Module 1: Design of Polymeric Materials

Example: A Biodegradable Plastic

Design Objectives:
Quantum mechanical calculations may be used to gain insight into the structure and properties of the solute (water, in this case). Visualization is an important tool for getting a qualitative understanding of the chemistry.
  1. CPK space filling models are commonly used to visualize relative size and geometry of a molecule.
  2. Molecular orbitals, for example the Highest Occupied Molecular Orbital can be displayed, showing their geometry with respect to the molecule.
  3. Isosurfaces of constant electrostatic potential provide information about the distribution of electron density around the nuclei of a molecule: negative isosurfaces(blue) indicate an electron-rich region, while positive isosurfaces (red) indicate an electron-poor region.
Physical interpretation behind equations, demonstration of important physical behaviors, and interactive manipulation of models to explore the influence of thermodynamics variables can be examined.

A typical procedure might be:

  1. Build model compounds and phases of materials.
  2. Input time, temperature, pressure, and other variables which control the state of the simulation.
  3. Simulate the model system using, for example, the Molecular Dynamics method to illustrate intra- and intermolecular interactions in classical mechanics.
Click here for 3 examples:
Examples of model construction for complex systems (for example, a solid polymer) can be presented and the calculation of physical properties from such a model demonstrated, step by step. This helps reinforce the intuitive connection relating molecular scale physics to engineering thermodynamics on the macroscale.
  1. Build a model of a rubbery polymer with "dissolved" gas molecules present. This example illustrated nitrogen molecules (in cyan) dissolved in a host of polydimehtylsiloxane (PDMS).
  2. Envision the 3-dimensional nature of the model by rotating it in space.
  3. Show how mathematical boundary conditions are handled by imposing periodicity.
  4. Employ molecular dynamics to follow the evolution of the molecular model in time and space. Such features as the difference in mobility between gas molecules and polymer molecules are forcefully apparent.
  5. Analysis and plotting of the data from simulation in terms of familiar equations and variable connects with the macroscopic world. The diffusion coefficient of the gas molecules in the polymer matrix, for example, can be determined from the limiting slope of the plot of Mean Square Displacement vs time, according to the Einstein relation.
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