PVDF thin films having high electromechanical efficiency and a gel casting method for forming same
A mechanically and piezoelectrically anisotropic polymer thin film may be formed by gel casting a solution that includes a 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 cast thin film. The thin film may also include up to approximately 90 wt. % of an additive and may be characterized by a bimodal molecular weight distribution of a crystallizable polymer where the molecular weight of the additive may be less than the molecular weight of the crystallizable polymer. In some examples, the polymer(s) and the additive(s) may be independently selected from vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinyl fluoride, etc. The anisotropic polymer thin film may be characterized by an electromechanical coupling factor (k 31 ) of at least 0.1.
1. A polymer thin film, comprising:
a crystalline PVDF-family polymer having a molecular weight of at least approximately 100,000 g/mol; and
an additive having a molecular weight less than the molecular weight of the crystalline PVDF-family polymer, wherein the additive comprises a thiol or an acid and the polymer thin film has an electromechanical coupling factor (k 31 ) of at least approximately 0.1.
2. The polymer thin film of claim 1 , wherein the crystalline PVDF-family polymer is oriented along a predetermined axis.
3. The polymer thin film of claim 1 , wherein the crystalline PVDF-family polymer 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.
4. The polymer thin film of claim 1 , 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. The polymer thin film of claim 1 , wherein the additive comprises one or more of a nucleation agent, a piezoelectric ceramic, and a cation.
6. The polymer thin film of claim 1 , wherein the additive comprises a non-reactive moiety selected from the group consisting of an ester, ether, hydroxyl, phosphate, fluorine, halogen, and nitrile.
7. The polymer thin film of claim 1 , wherein the additive comprises from approximately 0.1 wt. % to approximately 90 wt. % of the polymer thin film.
8. The polymer thin film of claim 1 , wherein the additive has a molecular weight of less than approximately 25,000 g/mol.
9. The polymer thin film of claim 1 , wherein the additive has a molecular weight of from approximately 25,000 g/mol to approximately 100,000 g/mol.