Reduced haze nanocomposite films

Abstract

Various embodiments provide compositions including nanoparticles, a polymer, and zinc oleate that each exhibit a measured haze of 22% or less.

Description

[0001] REDUCED HAZE NANOCOMPOSITE FILMS

[0002] CROSS-REFRENCE TO RELATED APPLICATION(S)

[0003] The present application claims priority to U.S. Application No. 63 / 613,868, filed December 22, 2023, the content of which is incorporated herein by reference in its entirety.

[0004] FIELD OF THE DISCLOSURE

[0005] The present invention is directed to reduction of haze in polymer nanoparticle composite films.

[0006] BACKGROUND OF THE DISCLOSURE

[0007] Haze is detrimental in materials designed to transmit light. Accordingly, an objective of the present invention is developing processes or compositions resulting in reduced haze.

[0008] SUMMARY OF THE DISCLOSURE

[0009] In one aspect of the invention, the haze of the quantum dot-containing composition is reduced by addition of minor amounts of selected solvents, e.g., toluene, octane, heptane, decane, dodecane, tetradecane and the like to the particular quantum dots prior to admixture and extrusion in particular polymers.

[0010] In another aspect of the invention, a composition is provided including: nanoparticles, a polymer, and zinc oleate whereby said composition exhibits a measured haze of 22% or less.

[0011] In yet another aspect of the invention, a composition is provided including: nanoparticles, a polymer, and zinc oleate whereby said composition exhibits a measured haze of 22% or less.

[0012] In still another aspect of the invention, a composition is provided including: a solvent, Zn-halide, and quantum dots selected from the group of selected from the group consisting of CuFeS2, CuFeSe , CuInZnS2, CuZnSnSe2, CuInS2, CuInSe2, CuInSexS2-x, CuInGaSexS2-x, AgInS2.

[0013] AgInSe2, AgInGaSe2S2-x, CUA1S2, CuAlSe2, CuAlGaSexS2-x, CdS, CdSe, ZnS and ZnSe.

[0014] BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Fig. 1 shows a picture of ethylene vinyl acetate (EVA) - quantum dot laminates: (a & b) such laminates extruded with quantum dots pre-treated with ZnCb and toluene; and, (c) such laminates with untreated quantum dots.

[0016] Fig. 2 is a table showing optical properties of ethylene vinyl acetate (EVA) - quantum dot laminates, such laminates either extruded with quantum dots either pre-treated with ZnCh and toluene or untreated quantum dots.

[0017] DEFINITIONS AND ABBREVIATIONS

[0018] The following explanations of terms and abbreviations are provided to better describe the present disclosure and to guide those of ordinary skill in the art in the practice of systems, methodologies and compositions disclosed herein.

[0019] As used herein, “comprising” means “including”, and the singular form “a” or “an” or “the” include plural references unless the context clearly indicates otherwise. Unless the context clearly indicates otherwise, the term “or” is inclusive, and thus refers to both a single element of stated alternative elements and a combination of two or more of those elements.

[0020] Unless explained otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one or ordinary skill in the art to which this disclosure relates. Suitable methods and compositions are described herein for the practice or testing of the systems, methodologies and compositions described herein. However, it is to be understood that other methods and materials similar, or equivalent to, those described herein may be used in the practice or testing of these systems, methodologies and compositions disclosed herein. Consequently, the systems, methodologies, compositions, and examples disclosed herein are illustrative only, and are not intended to be limiting. Other features of the present disclosure will be apparent to those skilled in the art from the following detailed description and the appended claims. Unless otherwise indicated, all numbers expressing quantities of components, percentages, temperatures, times, and so forth as used in the specification or claims are to be understood as being modified by the term “about”. Unless otherwise indicated, non-numerical properties such as colloidal, continuous, crystalline, and so forth as used in the specification or claims are to be understood as being modified by the term “substantially”, meaning to a great extent or degree. Accordingly, unless otherwise indicated implicitly or explicitly, the numerical parameter and / or non-numerical properties set forth herein are approximations, and the optimal values of these properties and parameters may depend on the desired properties sought, the limits of detection under standard test conditions or methods, the limitations of the processing methods, and / or the nature of the property or parameter. When directly and explicitly distinguishing embodiments from disclosed prior art, the embodiment numbers are not approximations unless the word “about” is recited.

[0021] Carcinogen: A material that has been shown to directly or indirectly cause cancer in any mammal. Emission spectrum: Those portions of the electromagnetic spectrum over which a fluorophore such as a QD (or a composition containing them) exhibits PL (in response to excitation by a light source) whose amplitude is at least 1% of the peak PL emission.

[0022] Fluorophore: A material which absorbs a first spectrum of light and emits a second spectrum of light. A material that exhibits luminescence or fluorescence.

[0023] Ligand: A ligand is an ion or molecule that binds to another, usually larger, molecule. In general, a ligand bonds to a metal atom, which in the case of the present disclosure, is part of a quantum dot and / or nanoparticle. A ligand may be configured to bind to a particular receptor, interact with various types of matter in prescribed ways, and / or the like. Capping ligands are configured to stabilize the interface where nanoparticles, such as quantum dots, interact with their surrounding medium.

[0024] Nanoparticle: A nanoscale particle of a solid material. The nanoparticles disclosed herein are preferably crystalline and have a size of less than 500 nanometers in dimension. The nanoparticles disclosed herein may form a colloidal suspension. Embodiments of the disclosed nanoparticles may be of a single material or may include an inner core and an outer shell of differing materials. The nanoparticles may further include a plurality of ligands bound to the nanoparticle outer surface. Exemplary nanoparticles which may be utilized in the compositions, systems and methodologies described herein may comprise metals, metal oxides, metal chalcogenides, semiconductors, and insulators. Nanoparticles may be crystalline (i.e., nanocrystals), amorphous, or mixtures thereof.

[0025] Photoluminescence (PL): The emission of light (electromagnetic radiation, in the form of photons) after the absorption of light. It is one form of luminescence (light emission) and is initiated by photoexcitation (excitation by photons).

[0026] Photosynthetic Active Radiation (PAR): The wavelength interval from 400 to 700 nanometers that photosynthetic organisms effectively use in photosynthesis.

[0027] Polar solvents: A polar solvent is any solvent containing an electric dipole. Exemplary polar solvents include acetone, ethanol, water, ethanol / water mixtures, isopropanol, isopropanol / water mixtures, methanol, methanol / water mixtures, dimethyl sulfoxide, diethyl sulfoxide, tetrahydrofuran, and tetrahydrofuran / water mixtures.

[0028] Polymers (as well as polar polymers): A large molecule, or macromolecule, composed of many repeating subunits. Polymers range from familiar synthetic plastics such as polystyrene or poly(methyl methacrylate) (PMMA), to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many smaller molecules, e.g., monomers. Exemplary polymers include poly(methyl methacrylate) (PMMA), a polyolefin elastomer (POE) such as ethlylene-1 -octene copolymer, polystyrene, silicones, epoxy resins and the like.

[0029] Polar polymers: Polymers containing only carbon and hydrogen atoms are non-polar polymers. Polar polymers typically contain other atoms such as chlorine, fluorine, oxygen, nitrogen, and sulfur whereby the polymer will contain a permanent electric dipole called a polar polymer. Exemplary polar polymers include poly vinyl alcohol, an ethylene vinyl alcohol copolymer, polyvinyl acetate, polyurethane, ethylene vinyl acetate, an acrylic polymer, polyvinyl butyral, and polyamides, e g., nylons.

[0030] Quantum Dots: A nanoparticle that exhibits size dependent electronic and optical properties due to quantum confinement. The quantum dots disclosed herein preferably have at least one dimension less than about 50 nanometers. The disclosed quantum dots may be colloidal quantum dots. Some of the quantum dots which may be utilized in the compositions, systems and methodologies described herein are made from a binary semiconductor material having a formula MX where M is a metal and X is typically selected from sulfur, selenium, tellurium, nitrogen, phosphorus, arsenic, antimony, or mixtures thereof. Exemplary binary quantum dots which may be used in the compositions, systems and methodologies described herein include CdS, CdSe, CdTe, PbS, PbSe, PbTe, ZnS, ZnSe, ZnTe, InP, InAs, CU2S, and I Ss Other quantum dots which may be utilized in the compositions, systems and methodologies described herein are ternary, quaternary, and / or alloyed quantum dots including, but not limited to, ZnSSe, ZnSeTe, ZnSTe, CdSSe, CdSeTe, HgSSe, HgSeTe, HgSTe, ZnCdS, ZnCdSe, ZnCdTe, ZnHgS, ZnHgSe, ZnHgTe, CdHgS, CdHgSe, CdHgTe, ZnCdSSe, ZnCdSeTe, ZnHgSeTe, ZnHgSSe, CdHgSSe, CdHgSeTe, Q1AIS2, CuAlSe , CuFeS2, CuFeSe2, CuAlSexS2-x, CuInS2, CuInSe2, CuInGaSe2, CuInZnS2, CuZnSnSe2, CuInSexS2-x, CuInZnSexS2-x, AgInS2, AgInSe2, AgInGaSexS2-x, and AgIn(Se,S)2 where (0 < x < 2) quantum dots, although the use of non-toxic quantum dots is preferred. Nontoxic quantum dots include those free, e.g., of cadmium, lead, and mercury. Embodiments of the disclosed quantum dots may be of a single material or may include an inner core and an outer shell of differing materials. The outer shell may be a thin shell or layer formed by any suitable method, such as cation exchange. The quantum dots further include a plurality of ligands bound to the quantum dot surface.

[0031] Quantum Yield (QY): The ratio of the number of emitted photons to the number of absorbed photons for the fluorophore.

[0032] Self-absorption: The percentage of emitted light from a plurality of fluorophores that is absorbed by the same plurality of fluorophores. Some quantum dots, including CuInS2, CuInSe2, CuInGaSe?, CuInZnS?, CuZnSnSe , CuIn(Se,S)2, CuInZn(Se,S)2, and AgIn(Se,S)2 and related compounds, are known to have uniquely low self-absorption.

[0033] Toxic: Denotes a material that can damage living organisms due to the presence of phosphorus or heavy metals such as cadmium, lead, or mercury.

[0034] Solubility: When used in reference to QDs, the ability of QDs to form a clear colloidal suspension without haze caused by formation of aggregates.

[0035] Colloidal suspension: A mixture consisting of a disperse phase (the suspended particles) and a continuous phase (the liquid medium of suspension), wherein the mixture either does not settle, or would take a very long time to settle appreciably.

[0036] Dispersibility: The ability of QDs to form a colloidal suspension.

[0037] Flocculation: A process whereby the disperse phase in a colloidal suspension forms aggregates and comes out of suspension.

[0038] DETAILED DESCRIPTION

[0039] The presently described invention shows approaches to the reduction of haze in polymer nanoparticle composite films. Such approaches can include use of, e.g., zinc oleate, or zinc chloride treated nanoparticles with a polymer matrix to reduce haze in comparison to compositions without the use of zinc oleate or use of untreated nanoparticles. Another approach can be through inclusion of a zinc halide, preferably zinc chloride although other halides may be used.

[0040] While not wishing to be bound by the present explanation, from review of the experimental observations and reasonings, it can be hypothesized that zinc treatments and / or additives aid in increasing the solubility of these QDs in selected host environments (liquid or solid). This can increase the dispersion of QDs within the polymer matrix, thus resulting in a reduction of the haze in these nanocomposite materials. EXAMPLES

[0041] The following examples are non-limiting and are merely intended to further illustrate the compositions, systems and methodologies described herein.

[0042] EXAMPLE 1

[0043] Samples including 1%, 5% and 10% by weight of solvents from the group of toluene, octane, heptane, decane, dodecane and tetradecane were mixed with CuInS2 quantum dots dispersed in ODE. They were then well mixed and extruded in Ethylene Vinyl Acetate polymer (MFI=0.4, VA= 13% v / v) using a twin-screw extruder. Trends in reduction of haze could be observed using this process, to below 10% (measured as the relative amount of scattered 780nm laser light versus what is transmitted, using an integrating sphere). During the course of this work, it was also found that the concentration of the QDs used in the polymer, influences the translucency of the composite material. On a separate set of experiments, it could also be seen that purification and ZnCh or Zn- oleate (zinc ions complexed with oleic acid) treatment before introducing toluene in the liquid, played an important role in reducing the haze with the trace amounts of solvents.

[0044] Fig. 1 shows a picture of EVA-QD laminates extrude with quantum dots treated with ZnCh and toluene (left two laminate strips) and with untreated quantum dots (right laminate strip). The table of Fig. 2 shows the optical properties of the same EVA-QD laminates as in Fig. 1. The results demonstrate that treatment of the dots with ZnCh and toluene show dramatic reduction in haze in comparison to untreated dots. Zn-oleate treatments have been observed to have similar benefits. At the same time, light transmission was also higher in the treated dots versus the untreated dots. This effect should work on any nanoscale particles that have a similar surface chemistry to the quantum dots reported herein. This may include other compositions such as metal oxides, chalcogenides, or other nanoparticles of various sizes. EXAMPLE 2

[0045] This example illustrates the relationship between the haze of an EVOH / quantum dot nanocomposite with and without excess zinc oleate.

[0046] Comparison between standard washed quantum dots both (a) with excess zinc oleate and (b) without excess zinc oleate shows a clear decrease in measured haze from 40% to 22% (measured as the relative amount of scattered 780nm laser light versus what is transmitted, using an integrating sphere). Additionally, modification of the washing process to use less solvent, and presumably, leave excess zinc oleate in the resultant quantum dot powder, also showed a decrease in haze from 40% to 19%. An added benefit of this modified washing process is in the reduction in the amount of solvent used in processing the quantum dots.

[0047] While not wishing to be bound by the present explanation, it is suspected that the zinc oleate acts as a solubility additive for the quantum dots and polar polymers because of the polar and non-polar sections of the molecule. This effect should work on any nanoscale particles that have a similar surface chemistry to the quantum dots reported herein. This may include other compositions such as metal oxides, chalcogenides, or other nanoparticles of various sizes.

[0048] EXAMPLE 3

[0049] A 50% solution of ZnCh in ethanol (0.1 ml-2ml) was added to a mixture of CuInS2 / ZnS quantum dots in toluene (0.5-2 g / 2-10ml), and stirred at ambient temperature overnight. The resulting suspension was centrifuged at 6000 RPM for 5 minutes, the clear supernatant was kept, and the precipitate was discarded. The quantum dots were then precipitated from the supernatant using an antisolvent (acetone or ethanol), and separated by centrifugation (6000 RMP for 2 minutes). The precipitate was dried under reduced pressure to give powdered quantum dots.

[0050] Data:

[0051] Table 1 : Comparison of liquid samples before and after various ZnCl treatments

[0052] Table 1 (above) shows an increase in QY for samples treated with ZnCl. The greatest increase is with sample C (e.g., C2 vs. Cl), which shows a 35% boost in QY

[0053] Table 2: Comparison of extruded samples with and without ZnCl treatment

[0054] Table 2 (above) shows the decrease in haze after ZnCl treatment on two sperate batches of dots. The best samples show a decrease in haze from 16.5% to 3.5% and from 16.6% to 2.6% for shell batches A and B respectively. The samples in the post ZnCl section of the table were prepared with varying amounts of ZnCl solution. EXAMPLE 4

[0055] Haze was reduced by improving dispersion of QDs in the polymer by adding specific amounts of QDs dispersed in toluene by adding ZnCh. The ratios of QDs to Zn-halide and solvents were essential in attaining the optimal dispersion, and indicated by low haze less than 10% and other optical properties such as PL QY and absorption. In one embodiment, using 1 g of filtered 590 nm emitting QDs in 10 mL of toluene, a POE 8401 polymer composite was made by first treating the solution with 0.4 mL of ZnCh solution before centrifuging the QDs to a powder. This powder was added to the POE polymer in a compounding step and the results are shown in in Tables 4-6.

[0056] EXAMPLE 5

[0057] Filtration-based purification of QD solutions directly affects the haze of the final nanocomposites. Defective and / or incomplete separation of QDs during a filtration process often yields lower quality (i.e., higher haze) than the same process with greater purity.

[0058] EXAMPLE 6

[0059] In all of the example described above, QD solutions were made with 1 -Octadecene solvent at approximately 60-80% concentration of QD solids (including organic and inorganic content). The variation of concentration can be because of the amount of non-emissive, organic or inorganic, phases / particulates in the system. 5 wt% toluene was added on the total mass of the QD-ODE solution for a composition with higher dispersion in a polymer. This solution was used during liquid injection extrusion to fabricate POE 8401-QD nanocomposites with peak emission near 600, 650, 800, and 850 nm. These polymers exhibited haze of around 20% or less.

[0060] EXAMPLE 7

[0061] Hexane treatment of QDs (see sample Ml in Table 3) can be an alternate treatment for the precipitated QDs. This can be done by suspending a QD powder that is made by purifying the reaction into hexane solvent. The QD suspension was then centrifuged into a “pellet” or “puck” of a non-QD precipitate / impurity that was polar and not well dissolved in hexane, and then purified QDs in hexane (the supernatant) was recovered. The supernatant was then crashed with a series of ethanol and acetone crashes, before ultimately being resuspended in toluene. The resulting material was a clean powder after 3 total washes as compared to an equivalent experiment where 7-12 washes was needed for the same purity. Thus, this approach of cleaning QDs can also be applied to making polymer composites. Extruding QDs purified by this method resulted in higher haze values for more polar polymers, but the result was improved in non-polar polymers. In general, this approach resulted in higher haze than alternative methods, but still less than about 40% haze.

[0062] EXAMPLE 8

[0063] Varying the formulation also led to varying solubility and haze of the dried power QDs in ODE solvent. Results are shown in Table 4-6.

[0064] Table 3: Compiled results of treated QDs in POE polymer

[0065] Table 4: Well filtered QD batches treated with varying amounts of ZnCh after cleaning with

[0066] Acetone and Toluene

[0067] Table 5: Incompletely filtered QD batches treated with varying amounts of ZnCh. Extra Toluene added to prevent solidifying of the solution after cleaning with Acetone and Toluene

[0068] Table 6: Well filtered QD batches treated with varying amounts of ZnCh after cleaning using

[0069] Hexane and Ethanol

[0070] The data presented above shows the potential of the ZnCl treatment as a procedure for increasing the QY and decreasing the haze in extruded films.

[0071] Although the present invention has been described with reference to specific details, it is not intended that such details should be regarded as limitations upon the scope of the invention. Various modifications, substitutions, combinations, and ranges of parameters may be made or utilized in the compositions, and methodologies described herein.

Claims

CLAIMSThat which is claimed:Claim 1: A composition comprising: nanoparticles, a polymer, and zinc oleate whereby said composition exhibits a measured haze of 22% or less.Claim 2: The composition of claim 1 wherein the polymer is selected from the group consisting of poly vinyl alcohols, an ethylene vinyl alcohol copolymer, polyvinyl acetates, polyurethanes, ethylene vinyl acetates, an acrylic polymer, polyvinyl butyral, nylon, polyethylene, and polyamides.Claim 3 : The composition of claim 1 wherein the polymer is an ethylene vinyl alcohol copolymer.Claim 4: The composition of claim 1 wherein said polymer is extruded.Claim 5: The composition of claim 1 wherein the nanoparticles are quantum dots selected from the group consisting of CuFeS , CuFeSe , CuInZnSs, CuZnSnSe , CuInS2, CuInSe2, CuInSexS2-x, CuInGaSexS2-x, AglnS , AgInSe2, AgInGaSe2S2-x, Q1AIS2, CuAlSe2, CuAlGaSexS2-x, CdS, CdSe, ZnS and ZnSe.Claim 6: A composition comprising: nanoparticles, a polymer, and zinc oleate whereby said composition exhibits a measured haze of 22% or less.Claim 7: The composition of claim 6 wherein said polymer is selected from the group consisting of poly vinyl alcohols, an ethylene vinyl alcohol copolymer, polyvinyl acetates, polyurethanes, ethylene vinyl acetates, an acrylic polymer, polyvinyl butyral, nylon, polyolefin elastomers, polyethylene, and polyamides.Claim 8: The composition of claim 6 wherein the polymer is an ethylene vinyl alcohol copolymer.Claim 9: The composition of claim 6 wherein said polymer is extruded.Claim 10: The composition of claim 6 wherein the nanoparticles are quantum dots selected from the group consisting of CuFeS2, CuFeSe2, CuInZnS2, CuZnSnSe2, CuInS2, CuInSe2, CuInSexS2-x, CuInGaSexS2-x, AgInS2, AgInSe2, AgInGaSe2S2-x, CUA1S2, CuAlSe2, CuAlGaSexS2-x, CdS, CdSe, ZnS and ZnSe.Claim 11 : A composition comprising: a solvent, Zn-halide, and quantum dots selected from the group of selected from the group consisting of CuFeS2, CuFeSe2, CuInZnS2, CuZnSnSe2, CuInS2, CuInSe2, CuInSexS2-x, CuInGaSexS2-x, AgInS2, AgInSe2, AgInGaSe2S2-x, CUA1S2, CuAlSe2, CuAlGaSexS2-x, CdS, CdSe, ZnS and ZnSe.Claim 12: The composition of claim 11 wherein said Zn-halide is ZnCh.Claim 13 : The composition of claim 11 wherein said solvent is selected from the group consisting of toluene, ethanol, acetone, acetonitrile, octadecene, methanol, and hexane.Claim 14: The composition of claim 11, further including a polymer selected from the group consisting of poly vinyl alcohols, an ethylene vinyl alcohol copolymer, polyvinyl acetates, polyurethanes, ethylene vinyl acetates, an acrylic polymer, polyvinyl butyral, nylon, polyethylene, and polyamides.Claim 15: The composition of claim 11, further including aluminum oxide, titanium dioxide, zinc oxide, cerium oxide and magnesium oxide.Claim 16: The composition of claim 11, wherein said composition is in an extruded film.Claim 17: The composition of claim 16, comprising at least five distinct layers selected from the group consisting of poly vinyl alcohols, an ethylene vinyl alcohol copolymer, polyvinyl acetates, polyurethanes, ethylene vinyl acetates, an acrylic polymer, polyvinyl butyral, nylon, polyethylene, and polyamides.Claim 18: The composition of claim 16, wherein said polymer film is less than 100 microns in thickness and has measured haze of less than 10%.Claim 19: The composition of claim 16, wherein said polymer film has a photoluminescence quantum yield of greater than 70%.Claim 20: The composition of claim 16, wherein said polymer film is stable under sunlight.

Images