Does any one have an idea about the material properties of the thin Films (within nm and um ranges of thickness ) of PVDF and its copolymers, such as P(VDF-TeFE), P(VDF-TrFE)56/44 mol%, P(VDF-TrFE)68/32 mol%, P(VDF-TrFE)65/35 mol%, P(VDF-TrFE)70/30 mol% and P(VDF-TrFE)77/23 mol% ?
Are they isotropic, anisotropic or orthotropic material?
How about the terpolymers P(VDF-TrFE-CFE) and P(VDF-TrFE-CTFE)?
Dear Tam,
my conjecture is as follows:
highly confined polymers show very peculiar behavior. Thin films are special cases as just one direction is ultra confined. Ultra-thin films are those thin film with a thickness lower than the size of the statistical macromolecule , Re.
Under such conditions, assuming that the film is obtained by casting a dilute solution and letting the solvent evaporate, polymer strands are preferentially oriented along the film plane directions. It is a sort of self (bi-axial) stretching.
The level of stretching can be calculated assuming that the bulk density and film density remain comparable.
Finally , with little or no interaction with the support, the film is orthotropic with two equivalent symmetry planes.
They are isotropic until poled; at which time they become anisotropic.
All poled piezoelectric materials are anisotropic.
Ultra-thin films, i.e., films thinner than 100nm) do not crystallize properly, do not pole well and exhibit very low d33 values, It is possibly from an inability to orient the crystals properly.
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