Structural, Energetic and Thermodynamic Studies of Acrylic (PAA, PMA and PMMA) and Allylamine (PAH) Polymers for Self Assembly

摘要

Organic polymer electrolytes are the most studied biocompatible materials used in applications related to implants, bio-sensors, drug delivery and tissue engineering. The goal of this research work is to study models of acrylic (PAA, PMA and PMMA) and allylamine (PAH) polymers, their interactions with supports and water solvent for their applications as biocompatible materials. Quantum Mechanical and Molecular Dynamics calculations are used to obtain ground state geometries of monomers and larger oligomers, enthalpies of formation, enthalpies of ionization, and ionization potentials. Hence, from the obtained ground state geometries of the repeat units of PAA, PMA PMMA and PAH, longer chains of respective polymers are constructed and the potential energies as well as charge distribution on the atoms calculated. Polymers in their neutral and ionized forms are modeled and the electrostatic potential derived charges on atoms are determined to have an estimate of the charge to be applied to the substrate to facilitate self-assembly. In addition to gas phase calculations, effects of solvent (water) on the polymers are also studied using Polarizable Continuum Model (PCM) calculations. Molecular Dynamics simulations are used to investigate the water sorption dynamics of the polymer chains and the electrostatic self-assembly of these polymers on titanium substrates. The percentage of water uptake by the polymers as a function of time is calculated and presented. Concentration profiles of the polymer and water in the simulated box is shown at various time steps to determine the amount of water associated around the polymer. PAA has shown higher water uptake among three polymers followed by PMA and PAH. The mean square displacement of water molecules in polymer systems of PAA, PMA and PAH are calculated and water diffusion coefficients found to be 2.3x10-3, 1.9 x10-3, and 1.3x10-4cm2/sec respectively. The electrostatic self assembly of PAA on titanium substrate is simulated using Molecular Dynamics. The model includes substrate (charge fraction=l), PAA (charge fraction=1) and water molecules (SPC model). The thickness of the layers of PAA deposited on the substrate is calculated as 1.16 ± 0.28 nm which is in agreement with the experimental reported value of 1-2nm at room temperature.