Multi-layer ligand exchange thermochromic systems
Ligand exchange of thermochromic, LETC, systems exhibiting a reversible change in absorbance of electromagnetic radiation as the temperature of the system is reversibly changed are described. The described LETC systems include one or more than one transition metal ion, which experiences thermally induced changes in the nature of the complexation or coordination around the transition metal ion(s) and, thereby, the system changes its ability to absorb electromagnetic radiation as the temperature changes. In accordance with one aspect of the present invention, a thermochromic device is disclosed comprising at least two thermochromic layers when each thermochromic layer includes a polymer, at least one transition metal ion, at least one HεL ligand capable of forming a HεMLC with the transition metal ion and at least one LεL ligand capable of forming an LεMLC with the transition metal ion. In accordance with yet another aspect of the present invention, the thermochromic device further includes a separator between the first and second thermochromic layers to prevent intermixing of the contents of the layers.
1. A thermochromic device that comprises:
first and second thermochromic layers, wherein each thermochromic layer respectively contains a polymer, at least one transition metal ion, at least one HεL ligand capable of forming a HεMLC with the transition metal ion, and at least one LεL ligand capable of forming a LεMLC with the transition metal ion;
wherein each layer exhibits a reversible net increase in light energy absorbance in the visible and/or NIR range as the temperature of the layer increases, and at elevated temperatures, the light energy absorbance of the HεMLC in the first layer is greater than the light energy absorbance of the HεMLC in the second layer for a portion of the visible and/or NIR range.
2. The device of claim 1 wherein at least one of the thermochromic layers exhibits a net increase in light energy absorbance within the visible range.
3. The device of claim 1 wherein at least one of the thermochromic layers exhibits a net increase in absorbance within the NIR range.
4. The device of claim 1 wherein the device additionally includes a separator between the first and second thermochromic layers to prevent intermixing of the contents of the layers.
5. The device of claim 4 wherein the separator has one or more surfaces that are excited.
6. The device of claim 4 wherein the absorbance of the device at 25° C. is less than about 0.3 throughout the visible and NIR range and the absorbance of the device at 85° C. is greater than about 0.8 at some wavelength in the visible or NIR range.
7. The device of claim 1 , wherein the transition metal ion is present in an amount from about 0.02 moles to about 0.4 moles per kilogram of polymer.
8. The device of claim 1 wherein the thermochromic layers exhibit c* of less than about 25 throughout the temperature range of 25 to 85° C. with Y from greater than about 70% at 25° C. and less than about 15% at 85° C.
9. The device of claim 1 wherein the thermochromic layers exhibit c* of less than about 20 throughout the range of 25 to 85° C. and a Y from greater than about 75% at 25° C. and less than about 15% at 85° C.
10. The device of claim 1 wherein the device includes a third thermochromic layer and the thermochromic layers exhibit c* of less than about 15 throughout the range of 25 to 85° C. and a Y from greater than about 80% at 25° C. and less than about 15% at 85° C.
11. The device of claim 1 wherein the thermochromic layers have a blue, green or bronze appearance at 25° C. and a c* of less than 20 at 85 C.
12. The device of claim 1 wherein the thermochromic layers exhibit an absorbance of about ≦0.2 at 25° C. and an absorbance of about ≧0.8 at 85° C. at each wavelength in the 400 to 700 nm range.
13. The device of claim 1 wherein at least one of the thermochromic layers contains two or more kinds of HεL's, at least one of which is a halide, a pseudohalide, a phosphine, or a phosphinate.
14. The device of claim 1 wherein at least one of the thermochromic layers contains a diol, triol, or polyol LεL in a layer of poly(vinyl butyral) wherein the layer contains less than 1% water by weight.
15. The device of claim 1 wherein the transition metal ions include Ni(II) and/or Co(II).
16. The device of claim 1 wherein a NIR absorbance is provided by a complex of iodide and Co(II) ion and thermochromic activity is provided by an increase in the concentration of a complex of iodide and Ni(II) ion.
17. The device of claim 1 wherein each thermochromic layer includes Ni(II) and a halide.
18. The device of claim 4 wherein the separator layer is selected from poly(methyl methacrylate), poly(ester-terephthalate), polycarbonate, poly(4-methyl-1-pentene), poly(vinyl propionate), poly(vinyl acetate), poly(vinyl methyl ether), poly(ethylene succinate), cellulose acetate butyrate, cellulose acetate, ethylene/vinyl acetate copolymer, ethyl cellulose, poly(methyl acrylate), poly(oxymethylene), poly(n-butyl methacrylate), poly(methyl methacrylate), polypropylene, methyl cellulose, poly(vinyl alcohol), poly(vinyl methyl ketone), poly(ethylene glycol dimethacrylate), poly(isobutylene), and polyethylene.
19. The device of claim 1 wherein the polymer is selected from poly(vinyl butyral); poly(hydroxyethyl methacrylate); poly(1-glycerol methacrylate); hydroxyalkylcelluloses; urethanes; poly(2-ethyl-2-oxazoline); poly(N-vinylpyrrolidone); poly(ethylene-co-vinylalcohol); poly(vinyl methyl ether); poly(vinylbutyral-co-vinylalcohol-co-vinylacetate); polyacrylamide; poly(N,N-dimethylacrylamide); polyvinylpyridines and copolymers which involve the aforesaid polymer functionalities.