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US-12618173-B2 - High modulus gel-spun PVDF fiber thin films

US12618173B2US 12618173 B2US12618173 B2US 12618173B2US-12618173-B2

Abstract

Mechanically and piezoelectrically anisotropic polymer fibers may be formed by spinning a polymer solution or gel that includes a high molecular weight crystallizable polymer and a liquid solvent. The solvent may be configured to interact with the polymer to facilitate chain alignment and, in some examples, create a higher crystalline content within the spun fibers. The polymer solution may also include a low molecular weight additive. The high and low molecular weight polymers may each be characterized by a bimodal molecular weight distribution where the molecular weight of the additive is less than the molecular weight of the crystallizable polymer. The polymer(s) and the additive(s) may be independently selected from vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinyl fluoride, etc. The spun fibers may be oriented, annealed, poled, and woven or laminated to form a polymer thin film having a high elastic modulus and a high electromechanical coupling factor.

Inventors

  • Sheng Ye
  • Jing Chen
  • Hao Mei
  • Andrew John Ouderkirk
  • Arman Boromand
  • Kristy Alana Jost
  • Nagi Hosni Elabbasi
  • Jonathan Robert Peterson
  • Christopher Yuan Ting Liao

Assignees

  • META PLATFORMS TECHNOLOGIES, LLC

Dates

Publication Date
20260505
Application Date
20230103

Claims (19)

  1. 1 . A polymer fiber comprising: a crystalline polymer comprising a material selected from the group consisting of vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinyl fluoride, homopolymers thereof, co-polymers thereof, tri-polymers thereof, and derivatives thereof, wherein the crystalline polymer has a molecular weight between 100,000 g/mol and 500,000 g/mol, wherein the polymer fiber is formed by stretching a gel spun polymer fiber at a stretch ratio between 8 and 40, annealing the stretched polymer fiber under an applied stress between 100 MPa and 250 MPa at a temperature greater than 80° C., and poling the annealed polymer fiber at an applied voltage between 200 V/micrometer and 600 V/micrometer, wherein the polymer fiber has a Young's modulus between 4 GPa and 15 GPa, and an electromechanical coupling factor (k 31 ) between 0.1 and 0.3.
  2. 2 . The polymer fiber of claim 1 , wherein the polymer fiber has a piezoelectric coefficient (d 31 ) of at least 5 pC/N.
  3. 3 . The polymer fiber of claim 1 , further comprising an additive having a molecular weight of less than 25,000 g/mol.
  4. 4 . The polymer fiber of claim 3 , wherein the additive comprises a moiety selected from the group consisting of vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinyl fluoride, homopolymers thereof, co-polymers thereof, tri-polymers thereof, and derivatives thereof.
  5. 5 . The polymer fiber of claim 1 , wherein a molecular weight distribution of polymers within the polymer fiber is selected from the group consisting of monodisperse, polydisperse, and bimodal.
  6. 6 . A polymer thin film comprising the polymer fiber of claim 1 .
  7. 7 . A polymer thin film, comprising: a plurality of polymer fibers each comprising a crystalline polymer comprising a material selected from the group consisting of vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinyl fluoride, homopolymers thereof, co-polymers thereof, tri-polymers thereof, and derivatives thereof, wherein the crystalline polymer has a weight average molecular weight between 100,000 g/mol and 500,000 g/mol; and the plurality of polymer fibers within the polymer thin film are formed by stretching a gel spun plurality of polymer fibers at a stretch ratio between 8 and 10, annealing the stretched plurality of polymer fibers under an applied stress between 100 MPa and 250 MPa at a temperature greater than 80° C., and poling the annealed plurality of polymer fibers at an applied voltage between 200 V/micrometer and 600 V/micrometer, wherein the polymer thin film has a Young's modulus between 4 GPa and 15 GPa, and an electromechanical coupling factor (k 31 ) between 0.1 and 0.3.
  8. 8 . The polymer thin film of claim 7 , wherein the crystalline polymer of the each of the plurality of fibers is preferentially oriented along a predetermined axis.
  9. 9 . The polymer thin film of claim 7 , further comprising an additive having a molecular weight of less than 25,000 g/mol.
  10. 10 . The polymer thin film of claim 7 , wherein the polymer thin film is optically clear and has less than 10% bulk haze.
  11. 11 . A method comprising: forming a polymer solution comprising a crystallizable polymer content selected from the group consisting of vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinyl fluoride, homopolymers thereof, co-polymers thereof, tri-polymers thereof, and derivatives thereof, and a liquid solvent; forming a gel from the polymer solution; spinning the gel to form a polymer fiber; stretching the polymer fiber to a stretch ratio between 8 and 40 to form an oriented fiber; annealing the oriented fiber under an applied stress between 100 MPa and 250 MPa at a temperature greater than 80° C.; and poling the oriented fiber at an applied voltage between 200 V/micrometer and 600 V/micrometer, wherein a Young's modulus of the oriented fiber is between 4 GPa and 15 GPa, and an electromechanical coupling factor (k 31 ) of the oriented fiber is between 0.1 and 0.3.
  12. 12 . The method of claim 11 , wherein forming the gel comprises a process selected from the group consisting of cooling the polymer solution, evaporating the liquid solvent, and adding a poor solvent to the polymer solution.
  13. 13 . The method of claim 11 , wherein spinning the gel comprises exposing the polymer fiber to a liquid solvent or a heated gas.
  14. 14 . The method of claim 11 , wherein spinning the gel comprises electro-spinning.
  15. 15 . The method of claim 11 , wherein an electric field is applied during or after the stretching.
  16. 16 . The method of claim 11 , wherein an electric field is applied during or after the annealing.
  17. 17 . The method of claim 11 , further comprising forming a polymer fiber thin film from the oriented fiber by a process selected from the group consisting of weaving, cross-linking, and laminating the oriented fiber.
  18. 18 . The method of claim 17 , further comprising weaving a selected number and type of the oriented fibers along each of two or more in-plane directions.
  19. 19 . The method of claim 17 , further comprising embedding the polymer fiber thin film in a polymer matrix.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of priority under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 63/315,695, filed Mar. 2, 2022, the contents of which are incorporated herein by reference in their entirety. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrate a number of exemplary embodiments and are a part of the specification. Together with the following description, these drawings demonstrate and explain various principles of the present disclosure. FIG. 1 is a flow chart of an example method for forming a spun PVDF fiber polymer thin film according to various embodiments. FIG. 2 is a plot showing the bimodal distribution of molecular weights among components of an example polymer gel according to some embodiments. FIG. 3 is a plot showing the bimodal distribution of molecular weights among components of an example polymer gel according to further embodiments. FIG. 4 is a plot showing the bimodal distribution of molecular weights among components of an example polymer gel according to still further embodiments. FIG. 5 is a schematic of an example gel spinning method for manufacturing PVDF fibers through precipitation in a solvent bath according to various embodiments. FIG. 6 is a schematic of an example gel spinning method for manufacturing PVDF fibers via solvent evaporation according to various embodiments. FIG. 7 is a schematic of an example electro-spinning method for manufacturing PVDF fibers according to further embodiments. FIG. 8 shows schematic cross-sectional views of electroded PVDF fibers with (A) opposing electrodes disposed over the fiber surface, and (B) opposing electrodes embedded within the fiber according to some embodiments. FIG. 9 shows a schematic cross-sectional view of an electroded PVDF fiber thin film according to some embodiments. FIG. 10 is a schematic illustration of a method for contact poling a PVDF fiber spun with a conductive core and a conductive coating according to some embodiments. FIG. 11 illustrates a method for contact poling a PVDF fiber thin film having (A) woven or (B) aligned PVDF fibers according to various embodiments. FIG. 12 illustrates a method for contact poling a PVDF fiber thin film woven with conductive filaments according to certain embodiments. FIG. 13 is an illustration of exemplary augmented-reality glasses that may be used in connection with embodiments of this disclosure. FIG. 14 is an illustration of an exemplary virtual-reality headset that may be used in connection with embodiments of this disclosure. Throughout the drawings, identical reference characters and descriptions indicate similar, but not necessarily identical, elements. While the exemplary embodiments described herein are susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, the exemplary embodiments described herein are not intended to be limited to the particular forms disclosed. Rather, the present disclosure covers all modifications, equivalents, and alternatives falling within the scope of the appended claims. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Polymer materials may be incorporated into a variety of different optic and electro-optic device architectures, including active and passive optics and electroactive devices. Lightweight and conformable, one or more polymer layers may be incorporated into wearable devices such as smart glasses and are attractive candidates for emerging technologies including virtual reality/augmented reality devices where a comfortable, adjustable form factor is desired. Virtual reality (VR) and augmented reality (AR) eyewear devices or headsets, for instance, may enable users to experience events, such as interactions with people in a computer-generated simulation of a three-dimensional world or viewing data superimposed on a real-world view. By way of example, superimposing information onto a field of view may be achieved through an optical head-mounted display (OHMD) or by using embedded wireless glasses with a transparent heads-up display (HUD) or augmented reality (AR) overlay. VR/AR eyewear devices and headsets may be used for a variety of purposes. Governments may use such devices for military training, medical professionals may use such devices to simulate surgery, and engineers may use such devices as design visualization aids. These and other applications may leverage one or more characteristics of thin film polymer materials, including piezoelectric properties to induce deformations and the refractive index to manipulate light. In various applications, optical elements and other components may include polymer thin films that have anisotropic mechanical or optical properties. The degree of optical or mechanical anisotropy achievable through conventional thin film manufacturing processes is typically limited, however, and is often exchanged fo