Piezoelectric polymer blend and composite compositions including lithium-doped potassium sodium niobate
A polymer composite exhibiting piezoelectric properties can be formed for flexible and/or thin film applications, in which the polymer composite includes a polymer matrix and a piezoelectric ceramic filler embedded in the polymer matrix. The polymer matrix may include at least two polymers: a first polymer and a second polymer. The first polymer may be a fluorinated polymer, and the second polymer may be compatible with the first polymer and have a dielectric constant of less than approximately 20. The piezoelectric ceramic filler can be lithium doped potassium sodium niobite (KNLN), and be approximately 40-70% by volume of the polymer composite. The remaining 30-60% by volume may be the polymer matrix, which may itself be approximately 5-20% by weight second polymer and 80-95% fluorinated polymer.
1. A polymer composite, comprising:
a polymer matrix comprising at least two polymers: a first non-piezoelectric polymer comprising poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVDF-TrFE-CFE), and a second non-piezoelectric polymer comprising polymethyl methacrylate or acrylonitrile-styrene-acrylate of 5-15 wt % of the at least two polymers;
wherein the polymer matrix exhibits piezoelectric properties independent of a piezoelectric filler.
2. The polymer composite of claim 1 , wherein the polymer composite further comprises a piezoelectric ceramic filler embedded in the polymer matrix, the piezoelectric ceramic filler comprising lithium doped potassium sodium niobate (KNLN).
3. The polymer composite of claim 1 , in which the second non-piezoelectric polymer is compatible with the first non-piezoelectric polymer.
4. The polymer composite of claim 1 , in which the at least two polymers comprise approximately ten percent by weight or more of the second non-piezoelectric polymer.
5. The polymer composite of claim 1 , in which the second non-piezoelectric polymer has a dielectric constant of less than approximately 20.
6. The polymer composite of claim 1 , further comprising a flexible substrate attached to the polymer composite, and in which the polymer composite is a mechanically-flexible thin film.
7. The polymer composite of claim 1 , wherein the polymer composite has a thickness between 50 and 200 microns.
8. The polymer composite of claim 1 , in which the polymer composite is characterized by a piezoelectric strain constant of between approximately 30 and approximately 70 pC/N, and by a piezoelectric voltage constant between approximately 100 and approximately 300 mV-m/N.
9. A method of manufacturing a thin film using the polymer composite as claimed in claim 1 .
10. The method of claim 9 , in which the method comprises:
dissolving the first polymer into a solution of the second polymer in a solvent to form a two-polymer solution, wherein the solvent is characterized by a dielectric constant of at least 20 and a boiling point of at least 80 degrees C.;
adding the piezoelectric ceramic filler to the two-polymer solution to form a dispersion or suspension;
forming the polymer composite thin film by casting and drying the solvent; and
subjecting the polymer composite to an electric polarization.
11. The method of claim 10 , in which dissolving the first polymer into the solution of the second polymer produces a two-polymer solution comprising 5 to 20 wt./vol % of polymer.
12. The method of claim 11 , further comprising annealing the polymer composite in an inert atmosphere.
13. A piezoelectric sensor comprising the polymer composite claim 1 , in which the piezoelectric sensor is configured to generate an analog signal proportional to an amount of deflection applied to the piezoelectric sensor by a user, in which the piezoelectric sensor is integrated in a mobile device.
14. The polymer composite of claim 2 , wherein
the piezoelectric ceramic filler is present in an amount of approximately 40-70% by volume of the polymer composite.
15. The polymer composite of claim 14 , wherein the second non-piezoelectric polymer comprises polymethyl methacrylate or acrylonitrile-styrene-acrylate of 8-12 wt % of the at least two polymers.
16. The polymer composite of claim 14 , wherein the second non-piezoelectric polymer comprises polymethyl methacrylate or acrylonitrile-styrene-acrylate of 10 wt % of the at least two polymers.
17. A polymer composite, comprising:
a polymer matrix comprising at least two polymers: a first non-piezoelectric polymer comprising poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVDF-TrFE-CFE), and a second non-piezoelectric polymer comprising 5-15 wt % of polymethyl methacrylate or acrylonitrile-styrene-acrylate;
wherein the polymer matrix exhibits at least two melting transitions.
18. The polymer composite of claim 1 , wherein the second non-piezoelectric polymer comprises 5-10 wt % of the at least two polymers.