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

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)

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Document Details

Document Type
Technical Report
Publication Date
Dec 12, 1994
Accession Number
ADA289821

Entities

People

  • George J. Kavarnos

Organizations

  • Naval Undersea Warfare Center

Tags

Communities of Interest

  • Energy and Power Technologies

DTIC Thesaurus Topics

  • Chemistry
  • Copolymers
  • Crystal Lattices
  • Crystal Structure
  • Crystallography
  • Crystals
  • Materials
  • Materials Science
  • Mechanics
  • Molecules
  • Piezoelectric Materials
  • Piezoelectric Polymers
  • Piezoelectricity
  • Polymer Chemistry
  • Polymers
  • Quantum Chemistry
  • Undersea Warfare

Fields of Study

  • Chemistry

Readers

  • Materials Science and Engineering.
  • Polymer Science and Technology
  • Quantum Chemistry

Technology Areas

  • Microelectronics
  • Space
  • Space - Hall-Effect Thruster