Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/005—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein

Definitions

• This invention generally relates to methods of coating particles; and, more specifically, to methods that are well suited for coating nanoparticles and to the particles formed by those methods.
• Nanoparticles are particles having a size on the _7 order of magnitude of 10 m. While such particles are known, per se, heretofore, these particles have not been extensively used. For several reasons, though, it is believed that nanoparticles will have very important commercial applications in the future. For example, in some cases, such as in photographic emulsions, nanoparticles coated with a given material may be suitable replacements for, and cost less than, larger, solid particles made from that given material. In addition, nanoparticles can be constructed so as to exhibit an enhanced plasmon resonance effect, which is the enhancement of electromagnetic fields in and around those particles, and these particles may be used in numerous specific methods and devices to enhance photo or optical processes that occur in those methods and devices. In other applications, nanoparticles may be very useful as nucleation centers, which may be used to form larger particles having specific constructions.
• An object of this invention is to provide new, coated particles, and new methods for coating particles. Another object of this invention is to coat -, nanoparticles with one or more layers of various types of materials such as metals, polymers and halides.
• a further object of the present invention is to provide a nanoparticle, and a method that may be used to form *- a nanoparticle, having a dielectric core coated with metal halide, such as silver halide.
• a further object of this invention is to provide a method that may be used to coat dielectric nanoparticles with a layer of a metal.
• Another object of the present invention is to provide a nanoparticle, and a method that may be used to form a nanoparticle, having a dielectric core covered with one shell of metal and another shell of a metal halide, e.g., silver halide.
• a first embodiment of this invention is a method for forming metal halide, e.g., silver halide, coated dielectric particles, comprising the steps of providing a
• 2 c second embodiment of this invention is a method of forming metal coated dielectric nanoparticles, comprising the steps of providing a source of metal ions, a source of an alcohol and a source of a ketone in an anaerobic liquid carrier having dispersed therein charged dielectric particles, and Q exposing the liquid carrier to light to cause the metal ions
• metal coated dielectric nanoparticles axe formed c by a method comprising the steps of orming metal halide coated nanoparticles, and exposing the coated nanoparticles to light and a reducing agent to change the metal halide to metal to form metal coatings over individual nanoparticles.
• metal halide coated nanoparticles axe formed c by a method comprising the steps of orming metal halide coated nanoparticles, and exposing the coated nanoparticles to light and a reducing agent to change the metal halide to metal to form metal coatings over individual nanoparticles.
• 10 coated dielectric nanoparticles may also be formed by a method comprising the steps of providing a source of metal ions, a source of halide ions and an election hole scavenger in a liquid carrier having dispersed therein negatively charged colloidal dielectric particles, reacting the metal
• a fifth embodiment of this invention is a method of forming metal coated dielectric nanoparticles, comprising the steps of providing a liquid carrier having dispersed therein dielectric nanoparticles having metal halide on the surfaces thereof, changing at least a portion of the metal halide on c individual nanoparticles to metal, adding metal ions and a sulfate reducing agent to the liquid carrier, and forming metal coatings on the nanoparticles from those metal ions, wherein the metal on the nanoparticles acts as a catalyst and accelerates the formation of the metal coatings.
• a first nanoparticle according to this inventions comprises a dielectric core, and a metal halide coating over this dielectric core.
• a second nanoparticle according to the present invention comprises a dielectric core, a metal coating disposed immediately over that core, and a layer of
• a third nanoparticle according to the present invention comprises a dielectric core, a layer of metal halide disposed immediately over that core, and another layer of metal disposed immediately over the metal halide coating.
• another nanoparticle according to the present invention comprises a dielectric core, a layer of one metal disposed over that core, and a layer of another metal disposed over that first metal layer.
• the present invention may be provided with an outer coating of a polymer material to prevent the particle from reacting chemically with any medium or environment in which the particle is used. Also, it may be desirable to provide these nanoparticles formed according to the present invention with
• -5- coverage of the core or of another coating may be preferred, however, for certain nanoparticles or for certain uses.
• FIGS 1 through 9 which are not drawn to scale, show various coated nanoparticles of the present invention.
• Figures 10 through 18 outline several processes of this invention that may be used to form the particles shown in Figures 1 through 9.
• Figure 19 is a transmission electron micrograph of silver-coated silver bromide nanoparticles.
• Figure 20 is a transmission electron micrograph of silver coated silver bromide nanoparticle treated with ammonia.
• Figure 21 shows various optical extinction spectra of silver coated silver bromide nanoparticles either untreated or treated with ammonia.
• the spectra of (a) to (d) are spectra of various illuminated solutions of Ag, Br, and EDTA. In going from (a) to (d) , the illumination time increases.
• the spectrum in(e) is a typical spectrum observed after the addition of ammonia to any of the above solutions.
• Figure 22 shows computed extinction efficiencies for silver-coated silver bromide particles in water.
• the diameter of the core particle is 20 nm and the thickness of the silver coats are indicated in nm.
• the spectrum marked solid is that of a homogeneous 20 nm diameter silver sphere.
• Figure 23 is an optical extinction spectrum of a measured silver coated silver bromide nanoparticle and two computed extinction spectra. The measured spectrum lies between the two computed spectra. In the upper curve all the
• Figures 1 through 9 show various particles all formed in accordance with the present invention; and generally, each of these particles comprises a dielectric core and one or more coatings over that core.
• the cores of all of these particles have sizes on the order of magnitude of a 0.5 to 200 nanometers, and thus are referred to as 5 nano-cores or nanoparticles.
• one coating of each particle is comprised of silver halide; and with some of these particles such as those shown in Figures 2 through 6, 8 and 9 at least one coating of each particle is comprised of a metal.
• Particle 12 of Figure 1 consists of core 12a and coating or shell 12b, the core consists essentially of a dielectric material such as silica, and the shell consists essentially of silver halide. Further, with this particle, shell 12b is disposed immediately over and substantially completely covers core 12a.
• This particle does not itself include any metal and thus does not exhibit the plasmon resonance effect.
• the silver halide in the particle may be changed to metal silver, either to form a layer of metal silver on the particle or to help form a layer of
• particle 14 of Figure 2 a metal coating such as silver, copper, aluminum, gold or palladium is disposed 5 between the dielectric core and the silver halide coating to increase the sensitivity of the silver halide to light. This increased sensitivity is caused by the plasmon resonance effect produced by the metal coating. More specifically, particle 14 consists of dielectric core 14a, metal•coating o 14b disposed immediately over and covering that core, and a layer of silver halide 14c disposed immediately over and covering layer 14b.
• Particle 16 of Figure 3 is similar to particle 14 of Figure 2 in that both of these particles include a dielectric core, one coating of silver halide and a second coating of a metal.
• the order of these coatings in particle 16, though, is the reverse of the order of these coatings in particle 14. More specifically, particle 16 consists of dielectric core 16a, a layer of silver halide 16b disposed o immediately over and covering core 16a, and a layer of a metal 16c disposed immediately over and covering the silver halide coating 16b.
• Particle 20 of Figure 4 comprises a dielectric core 20a, a layer of one metal 20b disposed over core 20a and a 5 layer of another metal 20c disposed over metal layer 20b.
• coating 20b completely covers core 20a
• coating 20c completely covers coating 20b.
• Particle 22 of Figure 5 is one specie of the general type of particle shown in Figure 4. More specifically, particle 22 comprises a dielectric core 22a, a layer of silver 22b disposed over core 22a, and a layer of another metal 22c disposed over the silver layer 22b with the specific particle configuration shown in Figure 5 coating 22b completely covers core 22a, and coating 22 ⁇ completely covers coating 22b.
• FIG. 6 shows 0 particle 24 comprising core 24a, first coating 24b and second coating 24c.
• Core 24a consists essentially of a dielectric material
• coating 24b consists essentially of a metal and is disposed immediately over core 24a
• coating 24c consists essentially of a polymer material and is disposed immediately 5 over shell 24b.
• Coating 24b may completely cover core 24a
• coating 24c may completely cover coating 24b.
• Figure 7 shows particle 26 comprising core 26a, first coating 26b and second coating 26c.
• Core 26a consists essentially of a dielectric material
• coating 26b consists essentially of o silver halide and is disposed immediately over core 26a
• shell 26c consists essentially of a polymer material and is disposed immediately over and completely covers shell 26b.
• Coating 26b may completely cover core 26a
• coating 26c may completely cover coating 26a. 5
• nanoparticles of this invention with interior coatings or shells of a polymer material, either to prevent other coatings or shells of the particles from chemically reacting with each other, or to prevent the core of the particle from chemically reacting Q with a coating or shell of the particle. This principle is
• Particle 30 is similar to particle 16 in that both of these particles include an inside dielectric core, a first metal coating and a second, silver halide coating.
• Particles 30 and 16 differ in that the former particle includes a third, polymeric coating disposed between the metal coating and the silver halide coating. More specifically, particle 26 includes core 30a and coatings 30b, c and d. Core 30a consists essentially of a dielectric material, and coating 30b consists essentially of a metal and is disposed immediately over and core 30a. Coating 30c consists of a polymeric material and is disposed immediately over shell 30b, and shell 30d consists essentially of silver halide and is disposed immediately over shell 30c. With the specific arrangement illustrated in Figure 8, coating 30b substantially completely covers core 30a, coating 30c substantially completely covers coating 30b, and coating 30d substantially completely covers coating 30c.
• Particle 32 is similar to particle 20, and both of these particles include a dielectric core and two metal coatings or shells. Particle 32 includes a further polymeric coating located between the two metal coatings to chemically insulate these two metal coatings from each other.
• particle 32 comprises core 32a and coatings 32b, c and d.
• Core 32a consists essentially of a dielectric material
• coating 32b consists essentially of a metal and is disposed immediately over core 32a.
• Coating 32c consists essentially of a polymeric material and is disposed immediately over coating 32b; and coating 32d consists essentially of a metal, which may or may not be the same as _ the metal of coating 32b, and is disposed immediately over polymeric coating 32c.
• Each of coatings 32b, c and d may form a respective one, at least substantially complete shell.
• Figures 1-9 are only representative of nano ⁇ particles formed according to the present invention, and in 0 particular, only illustrate the general relationship between the cores and the coatings or shells of the particles.
• the particle and the core thereof may have any suitable shapes, and specifically, the particles and the cores may have shapes other than spherical.
• the particles and the cores may be cylindrical 5 or ellipsoidal, have a thread-like shape, or be crystalline shaped.
• the actual crystal form of the core may be any suitable form; and, for example, these cores may be: Tetragonal crystal forms, o Orthorhombic crystal forms, Mon ⁇ clinic crystal forms, Triclinic crystal forms, Isometric crystal forms, Hexagonal crystal forms.
• the shapes of the nanoparticles may change as 5 they are made.
• dielectric material refers to a material which is a non-conductor or a
• the conductivity of this material may range -40 . 6 from as low as 0, but preferably 10 , to as high as 10 mhos. In a preferred embodiment, the conductivity ranges from 10 ⁇ to 10 mhos. In a most preferred embodiment the conductivity ranges from 10 -30 to 104 mhos.
• dielectric core include glass, silica, cadmium sulfide, gallium arsenide, polydiacetylene, lead sulfide, titanium dioxide, polymethylacrylate (PMMA) , silver bromide, carbon fibers, copper sulfide, silver sulfide and the like.
• metal includes any material having a negative dielectric constant, and so can include super conductors,. conducting polymers, materials with an anomolous dispersion of carrier electrons, and heavily doped semi conductors where free carrier electron motion dominates the dielectric function.
• the types of metals that can be coated onto the dielectric core in accordance with the methodology of the present invention include the transition metals, the lanthanides and the Group IIIA metals.
• the especially preferred transition metals include the Group VIII and IB metals, and Group IIIA metals, especially copper, silver, gold, iron, nickel, palladium, platinum, cobalt, rhodium, iridium, ruthenium, aluminum and the like.
• Especially preferred metals include copper, silver, gold, nickel, palladium, platinum and aluminum.
• the metal-halide coated nonoparticles can be prepared by providing a source of metal ions and a source of halide ions in a liquid carrier having dispersed therein charged colloidal dielectric particles and reacting the halide ions with the metal ions in the presence of the dielectric 2 particles to form coatings of metal halide over individual dielectric particles.
• silver halide coated dielectric particles such as particle 12 of Figure 1 t - can be prepared. More specifically, this procedure, generally, comprises the steps of providing a source of silver ions and a source of halide ions in a liquid carrier having dispersed therein charged colloidal dielectric particles, and reacting the halide ions with the silver ions o i n the presence of the dielectric particles to form coatings of silver halide over individual dielectric particles.
• Figure 10 outlines one preferred method for carrying out this process but this procedure is exemplary and is equally applicable to the other metal halides coating 5 dielectric particles.
• This method generally comprises the steps of providing an aqueous solution including negatively charged colloidal dielectric nanoparticles, positively charged silver ions, and a halide, and reacting the halide with the silver ions to bond, or grow, coatings of silver o halide on, and preferably completely covering, individual dielectric particles.
• concentrations of dielectric particles, silver ions and halide in the solution, and the length of time over which the coatings are allowed to grow on the dielectric particles are selected so that 5 coatings of a uniform preselected thickness are grown on those particles.
• the specific order in which the dielectric particles, the silver ions and the halide are added to the aqueous solution is not critical; and, for example, the dielectric particles may be dispersed in the solution, then 0 the silver ions may be added, and then the halide may be added.
• the pH of that solution is adjusted to and thereafter maintained at a level slightly above 2, and even more preferably, between about 3 and 5.
• the initial concentration of the silver ions in the solution is relatively low, less than 10 *" M; the initial concentration of the halide in the solution is slightly greater than, such as about 10% greater than, the concentration of the silver ions in the solution; and also, 5 the solution is constantly stirred while the halide is being added to it.
• the silver ions may be added to the solution in any suitable form, and for instance, these ions may be added in the form of a silver salt that is soluble in aqueous o solution, e.g., silver nitrate.
• the halide that is added to the solution may be any suitable halide, such as an alkali halide, e.g., sodium bromide, potassium bromide, potassium chloride, sodium chloride and the like.
• any suitable dielectric may be used in the above-discussed process, and the dielectric may be linear or non-linear and may have any suitable shape and size.
• the dielectric particles may be spherically shaped silica particles.
• the dielectric particles are these silica particles
• the silver ions are added to the solution in the form of silver nitrate
• the halide is sodium bromide
• the silver from the silver nitrate reacts with the bromide from the sodium bromide to form silver bromide, which bonds to and forms layers over the silica particles.
• a metal coating on a dielectric particle may be made by a process, generally, comprising the steps of providing a source of metal ions, a source of a secondary alcohol, preferably a lower secondary alkanol containing 3-7 carbon atoms and a source of a ketone preferable containing 3-7 carbon atoms in an anaerobic liquid carrier having dispersed therein charged dielectric particles, and exposing the liquid carrier to light, preferably ultraviolet light to cause the metal ions to attach to the dielectric particles and form metal coatings over individual dielectric particles.
• the term lower alkyl when used alone or in combination, contains 1-7 carbon atoms.
• alkyl groups may be straight chained or branched and include such groups as methyl, ethyl, proply, isopropyl, butyl, sec-butyl, isobutyl, t-butyl, pentyl, amyl, hexyl and the like.
• a secondary alkanol refers to a lower alkyl alcohol in which the hydroxy group is attached to a secondary carbon.
• Such groups include isopropanol, sec-butanol, and the like.
• the preferred ketone is acetone.
• Figure 11 outlines one preferred method for carrying out this process.
• This method generally comprises the steps of providing an aqueous solution including negatively charged colloidal dielectric particles, metal ions, isopropanol and acetone; removing oxygen from the solution; and exposing the solution to ultraviolet light to cause the metal ions to attach to the dielectric particles and form metal coatings completely covering individual dielectric particles.
• concentrations of the dielectric particles, the metal ions, the isopropanol and the acetone, and the length of time the c solution is exposed to the ultraviolet light are selected so that coatings of a uniform preselected thickness are formed on the dielectric particles.
• the acetone absorbs energy 0 from the ultraviolet light and then reacts with isopropanol to form isopropyl radicals.
• These radicals are powerful reducing agents and cause metal ions that have become attached to the dielectric particles to form metal molecules.
• the particular order in which the dielectric parti 1 es, the ( - metal ions, the isopropanol and the acetone are ac.. d to the aqueous solution is not critical; and, for instance, the isopropanol and acetone may be added to the solution, the dielectric particles may then be dispersed in the solution, and then the metals may be added.
• the light source used contain ultraviolet light. It is preferred that the light source contain wavelengths from 150-550 nm. The preferred wavelengths range from 200-400 nm.
• the intensity of light used range from 50 watts to 1.5 kilowatts, with the preferred intensity ranging from 250-1000 watts. Especially preferred intensity range from 350-550 watts, with an intensity of about 450 watts being the most preferred.
• the pH of the solution is adjusted to and .. thereafter maintained at a level slightly above 2, and even more preferably, between about 3 and 5. In this way, the dielectric particles do not have to be negatively charged when they are added to the solution and the acidity of the j . aqueous solution causes the dielectric particles to become negatively charged.
• the initial concentration of the metal ions in the solution is relatively low, such as 2 x l ⁇ " ⁇ M; and the initial concentrations of the ketone, e.g., acetone, and secondary alcohol, e.g., isopropanol in 0 the solution are about equal to each other and much greater than, such as about 400 times greater than, the initial concentration of the metal ions in the solution.
• the solution is stirred while exposed to the ultraviolet light.
• Numerous specific types of metal coatings may be made using a procedure as described above, and for example, the process may be used to form silver coated dielectric particles, gold coated particles or palladium coated particles.
• the metal ions may be provided in 0 the solution in any suitable manner; and, for example, these ions may be provided by adding a water soluble metal salt such as silver nitrate, to the solution.
• any suitable dielectric may be used in the above-discussed process, and the dielectric may be linear of non-linear and may have any suitable shape and size.
• the dielectric particles may be spherically shaped silica particles.
• the metal ions are added to the solution in the form of silver nitrate, then the ultraviolet light, in combination
• the following example illustrates this process for forming a metal silver coating over the silica particles.
• An aqueous solution is prepared by mixing the following solutions in a 50 ml beaker: (1) 0.5 ml of 0.01 M AgNO- *•*
• metal coated dielectric particles may also be made by a process employing photoreduction of metal (e.g,, silver) halide, and one such exemplary process is outlined in Figure 12.
• silver halide coated c - dielectric particles are made, for example, by the process discussed above in connection with Figure 10, and then the coated particles are exposed to light to change the silver halide coatings over the individual particles to metal silver coatings.
• a more integrated process is used to form metal coated dielectric particles.
• This process generally, comprises the steps of providing a source of metal ions, a source of halide ions and a source of an electron hole scavenger in a liquid carrier having dispersed therein negatively charged colloidal dielectric particles, reacting the metal ions with the halide ions in the presence of the dielectric particles and the electron hole scavenger to form metal halide coatings over individual dielectric particles, and exposing the liquid carrier to light to change the sliver halide coatings to metallic silver coatings.
• Figure 13 outlines a preferred method to implement this process using silver ions.
• dielectric particles are dispersed in a solution including silver ions, a halide and an electron hole scavenger, and the silver ions react with the halide to form silver halide coatings over, and which may completely cover, individual dielectric particles.
• the solution is then exposed to ultraviolet light, and this light changes the silver halide coatings to silver coatings.
• concentrations of the dielectric particles, the silver ions, the halide and the election hole scavenger in the solution, and the length of time the solution is exposed to the ultraviolet light are selected so that coatings of a uniform preselected thickness are formed on the dielectric particles.
• the initial concentration of metal (e.g., silver) ions in the solution is greater than the initial concentration of the halide in the solution; and for instance, the former concentration may be about 5 time the latter concentration.
• the metal ions may be in the solution in any suitable form, and for instance, if silver is the metal ion, these ions may be added to the solution in the form of a metal salt that is soluble in aqueous solutions, e.g., silver nitrate.
• the halide that is added to the solution may be any suitable halide, such as alkali halide, e.g., sodium bromide, potassium bromide, sodium chloride, potassium chloride and the like.
• any suitable dielectric may be used in this process, and the dielectric may be linear or non-linear and have any suitable shape and size.
• the dielectric particles may be spherically shaped silica particles.
• the silver ions are added to the solution in the form of silver nitrate, and (iii) the halide is sodium bromide, then the silver from the silver nitrate reacts with the bromide from the sodium bromide to form silver bromide coatings on the dielectric particles; and the ultraviolet light, in the presence of EDTA, then reduces the silver bromide coatings to metallic silver.
• EXAMPLE 2 The following example illustrates this process for forming silver coated dielectric particles.
• Metallic silver on Si0 2 particles can be obtained by photoreduction of silver halides, which are typically prepared in the presence of + + excess Ag ions.
• a hole (h ) scavenger, EDTA is added to the solution.
• One ml of a 0.002 M NaBr solution is added to the solution.
• the duration of illumination which is in the order of minutes, determines the color of the silver coated silica particles. This color is a result of the thickness of the silver layer, and can range from yellow to a purplish gray.
• a variation of the process described above may be employed to form metal coatings other than silver on nanoparticles, and this variation utilizes the fact that metallic silver on the dielectric particles will act as a catalyst to help grow metal coatings on those particles from other metal ions in the solution.
• a liquid carrier, or a solution is provided including dielectric particles having silver halide formed on those particles, at least a portion of the silver halide on individual nanoparticles is changed to metallic silver, and ions of a metal are added to the solution to form coatings of that metal completely covering individual dielectric particles, with the metallic silver on those particles acting as a catalyst to accelerate the formation of the metal coatings.
• These metal ions may be added to the solution in any suitable manner, and for instance, conventional photographic developing solutions may be added to the solution to reduce the metal ions.
• the resulting product comprises a dielectric core, a first coating of silver halide that substantially completely covers 1 the electric core, and a second coating of a metal that completely covers the layer of silver halide.
• the following example illustrates the coating of silver on an dielectric core of silver bromide.
• the silver ,_ bromide nanoparticles exposed briefly to intense UV light in the presence of EDTA have optical extinction spectra similar to those computed for distribution of silver coated silver bromide nanoparticles.
• intense it is meant that the intensity of the light ranges from 50 watts to 1.5 kilowatts, o with the preferred range being 250-550 watts, and the most preferred having a range of 350-550 watts.
• the plasmon resonance maximum is shifted to lower wavelengths, a result consistent with theory 5 so long as the coat thickness increases with exposure to light.
• the resonance maximum of the distributions of coated particles can be controllably shifted to 600 to 700 nm.
• Silver bromide colloids were prepared by rapidly mixing equal volumes of AgNO- and NaBr solutions. A growth stabilizer (SDS) and an electron donor (EDTA) were added
• the particle size distributions were characterized with transmission electron microscopy (JEOL 1200EX) .
• a typical micrograph is shown in Fig 19.
• a size distribution consistent with the limited micrograph data is the log normal distribution.
• N(r) N o exp(-((ln(r) - ln(r m ))/ln(s)) 2 ) , with r equal to 1 nm or less and s in the renge of 4 to 4.5 nm.
• the size distributions as determined by TEM did not appear to change markedly with exposure to light.
• Theoretical optical extinction spectra of individual silver coated spheres are shown in Fig. 22.
• the peak of the theoretical extinction shifts from red to blue as the ratio of coat thickness to core radius increases. This data is consistent with the measured spectra where the absorption maxima shifts toward the blue as the time of exposure increases, since the coat thickness should increase with exposure time.
• the computed spectra are very sensitive to the coat thickness. The measured spectra are much more broad than the spectra shown in Fig. 22 because of the distributions of core diameters and coat thicknesses.
• the magnitudes of the extinction spectra are also characteristic of silver coated particles. For example, at a wavelength of 700 nm the extinction cross section per unit volume of silver is 100's of times larger in a silver coated nanoparticle having the appropriate ratio fo core radius to coat thickness that it is in a solid silver sphere. The fact that the theoretical extinction is so large can be used to help verify that the particles are coated with silver. 2 However, since there is a broad distribution os sizes care must be taken in making the comparision.
• the reduced silver is in the form of a smooth coat on the surface of a spherical AgBr particle.
• the extinction efficiencies were computed using the separation of variables 5 solution for concentric spheres based on algorithms.
• the size distribution of the core particles is described by the log-normal distribution of the above equation.
• the values of were o determined by setting the total volume of all the particles prior to illumination in the distribution equal to the volume of AgBr.
• the initial total volume of AgBr was determined by solving the ionic equilibria equations including the Ag -EDTA complex.
• the size distribution of the coat thickness is a Gaussian, typically with a standard deviation of 2 to 8 nm.
• the silver coat may be formed either from the reduction of the silver halide of the initial particle, or from the reduction of Ag from 2 solution. Computations have been done for each of the two limiting cases.
• the total extinction is computed by numerically integrating over distributions of core radii
• N is the size disbribution of the coats
• Q is the extinction efficiency
• m is the refractive o index of the core
• m. is the refractive index of the coat.
• the refractive index of the silver was computer from the data of Hagemann et al. in J. 0£. Soc. 5 Am. , J55_, 742-744 (1975) and Kerker, in J. Op.
• the AgBr cores are not reduced in size as the coat grows.
• the Ag in the coat is assumed to come only from the reduction of AgBr at the surface of the particle and so the core shrinks - as the coat grows. Since the measured curve lies between the two computed spectra, the magnitudes of the plasmon enhanced extinction is in the range of values computed.
• the main parameters that can be adjusted in fitting the distributions to the spectra are: 1) the thickness and
• the silver coat is formed by the coalescing of many small silver particles.
• the coat may also contain some AgBr or voids, but it is homogeneous enough to have a refractive index similar to that of bulk islver.
• the bonds between the 0 particles may be relatively weak because the coat breaks into
• Silver coated dielectric particles may also be formed by a process utilizing chemical reduction of silver ions by hydroquinone at elevated temperatures.
• Solution 1 consists of particles which are smaller and better defined, appear darker, and were in the size range of 10 to 30 nm.
• the particle c size range was found to be between 40 to 100 nm, the particles were similarly dark, but contained elongated as well as spherical shapes.
• the final size distribution may be due in part to the non uniform size of the silica core particles, found to be between 7 to 11 nm by electron o microscopy.
• the coated particles may be removed from the solution in which they were prepared by dialysis, and then placed in a sodium dodecyl sulfate micellar solution or 5 a micro emulsion. Additional coatings of either silver halide, a metal or a polymer, may then be added until the desired final configuration is reached. Polymer coating of any of these particles may be readily achieved in a solution by the well known emulsion polymerization method, in which a suitable amount of monomer and initiator have been added.
• the reaction can be terminated by addition of 25 ml of a 1% solution of hydroquinone, and cooling the reaction mixture to room temperature.
• the particles are filtered, washed several times with doubly distilled water, resuspended in water, and further purified o by dialysis.
• Coating of carbon fibres with copper was carried out by photochemical reduction of Cu using highly reductive short lived 1-hydroxy-l-methylethyl radicals. These radicals were produced in situ by illuminating a mixuture of 1 M acetone and 1 M propanol-2 with a UV source of Hg-Xe lamp operated at 450 watt. The reaction can be presented by
• coated fibres washed with distilled water and observed under an optical microscope, show a very fine and smooth coating and visibly exhibit a metallic lustre of copper.
• the amount of copper on these fibres was detected using atomic absorption spectroscopy after removing the coat with 1 M nitric acid.
• the presence of copper on these fibres was also confirmed using Energy Dispersive Spectroscopy (EDS) , which shows a peak for copper.
• EDS Energy Dispersive Spectroscopy
• the thickness of the coat can be controlled by the copper concentration in ° solution and the duration of illumination. It can be readily varied in the range of tens of nanometers to microns.
• Figure 17 generally outlines a procedure to make particle 20 of Figure 4.
• metal coating 20b is formed over dielectric core 20a, for example using the method illustrated in Figure 13; and then silver halide coating 20c is made over metal layer 20b, for instance by generally following the method shown in Figure 10.
• Figure 18 generally illustrates a procedure to make particle 22 of Figure 5.
• metal coating 22b is formed over dielectric core 22a, for example by the process described above in connection with Figure 11, then polymer coating 22c is applied over coating 22b, and then silver halide layer 22d is formed over coating 22c, for example by generally following the procedure discussed above in connection with Figure 10.
• Methodology of the present invention are not limited to coating metals on a nanoparticle. Methods described herein can also be used to plate metals onto a substrate. This is especially useful if the substrate is a catalyst support system.
• the catalyst support system can be coated with metals, e.g.. Group VIII metals and provide a surface on which catalysis can occur.
• Catalyst support systems include zeolites, polystyrene, metal oxide, (e.g., titanium oxide) polymer support and the like.
• the methods of the present invention can be used to coat other surfaces.
• methodology of the present invention can be used to coat dielectric material, such as silica, glass, cadmium sulfide, gallium arsenide, polydiacetylene, lead sulfide, PMMA, silver bromide, carbon fibers, copper sulfide, silver sulfide, glass fibers, and the like.
• the methods of the present invention can also be used to plate metals onto other metals, especially Group VIII metals.
• the metals that can be plated onto the substrate include the lanthanide, the Group VIII metals, the Group IA metals and the Group IIIA metals.
• the preferred metals are silver, copper, gold, iron, nickel, palladium, platinum, cobalt, rhodium, iridium, ruthenium and aluminum.
• One of the preferred methods for coating metals onto the surface of a substrate entails providing a source of metal ions, secondary lower alkanol and a lower alkyl ketone distributed in an anerobic liquid carrier containing said substrate and exposing the liquid carrier to light to cause the metal ions to form metal and to plate onto the surface of the substrate. This procedure is used in the same manner as that described herein for coating a dielectric particle with the secondary alcohol, alkyl ketone, source of metal ions and light.
• a substrate is coated with metal (e.g. silver) halide by reacting a source of metal (e.g. silver) ions with a source of halide ions on the surface of a substrate in an anerobic carrier containing an electron scavenger and optionally a growth stabilizer.
• the substrate surface is then illuminated with light, whereby the metal (e.g. silver) halide coatings is converted to metal (e.g. silver) coating.
• halides may be replaced with organic anions, thereby forming other metal complexes.
• organic anions include such anions as acetate, formate, citrate, EDTA, malonate, and polypeptides prepared from the natural amino acids, such as poly GLU, poly ASP, and the like.

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• 1990
  • 1990-10-18 CA CA002070389A patent/CA2070389A1/en not_active Abandoned
  • 1990-10-18 EP EP90916962A patent/EP0605408A1/en not_active Withdrawn
  • 1990-10-18 JP JP51560990A patent/JPH05501928A/ja active Pending
  • 1990-10-18 WO PCT/US1990/006009 patent/WO1991006036A1/en not_active Application Discontinuation

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