Patent Application
20080004364
A fuller understanding of the present invention and the features and benefits thereof will be obtained upon review of the following detailed description together with the accompanying drawing, in which:
A method of laser processing comprises the steps of immobilizing a plurality of metal nanoparticles on a polymer support to form a nanoparticle coated support or physically dispersed metal nanoparticles in a polymer to form a nanoparticle/polymer composite. The polymer is optically transmissive at a given operating wavelength range. At least one material is placed in proximity to the coated support or the composite. The coated support or composite is irradiated with photons in the operating wavelength range by a laser source. The metal nanoparticles preferentially absorb the photons from the laser and transfer heat to the material in the vicinity of the nanoparticle. The localized heat is absorbed by the material promoting a chemical or physical transformation of that material. The coated support or composite can then be removed from the chemically or physically transformed material. Accordingly, the transformed material can be separated from the metal nanoparticles or the polymer support. The heat generated by laser irradiation of the nanoparticles is transferred to the surrounding material, causing physical (such as deformation, melting, crystallizing) or chemical (such as decomposition, isomerization, unimolecular or bimolecular reactions) transformations. These transformations can result in an optical property changes (such as refractive index change) of a contacting material to create useful micropatterns or microstructures on or within the material.
The polymer support can be selected from a variety of generally thermoplastic or thermoset polymers depending on the applications. For accelerating chemical reactions, nanoparticles are generally immobilized on thermoset polymers having high decomposition temperatures, generally in excess of 180° C. For other applications, such as direct laser writing of optical devices and microelectronics, the temperature increase of the polymer upon laser irradiation should be high enough to introduce the necessary optical or electrical property change, but low enough to prevent decomposition of the polymer.
A variety of metal nanoparticles may be used with the invention. Although described relative to Au nanoparticles, the invention may be practiced with other metal nanoparticles, including, for example, Ag, Pt, or Cu nanoparticles. Nanoparticles are preferably 1 to 100 nm is size and can be various shapes. The metal nanoparticle/polymer composite can be from 0.01 to 10 weight percent nanoparticles. For the purpose of the invention a metal nanoparticle is any nanoparticle with a surface that is essentially metallic. A thin oxide or nitride surface layer can exist on the metal surface. As such, a metal inorganic composite, such as a gold coated silica particle, is a metal nanoparticle of the invention.
The laser source is selected to provide irradiation at a wavelength in which the metal nanoparticles provide efficient absorption and scattering. For Au nanoparticles, 532 nm radiation provided by a Nd:YAG laser has been found to be efficiently coupled.
The invention can catalyze or accelerate a broadly defined group of chemical reactions. Chemical reactions can include any decomposition, isomerization, or other unimolecular or bimolecular reaction. Multiple reactions and repetitive reactions, such as polymerizations, can be carried out using systems according to the invention. The nanoparticle coated supports in the format of beads or films are generally suspended in the chemical reaction medium. Laser irradiation of the nanoparticle coated supports will generate heat around the addressed nanoparticle of the coated supports. When the heat is transferred to the reaction medium, the chemical reaction initiates. The region of heating is confined to a localized volume. Using the inventive system, chemical reactions that generally require significant heat to trigger the reaction (e.g. 200 to 400° C.) can be conducted where the bulk of the transforming material remains at a low temperature, for example room temperature, using a hand-held low power laser beam. The invention thus eliminates the need for hot plates, heating mantles or other conventional heating methods or equipment used for thermal energy-promoted chemical reactions. It also eliminates the need of water condensers or other cooling devices used in a typical chemical reaction apparatus to prevent the volatilization of the reaction solvents. This technique allows many chemical reactions to be conducted more conveniently and safely.
As noted in the Background, regarding chemical reactions, one cannot generally run a chemical reaction aided by a light source and metal nanoparticles in solution because of at least one of two unsolved issues. One unsolved issue is how to protect the nanoparticles from degradation during chemical reaction initiation. Another unsolved issue is how to separate the nanoparticles from the reaction mixture or product after the chemical reaction is completed. The present invention solves both of these previously unsolved issues.
As noted above, in one embodiment of the invention, the nanoparticles are immobilized on a thermally stable polymer support, such as polymer beads or polymer membranes. The nanoparticles can be non-covalently or covalently immobilized on to the polymer support. The nanoparticles can also be physically dispersed in a polymer to form a nanoparticle composite. The polymer is substantially transparent to the laser light and is selected to be stable throughout the temperature range required for the promoted reaction where the heat generated by the laser at the nanoparticles is transferred to the reaction medium in its proximity. By dissipating the heat from the nanoparticle into the surrounding environment, the nanoparticles and their support resist decomposition.
In a coated support embodiment, using, for example polymer beads or membranes to immobilize the nanoparticles, the supported nanoparticles can be easily removed from the reaction mixture by filtration. For soluble products the simple filtration is sufficient to separate the supported nanoparticles, for example the nanoparticle/polymer beads or polymer membrane, from the reaction product. For products that solidify during the reaction, a solvent that dissolves the product, but not the polymer of the support or composite, can be added before filtration. In some cases the product can be distilled from the polymer supported nanoparticles.
It should be understood that the Examples described below are provided for illustrative purposes only and do not in any way define the scope of the invention.
Laser Irradiation of Metal Nano Articles for Chemical Reactions
In one example, gold nanoparticles with diameter of 10 nm were immobilized on a cross-linked anionic exchange resin, AMBERLITE IRA-67™, by non-covalent bonds. The anionic exchange resin beads were a few hundred microns in diameter. The nanoparticle-loaded resin beads were suspended in a toluene solution of styrene monomer premixed with the thermal initiator 2,2′-azobis(2-methylpropionitrile (AIBN). The beads were irradiated with a 532 nm continuous wave Nd:YAG laser. The styrene polymerized into polystyrene after a few minutes of laser irradiation. The reaction was conducted in open air and no condenser was used in the reaction apparatus. The overall temperature of the reaction mixture remained at around room temperature. After the reaction, the anionic exchange resin beads were filtered from the polymer solution. Repeating the experiment without the nanoparticle-loaded resin did not result in polymerization. Neat styrene monomer also polymerized in the presence of the irradiated nanoparticle supported resin, but did not polymerize in the absence of the resin.
Laser-Assisted Controlled Heating of Solder Material
In a third example, a prophetic example, the photon-thermal energy conversion of nanoparticles is also used for controlled heating of solder materials. A nanoparticle/polymer composite film, having nanoparticles blended with the polymer, is applied on the surface of commercial solder wires or pastes that is lead-contained or lead-free. The polymer is a thermoset polymer that does not decompose at temperatures where the solder melts. The composite in contact with the solder can be irradiated by a laser beam. The heat generated from the laser excited nanoparticle/polymer composite transfers to the solder, causing localized heating and melting of the solder. Because the spot size of the laser beam is around a few hundreds of microns or smaller, very small amounts of solder can be applied to an electronic device in a controlled fashion. In other embodiments, nanoparticles can be immobilized by other transparent matrix materials such as a thermal conductive glass and used for the exemplary purposes as disclosed herein.
This invention can be embodied in other forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be had to the following claims rather than the foregoing specification as indicating the scope of the invention.
The present application incorporates by reference and claims priority to U.S. Provisional Patent Application Ser. No. 60/817,519 filed Jun. 29, 2006, entitled “Laser Irradiation of Metal Nonoparticle/Polymer Composite Materials for Chemical Reactions and Microprocessing Applications Therefrom.”
The U.S. Government may have certain rights to the invention based on National Science Foundation Career Award DMR 0239424 and 0552295, and NIRT award DMI 0506531.
| Number | Date | Country | |
|---|---|---|---|
| 60817519 | Jun 2006 | US |
