Patent Application
20070298242
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 drawings, in which:
Sunglasses according to the invention comprise a pair of lenses, the lenses being a single layer or multiple-layered structure including a nanoparticle/polymer composite and a layer comprising a dispersion of metal nanoparticles in a polymer. The composite layer comprises a continuous phase comprising at least one polymer, and a plurality of metal nanoparticles dispersed in the polymer continuous phase, thus forming a dispersed system. Preferred metals are noble metals such as gold and silver, with gold being the most preferred. As used herein, the metal nanoparticle is essentially a metal at the surface of the nanoparticle, hence metal-inorganic hybrid nanoparticles, for example core-shell nanoparticles such as gold deposited as a shell about a silica core, is included in the metal nanoparticles for use in the invention. The polymer is generally a dry solid in the completely fabricated lens such that the metal nanoparticles are locked in position to resist migration and to avoid the generation of optical defects on the lens surface by physically handling the lens or a device containing the lenses. The polymers are selected to resist the absorption of moisture from the environment such that the finished surfaces of a lens are not adversely altered during common use of the lens, for example as the lenses of sunglasses.
The “dispersed system” is defined herein as consisting essentially of fine insoluble particles throughout a continuous medium where the particles are uniformly and randomly positioned throughout the solid phase medium. The dispersed noble metal nanoparticle systems according to the present invention are clearly distinguishable from nanoparticle systems which feature nanoparticles in clumped, clustered, or otherwise segregated arrangements where the occurrence of particles are not uniformly distributed throughout the bulk of the medium.
The multiple-layered structure can be a conventional optically clear polymer or glass lens coated with a nanoparticle or nanoparticle/polymer composite layer on the surface. A multiple-layer structure can be a stacked laminate structure where at least one layer of the stack is a nanoparticle/polymer composite layer according to the invention.
Although described as being gold nanoparticles, the nanoparticles may also be silver nanoparticle materials, or a mixture of gold, silver and other nanoparticles which have high extinction coefficient at UVA, UVB, blue light and near IR spectral region. As used herein, nanoparticles refers to the average size of the gold or other particles being primarily, and preferably essentially entirely, nanosize (1 to 999 nm), such as having an average size less than 900 nm, 800 nm, 700 nm, 600 nm, 500 nm, 400 nm, 300 nm, 200 nm, 100 nm, or 50 nm. In a preferred embodiment, the average size is 20 to 100 nm. Nanoparticles of the same metal can be used as a mixture with different average sizes, such as 100 nm and 20 nm, to achieve an optical filtering effect. Nanoparticles with different shapes, such as spherical nanoparticles and rod-like nanoparticles, can be combined to achieve a desired optical protection across UVA, UVB, blue light and near IR spectral region. Nanoparticles can be of different types, for example a gold nanoparticle can be used with a core-shell nanoparticle with a silica core surrounded by a gold shell. Nanoparticles of different metals can be used in the practice of the invention.
In addition to the metal nanoparticles, more traditional dyes and metal oxide light absorbers and blockers that are commonly used in state of the art sunglasses can be incorporated into the lenses. These additional light modifying agents can be dispersed in the polymer phase with the metal nanoparticles or can reside is a second layer of a laminate, or in a bulk lens material that is coated with the metal nanoparticles or a nanoparticle/polymer composite layer.
The metal nanoparticles generally provide the desired light attenuation on filtering at levels below 1 percent by weight to about 0.01 percent by weight of the composite. For most applications this level can be below 0.5 percent by weight. Typically, levels in excess of 0.05 percent by weight are used to give a sufficient level of light attenuation or filtering and a preferred range of nanoparticle concentrations is generally from 0.05 to 0.5 percent by volume.
a) shows a substantially flat lens where the entire lens according to the embodiment of the present invention is a metal nanoparticle/polymer composite 101.
Embodied as sunglasses 200, as illustrated in
Sunglasses according to the invention provide maximum protection against a range of harmful electromagnetic wave irradiation wider than available sunglasses. By providing a high extinction coefficient towards UVA, UVB, blue light and near IR light, sunglasses according to the invention filter off these four most harmful solar irradiations to safe levels as defined by ANSI standards. The long-term protection effect of the nanoparticle sunglasses is significantly improved compared to the existing sun-block molecule-based sunglasses due to the much better photophysical and photochemical stability of nanoparticles compared to conventional organic sun-block molecules. Organic sun-block molecules tend to degrade after elongated exposure to sunlight, leading to a decrease in sun-block efficiency. In contrast, metal nanoparticles are much more stable under sunlight exposure as compared to than organic molecules. Furthermore, sunglasses formed from composites according to the invention can protect eyes from damage of laser irradiation to a certain energy level due to the optical limiting effect of metal nanoparticles, which can be very important for military and commercial airline pilots. The nanoparticle polymer composites based sunglasses are also more scratch-resistant and can last much longer than the currently available plastic sunglasses. The cost for producing nanoparticle glasses according to the invention are generally comparable to most commercial available plastic sunglasses.
The lenses can be formed using simple and inexpensive methods, such as the exemplary methods describe below. In a first exemplary embodiment, the nanoparticles and the polymer are preferably prepared separately. The polymer and metal (e.g. Au) nanoparticles can both be obtained from commercial sources. Preferred polymers include poly(methyl methacrylate) and polycarbonate which are approved and currently are used extensively for sunglasses manufacturing. Fillers, antioxidants and other additives can be present in the polymers.
The polymer and nanoparticles are mixed together in a solvent. Alternatively, a polymer/nanoparticle mixture may also be prepared by mixing nanoparticles into the molten polymer. Generally a dispersing agent is applied to the nanoparticles such that the agglomeration of the nanoparticles is inhibited and a good dispersion of nanoparticles in the polymer matrix is achieved. The dispersing agent can be a complexing agent, surfactant, polymer, dye, protein, DNA, or any other chemical or materials that make the nanoparticle soluble and stable. Common dispersing agents that can be employed include surfactants, oleylamine and alkanethiols. The metal nanoparticles can be dispersed in the polymers in a fluid state, either in the melt or in a solution of the polymer. Typically an organic solvent for the polymer is employed for a solution dispersing method. Any known dispersion technique can be employed to disperse the metal nanoparticles in the liquid polymer including mixing, shaking, or sonicating.
A lens according to the invention can be formed by simply casting the liquid nanoparticle/polymer mixture in a suitable mold or other container. When a solution is used to form the composite the solvent is removed to fix the lens. When a melt is used to form the composite, cooling results in the fixing of the lens. After drying or cooling, the lenses is obtained in a stable form where the nanoparticles are essentially fixed in a uniform but random manner in the composite layer. A second exemplary method involves coating a nanoparticle/polymer solution on a pre-made clear polymer or glass lens using spin coating, spray painting, or other film coating techniques. Alternately, at least one nanoparticle/polymer composite layer can be formed and fused with one or more other glass or polymer layers free of metal nanoparticles to form a laminate lens. The fusion of layers can be carried out with heating (e.g. room temperature) under a compressive force applied to the desired stack of layers. Since the nanoparticles are generally prepared prior to addition to the polymer matrix, there are no added impurities trapped inside the film, such as those that result from composites formed using in situ formation of the nanoparticle such as from a metal salt precursor. Accordingly, metal nanoparticle comprising films adapted for lenses according to the present invention are generally essentially free of salt, salt residue and other impurities which can adversely impact mechanical and optical properties (e.g. clarity). Using the methods described above, films according to the present invention have been found to provide predictable mechanical and optical properties.
The advantage of using metal nanoparticles as a sun-blocker for sunglasses and other sun and laser-blocking product according to the present invention is demonstrated by the following optical characteristics. As known in the art, the sun-block efficiency of an optical material is directly related to the extinction coefficient of the material at a particular wavelength. Overall, it has been reported that the cross section and the extinction coefficient of certain metal nanoparticles can be orders of magnitude higher than typical organic dye molecules. Significantly, the present invention has found that gold nanoparticles with a cross section (e.g. diameter) of 10 s of nanometers, such as 20-100 nm, exhibit a strong absorption around and below 520 nm. The extinction coefficient of a 40 nm gold nanoparticle is around 7.66×109 M−1cm−1, which is five orders of magnitude higher than the molar extinction coefficient of a typical dye molecule, indocyanine green (ε=1.08×104 M−1cm−1). Gold nanorods with dimension of 15 nm by 40-50 nm exhibit strong surface plasmon resonance absorption at 520 nm and 780 nm, extending to higher than 1000 nm. Core-shell structured metal-inorganic hybrid particles such silica (core)-gold (shell) nanoparticles can have tunable absorption from visible to the whole near IR region, i.e. 1400 nm. Metal nanoparticles such as gold and silver also exhibit nonlinear optical properties that most organic sun-blocking molecules lack. For example, the present invention has found at an incident laser energy with a fluence of 1 J/cm, a gold nanoparticle solution can block about 50% of the laser irradiation, as discovered in the inventor's research.
Although described as being used for sunglasses, the nanoparticle/polymer composite materials according to the invention can be used for other purposes. For example, the invention can be used for the lenses of ordinary glasses as well as goggles. Such composite materials may also be applied to glass windows as a window treatment to block excessive sunlight irradiation, or applied to the window of a scientific instrument or weapon to protect the instrument and weapon from laser damage.
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. 60/819,572 filed Jun. 26, 2006, entitled “Nanoparticle Sunglasses”.
The U.S. Government may have certain rights to the invention based on National Science Foundation DMR 0552295 and DMI 0506531.
| Number | Date | Country | |
|---|---|---|---|
| 60816572 | Jun 2006 | US |
