inorganic pigments and organic pigments, such as carbon black, are included in the porous microspheres of any of the previous embodiments.

[0134] In the 14th embodiment, the bulk sample of the porous microspheres exhibits a color observable by the human eye in any of the previous embodiments. In the 15th embodiment, the bulk sample of the porous microspheres exhibits an angle-independent color observable by the human eye in any of the previous embodiments. In the 16th embodiment, the bulk sample of the porous microspheres exhibits an angle-dependent color observable by the human eye in the porous microspheres of any of Embodiments 1 to 14.

[0135] In the 17th embodiment, the porous microspheres of any of the previous embodiments are monodisperse.

[0136] In the 18th embodiment, a composition includes a substrate and the porous microspheres of any of the previous embodiments. In the 19th embodiment, the composition of Embodiment 18 is an aqueous formulation, an oil-based formulation, a coating formulation, a food, an ink, a plastic, a cosmetic formulation, or a material for medical or security applications.

[0137] A non-limiting fifth group of embodiments of the present disclosure relating to metal oxide microspheres includes the following.

[0138] In a first embodiment, a porous microsphere comprising a metal oxide, wherein a bulk sample of the porous microsphere exhibits a color observable to the human eye; having two or more pore populations, each having an average pore diameter, and each population having a different average pore diameter, the porous microsphere.

[0139] In a second embodiment, the porous microsphere of embodiment 1 having an average diameter of about 0.5 μm to about 100 μm and an average porosity of about 0.10 to about 0.90 or about 0.10 to about 0.80; having two or more pore populations, each having an average pore diameter, and each population having a different average pore diameter; the average pore diameter being about 50 nm to about 999 nm; for example, having a first pore population having an average pore diameter of about 50 nm to about 999 nm and a second pore population having an average pore diameter of about 50 nm to about 999 nm, and the first average pore diameter and the second average pore diameter being different, the porous microsphere.

[0140] In a third embodiment, having an average diameter of about 1 μm to about 75 μm, about 2 μm to about 70 μm, about 3 μm to about 65 μm, about 4 μm to about 60 μm, about 5 μm to about 55 μm, or about 5 μm to about 50 μm; for example, from any of about 5 μm, about 6 μm, about 7 μm, about 8 μm, about 9 μm, about 10 μm, about 11 μm, about 12 μm, about 13 μm, about 14 μm, or about 15 μm to any of about 16 μm, about 17 μm, about 18 μm, about 19 μm, about 20 μm, about 21 μm, about 22 μm, about 23 μm, about 24 μm, or about 25 μm, the porous microsphere of embodiment 1 or 2.

[0141] In the fourth embodiment, a porous microsphere of any of the previous embodiments having an average porosity ranging from any of about 0.10, about 0.12, about 0.14, about 0.16, about 0.18, about 0.20, about 0.22, about 0.24, about 0.26, about 0.28, about 0.30, about 0.32, about 0.34, about 0.36, about 0.38, about 0.40, about 0.42, about 0.44, about 0.46, about 0.48, about 0.50, about 0.52, about 0.54, about 0.56, about 0.58, or about 0.60 to any of about 0.62, about 0.64, about 0.66, about 0.68, about 0.70, about 0.72, about 0.74, about 0.76, about 0.78, about 0.80, or about 0.90.

[0142] In the fifth embodiment, a porous microsphere of any of the previous embodiments having an average pore diameter ranging from any of about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 100 nm, about 120 nm, about 140 nm, about 160 nm, about 180 nm, about 200 nm, about 220 nm, about 240 nm, about 260 nm, about 280 nm, about 300 nm, about 320 nm, about 340 nm, about 360 nm, about 380 nm, about 400 nm, about 420 nm, or about 440 nm to any of about 460 nm, about 480 nm, about 500 nm, about 520 nm, about 540 nm, about 560 nm, about 580 nm, about 600 nm, about 620 nm, about 640 nm, about 660 nm, about 680 nm, about 700 nm, about 720 nm, about 740 nm, about 760 nm, about 780 nm, or about 800 nm.

[0143] In the sixth embodiment, a porous microsphere of any of the previous embodiments having an average diameter ranging from any of about 4.5 μm, about 4.8 μm, about 5.1 μm, about 5.4 μm, about 5.7 μm, about 6.0 μm, about 6.3 μm, about 6.6 μm, about 6.9 μm, about 7.2 μm, or about 7.5 μm to any of about 7.8 μm, about 8.1 μm, about 8.4 μm, about 8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μm, or about 9.9 μm.

[0144] In the seventh embodiment, a porous microsphere according to any of the previous embodiments having an average porosity ranging from any of about 0.45, about 0.47, about 0.49, about 0.51, about 0.53, about 0.55, or about 0.57 to any of about 0.59, about 0.61, about 0.63, or about 0.65.

[0145] In the eighth embodiment, a porous microsphere according to any of the previous embodiments having an average pore diameter ranging from any of about 220 nm, about 225 nm, about 230 nm, about 235 nm, about 240 nm, about 245 nm, or about 250 nm to any of about 255 nm, about 260 nm, about 265 nm, about 270 nm, about 275 nm, about 280 nm, about 285 nm, about 290 nm, about 295 nm, or about 300 nm.

[0146] In the ninth embodiment, an average diameter ranging from any of about 4.5 μm, about 4.8 μm, about 5.1 μm, about 5.4 μm, about 5.7 μm, about 6.0 μm, about 6.3 μm, about 6.6 μm, about 6.9 μm, about 7.2 μm, or about 7.5 μm to any of about 7.8 μm, about 8.1 μm, about 8.4 μm, about 8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μm, or about 9.9 μm; an average porosity ranging from any of about 0.45, about 0.47, about 0.49, about 0.51, about 0.53, about 0.55, or about 0.57 to any of about 0.59, about 0.61, about 0.63, or about 0.65; and an average pore diameter ranging from any of about 220 nm, about 225 nm, about 230 nm, about 235 nm, about 240 nm, about 245 nm, or about 250 nm to any of about 255 nm, about 260 nm, about 265 nm, about 270 nm, about 275 nm, about 280 nm, about 285 nm, about 290 nm, about 295 nm, or about 300 nm, of a porous microsphere according to any of the previous embodiments.

[0147] In the tenth embodiment, a porous microsphere according to any of the preceding embodiments, containing from about 60.0 wt% to about 99.9 wt% of a metal oxide, for example, any one of about 60.0 wt%, about 64.0 wt%, about 67.0 wt%, about 70.0 wt%, about 73.0 wt%, about 76.0 wt%, about 79.0 wt%, about 82.0 wt%, or about 85.0 wt% to any one of about 88.0 wt%, about 91.0 wt%, about 94.0 wt%, about 97.0 wt%, about 98.0 wt%, about 99.0 wt%, or about 99.9 wt% of the metal oxide, based on the total weight of the microspheres.

[0148] In the eleventh embodiment, a porous microsphere according to any of the preceding embodiments, wherein the metal oxide is selected from the group consisting of silica, titania, alumina, zirconia, ceria, iron oxide, zinc oxide, indium oxide, tin oxide, chromium oxide, and combinations thereof. In the twelfth embodiment, a porous microsphere according to any of the preceding embodiments, wherein the metal oxide is selected from the group consisting of silica, titania, alumina, and combinations thereof.

[0149] In the thirteenth embodiment, a porous microsphere according to any of the preceding embodiments, containing from about 0.1 wt% to about 40.0 wt% of one or more light absorbers, for example, any one of about 0.1 wt%, about 0.3 wt%, about 0.5 wt%, about 0.7 wt%, about 0.9 wt%, about 1.0 wt%, about 1.5 wt%, about 2.0 wt%, about 2.5 wt%, about 5.0 wt%, about 7.5 wt%, about 10.0 wt%, about 13.0 wt%, about 17.0 wt%, about 20.0 wt%, or about 22.0 wt% to any one of about 24.0 wt%, about 27.0 wt%, about 29.0 wt%, about 31.0 wt%, about 33.0 wt%, about 35.0 wt%, about 37.0 wt%, about 39.0 wt%, or about 40.0 wt% of one or more light absorbers, based on the total weight of the microspheres. In the fourteenth embodiment, a porous microsphere according to any of the preceding embodiments, containing one or more light absorbers selected from the group consisting of inorganic pigments and organic pigments, for example, carbon black.

[0150] In the 15th embodiment, a bulk sample of porous microspheres is any of the porous microspheres of the previous embodiments that exhibit a color observable by the human eye.

[0151] In the 16th embodiment, a porous microsphere is any of the porous microspheres of the previous embodiments that is monodisperse.

[0152] In the 17th embodiment, a bulk sample of porous microspheres is any of the porous microspheres of the previous embodiments that exhibit an angle-independent color observable by the human eye. In the 18th embodiment, a bulk sample of porous microspheres is any of the porous microspheres of Embodiments 1 to 16 that exhibit an angle-dependent color observable by the human eye.

[0153] In the 19th embodiment, a composition comprising a substrate and any of the porous microspheres of the previous embodiments. In the 20th embodiment, the composition of Embodiment 19 is an aqueous formulation, an oil-based formulation, a coating formulation, a food, an ink, a plastic, a cosmetic formulation, or a material for medical or security applications.

[0154] Examples Example 1 Polymer Microspheres A styrene / acrylic acid copolymer is produced as follows: 230 mL of deionized (DI) water is placed in a three-necked reaction flask equipped with a thermometer, a condenser, a magnetic stirring unit, and a nitrogen atmosphere. The water is heated to 80°C, and after adding 10 g of styrene with stirring, 100 mg of acrylic acid dissolved in 10 mL of DI water is added by syringe. After dissolving 100 mg of ammonium persulfate in 10 mL of DI water, it is added to the stirred mixture by syringe. The reaction mixture is stirred at 80°C for 24 hours. This polymer colloidal dispersion is allowed to cool to room temperature and purified by centrifugation to produce polystyrene nanospheres having an average particle size of 250 nm.

[0155] Similarly, a styrene / acrylic acid copolymer is produced to produce polystyrene nanospheres having an average particle size of 350 nm.

[0156] The first aqueous polystyrene colloidal dispersion (250 nm) and the second aqueous polystyrene colloidal dispersion (350 nm) are mixed at a wt / wt ratio of 7 / 3, and the mixture is diluted with deionized water to 1 wt%, and ultrasonicated so that the particles do not aggregate. The oil continuous phase contains 0.1 wt% polyethylene glycol / perfluoropolyether surfactant in the fluorinated oil. The aqueous colloidal dispersion mixture and the oil are each injected into a microfluidic device having a 50 μm droplet junction with a syringe connected to a pump. The system is left to equilibrate until monodisperse droplets are formed. The monodisperse droplets are collected in a reservoir.

[0157] The collected droplets are dried in an oven at 45 °C for 4 hours to obtain monodisperse polymer microspheres. The monodisperse polystyrene microspheres contain polystyrene nanospheres having a bimodal particle size distribution.

[0158] Example 2 Porous metal oxide microspheres Example 1 is repeated, and 1 wt% silica nanoparticles are added to the aqueous mixture of the first colloidal dispersion and the second colloidal dispersion, and then mixed with the oil phase to form a water-in-oil emulsion. The droplets collected from the microfluidic device are dried in the same manner as in Example 1 to form polymer template microspheres. The polymer template microspheres are placed on a silicon wafer, heated from room temperature to 500 °C over 3 hours, held at 500 °C for 2 hours, and then returned to room temperature over 3 hours to be calcined. Monodisperse silica microspheres having an average diameter of 15 microns containing two different average pore sizes are obtained.

[0159] Figures 2 and 3 are scanning electron microscope (SEM) images of polymer template microspheres and porous silica microspheres manufactured in the same manner.

[0160] Example 3 Porous silica microspheres containing a light absorber The product of Example 2 is physically mixed with carbon black aqueous dispersions or carbon black powders at different weight levels. Monodisperse porous silica microspheres containing carbon black at levels of 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, and 5 wt% based on the total weight of the microspheres are obtained.

[0161] Example 4 Drying method Examples 1 to 3 are repeated, where the drying step uses microwave irradiation, vacuum drying, and / or drying in the presence of a desiccant.

[0162] Example 5 Production of porous silica microspheres by spray drying A styrene / acrylic acid copolymer is produced as follows: 230 mL of deionized (DI) water is placed in a three-necked reaction flask equipped with a thermometer, condenser, magnetic stirring unit, and nitrogen atmosphere. The water is heated to 80 °C, and after adding 10 g of styrene with stirring, 100 mg of acrylic acid dissolved in 10 mL of DI water is added by syringe. After dissolving 100 mg of ammonium persulfate in 10 mL of DI water, it is added to the stirred mixture by syringe. The reaction mixture is stirred at 80 °C for 24 hours. The polymer colloidal dispersion is allowed to cool to room temperature and purified by centrifugation to produce polystyrene nanospheres having an average particle size of 250 nm.

[0163] Similarly, a styrene / acrylic acid copolymer is produced to produce polystyrene nanospheres having an average particle size of 350 nm.

[0164] Mix the first aqueous polystyrene colloidal dispersion (250 nm) and the second aqueous polystyrene colloidal dispersion (350 nm) at a wt / wt ratio of 7 / 3, dilute the mixture with deionized water to 1 wt%, add 1 wt% of silica nanoparticles to the mixture, and perform ultrasonic treatment so that the particles do not aggregate. Spray-dry the aqueous dispersion to obtain polymer template microspheres containing polydisperse polymer nanospheres and silica. Calcinate the microspheres by heating them from room temperature to 500 °C over 3 hours, holding them at 500 °C for 2 hours, and then returning them to room temperature over 3 hours. Porous silica microspheres are obtained.

[0165] Example 6 Visible Color of Bulk Samples In these examples of bulk colors, place 0.5 milligrams of the porous microspheres evenly in a 10 mL clear glass vial having a bottom area of 6 cm 2 . Observe the color with the human eye.

[0166] A sample of porous silica microspheres is produced in the same manner as in Example 2, where the polystyrene nanospheres have average particle sizes of 420 nm and 460 nm at a wt / wt ratio of 7:3. The sample exhibits a red color.

[0167] A sample of porous silica microspheres is produced according to the process of Example 5, where the polystyrene nanospheres have average particle sizes of 360 nm and 420 nm at a wt / wt ratio of 4:1, and the wt / wt ratio of polymer to silica is 4:1. Porous microspheres having a porosity of 0.55 and exhibiting an obvious green color are obtained. Samples with a wt / wt ratio of polymer to silica of 2:1 are also produced, obtaining porous microspheres having a porosity of 0.45 and exhibiting an obvious orange color.

[0168] Example 7 Zinc Oxide Porous Microspheres A sample of porous zinc oxide microspheres was produced according to the process of Example 5, where the polystyrene nanospheres had average particle sizes of 250 nm and 320 nm in a wt / wt ratio of 1:1, and the wt / wt ratio of the polymer to zinc oxide was 1:2.

[0169] Example 8 Silica / Titania Porous Microspheres A sample of porous microspheres containing silica and titania was produced according to the process of Example 2, where the polystyrene nanospheres had average particle sizes of 350 nm and 460 nm in a wt / wt ratio of 1:4, and the wt / wt ratio of the polymer to the total metal oxide was 3:1. The wt / wt ratio of silica to titania was 9:1.

Claims

1. A porous microsphere containing a metal oxide, having a continuous solid structure, wherein each porous microsphere has two or more pore populations with different average pore diameters distributed throughout the volume of the porous microsphere, the porous microsphere has an average diameter of 0.5 μm to 100 μm, the average pore diameter is selected independently from 120 nm to 800 nm, the porous microsphere has an average porosity of 0.10 to 0.80, and contains 60.0 wt% to 99.9 wt% of a metal oxide based on the total weight of the microsphere, a porous microsphere containing a metal oxide.

2. The porous microsphere according to claim 1, wherein a bulk sample of the porous microsphere exhibits a color observable to the human eye.

3. The porous microsphere, has an average diameter of 4.5 μm to 9.9 μm; has an average porosity of 0.45 to 0.65; and has an average pore diameter of 220 nm to 300 nm The porous microsphere according to claim 1 or 2.

4. The porous microsphere according to any one of claims 1 to 3, wherein the metal oxide is selected from the group consisting of silica, titania, alumina, zirconia, ceria, iron oxide, zinc oxide, indium oxide, tin oxide, chromium oxide, and combinations thereof.

5. The porous microsphere according to any one of claims 1 to 4, containing 0.1 wt% to 40.0 wt% of one or more light absorbers based on the total weight of the microsphere.

6. The porous microsphere according to any one of claims 1 to 5, wherein a bulk sample of the porous microsphere exhibits an angle-independent color observable to the human eye.

7. The porous microsphere according to any one of claims 1 to 6, wherein a bulk sample of the porous microsphere exhibits an angle-dependent color observable to the human eye.

8. The porous microsphere according to any one of claims 1 to 7, which is monodisperse.

9. A composition comprising a substrate and the porous microsphere according to any one of claims 1 to 8.

10. The composition according to claim 9, which is an aqueous formulation, an oily formulation, a coating formulation, a food, an ink, a plastic, a cosmetic formulation, or a material for medical or security applications.

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