High refractive index nanocomposite

Abstract

The current disclosure relates to a nanocomposites coating including metal oxide nanocrystals, the nanocomposites further include a mixture of acrylates monomers and oligomers to provide a curable coating that provides high refractive index, high transmittance, and high temperature stability.

Claims

1. A solventless nanocomposite comprising: an organic mixture comprised of a mixture of benzyl methacrylate (BMA) and trimethylolpropane triacrylate (TMPTA) monomers and/or oligomers in a weight ratio of BMA to TMPTA of 75:25 to 65:35, capped nanocrystals, wherein the nanocrystals are selected from the group consisting of ZrO.sub.2, HfO.sub.2, TiO.sub.2 and ZnO, and at least one curing agent or photo initiator, wherein the caped nanocrystals are present in the nanocomposite in an amount greater than 70% by weight to 90% by weight of the nanocomposite, and wherein the nanocomposite has a viscosity of less than 12,000 cPs at 20 C. as measured by a Brookfield RVDV-II+PCP cone and plate viscometer, and wherein the refractive index of the nanocomposite is in a range of 1.6 to 1.9 at a wavelength of 400 nm.

2. The nanocomposite of claim 1, wherein the nanocomposite has a transmittance of greater than 60% at a wavelength of 400 nm when measured by a spectrophotometer in a 1 cm path length cuvette.

3. The nanocomposite of claim 1 wherein the capped nanocrystals are capped with at least one capping agent selected from the group consisting of 2-[2-(2-9-methoxyethoxy) ethoxy]acetic acid, methoxy(triethyleneoxy) propyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, n-octyl trimethoxysilane, dodecyltrimethoxysilane and m,p-ethylphenethyl trimethoxysilane.

4. A coated substrate comprising a substrate having a surface, and a coating comprised of the solventless nanocomposite according to claim 1 coated on at least a portion of the surface of the substrate.

5. The coated substrate of claim 4, wherein the coating is cured, and wherein a 1 m thickness of the cured coating of the nanocomposite has a transmittance of greater than 89% at a wavelength of 400 nm.

6. The coated substrate of claim 4, wherein the coating is cured, and wherein the cured coating has a refractive index greater than 1.8 at a wavelength of 400 nm.

7. The coated substrate of claim 4 wherein the substrate comprises glass, indium tin oxide (ITO), doped ZnO, GaN, AlN, SiC, poly(3,4-ethylenedioxythiophene) (PEDOT), poly(styrene sulfonate) (PSS) doped PEDOT, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or doped poly(4,4-dioctylcyclopentadithiophene).

8. The coated substrate of claim 4, wherein the capped nanocrystals comprise ZrO.sub.2 nanocrystals capped with at least one capping agent selected from the group consisting of methoxy(triethyleneoxy)propyltrimethoxysilane, 3-methacryloyloxypropyl trimethoxysilane and 2-[2-(2-9-methoxyethoxy)ethoxy]acetic acid, and wherein the coating is thermally stable up to a temperature of 175 C. without cracking.

9. The coated substrate of claim 5, wherein the coating is cured, and wherein a 1 m thickness of the cured coating of the nanocomposite has a haze of less than 2%.

10. The coated substrate of claim 5, wherein the coating is cured, and wherein a 1 m thickness of the cured coating of the nanocomposite has a haze of less than 1.5%.

11. The coated substrate of claim 5, wherein the coating is cured, and wherein a 1 m thickness of the cured coating of the nanocomposite has a haze of less than 1%.

12. The coated substrate of claim 5, wherein the coating is cured, and wherein a 1 m thickness of the cured coating of the nanocomposite has a haze of less than 0.5%.

13. A zirconium oxide nanocomposite comprising: an organic mixture comprised of benzyl methacrylate (BMA) and trimethylolpropane triacrylate (TMPTA) monomers and/or oligomers in a weight ratio of BMA to TMPTA of 75:25 to 65:35, zirconium nanocrystals capped with at least one capping agent selected from the group consisting of methoxy(triethyleneoxy)propyltrimethoxysilane, 3-methacryloyloxypropyl trimethoxysilane and 2-[2-(2-9-methoxyethoxy)ethoxy]acetic acid, and at least one curing agent or photo initiator, wherein the capped zirconium nanocrystals are present in the nanocomposite in an amount of 50-80% by weight of the nanocomposite, and wherein the nanocomposite has a viscosity of less than 12,000 cPs at 20 C. as measured by a Brookfield RVDV-II+PCP cone and plate viscometer, and wherein the refractive index of the nanocomposite is in a range of 1.6 to 1.9 at a wavelength of 400 nm, and wherein a coating of the nanocomposite when cured is stable up to a temperature of 175 C. without cracking.

Description

LIST OF FIGURES AND TABLE

(1) FIG. 1a: UV absorption spectrum of film from formulation (ZrO.sub.2-(2-[2-(2-9-methoxyethoxy)ethoxy]acetic acid) in 70:30 BMA-TMPTA) after post bake at (101) 120 C for 3 minute in air, (102) thermal bake at 175 C for 1 hour under N.sub.2.

(2) FIG. 1b: UV transmission spectrum of film from formulation (ZrO.sub.2-(2-[2-(2-9-methoxyethoxy)ethoxy]acetic acid) in 70:30 BMA-TMPTA) after post bake at (201) 120 C for 3 minute in air, (202) thermal bake at 175 C for 1 hour under N.sub.2.

(3) FIG. 2a: UV absorption spectrum of film from formulation (ZrO.sub.2-(2-[2-(2-9-methoxyethoxy)ethoxy]acetic acid) in 70:30 BMA-TMPTA) after post bake at (101) 120 C for 3 minute in air, (103) thermal bake at 200 C for 1 hour under N.sub.2.

(4) FIG. 2b: UV transmission spectrum of film from formulation (ZrO.sub.2-(2-[2-(2-9-methoxyethoxy)ethoxy]acetic acid) in 70:30 BMA-TMPTA) after post bake at (201) 120 C for 3 minute in air, (203) thermal bake at 200 C for 1 hour under N.sub.2.

(5) FIG. 3a: UV absorption spectrum of film from formulation (ZrO.sub.2-(2-[2-(2-9-s methoxyethoxy)ethoxy]acetic acid) in 70:30 BMA-TMPTA) after post bake at (101) 120 C for 3 minute in air, (104) thermal bake at 200 C for 2 hour under N.sub.2.

(6) FIG. 3b: UV transmission spectrum of film from formulation (ZrO.sub.2-(2-[2-(2-9-s methoxyethoxy)ethoxy]acetic acid) in 70:30 BMA-TMPTA) after post bake at (101) 120 C for 3 minute in air, (104) thermal bake at 200 C for 2 hour under N.sub.2.

(7) Table 1: Film results of capped ZrO.sub.2 nanocrystals in monomer mixture. Good indicates that the film does not yellow or crack when heated at those indicated temperatures. Cracked indicates that the film cracked during thermal baking. Disadvantage of this formulation is that it comprises of PGMEA to aid in the solubility.

EXAMPLES

Example 1

(8) In one example of said exemplary non-limiting formulation, acrylic monomers, benzyl methacrylate (BMA) and trimethylolpropane triacrylate (TMPTA), was mixed in a mass ratio of 70-75 to 25-30. 1-5 wt % of benzophenone as photo initiator, was dissolved in the monomer mix either by stirring or vortexing at temperature of 20-30 C. The solution was then filtered to remove dusts and then added to dry ZrO.sub.2 nanocrystal and allowed to soak in the monomer blend until no ZrO.sub.2 powder was observed. In large scale, gently shaking the dried nanocrystals with the monomer blend is acceptable. Once all ZrO.sub.2 nanocrystals powder was completely dispersed in BMA-TMPTA, the viscous suspension was mixed for 10-15 hours. Finally, the viscous suspension was filtered before processing the film.

(9) The suspension was validated by coating films and characterizing the physical properties of the films such as thermal stability and transmittance.

(10) As a standard method, the suspension was coated on a 2 silicon wafer or fused silica wafer to inspect its quality. The wafers were cleaned before applying the film to remove contaminants and dusts. 3-4 micron thick film was spin coated on silicon wafer at 1000-4000 rpm for 1-5 minute.

(11) An optional pre-bake process at 90 C may be performed to remove the residual solvent if that is a concern. In these formulations the solvent is typically less than 10 wt %, more preferably less than 1 wt %. The film was inspected for defects from undispersed particles or air bubbles. If no defects were observed, its surface roughness is measured using a surface profilometer.

(12) The film coated on glass slide or fused silica wafer was cured by UV exposure for 60-200 seconds using a Dymax EC-5000 system with a mercury H bulb and then post-baked for 2-5 minutes at 120-150 C under air. Further, the thermal stability of the film was tested by heating the film at a temperature of 175 C or above, more preferably 200 C, under nitrogen atmosphere for 1-2 hours. A crack free, colorless film is desirable and indicates a good formulation.

(13) These film demonstrate a refractive index of 1.80 or greater at 400 nm and transmittance>89% at 400 nm.

(14) The refractive index is measured with a Woollam M-2000 spectroscopic ellipsometer in the spectral range from 350 nm to 1700 nm and the transmittance was measured using a Perkin Elmer Lambda 850 Spectrophotometer.

(15) This example formulation with 65-75:25-35 mass ratio of BMA to TMPTA with nanocrystal loading of 50 wt % and above produced films that are UV curable and can withstand a thermal baking at 200 C for 1-2 hour under nitrogen, as shown in Table 1.

Example 2

(16) Films spin coated from formulation containing zirconium oxide nanocrystals capped with 2-[2-(2-9-methoxyethoxy)ethoxy]acetic acid at 50-80 wt % loading in the BMA-TMPTA (65-75:25-35 mass ratio) were stable and did not crack when heated at temperatures up to 200 C. However, films from formulation containing zirconium oxide nanocrystals capped with 2-[2-(2-9-methoxyethoxy)ethoxy]acetic acid at 82-85 wt % loading in the BMA-TMPTA (65-75:25-35 mass ratio) were stable only at temperatures below 120 C, as shown in Table 1. Also, zirconium oxide nanocrystals modified with other capping agents such as methoxy(triethyleneoxy)propyltrimethoxysilane and/or 3-methacryloyloxypropyltrimethoxysilane and/or n-octyl trimethoxysilane and/or dodecyltrimethoxysilane and/or m,p-ethylphenethyl trimethoxysilane formed good dispersions in BMA-TMPTA mixture, as well as good films, but was only stable up to 120 C.

(17) One advantage of this exemplary non-limiting embodiment is that both monomers are in liquid form at room temperature so no solvent is necessary at room temperature and the film is UV curable. Surface modified ZrO.sub.2 nanocrystals are dispersed directly in the monomer. Such a direct dispersion eliminates, for example, the need to remove the solvent at a later step.

(18) Nanocrystals of the exemplified embodiments of the present disclosure have been surface modified with various capping agents such as 2-[2-(2-9-methoxyethoxy) ethoxy]acetic acid and/or methoxy(triethyleneoxy)propyltrimethoxysilane and/or 3-methacryloyloxypropyltrimethoxysilane and or n-octyl trimethoxysilane and/or dodecyltrimethoxysilane and/or m,p-ethylphenethyl trimethoxysilane. In an exemplified method of producing the capped nanocrystals of the present disclosure, the as-synthesized nanocrystals are allowed to settle for at least 12 hours after synthesis. Since the nanocrystals are surface modified in a solvent other than the synthesis solvent, the nanocrystals are separated from the reaction liquid by decanting off the reaction liquid and rinsing the nanocrystals with the capping solvent. The rinsing solvent is decanted off to obtain a wet cake of uncapped nanocrystals.

(19) For the surface modification of the nanocrystals with 2-[2-(2-9-methoxyethoxy) ethoxy]acetic acid, the nanocrystals are suspended in the capping solvent, for example, toluene for 2-[2-(2-9-methoxyethoxy)ethoxy]acetic acid modification, at a loading of 10 wt % or greater, or 20 wt % or greater, or 30 wt % or greater, calculated based on the weight of the wet nanocrystal cake. While the suspension is stirred, the capping agent is added to it slowly. The amount of capping agent used is in the presently exemplified embodiment 8-60 wt % to the weight of the wet nanocrystal cake. The suspension is allowed to stir at 20-27 C. for 10-30 minutes and then refluxed at the boiling point of the capping solvent for 30-60 minutes. After refluxing, the clear solution is cooled to 50-60 C. slowly. This suspension is then filtered to remove dusts and aggregates bigger than 200 nm sizes.

(20) The capped nanocrystals are then precipitated out from the capping solvent using heptane (2-4 times the mass of the capped solution). The precipitated nanocrystals are collected by centrifugation. The nanocrystal thus collected is dispersed in tetrahydrofuran (THF) and again re-precipitated using heptane. This process is repeated twice. The wet cake of nanocrystals collected in the final step is dried under vacuum for at least 12 hours.

(21) TABLE-US-00001 TABLE 1 Content of Post baked Post baked Post baked ZrO.sub.2 to at 120 C./ at 175 C./ at 200 C./ Monomer mix monomer Capping agent 60/air 60/N.sub.2 N2/60 min 2-10 wt % Bisphenol 50-80 wt % 2-[2-(2-9- good cracked A diglycerolate methoxyethoxy) dimethacrylate in ethoxy]acetic acid BMA 2-25 wt % TMPTA 50-80 wt % methoxy(triethyleneoxy) good cracked in BMA propyltrimethoxysilane and 3- methacryloyloxypropyl trimethoxysilane 25-30 wt % TMPTA 50-80 wt % methoxy(triethyleneoxy) good good cracked in BMA propyltrimethoxysilane and 3- methacryloyloxypropyl trimethoxysilane 20-30 wt % TMPTA 50-80 wt % 2-[2-(2-9- good good good in BMA methoxyethoxy) ethoxy]acetic acid 25-30 wt % TMPTA 50-80 wt % methoxy(triethyleneoxy) good cracked cracked in BMA propyltrimethoxysilane 25-30 wt % TMPTA 82-86 wt % 2-[2-(2-9- good cracked cracked in BMA methoxyethoxy) ethoxy]acetic acid