Molecular Dynamics Simulations of Diffusion in Polymers

Zach Eldridge

Department of Mechanical EngineeringUniversity of Arkansas

Fayetteville, AR 72701 USA

REU 2nd Week Seminar – Friday May 29th, 2009

Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering

Background

• What is Molecular Dynamics? Molecular dynamics is a form of computer simulation used to

observe the behavior of atoms and molecules, which cannot be easily observed during experiments.

Through the use of computer algorithms and known laws of physics, mathematics, and chemistry we are able conduct an experiment and model it through a simulation.

Through analysis of the simulation we are able to study the behavior of the material.

Nano Indention

Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering

My Project

• Methodology The main objective of the research is to study diffusion of gas

penetrates through PDMS (Polydimethylsiloxane) PDMS – the most widely used silicon based organic polymer. It is composed of Oxygen,

Siliocon and a methly, a CH2 or CH3. Common uses include contact lenses and shampoo.

Penetrates – for the most part we will be studying CH4, methane, and its effects.

PDMS 1 PDMS 2

Molecular dynamics simulation will allow us to calculate the diffusion coefficients of the penetrate through the PDMS and evaluate the role of concentration and distribution of penetrates

Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering

My Project Objectives

• Short Term Objectives (1-3 weeks) Become familiar with Lammps, Ensight, and Linux Read to understand diffusion and polymers

• Long Term Objectives (4-10 weeks) Perform simulations that model the diffusion of methane through a

PDMS polymer. Analyze the results of the simulation to determine the diffusion

coefficient of methane, and the effects of concentration and distribution.

Write a final report that discusses my research and the outcomes.

Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering

Sensor schematic Corrosion is measured through changes in electrical

resistivity

Composite schematic Diffusion of particles through composite

samples will be studied via molecular dynamics

Molecular Dynamics Simulation• United-atom model of polymer• Self-avoiding random walk construction• Initial tasks focused on code development

sim

ulat

ion

Huang and Spearot, University of Arkansas, CMMI Award #800718

Rationale

Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering

Research Tools

• Lammps Lammps is the molecular dynamics software we use to create and

manipulate the experiments. Using Linux computer code we create the experiment in a file which

tells the computer how to run the experiment and the different properties we would like it compute during the experiment.

Because the amount of information being processed we have to use the supercomputer “Trillion” to run the simulations.

Trillion

Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering

Research Tools

• Ensight Ensight is the computer program we use to visualize the simulations

after the experiment has been run through “Trillion”. It allows us to make observations about such things as: potential /

kinetic energy, displacement, temperature, centro-symmetry, etc.

Oxygen Diffusion through Polymer

Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering

Works cited

• (2009, May 11). Polydimethylsiloxane. Retrieved May 26, 2009, from Wikipedia Web site: http://en.wikipedia.org/wiki/Polydimethylsiloxane

• (2009, April 14). Arkansas High Performance Computing Center. Retrieved May 26, 2009, Web site: http://hpc.uark.edu/about.html

• Kam Liu, Wing Ensight.com. Retrieved May 26, 2009, Web site: http://www.ensight.com/component/option,com_zoom/Itemid,41/PageNo,2/catid,4/hit,1/key,15/page,view/

• Wag.caltech.edu. Retrieved May 26, 2009, from Gallery of Polymers and Polymer Simulation Web site: http://www.wag.caltech.edu/gallery/pvcdco2.gif

• Dr. Douglas Spearot – Faculty Advisor, Alex Huang – Graduate Student Advisor