ELECTROCHROMIC SOLUTION

Abstract

The present invention relates to an electrochromic solution and a use thereof, wherein the said solution comprises: a solvent; a thickening polymer agent having a molecular weight of at least 50,000 g/mol, preferably 200,000 g/mol, more preferably of at least 250,000 g/mol; at least an additive having a molecular weight between 300 and 50,000 g/mol, preferably between 320 and 20,000 g/mol; a redox chemical mixture in solution in said solvent said mixture being constituted of at least one electrochromic reducing compound and at least one electrochromic oxidizing compound, and which colors in the presence of an applied voltage and which bleaches to a colorless condition in the absence of an applied voltage. The invention further relates to a device comprising said solution.

Claims

1. An electrochromic solution, comprising: a solvent; a thickening polymer agent having a molecular weight of at least 50,000; at least an additive having a molecular weight between 300 and 50,000 g/mol; and a redox chemical mixture in solution in the solvent, the mixture being constituted of at least one electrochromic reducing compound and at least one electrochromic oxidizing compound, and which colors in the presence of an applied voltage and which bleaches to a colorless condition in the absence of an applied voltage.

2. The electrochromic solution according to claim 1, wherein the solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone, acetronitrile, propionitrile, benzonitrile, glutaronitrile, methylglutaronitrile, dimethylformamide, N-methylpyrrolidone, sulfolane, 3-methyl sulfolane, methyl propionate, ethylene glycol, ethylene carbonate, propylene glycol diacetate, propylene glycol methyl ether acetate, ionic liquids, and mixtures thereof.

3. The electrochromic solution according to claim 1, wherein the thickening polymer agent is a vinyl acetate polymer.

4. The electrochromic solution according to claim 1, wherein the additive is an ester derivative of benzoic acid or an ester derivative of phthalic acid, or a mixture thereof.

5. The electrochromic solution according to claim 1, wherein the additive is an ester derivative of benzoic acid of formula (I) or (II): ##STR00148## wherein R.sub.1 and R.sub.2 are same or different and are selected from H, optionally substituted alkyl, optionally substituted aryl, or optionally substituted cycloalkyl, wherein n is an integer ranging from 1 to 10, and wherein m is an integer ranging from 1 to 10.

6. The electrochromic solution according to claim 1, wherein the additive is selected from the group consisting of bis (2-ethylhexyl phthalate) (DEHP), diisononyl phthalate (DINP), dioctyl phthalate (DNOP), diisodecyl phthalate (DIDP), dipropylheptyl phthalate (DPHP), di-2-ethylhexyl terephthalate (DOTP or DEHT) and a mixture thereof.

7. The electrochromic solution according to claim 1, wherein the additive is selected from the group consisting of polyethylene glycol diacrylate (or methacrylate), polyethylene glycol diepoxy, polypropylene glycol diacrylate (or methacrylate), polypropylene glycol diepoxy and mixture thereof.

8. The electrochromic solution according to claim 1, wherein the additive is selected from the group consisting of poly(methyl methacrylate) (PMMA), polyvinyl acetate (PVA), polyvinyl butyral (PVB), cellulose acetate butyrate (CAB) and mixture thereof.

9. The electrochromic solution according to claim 1, wherein the electrochromic solution comprises at least two additives independently selected from the group consisting of ester derivatives of benzoic acid, ester derivatives of phthalic acid, glycol derivatives and low molecular weight polymers.

10. The electrochromic solution according to claim 1, wherein a content of the additive is from 5 to 60 wt %, relative to a total weight of the electrochromic solution, and wherein a content of the thickening polymer agent is from 1 to 30 wt %, relative to the total weight of the electrochromic solution.

11. The electrochromic solution according to claim 1, wherein the thickening polymer agent is a vinyl acetate polymer present from 5 to 15 wt % by weight relative to a total weight of the electrochromic solution and the additive is polypropylene glycol dibenzoate or polyethylene glycol dibenzoate present from 15 to 25 wt % by weight relative to the total weight of the electrochromic solution.

12. The electrochromic solution according to claim 1, wherein the at least one electrochromic reducing compound is selected from the group consisting of ferrocene, ethyl ferrocene, t-butyl ferrocene, phenoxazine, N-benzylphenoxazine, phenazine, 5,10-dihydrophenazine, N,N,N′,N′-tetramethyl-p-phenylenediamine, phenothiazine, 10-methylphenothiazine isopropylphenothiazine, thianthrene, and tetrathiafulvalene.

13. The electrochromic solution according to claim 1, wherein the at least one electrochromic oxidizing compound is selected from the group consisting of alkylviologens, arylviologens, arylalkylviologens, alkylarylviologens, anthraquinone and derivatives thereof.

14. An electrochromic device comprising the electrochromic solution of claim 1.

15. The electrochromic device according to claim 14, wherein the electrochromic device is selected from the group consisting of optical lenses, optical filters, attenuators, windows, visors, goggles, mirrors and displays.

16. The electrochromic solution according to claim 1, wherein the additive is selected from the group consisting of dipropylene glycol dibenzoate (DPGDB), tripropylene glycol dibenzoate (TPGDB), diethylene glycol dibenzoate (DEGDB), triethylene glycol dibenzoate (TEGDB) and a mixture thereof.

Description

EXAMPLE

[0095] This invention will be further illustrated by the following non-limiting examples which are given for illustrative purposes only and should not restrict the scope of the appended claims.

[0096] Four electrochromic samples have been made with four different electrochromic solutions to demonstrate the effect of the combination of the two types of compounds, the thickening polymer agent and the additives on both the leakage current/bleaching rate and viscosity.

[0097] Solution 1 was prepared by dissolving, in propylene carbonate (98.96 wt %): [0098] the electrochromic reducing compound 10-methylphenothiazine (0.35 wt. %), [0099] the electrochromic oxidizing compound ethyl viologen diperchlorate (0.69 wt. %).

[0100] Solution 2 was prepared by dissolving, in propylene carbonate (90.96 wt %): [0101] the electrochromic reducing compound 10-methylphenothiazine (0.35 wt. %), [0102] the electrochromic oxidizing compound ethyl viologen diperchlorate (0.69 wt. %), [0103] the thickening polymer agent PVAC (8 wt. %).

[0104] Solution 3 was prepared by dissolving, in propylene carbonate (86.96 wt. %): [0105] the electrochromic reducing compound 10-methylphenothiazine (0.35 wt. %), [0106] the electrochromic oxidizing compound ethyl viologen diperchlorate (0.69 wt. %) [0107] the thickening polymer agent PVAC (12 wt. %).

[0108] Solution 4 was prepared by dissolving, in propylene carbonate (70.96 wt. %): [0109] the electrochromic reducing compound 10-methylphenothiazine (0.35 wt. %), [0110] the electrochromic oxidizing compound ethyl viologen diperchlorate (0.69 wt. %) [0111] the thickening polymer agent PVAC (8 wt. %), [0112] the additive polyethylene glycol dibenzoate (PEGDB) in liquid form (20 wt. %).

[0113] Propylene carbonate, ethyl violologen diperchlorate, 10-methylphenothiazine are sold by Sigma Aldrich.

[0114] The PVAC used is sold under the name Vinnapas UW25FS by Wacker. It has a molecular weight of 540,000 g/mol measured by SEC, PS-Standard.

[0115] The PEGDB used is Poly(ethylene glycol) dibenzoate sold by Sigma Aldrich having a molecular weight of 410 g/mol and a boiling point of 217° C.

[0116] A tank was filled at room temperature and atmospheric pressure with the electrochromic solutions 1 to 4 as described above. A cell was then placed vertically in the tank under atmospheric pressure in such way that the opening was located above the solution level. This cell included two mineral glass substrates facing each other, the internal sides of which were coated with transparent conductive electrodes made of indium tin oxide (ITO). The substrates were held at fixed distance from one another by using spacers of 150 μm, in order to form a gap. The edge of the cell was sealed with a UV curable adhesive in such a way that an opening of 5 mm was left.

[0117] The tank with the cell was placed in a vacuum-desiccator, which was evacuated to 0.5 mBar. During the aeration of the tank under the introduction of an inert gas, the electrochromic formulation filled the entire volume of the gap through the opening. The opening was then sealed with a UV curable adhesive in order to make the cell hermetic. The electrical connection was made by two silver plated copper wires, sealed on each ITO glass substrate with a silver charged epoxy adhesive.

[0118] Current consumption is measured with a common amperometer, when the current stabilizes typically after one minute.

[0119] The viscosity is measured by using a Brookfield viscosimeter.

[0120] The sample is put in a spectrophotometer and the bleaching rate is the time measured at from the higher value of visual transmission (Tv=85%) to reach 10% of transmission (Tv) under activation. Applied voltage is 1.2V to reach 10% of transmission.

[0121] The results regarding current consumption, bleaching rate and viscosity are provided in Table 1.

TABLE-US-00003 TABLE 1 Current consumption Bleaching Viscosity (cP) (mA) rate (s) at 25° C. Solution 1 16.5 mA 8 3 Solution 2 12.3 mA 13 420 Solution 3 9.1 mA 15 2500 Solution 4 (invention) 6.25 mA 21 1000

[0122] Solution 1 containing only solvent and electrochromic compounds (methylphenothiazine and ethyl viologen diperchlorate) show a high current consumption. The segregating effect is visible after 1 hour.

[0123] PVAC at 8 wt % and 12 wt % is added to solutions 2 and 3. It is thus observed that the leakage current is reduced and the viscosity increases, especially when PVAC is added at 12 wt %. In the latter case a viscosity of 2500 cP is considered to be a very high value. In both of these cases, the segregation effect is removed and current decreases.

[0124] In solution 4, by adding 8 wt % of PVAC and 20 wt % of liquid PEGDB, segregation is removed; the current consumption is strongly reduced with a moderate increase of the viscosity compared to sample with solution 3. The addition of PEGDB increase the viscosity from 420 to 1000 cP measured at 25° C.;

[0125] Thus, the inventive solution 4 strikes a good balance between leakage current/bleaching rate and viscosity due to the synergetic effect obtained from the use of the thickening polymer agent and additive.