Temperature activated optical films

Abstract

The present invention discloses a multilayer dielectric optical structure wherein one of the optical materials in the multilayer structure shows an optically isotropic state above and a birefringent state below a characteristic temperature Tc near the room temperature. The optical structure reflects a predetermined wavelength range of electromagnetic radiation above the Tc but allow the same to transmit through below the Tc. The predetermined wavelength can be the near infrared radiation from 700 nm to 2500 nm, and the optical structure rejects solar heat in warm summer days but admits the same to interior on a colder winter day.

Description

CROSS-REFERENCE[0001]This application is a continuation of U.S. Non-Provisional application Ser. No. 12 / 152,969, filed May 19, 2008, which claims the benefit of U.S. Provisional Application No. 60 / 930,894, filed May 18, 2007, the contents of both of which are incorporated herein by reference in their entirety.BACKGROUND OF THE INVENTION[0002]The present invention generally relates to a multilayer dielectric optical structure that selectively reflects a predetermined wavelength of electromagnetic radiation. More particularly, this invention relates to the optical structure whose change of optical property is activated by temperature.[0003]Glass windows are widely used in residential and commercial buildings for the purpose of natural light collection as well as for aesthetic reasons. However, glass windows, as they are generally a thin and transparent barrier separating the interior for example an office space to the outside environment, can readily exchange heat with the outside env...

AI Technical Summary

Benefits of technology

"The present invention provides a multilayer dielectric optical structure that is made of polymer and liquid crystal materials. The optical structure is substantially transparent of visible and infrared light when temperature is below a transition temperature in the range between 15-35 degree Celsius, while has high reflectance of infrared light when temperature is above the transition temperature. The number of layers required to reflect a wide band of infrared light is between 100 to 1000 layers. The film or window made of this optical structure is particularly useful for passive solar energy control. It has high visible light transmittance, significantly lower infrared transmittance above the transition temperature, has a sufficiently low transition temperature range to be useful in a wide variety of climatic conditions, and the only activation required is the change in ambient temperature that the films or windows can directly sense. The present invention meets the needs by providing an optical structure that transmit visible lights and infrared radiation at a temperature below a characteristic transition temperature, reflect the infrared radiation when temperature is above the transition temperature. It is flexible, transparent at all temperatures, and can be easily mass-produced and retrofit into existing windows. The optical system reflects a broadband of infrared radiation when temperature is above the transition temperature while it is transparent to visible light."

Problems solved by technology

This system is not useful for present application because its temperature dependence changes slowly over a wide range of temperature.

A significant difficulty in implementing such a device, aside from any performance issues, is that there must be a significant reservoir to hold such solvents.

In addition, vanadium oxides in temperatures below or above the transition temperature absorb a significant portion of visible light, which makes the technology less attractive for window applications.

However, the optical properties including its reflectance will not change with the temperature, and the resulting optical structure will reject solar energy on a warmer summer day, which is desirable, as well as on a cold winter day if so designed, which is not desirable.

However, the transition temperature of ferroelectric materials occur at about 120° C., the induced index of refraction change is about 0.03, and as both layers are optically isotropic in the reflection mode at high temperature, the device will only reflect a nearly normal incident single wavelength light at very high temperatures, and it will require a large number of layers, greater than 5000 to achieve significant reflection across a broadband of near infrared radiations, therefore that will not be applicable for adjusting solar energy control at room temperature range.

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