Accession Number : ADA289821

Title :   Molecular Modeling: An Approach for the Study of Piezoelectric Polymers.

Descriptive Note : Final rept.,

Corporate Author : NAVAL UNDERSEA WARFARE CENTER NEWPORT DIV NEW LONDON CT NEW LONDON DETACHMENT

Personal Author(s) : Kavarnos, George J.

PDF Url : ADA289821

Report Date : 12 DEC 1994

Pagination or Media Count : 61

Abstract : This report describes the use of molecular modeling and computational chemistry techniques to investigate and tailor the piezoelectric properties of polyvinylidene fluoride (PVDF) and its copolymer with trifluoroethylene (PVDF-TrFE) for underwater hydrophone and acoustic projector applications. The effect of changing the ratios of vinylidene fluoride and trifluoroethylene monomers was studied using a combination of semiempirical molecular orbital theory, molecular mechanics, and crystal packing approaches. Molecular mechanics calculations on model end-capped polymer chains show that the tgtg'conformation of PVDF is 0.5 to 0.7 kcal/mol more stable than the all-trans formation but that for copolymer compositions less than 90 mol% vinylidene fluoride (VDF), the all-trans conformation is favored. Crystal packing calculations confirm the stability of the tgtg' for PVDF and the all-trans for the copolymers. To calculate the elastic compliances of PVDF and copolymer unit cell crystals along the poling direction, the b-axes were deformed in small increments and the crystal packing energies of each deformed structure were calculated. This procedure was used to determine the elastic compliances, which were calculated to be 2.59 x 10(exp-11)sq m2/N for PVDF, 3.97 x 10(exp-11)sq m/N for 75 mol% VDF copolymer, and 5.38 x 10(exp-11)sq m/N for 50 mol% VDF copolymer. The d33c constants of the unit cells were calculated to be -3.3 pC/N for PVDF, -4.0 pC/N for 75 mol% VDF copolymer, and -4.3 pC/N for 50 mol% VDF copolymer. Although these values are much lower than the experimental d33 constants of semicrystalline polymer, a procedure used to calculate the d33 constants of semicrystalline polymer yields d33 constants much more in agreement with the experimental values. (jg)

Descriptors :   *MODELS, *PIEZOELECTRIC MATERIALS, *MOLECULAR ORBITALS, *POLYVINYLIDENES, COMPUTATIONS, MOLECULES, CELLS, POLYMERS, QUANTUM THEORY, DEFORMATION, ENERGY, ELASTIC PROPERTIES, COPOLYMERS, CRYSTALS, MECHANICS, ETHYLENE, CHEMISTRY, PACKAGING, HYDROPHONES, FLUORIDES, PIEZOELECTRIC EFFECT, UNDERWATER, SONAR PROJECTORS, VINYL PLASTICS.

Subject Categories : Polymer Chemistry
      Inorganic Chemistry
      Physical Chemistry
      Atomic and Molecular Physics and Spectroscopy

Distribution Statement : APPROVED FOR PUBLIC RELEASE