Patent Application
20100224026
This invention relates to a process for the production of nanoparticles. In particular the invention relates to a process for the production of large quantities of nanoparticles.
Nanoparticles can be synthesised from a range of materials including dielectric inorganic, organic, polymer and metallic materials. Nanoparticles have been utilised in a number of different fields of technology ranging from paints to biomolecular diagnostics. Over the last few years there has been an increase in the number of uses of nanoparticles, such an increase has resulted in a need to producing nanoparticles in large quantities while maintaining batch reproducibility.
WO 04/086044, the entire contents of which is incorporated herein by reference, describes a two-step wet chemistry batch process for synthesising silver seeds and growing the synthesized silver seeds to produce a range of silver nanoparticles. However, the quantity of silver nanoparticles produced by a wet chemistry batch reaction process are limited.
The invention provides a process for synthesising silver nanoparticles comprising the steps of:
Silver nanoparticles produced by the process may have an average diameter of between 5 nm and 100 nm and a UV-vis spectrum peak in the 420 nm to 900 nm region
In one embodiment, both steps (a) and (b) may be performed using microfluidic flow chemistry.
The silver source may be a silver salt, for example silver nitrate.
The silver source may be a complexed silver compound or salt.
The silver source may be dissolved in a capping agent solution, for example a capping agent solution selected from the group consisting: Trisodium Citrate, Cetyl -trimethyl-ammonium-bromide.
The reducing agent may be selected from the group consisting: sodium borohydride, ascorbic acid.
The ratio of silver source: reducing agent may be about 1:8.
Step (a) may be performed using microfluidic flow chemistry with a flow rate of between 3 ml/min and 10 ml/min for the silver source.
Step (a) may be performed using microfluidic flow chemistry with a flow rate of about 1 ml/min for the reducing agent.
Step (a) may be performed at 0° C.
In one embodiment, step (b) may further comprise the step of aging the silver seeds. The aging step may comprise:
The silver source of the aging step may be the same as the silver source used in step (a).
The polymeric stabiliser may be water soluble. The polymeric stabiliser may have a molecular weight between 10 kDa and 1300 kDa. The polymeric stabiliser may be selected from one or more of the group consisting: poly(vinyl alcohol), poly(vinyl pyrollidone), poly(ethylene glycol), and poly(acrylic acid). For example, the polymeric stabiliser may be poly(vinyl alcohol).
The aging step may further comprise the step of reducing the silver source present in the silver source-polymeric stabiliser-silver seed mixture. The silver source may be reduced by ascorbic acid.
Step (b) of the process may be carried out at a temperature of between 10° C. to 60° C. For example, step (b) is carried out at a temperature of 40° C.
The nanoparticles produced by the process may be stable in an aqueous solution.
The nanoparticles produced by the process may have a colour tunability throughout the visible and near infra red spectrum.
The nanoparticles produced by the process may be red in colour in a colloidal aqueous solution.
The nanoparticles produced by the process may comprise at least 30% non-spherical shaped nanoparticles.
The nanoparticles produced by the process may comprise at least 50% non-spherical shaped nanoparticles. For example, at least 70% non-spherical shaped nanoparticles.
The non-spherical shaped nanoparticles may be triangular and/or hexagonal and/or truncated triangular in shape.
The nanoparticles produced by the process may have a UV-vis spectral peak in the 345 nm region.
The nanoparticles produced by the process may have a UV-vis main spectral width FWHM of less than 300 nm. For example, a UV-vis main spectral width FWHM of less than 150 nm, such as a UV-vis main spectral width FWHM of less than 120 nm or a UV-vis main spectral width FWHM of less than 100 nm.
The invention further provides a process for synthesising silver nanoparticles comprising the steps of:
The silver seeds may be grown in step (b) by mixing a silver source solution and a reducing agent solution. The silver source solution may comprise silver seeds. The reducing agent solution may comprise silver seeds. The silver source solution may comprise a stabiliser. The reducing agent solution may comprise a stabiliser.
The solutions may be pressurised to at least about 35 MPa such as in the range of between about 35 MPa to about 275 MPa. The solutions may be pressurised at about 140 MPa. The solutions may have a shear rate of at least about 1×106 s−1 such as in the range of about 1×106 s−1 to about 50×106 s−1.
The solutions may have a flow rate of at least about 10 ml/min such as at least about 100 ml/min or at least about 1 l/min, for example at least about 10 l/min.
The solutions may be introduced separately. Each solution may have a different flow rate or each solution may have the same flow rate. The solutions may be added at different concentrations.
The residence time of the solutions in a mixing chamber of a microfluidic system may be less than about 1 ms. The residence time of the solutions in a mixing chamber of a microfluidic system may be between about 2 μs and about 1 ms.
Step (b) may be carried out at a temperature of between about 10° C. to about 60° C., for example about 40° C.
The silver source may be a silver salt such as silver nitrate. The silver source may be present at a concentration between about 10−3M to about 10−1M.
The stabiliser may be a polymeric stabiliser. The polymeric stabiliser may be water soluble. The polymeric stabiliser may have a molecular weight of between about 10 kDa and about 1300 kDa. The polymeric stabiliser may be selected from one or more of the group consisting: poly(vinyl alcohol), poly(vinyl pyrollidone), poly(ethylene glycol), poly(sodium styrenesulphonate) and poly(acrylic acid). The polymeric stabiliser may be poly(vinyl alcohol). The polymeric stabiliser may be present at a concentration of about 10−2 wt % to about 10 wt %.
The stabiliser may be trisodium citrate. The trisodium citrate may be present at a concentration of between about 10−3M to about 10−1M.
The reducing agent may be ascorbic acid. The reducing agent may be present at a concentration of about 10−3M to about 10−1M.
The silver seeds may be present at a concentration of between about 10−8M to about 10−4M of silver.
The silver source in step (a) may be a silver salt such as silver nitrate. The silver source in step (a) may be dissolved in a capping agent solution. The capping agent solution may comprise trisodium citrate and/or cetyl-trimethyl-ammonium-bromide.
The reducing agent in step (a) may be sodium borohydride and/or ascorbic acid
The ratio of silver source: reducing agent in step (a) may be 1:8.
Step (a) may be performed using microfluidic flow chemistry. The solutions may be introduced separately. Each solution may have a different flow rate. Each solution may have the same flow rate. The solutions may be added at different concentrations. The flow rate of the silver source solution may be between about 3 ml/min and about 10 ml/min such as about 8 ml/min. The flow rate of the reducing agent solution may be between about 0.5 ml/min and about 1.5 ml/min such as about 1 ml/min.
Step (a) may be performed using pressurised microfluidic flow chemistry. The solutions may be pressurised to at least about 35 MPa. The solutions may be pressurised in the range of about 35 MPa to about 275 MPa such as about 140 MPa. The solutions may have a shear rate of at least about 1×106 s−1 such as in the range of about 1×106 s−1 to about 50×106 s−1. The solutions may have a flow rate of at least about 10 ml/min. The solutions may have a flow rate of at least about 100 ml/min. The solutions may have a flow rate of at least about 1 l/min. The solutions may have a flow rate of at least about 10 l/min. The residence time of the solutions in a mixing chamber of a microfluidic system may be less than about 1 ms. The residence time of the solutions in a mixing chamber of a microfluidic system may be between about 2 μs and about 1 ms.
Step (a) may be performed at about 0° C.
The invention also provides a process for producing silver nanoparticles comprising the steps of:
The polymer may be a polyanionic polymer. The polymer may be a derivative of polysulphonate. The polymer may be a derivative of polystyrene sulphonate. The derivative may be an inorganic salt of polystyrene sulphonate. The derivative may be a monovalent salt of polystyrene sulphonate. The polymer may be poly (sodium styrenesulphonate) (PSSS). The PSSS may have a molecular weight between about 3 KDa to about 1,000 KDa such as about 1,000 KDa. The concentration of polymer in the silver seed preparation may be about 2.5 mg/ml to about 250 mg/ml such as about 25 mg/ml. The step of preparing silver seeds may be carried out at room temperature. The step of growing the silver seeds may be carried out at room temperature.
The invention further provides a process for synthesising silver nanoparticles comprising the steps of:
The water soluble polymer may be a polyanionic polymer. The polymer may be a derivative of polysulphonate. The polymer may be a derivative of polystyrene sulphonate. The derivative may be an inorganic salt of polystyrene sulphonate.
The derivative may be a monovalent salt of polystyrene sulphonate. The polymer may be poly (sodium styrenesulphonate) (PSSS). The PSSS may have a molecular weight of between about 3 KDa to about 1,000 KDa such as about 1,000 KDa. The concentration of polymer may be between about 10−1 mg/l to about 250 g/l. The concentration of polymer may be between about 10−1 mg/l to about 1 g/l. The concentration of polymer may be between about 2.5 g/l to about 250 g/l.
Step (a) is performed in the presence of the water soluble polymer.
The silver seeds may be grown in step (b) by mixing a silver source solution and a reducing agent solution. The silver source solution may comprise silver seeds. The reducing agent solution may comprise silver seeds. The silver source solution may comprise a stabiliser. The reducing agent solution may comprise a stabiliser.
The silver source may be a silver salt such as silver nitrate. The silver source may be present at a concentration between about 10−3M to about 10−1M.
The stabiliser may be a polymeric stabiliser. The polymeric stabiliser may be water soluble. The polymeric stabiliser may have a molecular weight between about 10 kDa and about 1300 kDa. The polymeric stabiliser may be selected from one or more of the group consisting: poly(vinyl alcohol), poly(vinyl pyrollidone), poly(ethylene glycol), poly(sodium styrenesulphonate) and poly(acrylic acid). The polymeric stabiliser may be poly(vinyl alcohol). The polymeric stabiliser may be present at a concentration of between about 10−2 wt % to about 10 wt %.
The stabiliser may be trisodium citrate. The trisodium citrate may be present at a concentration of between about 10−3M to about 10−1M.
The reducing agent may be ascorbic acid. The reducing agent may be present at a concentration of between about 10−3M to about 10−1M.
The silver seeds may be present at a concentration of between about 10−8M to about 10−4M of silver.
Step (b) may be carried out at a temperature of between about 10° C. to about 60° C. such as about 40° C.
Step (b) may be preformed using microfluidics. The solutions may be introduced separately. Each solution may have a different flow rate. Each solution may have the same flow rate. The solutions may be added at different concentrations
Step (b) may be performed using pressurised microfluidic flow chemistry. The solutions may be pressurised to at least about 35 MPa. The solutions may be pressurised in the range of about 35 MPa to about 275 MPa such as at about 140 MPa. The solutions may have a shear rate of at least about 1×106 s−1 such as in the range of between about 1×106 s−1 to about 50×106 s−1.
The solutions may have a flow rate of at least about 10 ml/min. The solutions may have a flow rate of at least about 100 ml/min. The solutions may have a flow rate of at least about 1 l/min. The solutions may have a flow rate of at least about 10 l/min.
The residence time of the solutions in a mixing chamber of a microfluidic system may be less than about 1 ms. The residence time of the solutions in a mixing chamber of a microfluidic system may be between about 2 μs and about 1 ms.
The silver source of step (a) may be a silver salt such as silver nitrate. The silver source of step (a) may be dissolved in a capping agent solution. The capping agent solution may comprise trisodium citrate and/or cetyl-trimethyl-ammonium-bromide.
The reducing agent of step (a) may comprise sodium borohydride and/or ascorbic acid.
The ratio of silver source: reducing agent in step (a) may be 1:8.
Step (a) may be carried out at a temperature of about 0° C.
Step (a) may be performed using microfluidic flow chemistry. The solutions may be introduced separately. Each solution may have a different flow rate. Each solution may have the same flow rate. The solutions may be added at different concentrations. The flow rate of the silver source solution may be between about 3 ml/min and about 10 ml/min such as about 8 ml/min. The flow rate of the reducing agent solution may be between about 0.5 ml/min and about 1.5 ml/min such as about 1 ml/min.
Step (a) may be performed using pressurised microfluidic chemistry. The solutions may be pressurised to at least about 35 MPa. The solutions may be pressurised in the range of about 35 MPa to about 275 MPa such as about 140 MPa. The solutions may have a shear rate of at least about 1×106 s−1 such as in the range of about 1×106 s−1 to about 50×106 s−1.
The solutions may have a flow rate of at least about 10 ml/min. The solutions may have a flow rate of at least about 100 ml/min. The solutions may have a flow rate of at least about 1 l/min. The solutions may have a flow rate of at least about 10 l/min.
The residence time of the solutions in a mixing chamber of a microfluidic system may be less than about 1 ms. The residence time of the solutions in a mixing chamber of a microfluidic system may be between about 2 μs and about 1 ms.
The silver nanoparticles synthesised by the processes described herein may have an average diameter of between 5 nm and 100 nm and a UV-vis spectrum peak in the 420 nm to 900 nm region
The silver nanoparticles synthesised by the processes described herein may have an average diameter of between about 5 nm and about 100 nm and an optical absorption spectrum peak in the region of about 900 nm to about 1610 nm.
The nanoparticles may be stable in an aqueous solution.
The nanoparticles may have a colour tunability throughout the visible and near infra red spectrum.
The nanoparticles may be red in colour in a colloidal aqueous solution.
The nanoparticles may comprise at least 30% non-spherical shaped nanoparticles.
The nanoparticles may comprise at least 50% non-spherical shaped nanoparticles.
The nanoparticles may comprise at least 70% non-spherical shaped nanoparticles.
The nanoparticles may comprise at least 95% non-spherical shaped nanoparticles.
The non-spherical shaped nanoparticles may be triangular and/or hexagonal and/or truncated triangular in shape. The non-spherical shaped nanoparticles may be triangular in shape (nanoprisms).
The non-spherical shaped nanoparticles may be plate like having an aspect ratio of between about 1:2 to about 1:10. for example triangle edge length of about 45 nm and height about 5 nm.
The nanoparticles may have an optical absorption spectrum peak in the region of about 340 nm±10 nm.
The nanoparticles may have an optical absorption spectrum peak in the region of about 335 nm to about 338 nm.
The nanoparticles may have a UV-vis spectral peak in the 345 nm region.
The nanoparticles may have a main optical absorption spectrum peak width (FWHM) of less than about 300 nm.
The nanoparticles may have a main optical absorption spectrum peak width (FWHM) of less than about 150 nm.
The nanoparticles may have a main optical absorption spectrum peak width (FWHM) of less than about 120 nm.
The nanoparticles may have a main optical absorption spectrum peak width (FWHM) of less than about 100 nm.
Continuous microfluidic flow synthesis of gold nanoparticles with online optical monitoring has been described however the volume productions are restricted to the order of milliliters per hour. Microfluidic processes of the invention can produce large volumes of high definition silver nanoparticles. The silver nanoparticles produced by a microfluidics process as described herein have improved physical properties, for example narrower size distribution, increased presence of shaped nanoparticles, higher uniformity of samples, better and higher batch to batch reproducibility, compared to nanoparticles produced by a conventional wet chemistry method including,
Silver nanoparticles produced in accordance with the processes described herein may possess one or more of the following characteristics:
Improvements in the production of silver nanoparticles using the Microfluidics technology described herein compared to the conventional wet chemistry process include:
Properties of high definition silver nanoparticles include:
Properties of high definition silver nanoparticles which can be observed in the UV-Vis absorption include:
Microfluidics can be used to produce shaped silver nanoparticles with the advantage that the microfluidics synthesis process produced a half litre per batch (and is capable of producing several litres per hour at flow rates typically in the range 10 ml/minute to 500 ml/minute) while the wet chemistry method is limited to 100 ml production. TEM images of microfluidics process produced silver nanoparticles confirmed a significant improvement in the size distribution of the nanoparticles compared to nanoparticles prepared using a conventional wet chemistry technique. We have found that nanoparticles produced by the microfluidic processes described herein have a greater batch to batch reproducibility of physical characteristics compared to nanoparticles produced by a conventional wet chemistry process. Furthermore, nanoparticles produced by the microfluidic process have long term stability in water or aqueous solution suspension, in particular the nanoparticles do not aggregate or sediment over time.
Optimisation of the microfluidic processes, both the chip and the processor routes, will enable a controlled scale-up of the production of high quality high definition silver nanoparticles in a range of shapes, sizes, colours, and/or surface chemistries. The microfluidic processes described herein can be adapted for the scaled up production of a range of high quality nanoparticles.
The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:—
We describe an improved process for producing nanoparticles, which is suitable for the production of size-controlled nanoparticles having controlled dominant shapes, such as silver triangular nanoplates. The process for producing discrete high definition silver nanoparticles comprises two steps: step (a) synthesizing silver seeds and step (b) growing silver seeds into silver nanoparticles.
The invention provides a microfluidic process for producing discrete high definition silver nanoparticles. Microfluidic technologies can be applied to at least the growth step (step (b)) or to both the silver seed production and growth steps (steps (a) and (b)).
By using microfluidic methods, we can produce discrete high definition silver nanoparticles in a predetermined and controlled manner. The nanoparticles produced using the processes described herein are highly shaped, e.g. contain a high percentage of triangles and hexagons compared to spheres, and/or have a narrow size distribution in a desired size range such as about 25 nm or about 30 nm or about 40 nm or larger or smaller and/or have a UV-visible optical absorption spectrum with a main peak at wavelengths longer that about 400 nm. The full width at half maximum (FHWM) of the main peak may be less than about 100 nm.
By employing a combination of both microfluidics chip and microfluidics processor methods for steps (a) and (b) we have devised a process that enables the scaled-up production of discrete high definition silver nanoparticles. The silver nanoparticles produced by the microfluidic process described herein have a high batch to batch reproducibility and improved physical properties including a narrower size distribution, an increased presence of shaped nanoparticles and a higher uniformity between the silver nanoparticles. The microfluidic methods also allow the size, shape, spectral profile and surface chemistries of the discrete high definition silver nanoparticles to be controlled. The microfluidic synthesis processes described herein can be adapted for the scaled up production of a range of high quality nanoparticles both metallic and non metallic.
It will be appreciated that scaled up production requires larger volumes of reagents and for the synthesis process to be successful, the reagents have to be thoroughly mixed. We have surprisingly found that in order to produce nanoparticles having a controlled shape and size the reagents should be mixed in small volumes such as between about 10 picoliters (pl) to about 100 μl, microfluidic methods are ideal for the thorough and rapid mixing of reagents in such small volumes.
In some embodiments, mixing of the reagents may be performed in small volumes in a microfluidic reactor at high or differential flow rates. For example at flow rates between about 1 ml/min to about 10 ml/min for low pressure systems and flow rates of at least 10 ml/min up to litres/min for high pressure systems. The reagents used in step (a) and/or step (b) of the process may have differential flow rates. The flow rate of individual reagents can be variably controlled within a microfluidic reaction system resulting in the reagent solutions being rapidly and thoroughly mixed.
We have also found that the ratio of the reagents, and/or the ratio at which the reagents are mixed can impact the physical properties of the nanoparticles formed. For example, an excess of about eight times the reducing agent solution to the silver salt solution has been found to be optimum for the reaction chemistry for producing silver seeds in step (a) of the process.
The performance of certain aspects of the reaction chemistry, for example in step (b) of the process may require a microfluidic reactor which is capable of delivering reagent solutions under high pressures for example between about 35 MPa to about 275 MPa (about 5000 psi to about 40000 psi), such as about 140 MPa (about 20000 psi). Mixing reagents under pressure in step (a) and/or step (b) of the process may assist with the rapid and thorough mixing of the reagents.
The use of high pressure flow and/or variable differential flow rates of reagents may allow for a uniform reaction to take place. The pressure and flow rate of reagents and the dimensions of the microfluidic reactor may be such that a turbulent flow of reagents is generated at the point at which the reaction takes place. Turbulent flow of reagents may thereby promote thorough mixing of the reagents and maintain consistent control of the reaction chemistry in a continuous microfluidic flow process. By maintaining consistent control of the reaction chemistry, we have been able to produce silver nanoparticles having physical characteristics within a well defined process envelope.
The microfluidic reactor, when designed and operated as described herein will maintain a continuous flow and through mixing of reagents under controlled conditions thereby allowing a true scaling up of the reaction chemistry without compromising the quality of the nanoparticles produced.
Advantageously, the thorough and rapid mixing of reagents according to the process described herein allows for certain desired characteristics of the silver nanoparticles to be controlled and reproducible produced. Such controlled reproducibility is not possible in a conventional wet batch chemistry reaction in which reagents are mixed in higher volumes compared to the microfluidic process resulting in variations in nanoparticle characteristics both within a batch, and between batches.
Steps (a) and (b) can be combined in some embodiments of the invention to produce a single step microfluidic production method for nanoparticles.
Depending on the properties of the nanoparticles desired, the order of addition of the reagents, the type of reagents used, and/or the concentration of the reagents can all be varied and in some embodiments additional reagents can be introduced into the reaction. By varying these reagent parameters the physical properties and attributes of the nanoparticles, such as their size, shape, thickness and their optical spectrum can controllably tuned.
The microfluidic methods described herein enable the reproducible production of high definition silver nanoparticles with predetermined, size, shape, narrow distribution of size and shape.
We have demonstrated that a microfluidics processor method can be used to produce discrete high definition silver nanoparticles in large volume batches. By tailoring pressure and shear rate parameters, silver nanoparticles can be produced on an industrial scale while retaining control of the reaction chemistry conditions necessary to produce controlled size and shape range silver nanoparticles. We used a high pressure (for example in the range of about 35 MPa to about 275 MPa, such as about 140 MPa), high shear rate (for example between about 1×106 s−1 to about 50×106 s−1, typically about 107 s−1) microfluidics processor method to produce silver nanoparticles in 500 ml batches. The process is capable of producing several liters per hour at flow rates typically in the range of about 10 ml/minute to about 500 ml/minute, while a wet chemistry method is limited to 100 ml batch production.
The invention is further illustrated with reference to the following non-limiting examples.
We have found that by using microfluidic technologies for the production of silver seeds control over the synthesis of the silver seeds is an important factor in producing discrete high definition silver nanoparticles with predetermined, size, shape and a narrow distribution of size and shape
The constituent chemicals and products may vary from those detailed in
In an alternative process, product 1 is a sodium borohydride (NaBH4) and Trisodium Citrate (TSC) solution and product 2 is a silver nitrate (AgNO3) solution. The microfluidics set-up for the production of the silver seeds is as shown in
Optionally, a polymer such as poly(sodiumstyrene sulfonate) (PSSS) may be added to step (a). For example, PSSS could be included in one or more of the silver nitrate solution, trisodium citrate solution, and sodium borohydride solution at a concentration of about 10−4 M.
Referring to
Dissolve 5 mg of silver nitrate and 7.4 mg of trisodium citrate in 100 ml of iced cooled water in an ice bath (solution 2 of
Connect solution 1 and solution 2 to pump 1 and pump 2 respectively (see setup of
Set pump 1 and pump 2 flow rates for example at 1 ml/min and 8 ml/min respectively;
Run pump 2, while pump 1 is still running and collect by-product for 30 s.
Collect 5 ml of final seed product, while pump 1 and pump 2 are still running.
Stop both pump 1 and pump 2.
A more generic setup for reagent input sequencing for general nanoparticle production is shown in
The results from experiments using a generic microfluidic chip system for the production of silver seeds (step (a)) are given below. In these cases the second step, (the growth of these seeds to produce discrete high definition silver nanoparticles) was carried out using a conventional batch chemistry method.
In this example, silver seeds were synthesised using a generic microfluidic chip system according to the following method:
37.8 mg of sodium borohydride (0.01M) was dissolved in 100 ml of water (solution 1 of
Pump 1 was run for 30 s and the by-product collected. With pump 1 still running, pump 2 was run for 30 s and the by-product collected. Prior to stopping the pumps, 5 ml of final seed product was then collected while pumps 1 and 2 were still running.
In this example silver seeds were grown into nanoparticles (step (b)) using the conventional wet chemistry method below.
45 ml of 1 wt % polyvinyl alcohol (PVA) and 1.25 ml of 0.01M silver nitrate (AgNO3) were placed in a 400 ml beaker equipped with a 5 cm magnetic stirrer.
The beaker was placed on a hot plate set at 40° C. and the solution was stirred for 45 minutes in the dark. 0.5 ml silver seed solution from step (a) above was diluted with 5 ml PVA and added to the PVA-AgNO3 solution. Approximately 30 s after the silver seed solution was added to the PVA-AgNO3 solution 250 μl of 0.1M ascorbic acid was added to the mixture in one rapid shot.
The nanoparticles of
We used a microfluidics processor to carry out step (b), the growth of silver seeds to produce high quality discrete high definition silver nanoparticles. In this Example, the silver seeds were synthesised using a conventional wet chemistry method.
We used the Microfluidics International Corporation microfluidics processor technology described in Example 4 above to create a 500 ml batch of discrete high definition silver nanoparticle solution. Referring to
Blocking and clogging difficulties were encountered in some experiments when a microfluidic chip systems was used for carrying out step (b), the growth of discrete high definition silver nanoparticles from silver seeds. It was found that blocking and clogging of the microfluidic system could be overcome if the reagents were under pressure for this step. A limited number of suitable commercial microfluidics processors are available, and have heretofore been used for processes other than chemical reactions. In this Example we used a microfluidics system supplied by a company now known as Microfluidics International Corporation located at 30 Ossipee Road, P.O. Box 9101 Newton, Mass. 02464-9101, U.S.A. This microfluidics processor operates at very high pressures of the order of about 140 MPa (about 20,000 psi) and provides high shear rates in the range of about 1×106 s−1 to about 50×106 s−1, thereby maximizing the energy-per unit fluid volume.
The microfluidics processor used allowed the reagent streams to be pressurized so that the reagent streams traveled at high velocities to meet in a reaction chamber where turbulent mixing took place. The microfluidics processor also allowed for continuous flow of the reaction product (silver nanoparticles). Details of typical processor operating parameters are given in Table 2 below.
A TEM image of the silver seeds produce (product 5) is shown in
The Microfluidics International Corporation microfluidics processor technology described in Example 4 above was also applied to the production of silver seeds (step (a)) and in a further stage these microfluidic processor produced seeds were grown to produce discrete silver nanoparticles (step (b)) also using a microfluidics processor.
In this example the following method was used:
Step (a)—Synthesising Silver Seeds
A solution comprising 2.94×10−4M AgNO3 and 2.5×10−4M TSC and 10−4M PSSS in water was made and poured into the reservoir of a microfluidics processor. A 0.01M solution of NaBH4 was introduced into the microfluidics processor. The NaBH4 and AgNO3-TSC solutions were mixed at flow rates of 15 ml/min and 485 ml/min respectively with a continuously flowing stream of the AgNO3-TSC solution and the material was processed for one pass at 140 MPa (20,000 psi).
Step (b)—Growing Silver Nanoparticles
An aqueous solution of 1 wt % PVA, 0.01M AgNO3 and 10−4 M PSSS in water was made in a beaker equipped with a magnetic stir bar (the total volume was 500 ml). The beaker was placed on a hot plate set at 40° C. and stirred for 45 minutes in the dark. 5 ml if silver seed solution from step (a) above was diluted in 50 ml PVA and added to the beaker.
Approximately 30 s after the silver seed solution was added to the beaker, the PVA-AgNO3-PSSS-silver seed solution was placed in the reservoir of a microfluidics processor. A 0.01M solution of ascorbic acid solution was introduced to a 475 ml/min continuously flowing stream of PVA-AgNO3-PSSS-silver seed solution at a rate of 25 ml/min. The material was processed for 1 pass at 35 MPa (20,000 psi).
The UV-visible spectrum of silver seeds produced using a microfluidics processor and the discrete high definition silver nanoparticles produced by the subsequent growth of these microfluidics processor produced silver seeds also using a microfluidics processor are shown in
Referring to
A wet chemistry method was used to synthesize silver seeds (step (a)) and growing the silver seeds to form discrete silver nanoparticles (step (b)), as described in WO04/086044. Briefly, silver seeds were formed from vigorously stirring an aqueous mixture of silver nitrate, trisodium citrate and sodium borohydride. The typical ratio of silver nitrate: trisodium citrate was about 1:1 and the typical ratio of silver nitrate: sodium borohydride was about 1:8.
The wet chemistry method has a restricted production volume in the order of about 50 ml, with a maximum of up to about 100 ml of discrete silver nanoparticles being produced in any one batch. Batch to batch reproducibility difficulties are experienced, as indicated by the diverse range of UV-Visible spectra of discrete silver nanoparticles using wet chemistry prepared under precisely the same conditions as shown in
This is in direct contrast to the results for the microfluidic methods for discrete silver nanoparticle production where discrete silver nanoparticles with narrow size distribution, high percentage of shaped nanoparticles and very similar UV-visible spectral profiles with peak maximum wavelengths within 1 nm can be readily prepared, as indicated by the discrete silver nanoparticles shown in
We have found major differences in the performance of the wet chemistry and microfluidic produced silver seeds in terms of, reproducibility, control over size, shape, size and shape distribution, percentage of shaped and unshaped nanoparticles present in discrete silver nanoparticle batches produced subsequently from the seeds, either by employing conventional wet chemistry or microfluidics methods to carry out step (b), the growth of the silver seeds to from discrete silver nanoparticles. We have found that the control and precision afforded by microfluidics methods for the production of silver seeds is important in achieving discrete silver nanoparticles with the required characteristics, controlled size, narrow size distribution, high presence of shaped nanoparticles and good batch to batch reproducibility. Thus, microfluidics methods, such as microfluidics processors, can be readily applied to produce litres per hour of the discrete silver nanoparticles with out sacrificing quality.
We describe a rapid and readily reproducible seed-based method for the production of high quality silver nanoprisms in high yield (at least 95%). The edge-length and the position of the main plasmon resonance of the nanoprisms can be readily controlled through adjustment of reaction conditions. From UV-Vis spectra of solutions of the nanoprisms, the inhomogeneously broadened line width of the in-plane dipole plasmon resonance is measured and trends in the extent of plasmon damping as a function of plasmon resonance energy and nanoprism size have been elucidated. In-depth analysis of the lamellar defect structure of silver nanoprisms confirms that the defects can lead to a transformation of the crystal structure in the vicinity of the defects. These defects can combine give rise to lamellar regions, thicker than 1 nm, that extend across the crystal, where the silver atoms are arranged in a continuous hcp structure. This hcp structure has a periodicity of 2.50 Å, thus explaining the 2.50 Å lattice fringes that are commonly observed in <111> oriented flat-lying nanoprisms.
Nanoparticles of noble metals such as silver are of considerable interest in nanotechnology. This stems largely from the collective oscillation of the conduction electrons in resonance with certain frequencies of incident light, leading to an extinction known as a surface plasmon resonance (SPR).[1,2,3,4,5] The spectral position of the resonance is highly dependent on nanoparticle size and shape and also depends on the refractive index of the metal and the surrounding medium.
One of the key, and most interesting, properties of highly-shaped metal nanoparticles is the fact that at the SPR of a metal nanoparticle, the electric field intensity near the surface of the nanoparticle is enhanced strongly relative to the applied field.[1,6] Two potential applications of this field enhancement are Surface Enhanced Fluorescence (SEF)[7,8,9,10,11,12] and Surface Enhanced Raman Spectroscopy (SERS).[13,14] The degree of enhancement is dependent on a number of factors. One of these is shape. It has been shown by discrete dipole approximation (DDA) calculationst[6] that nanorods and nanoprisms show a much higher degree of enhancement of the local field than spheres. Recently, electron energy-loss spectroscopy (EELS)[15,16] has permitted high-resolution probing of the SPR on metal nanorods and nanoprisms and has generated results consistent with the optical spectra and calculations.
Another factor that affects the field enhancement is damping of the surface plasmon, which is characterized by the dephasing time, T2. The field enhancement factor, if is directly proportional to the dephasing time T2, of the SPR (|f|αT2), where T2=2
Similarly, more recent experiments have shown that line widths for the SPRs of Au—Ag nanoboxes are much broader than those of gold nanorods with comparable plasmon resonance energies.[24] In addition, Ginger and co-workers have studied the line widths of scattering spectra of individual silver nanoprisms and found that the line widths increase both as the particle volume increases and as the plasmon resonance energy increases.[20]
Potential applications such as SEF and SERS are the driving force for the development of synthetic approaches that involve a high-degree of control over the final nanoparticle morphology. Silver nanoprisms have received considerable attention as the in-plane dipole SPR can be tuned across the entire visible spectrum from ˜400 nm to the near infra-red (NIR). The syntheses that exist for the production of silver nanoprisms can be generally placed into either of two categories: photochemical (plasmon-driven synthesis)[25,26,27,28,29] and thermal.[13,30,31,32,33,34,35,36,37,38,39] Photochemical syntheses have produced the highest quality samples to date but this approach typically involves days for the preparation of a sample. Thermal approaches are much quicker but often produce samples with a range of shapes and sizes.
There has been extensive research investigating the different factors that influence particle size and shape. Until recently, some explanations for the existence of anisotropic growth in an isotropic medium were based upon the assembly of surfactant molecules into a template whose shape then defines the growth of the crystal,[40,41] particularly for nanorods and nanowires. It has been more commonly thought that there is preferential adsorption of organic molecules, such as polymers and surfactants, to less stable crystal faces such as {100} and {110}. In this model, there is a much faster rate of addition of metal atoms at to the more exposed faces, resulting in preferred growth directions. For example the preferred binding of polyvinylpyrrolidone (PVP) to the {100} side faces of decahedral silver nanoparticles leading to silver nanowires with 5-fold symmetry due to growth on the {111} end faces[42] and to the {100} faces of single crystal silver nanoparticles leading to silver nanocubes as a result of the faster growth on the {111} faces;[43,44] the preferential adsorption of cetyltrimethylammonium bromide (CTAB) surfactant on the {100} side faces of decahedral gold nanoparticles leading to gold nanowires with 5-fold symmetry due to growth on the {111} end faces;[45,46,47] the preferential adsorption of CTAB-Ag+ on the {100} and {110} side faces of single crystal gold nanoparticles leading to single crystal nanorods due to preferred growth on the mostly {111} end faces;[48,49,50] the preferential adsorption of cetyltrimethylammonium tosylate (CTAT) on the {100} faces of decahedral silver nanoparticles leading to silver nanorods with 5-fold symmetry.[51] In addition, recent computational work has been successful in predicting anisotropic growth based on the face-selective binding of surfactants.[52]
Nevertheless, even for these examples, it is clear that the anisotropic growth that results from the preferential binding of organic species to certain crystal faces relies on the underlying twinning or defect structure of the seed particles since this is what determines the type and orientation of the crystal faces that are exposed to the growth medium. This is all the more apparent when we consider that in most syntheses a range of particle shapes are observed and yet the same shaped particle can be the major product of very different syntheses. Furthermore, anisotropic structures such as nanoprisms present a particular challenge to the face-selective binding model in that gold and silver nanoprisms typically have large flat {111} faces, with two-dimensional growth from the edges. Many syntheses for nanoprisms take place in the presence of such stabilizers as PVP or surfactants, yet unlike the nanowire, nanorod and nanocube examples listed above, growth is restricted in the <111> direction. This would suggest that it is quite possible that the organic stabilizers that are often present in the syntheses of nanoprisms provide a general stabilization of the growing nanoprisms and may play little or no shape-directing role.
Indeed, the internal defect structure has been implicated as a direct factor influencing crystal growth. Specifically, defects such as twinning that arise during the early stages of particle formation give rise to preferred growth directions where the defects are exposed to the growth medium. In the case of nanoprisms, parallel stacking faults in the <111> direction have been observed with these making contact with the growth medium at the edges, precisely where growth occurs.[53] The silver halide growth model has also been resurrected as a way of explaining particle growth in many synthesis methods.[54,55,56,57] In this model, twin planes form reentrant grooves, which are favorable sites for the attachment of adatoms. A single twin plane is expected to direct growth in two dimensions but limit the final size of the nanoprism, while the presence of two parallel twin planes would allow the fast growing edges to regenerate one another, allowing shapes such as hexagonal nanoplates to form. Very recently, Rocha and Zanchet have studied the defects in silver nanoprisms in some detail and have shown that the internal structure can be very complex with many twins and stacking faults.[58] These defects are parallel to each other and the flat {111} face of the nanoprism, subdividing it into lamellae which are stacked in a <111> direction, and are also present in the silver seeds. In that paper, it was demonstrated how the planar defects in the <111> direction could give rise to local hexagonally close-packed (hcp) regions. These would in turn explain the 2.50 Å lattice fringes that are observed in <111> orientated nanoprisms, which have hitherto been attributed to formally forbidden ⅓{1422} reflections.[52,53,54,59]
We describe a thermal synthetic procedure that selectively produces (>95%) silver nanoprisms in high yield. The as prepared samples are sufficiently monodisperse that important features of the SPR of silver nanoprisms are visible. Trends in the evolution of the degree plasmon damping as a function of plasmon resonance energy and nanoprism size can be elucidated through analysis of the UV-Vis spectra. The TEM data reveals that the defects have a significant impact on the crystal structure of silver nanoprisms and have important implications for understanding of the role of defects in the anisotropic growth mechanism for silver nanoprisms.
In a typical experiment, silver seeds are produced by combining aqueous trisodium citrate (5 ml, 2.5 mM), aqueous poly(sodium styrenesulphonate) (PSSS; 0.25 ml, 500 mg L−1; Aldrich 1,000 kDa) and aqueous NaBH4 (0.3 ml, 10 mM, freshly prepared) followed by addition of aqueous AgNO3 (5 ml, 0.5 mM) at a rate of 2 ml min−1 while stirring continuously.
The nanoprisms are produced by combining 5 ml distilled water, aqueous ascorbic acid (75 μl, 10 mM) and various quantities of seed solution, followed by addition of aqueous AgNO3 (3 ml, 0.5 mM) at a rate of 1 ml min−1. After synthesis, aqueous trisodium citrate (0.5 ml, 25 mM) is added to stabilize the particles and the sample is diluted with distilled water as desired. Distilled water is used throughout for all solutions. The synthesis is complete after the 3 minutes required for addition of the AgNO3 during which time the colour of the solution changes as the SPR red-shifts in response to nanoprism growth.
Samples were prepared for XRD measurements by concentrating a nanoprism sample by centrifugation. A viscous nanoprism mixture was prepared by adding the few drops of concentrated nanoprism solution to a few drops of aqueous 5% w/v poly(vinyl alcohol) (PVA). This was added to the glass slide for XRD analysis (Philips X′Pert Pro) and allowed to dry.
All TEM images were taken using a JEOL JEM-2100 LaB6 at 200 kV.
We describe a method for silver nanoprism synthesis that is a seed-based thermal synthetic procedure that selectively produces (>95%) silver nanoprisms in a rapid and reproducible manner; and under very mild conditions (room temperature and water as solvent). The method involves the silver seed-catalyzed reduction of Ag+ by ascorbic acid, and surprisingly results in a minimal concentration of spherical nanoparticles being produced. The spectral position of the SPR can be tuned by controlling the size of the nanoprisms, without any significant variation in thickness. This can be achieved through adjustment of the number of seeds in the growth mixture.
A typical example of the nanoprisms produced with this method is shown in
A key ingredient for production of high quality samples is poly(sodium styrenesulphonate) (PSSS), which is used as a stabilizer in the seed production step. If PSSS is left out or only added to the seed solution after seed production, then there is a diversity of nanoparticle shapes and sizes, this is shown clearly in
Generally, the amount of citrate present in the synthesis of many of the samples is very low. For example, in a synthesis that uses 100 μl of seed solution there is 118 nmol of citrate in the solution during the growth step, while 1,500 nmol of Ag+ is added. This contrasts with previously reported results which indicate that a low citrate/Ag+ ratio (<1) resulted in triangular and hexagonal structures with a broad range of sizes (30 to 300 nm) while a high citrate/Ag+ ratio (>1) was required for nanoprisms to be the major product.[33] This was reasoned to be the result of citrate likely effecting the face-selective growth by adsorbing more strongly to the flat {111} face of the nanoprisms. Here, analysis of samples by UV-Vis indicates that increasing the amount of citrate used in the synthesis does not increase the anisotropy of the nanoprisms. The high-quality nanoprisms we have obtained with relatively low quantities of citrate present indicate that it is more likely that the defect structure of the seeds, rather than the presence of citrate in the growth step, is the basis for anisotropic growth into nanoprisms. Referring to
To characterize the nanoprisms produced by this method and explore the relationship between nanoparticle dimensions and the position of the main SPR, TEM analysis of statistically significant numbers of nanoprisms from four samples was carried out. The positions of the main SPRs of these samples were well separated as can be seen in
Examples of TEM images of nanoprisms from samples 1 to 4 are shown in
According to theory, the position of the band should depend linearly on edge length and on the inverse of the thickness.[3] Indeed, by plotting the λmax against L/T, where L is the nanoprism edge-length and T is the nanoprism thickness, we find a linear relationship as can be seen in
To study the optical properties of the nanoprisms, a series of samples of increasing edge-length was prepared. These samples display a progression in color as the main SPR is increasingly red-shifted as the nanoprism edge-length increases. These samples are shown in
The lateral dimensions of the triangular nanoparticles can be controlled by adjusting the extent of growth. This is controlled by adjusting the number of seeds in the reaction, which in turn is determined by the volume of seed solution used in this growth stage. There is a linear relationship between the position of the in-plane dipole plasmon band and the dimensions of the nanoparticles.
The ultimate size of the nanoprisms can be tuned by controlling the ratio of silver ion: silver seed in the growth step. For example for the samples 1 to 10 described herein the following ratios may be used:
Examples of four samples (1 to 4) with TEM analysis are shown in
In
In
The degree of radiation damping increases with nanoparticle volume, so the degree of radiation damping must be increasing. However, since the line widths narrow with increasing volume, this indicates that there is an overall decrease in plasmon damping. Therefore there must be a decrease in non-radiative damping that far outweighs any increase in radiation damping. Thus the degree of radiation damping in these nanoprisms must be very small. This behaviour is very similar to that observed in gold nanorods with a narrow range of diameters but with a large range of aspect ratio,[18] On the other hand, Munechika et al. show that the line widths of the SPRs obtained from their individual silver nanoprisms increase with nanoprism volume.[20]
If the in-plane dipole SPR is sufficiently red-shifted and the samples are sufficiently monodisperse, then the in-plane quadrupole SPR should be visible. This is clearly the case for many of the spectra in
Optical properties aside, the structural properties of silver nanoprisms are a source of much interest. The TEM analysis of these nanoprisms in this Example provides direct evidence of a defect-induced arrangement of silver atoms that not only results in a hcp structure in the vicinity of the defects but also in multiple defects combining to yield a continuous hcp lamellar region of about 1.5 nm in thickness. As shown in detail below, this hexagonal arrangement of atoms propagates perpendicular to the flat {111} face of the nanoprism with a spacing of 2.50 Å and thereby explains the commonly observed 2.50 Å lattice fringes in flat-lying silver nanoprisms as shown in
To investigate this possible hcp arrangement of atoms we have performed detailed TEM studies of vertically oriented silver nanoprisms. A typical sample of flat-lying nanoprisms is shown in
For the correct orientation to occur, the nanoprisms firstly need to be vertically orientated as in the stacked formation as shown in
In fact, there are so many defects in the nanoprism here that a significant continuous portion of the crystal has a hcp arrangement; a lamellar region about 1.5 nm thick. This is highlighted by the superposition of a zigzag pattern on the TEM image in the top of
The reconstruction of the silver lattice is illustrated schematically in
Further evidence of the transformation of the crystal structure to hcp is provided by x-ray diffraction (XRD) data from our nanoprisms. These show peaks for the fcc silver lattice, as expected, but also show two further peaks corresponding to reflections that are predicted to arise from a hcp arrangement as indicated in reference 57. This is shown in
Since a significant portion of the nanoprism maintains its fcc structure, as evidenced by the TEM analysis in
The familiar triangular shape and constant thickness of nanoprisms results from highly selective lateral growth from the edges. Due to the lamellar defect structure of the nanoprisms, it is precisely at these edges where the defects are exposed to the growth solution. Thus the significant rearrangement of the crystal structure described here very likely plays a crucial role in giving rise to two-dimensional growth. The hcp crystal faces (or defect-rich regions) at the edges must support a much faster rate for the addition of silver atoms during growth, compared to the {111} or {100} faces. Since the hcp structure is not the natural crystal structure for silver, it must therefore be less stable than the fcc structure, making it likely that the edges where the hcp structure is exposed to the growth medium are less stable than the {111} or {100} faces. This higher degree of instability may be the basis of the faster two-dimensional growth at the edges. The hcp and fcc crystal structures both have a hexagonal symmetry so it remains to be explained why triangles, and not hexagonal nanoplates, are the preferred outcome of two-dimensional growth.
To explain this let's consider a flat, <110> oriented, fcc single crystal as shown in the schematic in
Next consider a more realistic version of a hexagonal nanoplate that could be the result of initial two-dimensional growth from the seed, see
At this point it is worth recalling the silver halide growth model,[53,54,55,56] where anisotropic growth is promoted by the presence of twin planes in nanoparticle nuclei. At the edges of the nuclei where the twin plane is exposed to the growth medium, alternating concave and convex {111} surfaces are formed with growth occurring much faster on the concave surfaces, which grow themselves out of existence leaving a triangular nanoprism of a size defined by the size of the particle at the time of twinning.[53,54] The presence of two twin planes can result in larger hexagonal nanoplates being formed. This silver halide model for anisotropic growth is not entirely consistent with our observations. Firstly, our analysis shows that several stacking faults can be present in a nanoprism and can even combine to yield continuous hcp regions. Secondly, our nanoprisms do not stop growing once the triangular shape has been established. As can be seen in
The faster growth on hcp and fcc {100} faces runs counter to what is normally observed in noble metal nanorod and nanocube syntheses that involve the use of surfactants or polymers to influence shape. As mentioned earlier, in these syntheses organic species tend to prefer to stick to less stable crystal faces such as {110} and {100} leading to preferred growth on {111} planes. We note that in our synthesis the amounts of potentially shape-directing organic species are very low. For example, PSSS is used to enhance the quality of the seeds during their synthesis, but even though growth is quite uncontrolled when it is completely absent, a very large fraction of the particles are anisotropic and are mostly nanoprisms and nanoplates. Also, as mentioned earlier, the amount of citrate used in the growth step of our synthesis is very low. It seems plausible therefore that in the absence of strongly coordinating species, the lower stability of {100} faces may lead them to grow faster than {111} faces.
We have devised a straightforward, non-photochemical, room temperature procedure for the synthesis of silver nanoprisms. The as prepared silver nanoprisms are sufficiently monodisperse that it has been possible to investigate trends in the extent and nature of plasmon damping through measuring the inhomogeneously broadened line width of the SPR from UV-Vis measurements. We have found that there is a decrease in plasmon damping with decreasing plasmon resonance energy, consistent with observations by other researchers. However, the decrease in plasmon damping is also associated with an increase in nanoprism size: Radiation damping scales with nanoparticle volume so the observed decrease in overall damping implies that the amount of radiation damping is small and whatever increase in radiation damping there is, it is outweighed by the decrease in non-radiative damping as the plasmon resonance energy decreases. These results indicate that, at least at low plasmon resonance energies, there is very little damping of the plasmons and that thin (˜5 to 6 nm thick) silver nanoprisms are ideally suited for applications that rely on enhancement of the local field. This needs to be confirmed by measurements on individual nanoprisms of the homogeneous line width.
We have shown that silver nanoprisms possess many defects in the <111>direction perpendicular to the flat face of the nanoprisms and that these can combine to give rise to a hcp layer sandwiched between two fcc layers. This hcp layer has a periodicity of 2.50 Å that provides an explanation for the commonly observed 2.50 Å lattice fringes in flat-lying nanoprisms. Furthermore, this two-dimensional hcp layer is most likely the main explanation for the two-dimensional lateral growth, with the triangular shape of the nanoprisms being driven by the asymmetric distribution of crystal faces at the edges, which is in turn determined by the asymmetric thicknesses of the fcc layers on either side of the hcp layer. The silver halide model is perhaps a good starting point for understanding anisotropic growth in as much as it identifies defects as crucial, however it apparently does not adequately explain the growth patterns of metal nanoprisms. We believe that the defect-induced arrangement of silver atoms into continuous hcp regions, as reported here, represents a significant insight into the growth mechanisms of anisotropic metal nanoparticles.
In this example we used a generic microfluidic chip system for the production of silver seeds (step (a)) and step b) was carried out by systematically changing the volume of seeds added to the growth step. The nanoparticles produced were size and colour tuned triangular nanoplates (nanoprisms).
Referring to
Solution 1 and solution 2 were connected to pump 1 and pump 2 respectively (see setup of
Microfluidics was used for step (b) (growing the silver seeds synthesized in step (a) into nanoparticles) to produce colour tuned triangular nanoplates from the silver seed synthesised by microfluidics method with a flow rate ratio of 1:1 of solution 1 (AgNO3) and solution 2 (NaBH4, PSSS and TSC) described above.
5 mL of water, 75 μl of 10 mM ascorbic acid and μL volumes of the seeds, as specified in Table 4, below were stirred together in a beaker using a magnetic at a rate of 500 rpm. Using pump 1, 3 mL of silver nitrate 5×10−4 M was added at a rate of 1 mLmin−1. 500 μL 2.5×10−2M trisodium citrate was then added to stabilize the particles and the final volume was brought up to 10 mL using water.
Step (b) may be carried out using the high pressure microfluidics process which would enable the production of large volumes of size and shape controlled triangular silver nanoplates. Within the microfluidics production the flow rates, the flow rate ratios the reagents and their relative concentrations, volumes and mixing configuration, order and conditions may be adjusted for each specific type of nanoparticle seeds to be produced. In addition a polymer maybe added at any of solutions or at any of the preparation stages to further modify the surface chemistry, the stability or the durability of the silver nanoparticles for applications such as functionalisation or industrial processing.
A microfluidics processor technology as described above in examples 4 and 5 was used to create seven batches of discrete high definition silver nanoparticle solutions of varied formulations, as described in Table 5 below.
The invention is not limited to the embodiment hereinbefore described, with reference to the accompanying drawings, which may be varied in construction and detail.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007/0931 | Dec 2007 | IE | national |
| 2008/0326 | Apr 2008 | IE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IE2008/000097 | 10/6/2008 | WO | 00 | 4/1/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 60960577 | Oct 2007 | US | |
| 61071392 | Apr 2008 | US |
