![Page 1: Molecular Dynamics Simulations of Diffusion in Polymers](https://reader035.vdocuments.us/reader035/viewer/2022062321/56813048550346895d95f402/html5/thumbnails/1.jpg)
Molecular Dynamics Simulations of Diffusion in Polymers
Zach Eldridge
Department of Mechanical EngineeringUniversity of Arkansas
Fayetteville, AR 72701 USA
REU Advisor: Dr. Douglas SpearotGrad Student Advisor: Mr. Alex Sudibjo
Research Symposium – July 20, 2009
![Page 2: Molecular Dynamics Simulations of Diffusion in Polymers](https://reader035.vdocuments.us/reader035/viewer/2022062321/56813048550346895d95f402/html5/thumbnails/2.jpg)
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
![Page 3: Molecular Dynamics Simulations of Diffusion in Polymers](https://reader035.vdocuments.us/reader035/viewer/2022062321/56813048550346895d95f402/html5/thumbnails/3.jpg)
Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering
My Project
• Objectives• The main objective of this research is to study diffusion of methane
gas penetrates through PDMS (Polydimethylsiloxane)• PDMS – the most widely used silicon based organic polymer. It is composed of Oxygen,
Siliocon and a methyl, CH3. Common uses include contact lenses and shampoo.
• Penetrate – Methane, CH4
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
![Page 4: Molecular Dynamics Simulations of Diffusion in Polymers](https://reader035.vdocuments.us/reader035/viewer/2022062321/56813048550346895d95f402/html5/thumbnails/4.jpg)
Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering
My Project
• Simulations Conditions• Concentrations – percent of the total weight of the system
• .264% = 15 atoms, .529% = 30 atoms, .793% = 45 atoms, 1.06% = 60 atoms
• Volumes – Initial volume of methane molecules
• 1000 Å3, 8000 Å3, 27000 Å3, 64000 Å3, 125000 Å3
• Temperatures – Temperature the simulation runs at
• 200 K, 250 K, 300 K, 350 K, 400 K
1000 Å3 initial volume 125000 Å3 initial volume
![Page 5: Molecular Dynamics Simulations of Diffusion in Polymers](https://reader035.vdocuments.us/reader035/viewer/2022062321/56813048550346895d95f402/html5/thumbnails/5.jpg)
Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering
Research Methods
• Create simulation in Linux using Lammps code
• Run simulation through a super computer, Trillion
• Output visual data to Ensight
• Output mean squared displacement data to Excel
• Normalize data and create graphs
• Use slope of trendline to calculate the diffusion coefficient D
• Solve for Q, activation energy Kcal/mol, using the value of D
• Average all Q and calculate D0, diffusion constant (cm2/s)
• Equations
• D = (1/6)slope
• Q = (Rln(D1 / D2))/( 1/T2 – 1/T1)
• D0 = D1/exp(-Q/RT1)
![Page 6: Molecular Dynamics Simulations of Diffusion in Polymers](https://reader035.vdocuments.us/reader035/viewer/2022062321/56813048550346895d95f402/html5/thumbnails/6.jpg)
Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering
Results
-20
0
20
40
60
80
100
120
140
10 20 30 40 50 60
Tota
l MSD
(Å
2 )
Time (ps)
Conc. = 1.06% Vol = 125000 Å3
200k
250k
300k
350k
400k
•Equilibrium Reached at 10 ps•Low fluctuation in MSD
-10
0
10
20
30
40
50
60
25 30 35 40 45 50 55
Tota
l MSD
(Å
2 )
Time (ps)
Conc. = .793% Vol = 125000 Å3
200k
250k
300k
350k
400k
•Equilibrium reached at 25 ps•Low fluctuation in MSD
![Page 7: Molecular Dynamics Simulations of Diffusion in Polymers](https://reader035.vdocuments.us/reader035/viewer/2022062321/56813048550346895d95f402/html5/thumbnails/7.jpg)
Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering
Results Cont.
•Equilibrium reached at 30 ps•High fluctuation in MSD
-10
0
10
20
30
40
50
60
30 35 40 45 50 55
Tota
l MSD
(Å2 )
Time (ps)
Conc. = 1.06 Vol = 1000 Å3
200k
250k
300k
350k
400k
![Page 8: Molecular Dynamics Simulations of Diffusion in Polymers](https://reader035.vdocuments.us/reader035/viewer/2022062321/56813048550346895d95f402/html5/thumbnails/8.jpg)
Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering
Results Cont.
Concentration Volume (Å3)
Temperature (K)
Average Q (Kcal/mol)
D0 x 10-3
(cm2/s)
1.06% 1000
125000
200250300350400
200250300350400
2.789
2.642
2.4 1.23 1.61 1.351.50
3.431.251.311.291.25
.793% 125000 200250300350400
2.704 4.51.01.1
5.971.0
![Page 9: Molecular Dynamics Simulations of Diffusion in Polymers](https://reader035.vdocuments.us/reader035/viewer/2022062321/56813048550346895d95f402/html5/thumbnails/9.jpg)
Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering
Conclusion
• Smaller the initial volume – longer it takes to reach equilibrium
• Larger concentration – less fluctuation in MSD values
• Smaller the initial concentration – longer it takes reach equilibrium
• D0 is concentration dependent• The values of D0 for concentration of .793% were between 19% -
37% below the values for 1.06%.
![Page 10: Molecular Dynamics Simulations of Diffusion in Polymers](https://reader035.vdocuments.us/reader035/viewer/2022062321/56813048550346895d95f402/html5/thumbnails/10.jpg)
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 Sudibjo – Graduate Student Advisor
![Page 11: Molecular Dynamics Simulations of Diffusion in Polymers](https://reader035.vdocuments.us/reader035/viewer/2022062321/56813048550346895d95f402/html5/thumbnails/11.jpg)
Multiscale Mechanics of Materials Laboratory, Department of Mechanical Engineering
Conclusion
Questions?