Quantum Mechanics and Molecular Mechanics Studies on Energetics and Nucleation

1. Db  b c a y x e Sxx y Syy Sxy x PVDF P(VDF-TrFE) Multi-Scale Modeling of Electro-Active Polymers: Towards Computational Materials DesignHaibin Su, Alejandro Strachan (LANL), Tahir Cagin, Albert Cuitino (Rutgers)& William A. Goddard IIIMaterials and Process Simulation Center, Beckman Institute, California Institute of Technology, Pasadena, California 91125 Molecular Dynamics Studies on Interface Mobility and Chain Sliding Multi-Scale-Modeling Roadmap Perpendicular to the chains Polar (all trans) Non-Polar (T3G) 0.5 Strain rate 3.85 x 1010 (1/s) 0.4 Meso- Macro-scale Nanostructure-properties relationships Constitutive Laws 0.3 Perpendicular to the chains 0.2 0.1 Shear Stress (GPa) xz 0 yz time = 0 ps time = 3 ps -0.1 Along the chains Almost completely polar xy -0.2 25 30 0 5 10 15 20 Time (ps) xy 0.16 time = 6 ps time = 9 ps 0.14 0.0040 0.12 0.0035 Perpendicular to the chains 0.10 Mobility ( m/s ) 0.0030 Force Fields and MD Elastic, dielectric constants Nucleation Barrier Domain wall and interface mobility Phase transitions Anisotropic Viscosity 0.08 Shear Stress (GPa) Perpendicular to the chains 0.0025 Viscosity (Pa.s) 0.0020 yz ab initio QM EoS of various phases Torsional barriers Vibrational frequencies 0.029 0.00065 0.00060 Along the chains Along the chains 0.00055 0.009 0.00050 1.8 2.8 3.8 4.8 5.8 6.8 2.0 3.0 4.0 5.0 6.0 7.0 strain rate (1010 1/s) strain rate (1010 1/s) Stress (Gpa) Quantum Mechanics and Molecular Mechanics Studies on Energetics and Nucleation Meso-Macro-Scale Modeling on Phase Transformation Nucleation of a G bond in an all-T Configuration Phase transformation from non-polar to polar (polarization) driven by applied strain for a single nucleation site • Eulerian code • Coupled electromechanical response • Long-range interaction • Hierarchical Multiscale: Parameters obtained from atomistics • Interface tracking – level set • Nucleating mechanism with G0 Energy Barrier • Propagation mechanism driven by global minimization of Gibbs free energy – Gm (Energy Barrier for motion) Phase I: All Trans Phase II TGTG’ Phase III T3GT3G’ y x Energy ( kcal / mol ) Represents ferroelectric phase Torsional angle (degree) Restraint is applied to bond 0 ALLOWS FOR ARBITRARY SHAPES AND GENERAL ELECTROMECHANICAL BC IN 2D and 3D ( Energy in kcal / mole per carbon ) • Torsions of bonds +1 and -1 remain ~180° • Intrinsic Conservation of Torsion Angles Mechanically driven non-polar (T3G) to polar (all-trans) transformation +1 +2 -2 -1 0 C C C C C C Strain () Load Initial condition Non-polar (T3G) Angle (degree) Angle (degree) Deformed Undeformed (all-trans) SeqQuest code (P. Schultz, SNL), DFT, GGA-PBE, pseudopotentials, Gaussian basis set Torsional angle (degree) Torsional angle (degree) Complex nucleation of polar phase