AQUEOUS COMPOSITION CONTAINING SUSPENDED ZNO PARTICLES

Abstract

The invention relates to an aqueous composition comprising a suspension of ZnO particles and a polymer stabiliser containing carboxylic acid functions and carboxylic acid salt functions.

Claims

1. An aqueous composition comprising a suspension of ZnO particles and a polymer stabilizer containing carboxylic acid functions and carboxylic acid salt functions.

2. The composition according to claim 1, wherein the polymer stabilizer is a copolymer of (meth)acrylic acid and a (meth)acrylic acid salt.

3. The composition according to claim 1, wherein the polymer stabilizer is a mixture of a (meth)acrylic acid polymer and a (meth)acrylic acid salt polymer.

4. The composition according to claim 1, wherein the molar ratio of carboxylic acid functions to carboxylic acid salt functions is included between 25/75 and 75/25.

5. The composition according to claim 1, wherein the polymer stabilizer is a mixture of a (meth)acrylic acid polymer and a (meth)acrylic acid salt polymer, where this mixture has a mass ratio included between 25/75 and 75/25.

6. The composition according to claim 1, wherein the stabilizer represents 0.01 to 10% by weight relative to the weight of the aqueous composition.

7. The composition according to claim 1, wherein the ZnO particles represent 0.1 to 20% by weight relative to the weight of the aqueous composition.

8. The composition according to claim 1, comprising between 0.5 and 0.7% by weight of polymer stabilizer; wherein the polymer stabilizer is constituted of a mixture of: poly((meth)acrylic acid) having a molecular weight less than or equal to 240,000 g/mol; and of poly(methacrylic acid sodium salt) having a molecular weight less than or equal to 240,000 g/mol.

9. The composition according to claim 1, wherein said composition is dehydrated.

10. A method for preparing the composition according to claim 1, comprising the following steps: preparing an aqueous solution comprising a polymer stabilizer containing carboxylic acid functions and carboxylic acid salt functions; adding a zinc precursor; forming ZnO particles by hydrolysis of the zinc precursor; and producing aqueous composition comprising a suspension of ZnO particles and a polymer stabilizer.

11. The method according to claim 10, wherein the zinc precursor is chosen from the group consisting of ZnR.sub.2; Zn(OR).sub.2; Zn(NR.sub.2).sub.2; and Zn(O—C(═O)R.sub.2; R being a hydrocarbon group comprising 1 to 18 carbon atoms.

12. A method of preparing an article selected from the group consisting of photovoltaic cells, paint, cosmetics, textiles, electronics, biosensors, and anti-microbial and anti-fouling coatings, the method comprising using the composition according to claim 1 to prepare the article.

13. The composition according to claim 1, wherein the polymer stabilizer is selected from: a copolymer of (meth)acrylic acid and a (meth)acrylic acid salt; and a mixture comprising a (meth)acrylic acid polymer and a (meth)acrylic acid salt polymer.

14. The composition according to claim 13, wherein the stabilizer represents 0.01 to 10% by weight relative to the weight of the aqueous composition.

15. The composition according to claim 13, wherein the molar ratio of carboxylic acid functions to carboxylic acid salt functions is included between 25/75 and 75/25.

16. The composition according to claim 15, wherein the ZnO particles represent 0.1 to 20% by weight relative to the weight of the aqueous composition.

17. The composition according to claim 15, wherein the stabilizer represents 0.01 to 10% by weight relative to the weight of the aqueous composition.

18. The composition according to claim 17, wherein the ZnO particles represent 0.1 to 20% by weight relative to the weight of the aqueous composition.

19. The composition according to claim 1, wherein: the molar ratio of carboxylic acid functions to carboxylic acid salt functions is included between 25/75 and 75/25; the ZnO particles represent 0.1 to 20% by weight relative to the weight of the aqueous composition; and the polymer stabilizer represents 0.5 to 0.7% by weight relative to the aqueous composition, and said polymer stabilizer is constituted of a mixture of: poly((meth)acrylic acid) having a molecular weight less than or equal to 240,000 g/mol; and of poly(methacrylic acid sodium salt) having a molecular weight less than or equal to 240,000 g/mol.

20. The method according to claim 12, comprising dehydrating the composition.

Description

DESCRIPTION OF FIGURES

[0069] FIG. 1 shows an image obtained by transmission electron microscopy of an aqueous ZnO suspension according to the invention of which the polymer stabilizer has a molar ratio of carboxylic acid functions/carboxylic acid salt functions of 50/50.

EXAMPLES OF EMBODIMENTS OF THE INVENTION

[0070] 1/ Influence of the Carboxylic Acid/Carboxylate (COOH/COO—) Mass Ratio on the Formation of a Stable Suspension.

[0071] Eight compositions comprising ZnO particles have been prepared. These compositions all comprise 0.63% by weight of stabilizer and 0.65% by weight of ZnO particles.

[0072] The nature of the stabilizer used is specified in table 1, for both the compositions according to the invention (INV-1 to INV-6) or for counter-examples (CE-1 and CE-2).

TABLE-US-00001 TABLE 1 Nature of the stabilizer according to the compositions prepared (mass percentages). Examples CE- INV- INV- INV- INV- INV- INV- CE- 1 1 2 3 4 5 6 2 PAAH  0% 25% 35% 50% 65% 70% 75% 100% PAA-Na 100% 75% 65% 50% 35% 30% 25%  0% PAAH: poly(acrylic acid) (2000 g/mol) PAA-Na: poly(sodium acrylate) (4000 g/mol)

[0073] The compositions were prepared according to the following procedure:

[0074] stabilizer in 25 mL of water added;

[0075] 2.0 mmol of diethyl zinc (1.8 mL of commercial solution at 15% by mass in toluene) added by drops while stirring;

[0076] hydrolysis of ZnEt.sub.2 and formation of ethane according to the following reaction: ZnEt.sub.2+H.sub.2O.fwdarw.>ZnO+2 EtH

[0077] Stirring is maintained for 1 or 24 hours at ambient temperature, preferably 1 hour.

[0078] The resulting composition has the form of:

[0079] a clear suspension (INV-2 to INV-5)

[0080] a cloudy suspension (INV-1 and INV-6);

[0081] a powder that cannot be dispersed in water but can be dispersed in a water+PAAH mixture (CE-1 and CE-2). In this case, the powders that can be redispersed in water+PAAH reemit in UV, which is not compatible with use in the photovoltaic field.

[0082] To characterize these compositions, they were lyophilized.

TABLE-US-00002 TABLE 2 Characterization of lyophilized compositions of ZnO particles. Examples INV- 3 CE- INV- INV- (FIG. INV- INV- INV- CE- 1 1 2 1) 4 5 6 2 Appear- − + ++ ++ ++ ++ + − ance QY 4% 2% 8% 20-25% 5% 11% 7% 20-36% λ (nm) 620 540 540 530 420 380 400 550 pH 8.9 10.8 10.7 10.0 8.9 8.8 8.6 3.4 λ corresponds to the maximum emission wavelength.

[0083] Appearance of the Composition:

[0084] −: powder and supernatant solution, and powder that is not redispersable in water

[0085] +: cloudy suspension, and lyophilized powder that can be redispersed in water

[0086] ++: clear suspension, stable for several months, and lyophilized powder that can be redispersed in water

[0087] The result given in Table 2 show that the best results in terms of photoluminescence and QY are obtained when the stabilizer is 100% PAAH (CE-2). However, the aqueous composition CE-2 does not comprise a suspension of ZnO particles.

[0088] As regards the compositions according to the invention, composition INV-3 (50% PAAH and 50% PAA-Na) emits at 530 nm and has a luminescence yield between 20 and 25%, which gives it very attractive properties for use in the photovoltaics domain.

[0089] Without wanting to be restricted by any theory, the Applicant considers that the ZnO particles can attach to the carboxylic acid functions whereas the carboxylic acid salt functions allow the ZnO particles to disperse without attachment thereto.

[0090] The quantum yield QY corresponds to the number of photons emitted relative to the number of absorbed photons. It is expressed as a percentage.

[0091] 2/ Influence of the Quantity of Polymer Stabilizer on the Formation of a Stable Suspension.

[0092] The following examples relate to compositions obtained by hydrolysis of ZnEt.sub.2 in the presence of 3.15% to 0.126% by weight of polymer stabilizer constituted of 50% by weight of PAAH (2000 g/mol) and 50% by weight of PAA-Na (4000 g/mol). In these examples, the mass ratio of COOH to COO− functions remains stable; only the mass concentration of the PAAH+PAA-Na stabilizer changes.

TABLE-US-00003 TABLE 3 QY as function of the quantity of stabilizer. INV-7 INV-8 INV-9 INV-10 INV-11 Quantity of PAAH + 0.126 0.315 0.63 1.26 3.15 PAA-Na stabilizer QY 2 14 25 6 6 Appearance ++ ++ ++ ++ ++ Appearance of the composition: ++: clear suspension, stable for several months, and lyophilized powder that can be redispersed in water

[0093] Examples INV-7 to INV-9 produce stable and clear suspensions with a maximum emission between 500 and 600 nm. For examples INV-10 and INV-11, the emission is shifted to between 350 and 450 nm.

[0094] In addition, the higher the stabilizer quantity, the more the compound is amorphous and the greater is the mass loss observed in TGA (thermogravimetric analysis). For these less crystalline compounds, the luminescence band is shifted toward high energies (blue-shift) between 350 and 450 nm.

[0095] 3/ Influence of the Molecular Weight of the Polymer Stabilizer on the Formation of a Stable Suspension.

[0096] The following examples relate to compositions obtained by hydrolysis of ZnEt.sub.2 in the presence of a polymer stabilizer with a molecular weight included between 2000 and 240,000 g/mol (Table 4).

[0097] These examples relate to a ZnO suspension containing 0.63% by mass of polymer stabilizer PAAH/PAA-Na (50:50 mixture by weight), where the PAAH molecular weight varies from 2000 to 240,000 g/mol, and the PAA-Na molecular weight varies from 2000 to 240,000 g/mol. In all these compositions, the COOH/COO-mass ratio remains at 50/50.

[0098] The PAA-Na used is previously obtained by polymerization of sodium acrylate or by neutralization of poly(acrylic acid) by the addition of sodium hydroxide.

[0099] All these examples have produced a clear and stable suspension for several months, whose lyophilized powder can be redispersed in water.

[0100] Generally, the longer the PAA-Na chain (higher molecular weight), compared to the PAAH chain, the faster the suspension is obtained.

TABLE-US-00004 TABLE 4 Quantum yields (QY) and maximum emission wavelengths (λ, nm) as a function of the molecular weights of the PAAH and PAA-Na polymers. QY λ (nm) QY λ (nm) QY λ (nm) QY λ (nm) QY λ (nm) PAA-Na PAAH 2000 4000 5000 100,000 240,000 2000 16% 550 25% 550 18% 560 18%  540 16%  545 5000 16% 536 23% 545 16% 550 7% 539 7% 527 100,000 17% 536  6% 438  7% 512 5% 406 6% 521 240,000 34% 550  6% 452  2% 497 9% 484 9% 525

[0101] Table 4 gives the quantum yields (QY) for different PAAH/PAA-Na mixtures (50/50 ratio by weight) as a function of their molecular weight.

[0102] These compositions emit in the wavelengths that correspond to the green-orange color, which is more advantageous for applications in photovoltaic cells than emission in the blue.

[0103] 4/ Quantum Yield as a Function of the PAAH/PAA-Na Mixture.

[0104] The following examples relate to compositions obtained by hydrolysis of ZnEt.sub.2 in the presence of 0.4 to 1% by weight of polymer stabilizer (PAAH+PAA-Na) constituted of 50% by weight of PAAH (2000 g/mol) and 50% by weight of PAA-Na (4000 g/mol). In this composition, the COOH/COO— molar ratio varies as a function of the initial percentages by mass (concentrations) of the PAAH and PAANa solutions.

TABLE-US-00005 TABLE 5 Quantum yield (QY, %) as a function of the PAAH/PAA-Na weight ratio. PAA-Na 0.40% 0.45% 0.50% 0.63% 0.8% 1% by by by by by by PAAH mass mass mass mass mass mass 0.40% by mass 10 ± 1  6 ± 1 0.45% by mass 10 ± 1 10 ± 1 0.50% by mass  8 ± 1  7 ± 1 0.63% by mass 10 ± 1 25 ± 1 14 ± 1 17 ± 1  0.8% by mass 15 ± 1 16 ± 1 28 ± 1   1% by mass 25 ± 1 26 ± 1 11 ± 1
According to table 5, the best results for quantum yield (QY) are obtained when the composition comprises 0.63 to 1% by weight of PAAH and 0.63 to 1% by weight of PAA-Na.

[0105] In these examples, a composition containing 1% by mass of stabilizer (PAAH +PAA-Na) is obtained from a mixture of 50% by mass of a first solution of PAAH at 1% by mass and 50% by mass of a second solution of PAA-Na at 1% by mass.