CROSS-REFERENCES TO RELATED APPLICATIONS This Application takes priority to US 62/836249 filed on 19 April 2019 and incorporates that application in its entirety herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR

DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A

COMPACT DISC

Not Applicable

FIELD OF INVENTION

The present invention is related to polyimide films; and more specifically freestanding thin polyimide films doped with nanoparticles. BACKGROUND OF INVENTION

Thin films are used in in a wide range of industries for applications requiring a range of optical, electromagnetic, and physical properties. Made as freestanding membranes, they offer optical and physical filtering properties as well as the capability to separate regions of disparate pressures. Polymer films, and polyimide films, in particular, offer exceptional strength that allows their production in ultrathin regimes of several microns and below. Polymers having ultrathin thicknesses have found applications that include, but are not limited to, photon transmission filters and windows for extreme ultraviolet through soft x-rays (tens of electron volts through several thousand electron volts), separation of gases of high pressures for proportional counter detectors, and containment of fuel for fusion reactions. Polymer films of different chemical composition and structure have different physical and optical properties, but for a given composition and structure, the properties of different films remain largely similar. For some applications, it is desirable to maintain most of the properties of a film while altering or improving others. For example:

• the addition of nanoparticles with particular optical absorption profiles can increase the absorption of optical photons to improve photothermal coupling to the film’s environs, particularly for control of the film temperature;

• the addition of elemental or chemical species offers in situ tracer particles to identify film location, density, elongation, and other properties; and

e the formation of a polymer around the nanoparticle or the incorporation of the nanoparticle into the polymer structure can change the physical properties such as the modulus of elasticity and yield strength.

These modifications to a polymer’s characteristics while maintaining the other desirable properties of the polymer are enabled by the development of nanoparticles of various materials and geometry. Varieties of nanoparticles, both existing and still to be developed, can be incorporated into ultrathin films through the invention described herein to achieve novel modifications to polymers.

SUMMARY OF THE INVENTION

The invention described herein is a freestanding ultrathin polymer film that allows for increased conductivity, strength, traceability, and usable energy range.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent in the following detailed descriptions of the preferred embodiment with reference to the accompanying drawings, of which:

Fig. 1 A is an embodiment of prior art;

Fig. IB is an embodiment of prior art;

Fig. 1C is an embodiment of prior art;

Fig. 2A is an embodiment of the invention;

Fig. 2B is a cross-section taken from A-A of Fig. 2A.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, the use of similar or the same symbols in different drawings typically indicate similar or identical items, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. One skilled in the art will recognize that the herein described components (e.g., operations), devices, objects, and the discussion accompanying them are used as examples for the sake of conceptual clarity and that various configuration modifications are contemplated. Consequently, as used herein, the specific exemplars set forth and accompanying discussion are intended to be representative of their more general classes. In general, use of any specific exemplar is intended to be representative of its class, and the non-inclusion of specific components (e.g., operations), devices, and objects should not be taken as limiting.

The present application may use formal outline headings for clarity of presentation. However, it is to be understood that the outline headings are solely for presentation purposes, and that different types of subject matter may be discussed throughout the application (e.g., device(s)/structure(s) may be described under process(es)/operations heading(s) and/or process(es)/operations may be discussed under structure(s)/process(es) headings; and/or descriptions of single topics may span two or more topic headings). Hence, the use of the formal outline headings is not intended to be in any way limiting. By way of overview, embodiments for freestanding ultrathin film doped with nanoparticles are provided herein.

Doped polymers are known in the art. For example, in the late 1960s, dye doped polymers were used as laser gain media, and carbon doped polymers were developed to modify optical opacity and electrical and thermal characteristics of films. However, the doping and polymer fabrication processes kept thicknesses above twenty- five microns or required the film to be attached to a permanent substrate.

Thin films may be produced by any known method, including spin coating, dip coating, and doctor blade coating, or by growth through a vapor deposition process.

For example, referring to Figs. 1A-1C, a method to manufacture a polymer film 100 is comprised of layering placing a sacrificial layer 104 on a substrate 102. The substrate 102 may be silicon or other nonreactive material. The sacrificial layer 104 may be made from a salt, soap, or other release agent. A thin layer of polymer (or polymer film) 106 is layered onto the sacrificial layer 104.

The polymer film 106 may be removed from the substrate 102 by immersing the substrate 102 into a water bath or other agent that will dissolve the sacrificial layer 104. As the sacrificial layer 101 dissolves, the polymer film 106 is removed from the substrate 101. In some methods, the polymer film 106 is cured. In some embodiments, a sacrificial layer 104 may not be used.

Thin films may be doped by any known method. In some methods, nanoparticles may be mixed into the polymer 106 in the precursor phase prior to polymerization into the polymer film 106 onto the sacrificial layer 104. In some methods, nanoparticles may be added to the polymer film 106 after deposition but before it is cured. In some methods, nanoparticles may be bombarded onto the polymer film 106 after it has been cured or inserted into a permeable film via other mechanical transport. The films may be produced as freestanding membranes through any known method, including: the use of a sacrificial layer; ablation, decomposition, or dissolution of a substrate; mechanical or thermodynamic separation from a substrate; and polymerization on a liquid surface.

Figs.2A - 2B show an embodiment of a freestanding ultrathin polymer film doped with a plurality of nanoparticles 200, where the polymer film 210 has a thickness of less than 8 pm. In some embodiments, the polymer 210 is a polyimide.

In some embodiments, the nanoparticles 220 have unequal axes where at least one axis has a length that is less than the thickness of the polymer film 210. Empirical evidence suggests that polymer film strength begins to weaken when the minor axis is significantly greater than ten percent (10%) of the film thickness.

The thickness of the polymer film 210 is based on its application. For example, for photonic applications, minimal thickness is used for photon transmission; for spaceflight and for gas separation, thicker films may be used for higher strength.

Nanoparticles 220 may be chosen based on the application for which the freestanding polymer film doped with nanoparticles 200 is to be used. That is, nanoparticles 220 may be chosen based on: their intrinsic properties such as optical properties like photon absoiption and scattering cross sections; by composition for tracer particles; or on their ability to modify the polymer film 200. Nanoparticles 220 may also be chosen by how they modify film properties, including but not limited to: thermal and electrical conductivity elastic modulus, and yield strength. In embodiments, the nanoparticles 220 may have a high adsorption cross section and efficient conversion of absorbed photons into thermal energy for photonic heating the film. In an embodiment, the nanoparticles 220 may have a geometric cross section less than the absorption cross section due to surface plasmon resonance (“SPR”) of the nanoparticles 220, allowing tunable absorption of specific regions of the electromagnetic spectrum, with the nanoparticles 220 selected by material and geometry to define the SPR.

In some embodiments, the nanoparticles 220 may be shaped as rods, spheres, plates, cubes, shells, and crosses, amongst others. In some embodiments, the nanoparticles 220 may be coinage elements, C03O4 _, or carbon. It will be clear to any person having ordinary skill in the art that nanoparticles 220 can be manufactured in any shape and from any element or combination of elements.

In some embodiments, the ratio of nanoparticles 220 to polymer film 210 can be based on a volume, mass, or atomic ratio. In some embodiments, the atomic ratio of nanoparticles to polymer film 210 can range from 0.1%-50%.

In some embodiments, the placement and orientation of the nanoparticles 220 are randomly distributed. In some embodiments, the position and orientation of the nanoparticles 220 are controlled. The position and orientation of nanoparticles 220 may be controlled, for example, by magnetic orientation during curing.