Methods for fabricating thermochromic filters
Thermochromic liquid crystal filters are fabricated by providing two polarizers oriented at offset polarity with respect to each other; providing alignment structures adjacent the inner surfaces of the polarizers; placing a plurality of spacers between the polarizers; and filling a space created by the spacers with a thermotropic liquid crystal that acts as a wave block in an isotropic state and acts to rotate the polarization of light in a nematic state. Alternatively, the filters can be created by encapsulating a thermochromic liquid crystal with a polymer material to form a flexible film and orienting the thermochromic liquid crystal in the polymer material to create a structure that functions as a thermochromic optical filter. Such filters can control the flow of light and radiant heat through selective reflection, transmission, absorption, and/or re-emission. The filters have particular application in passive or active light-regulating and temperature-regulating films, materials, and devices, and particularly as construction materials.
1. A method for constructing a thermotropically-actuated distributed Bragg reflector comprising:
combining a photopolymer and a thermotropically-actuated liquid crystal;
aligning the liquid crystal such that an optical index of the liquid crystal matches an optical index of the photopolymer when the liquid crystal is in an ordered state, and such that the optical index of the liquid crystal mismatches the optical index of the photopolymer when the liquid crystal is in a disordered state; and
photopolymerizing the photopolymer to enclose the thermotropically-actuated liquid crystal such that the liquid crystal is free to transition between the ordered and disordered states responsive to temperature changes;
wherein the aligning operation includes providing an electric field across the liquid crystal to align the optical index of the liquid crystal at the optical index of the photopolymer during the photopolymerizing operation.
2. The method of claim 1 , wherein the photopolymerizing operation further comprises:
photopolymerizing the photopolymer in layers; and
trapping the liquid crystal between adjacent layers of the photopolymer in an alternating structure.
3. The method of claim 1 further comprising mixing the photopolymer and the thermotropically-actuated liquid crystal, wherein the liquid crystal is encapsulated interstitially within the photopolymer during the photopolymerization operation.
4. The method of claim 1 further comprising doping the liquid crystal with dye molecules having absorptive, reflective, or diffusive properties, or any combination thereof.
5. The method of claim 4 further comprising mixing a surface coupling agent with the liquid crystal.
6. The method of claim 5 , wherein the surface coupling agent is an amphiphilic compound.
7. The method of claim 4 , wherein the dye is either a positive dichroic dye or a negative dichroic dye.
8. The method of claim 4 , wherein the dye is absorptive of light polarized along an axis of a molecule of the dye.
9. A method for constructing a thermotropically-actuated distributed Bragg reflector comprising:
combining a photopolymer and a thermotropically-actuated liquid crystal;
aligning the liquid crystal such that an optical index of the liquid crystal matches an optical index of the photopolymer when the liquid crystal is in an ordered state, and such that the optical index of the liquid crystal mismatches the optical index of the photopolymer when the liquid crystal is in a disordered state;
photopolymerizing the photopolymer in layers to enclose the thermotropically-actuated liquid crystal such that the liquid crystal is free to transition between the ordered and disordered states in response to temperature changes; and
trapping the liquid crystal between adjacent layers of the photopolymer in an alternating structure.
10. The method of claim 9 further comprising doping the liquid crystal with dye molecules having absorptive or reflective properties.
11. The method of claim 10 further comprising mixing a surface coupling agent with the liquid crystal.
12. The method of claim 11 , wherein the surface coupling agent is an amphiphilic compound.
13. The method of claim 10 , wherein the dye is either a positive dichroic dye or a negative dichroic dye.
14. The method of claim 10 , wherein the dye is absorptive of light polarized along an axis of a molecule of the dye.