Heat dissipative and lightweight optical elements having increased strength and stiffness
A polymer thin film includes polyethylene having a weight average molecular weight of at least approximately 500,000 g/mol, where the thin film is characterized by transparency within the visible spectrum of at least approximately 80%, bulk haze of less than approximately 5%, and an in-plane elastic modulus of at least approximately 10 GPa. The polymer thin film may be thermally conductive and may be incorporated into an optical element and configured to dissipate heat, such as from a light-emitting device.
1 . A multilayer polymer thin film comprising:
a first polyethylene thin film having a first in-plane orientation of crystalline axes and a weight average molecular weight of at least approximately 500,000 g/mol; and
a second polyethylene thin film having a second in-plane orientation of crystalline axes and a weight average molecular weight of at least approximately 500,000 g/mol, wherein the multilayer polymer thin film comprises:
transparency within the visible spectrum of at least approximately 80%;
bulk haze of less than approximately 5%; and
an in-plane elastic modulus of at least approximately 10 GPa.
2 . The multilayer polymer thin film of claim 1 , comprising transparency within a infrared spectrum of at least approximately 80%.
3 . The multilayer polymer thin film of claim 1 , comprising transparency within a radio frequency spectrum of at least approximately 80%.
4 . The multilayer polymer thin film of claim 1 , comprising an in-plane tensile strength of at least approximately 0.5 GPa.
5 . The multilayer polymer thin film of claim 1 , wherein an in-plane thermal conductivity of the thin film is anisotropic.
6 . The multilayer polymer thin film of claim 1 , comprising an in-plane thermal conductivity of at least approximately 5 W/mK.
7 . The multilayer polymer thin film of claim 6 , wherein an in-plane anisotropy of the thermal conductivity is at least 2:1.
8 . The multilayer polymer thin film of claim 1 , comprising a crystalline polyethylene content of at least approximately 30%.
9 . The multilayer polymer thin film of claim 1 , wherein a density of the polyethylene is less than approximately 1.5 g/cm 3 .
10 . The multilayer polymer thin film of claim 1 , comprising a thickness of at least approximately 5 micrometers.
11 . A multilayer thin film comprising:
a first crystalline polymer layer and a second crystalline polymer layer, the first crystalline polymer layer having a first in-plane orientation of crystalline axes and the second crystalline polymer layer having a second in-plane orientation of crystalline axes such that the crystalline axes of the first and second crystalline polymer layers are rotationally misoriented in-plane by an angle (θ), where 0<θ≤90°, each of the first and second crystalline polymer layers comprise a weight average molecular weight of at least approximately 500,000 g/mol and the multilayer thin film comprises at least two attributes (i-iv) selected from the group consisting of:
(i) transparency within a visible spectrum of at least approximately 80%;
(ii) bulk haze of less than approximately 5%;
(iii) an in-plane elastic modulus of at least approximately 10 GPa; and
(iv) an in-plane thermal conductivity of at least approximately 5 W/mK.
12 . The multilayer thin film of claim 11 , wherein the thin film comprises at least three of the attributes (i-iv).
13 . The multilayer thin film of claim 11 , comprising a crystalline polymer content of at least approximately 30%.
14 . The multilayer thin film of claim 11 , wherein a density of the crystalline polymer is less than approximately 1.5 g/cm 3 .
15 . The multilayer thin film of claim 11 , wherein the crystalline polymer comprises polyethylene.