UC San Diego

Polymer-air multilayer (PAM) was developed to improve the building window energy efficiency. It consists of multiple layers of polymer films, separated by spacer bars at the edges. The air gap between adjacent polymer layers is 0.5~1 mm thick. PAM enhances window thermal insulation by suppressing all of conductive, convective, and radiative heat transport. The U-factor of a 6-mm-thick 4-layer PAM can be close to or below 0.5 Btu/(h∙ft^2∙℉).

Corona charging and liquid flow electrification were investigated to generate a repulsive pressure of the polymer layers. It helps with materials handling and assembling and improves the structural stability. Dipolar charges can be controlled by the grid voltage in corona charging. Surface charges can be adjusted by liquid flow with appropriate ion size, ion concentration, and flow rate.

To further raise the resistance to radiative heat transfer, a low-emissivity (low-e) coating could be applied on the outer surface of PAM. Because a typical low-e coating would decrease the visual transmittance by more than 20%, in order to keep the overall visual transmittance above 70%, the layer count of PAM should be reduced to 1 or 2. A 4-mm-thick 1-layer PAM or a 3-mm-thick 2-layer PAM could achieve a low U-factor around 0.5 Btu/(h∙ft^2∙℉).

Anti-reflection (AR) coating was utilized to maximize the visual transmittance of PAM. The top candidate of the coating material is polymethyl methacrylate (PMMA). With a thin PMMA AR coating, the visual transmittance of 4-layer PAM, 1-layer PAM, and 2-layer low-emissivity PAM were enhanced to 80.3%, 76.9% and 74.5%, respectively. Haze of all the samples was below 1%.

The PAM technology has broad applications not only for building windows, but also for smart walls, roofs, and doors. In addition, it may also be relevant to the automobile, electronics, aerospace, and military industry.