ULTRA-HIGH MODULUS AND RESPONSE PVDF THIN FILMS
A polymer thin film includes polyvinylidene fluoride (PVDF) and is characterized by a Young's modulus along an in-plane dimension of at least 4 GPa, an electromechanical coupling factor (k 31 ) of at least 0.1 at room temperature. A method of manufacturing such a polymer thin film may include forming a polymer composition into a polymer thin film, applying a tensile stress to the polymer thin film along at least one in-plane direction and in an amount effective to induce a stretch ratio of at least approximately 5 in the polymer thin film, and applying an electric field across a thickness dimension of the polymer thin film. Annealing and poling steps may separately or simultaneously accompany and/or follow the act of stretching of the polymer thin film.
1 . A polymer thin film comprising polyvinylidene fluoride (PVDF) and characterized by:
a Young's modulus along an in-plane dimension of at least approximately 4 GPa; and
an electromechanical coupling factor (k 31 ) of at least approximately 0.1 at 25° C.
2 . The polymer thin film of claim 1 , wherein the polyvinylidene fluoride comprises a moiety selected from the group consisting of vinylidene fluoride (VDF), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), vinyl fluoride (VF), and homopolymers, copolymers, tri-polymers, derivatives and mixtures thereof.
3 . The polymer thin film of claim 1 , wherein a composition of the polymer thin film is characterized by a bimodal molecular weight distribution.
4 . The polymer thin film of claim 1 , wherein a composition of the polymer thin film is characterized by a polydisperse molecular weight distribution.
5 . The polymer thin film of claim 1 , wherein the Young's modulus is at least approximately 4 GPa along each of a pair of mutually orthogonal in-plane dimensions.
6 . The polymer thin film of claim 1 , wherein the electromechanical coupling factor (k 31 ) is at least approximately 0.15 at 25° C.
7 . The polymer thin film of claim 1 , wherein a piezoelectric coefficient (d 31 ) of the polymer thin film is at least approximately 5 pC/N.
8 . The polymer thin film of claim 1 , wherein the polymer thin film is characterized by at least approximately 80% transparency at 550 nm and less than approximately 10% bulk haze.
9 . The polymer thin film of claim 1 , comprising at least approximately 40% total crystalline content.
10 . The polymer thin film of claim 1 , comprising at least approximately 30% total beta phase content.
11 . A polymer article characterized by:
a Young's modulus along at least one dimension of at least approximately 4 GPa;
an electromechanical coupling factor (k 31 ) of at least approximately 0.1 at 25° C.; and
optical transparency along a thickness dimension of at least approximately 80%.
12 . The polymer article of claim 11 , comprising at least approximately 30% total beta phase content.
13 . A method comprising:
forming a polymer composition into a polymer thin film;
applying a tensile stress to the polymer thin film along at least one in-plane direction and in an amount effective to induce a stretch ratio of at least approximately 5 in the polymer thin film; and
applying an electric field across a thickness dimension of the polymer thin film.
14 . The method of claim 13 , wherein the forming comprises a process selected from the group consisting of casting, extruding, molding, and calendaring.
15 . The method of claim 13 , wherein the polymer composition comprises a mixture of a high molecular weight polymer and one or more of a low molecular weight polymer and an oligomer.
16 . The method of claim 13 , further comprising heating the polymer thin film while applying the tensile stress.
17 . The method of claim 13 , further comprising heating the polymer thin film to a temperature of at least 10° C. less than a melting peak temperature of the polymer composition while applying the tensile stress.
18 . The method of claim 13 , further comprising heating the polymer thin film after applying the tensile stress.
19 . The method of claim 13 , wherein the electric field is applied while applying the tensile stress or after applying the tensile stress.
20 . The method of claim 13 , wherein the electric field is applied while heating the polymer thin film or after heating the polymer thin film.